Your weighbridge suggestions are of no help as they don't explain anything unless you accept that the weight of the tow vehicle and caravan is not altered in any way by the use of a WDH. This is basic high school physics that you still refuse to accept because it destroys your arguments.
This is the same Newtonian physics that NASA relies upon in all its space missions. You on the other hand dismiss it as rubbish.
Go get that text book I suggested and actually learn some physics.
Alan
the weight of the tow vehicle and caravan stay the same (total, except for weight of WDH) but the distribution of weight changes, from rear axle of tug to front axle of tug and trailer axle(s) by the WDH trying to lift back of tug
yobarr said
10:32 AM Jan 16, 2024
Brenda and Alan wrote:
Yobarr
Your belief in spite of evidence to the contrary that the tow ball weight does not change leads you to the conclusion that the car gets lighter and the van heavier. This is in direct conflict with newtons law of universal gravitation and a simplified version his second law of motion.
You constantly fail to address this anomaly and blunder on regardless.
Just for once give us your new version of gravity to explain your belief.
Alan
PS I repeatedly try to explain the principles of physics involved in this discussion, but you continually use bluster and side tracking to avoid tackling the hard questions.
Alan, have you ever considered that you could become a mukti-millionaire, maybe even move from Flowerdale, were you to prove to HR that for 50 years their design team, manufacturing team, and their marketing team have been giving incorrect advice to their customers. No, didn't think so.
You are totalling misinterpreting and cherry-picking points in my posts, whether intentionally or not, and this helps nobody.
-- Edited by yobarr on Tuesday 16th of January 2024 10:35:07 AM
Gundog said
01:31 PM Jan 16, 2024
dogbox wrote:
The weight of the tow vehicle and caravan stay the same (total, except for weight of WDH) but the distribution of weight changes, from rear axle of tug to front axle of tug and trailer axle(s) by the WDH trying to lift back of tug
Sorry but only a fool would weigh their tow vehicle to establish axle weights and GVM without the hitch head and bars, and the brackets fitted to the caravan.
When the WDH is engaged yes it lifts the back of the tug and front of the van thus distributing weight across all axles, not even HR has proven that weight has changed on the towball, because there is no load cell placed under the tow hitch to display the actual weight.
Unfortunately this is circular argument because the anti WDH people will use stupid unsupported statements and their version of physics to pooha those who support the use of a WDH. Whilst Allen defend his position with passion, but there is far too much credence placed on towball weight, after you establish your static towball weight, when its connected to the tug it means SFA because its all part of the combination.
RAvanner said
03:00 PM Jan 16, 2024
In my original post I advised several points, some of which are repeated below.
A WDH does not violate Newtons laws;
A WDH obeys the laws of statics in that the sum of the forces acting on the system is zero. Also, that the sum of the moments acting on the system is zero;
There is no movement of mass;
Reaction forces change because of where the weight distribution acts on the caravan chassis and the resultant moments that this reaction generates;
The ball load does not change; added see below
The solution to Kleins equations requires that the ball load apparently increases. Again, in truth it does not change. added see below
The following results appeared very much scrambled originally so are repeated here.
Vehicle only front axle 1160 kg, rear axle 1300 kg for a total of 2460 kg.
With ball load of 320 kg front axle 1020 kg, rear axle 1760 kg total 2780 kg
With load levelling front axle 1140 kg, rear axle 1600 kg total 2740 kg. To van axle 40 kg
Since the post there have been several comments/questions.
One related to the use of SAE J 2807 and how this had been extrapolated to a WDH. SAE J 2807 make numerous mentions of WDHs. Clause 4.4.3 sets out a number of conditions and gives values for FALR. The target value is 50% and the range 40 to 60 %. I have quoted the average value of a 40 to 60% range. This is a direct quote and is perfectly reasonable. There is also a whole appendix which describes the set-up
The reference is not a statement that anyone should use this value, it is a starting point to consider.
If manufacturers information for the vehicle or the hitch is available the best advice is to follow the information.
In Klein's original works he carries out experiments with what is quoted as being 0% and ??% and 25% load front axle load restoration (FALR) in his original work the definition of FALR is different from that of SAE.
The SAE 50% is very close to Kleins 25% value.
Further Hayman Reese were once advocates of 100% FALR but now suggest a value of approximately 50%. Safe Weigh hitches (please check website) offer a pressure/load gauge on their hitch and advise what the load should. The recommended load equates to an approximate 50% FALR. So now manufacturers of hitches who make money from their product and do not want to get sued also suggest a 50% FALR.
Which is equal to the value stated in SAE J 2708 the standard, albeit without the conditions of the standard.
Another comment has suggested that there is some inference that there would need to change the gravitational constant. It changes enough on its own, but the commonly accepted value is 9.807 m/sec/sec. and is not used in the solution anyway. A WDH does not violate the first two dot points above and does not change the gravitational constant. Commentator has provided a theory as to how the WDH should be calculated, but fails to achieve the load levelling axle loads above described as being from a check weigh at Yarragon. A theory which fails to give answers that are close to the actual figures is probably incorrect.
The fourth dot point explains how a WDH works. But let me add a clarification. The ball load which results from the caravan being hitched to the vehicle is a constant value but it is not the total of the forces which act at the ball. The total force which must be used is BL in kg + (1-762/ball to van axle distance) * LL in kg. For a standard 30-inch spring bar. It is then a moment calculation.
The additional force to the caravan axles is (762/ball to van axle distance) * LL in kg. for proof of this please check the Weigh Safe website and have a play with their calculator.
Yet another comment questions whether it is correct that a ball load reduces the understeer gradient and a WDH reduces it further. It is correct. Reference any of Klein, Rivers, Pacejka.
Another question relates to the recommended values of lateral acceleration at which the understeer gradient falls to zero. I have advised the minimum value from SAE J2807 of 0.3 g which is at 100% load levelling SAE J 2807 also identifies another value of 0.4 g at 50 % load levelling. The latter value is difficult to achieve.
I have probably missed some comments so I apologize to those with unanswered questions.
As well, after reading a comment on LC 200s yesterday, what is the real question? How it works, the FALR, the ball load, the distribution to the caravan, or a contest between good and evil?
One last point. A WDH does not change the mass of the car. The results above defined at a weighbridge or equal illustrate that the axle weights are different. This occurs through the lever system that creates moments.
Trusting that everyone has fun with this and stays safe throughout the year
dogbox said
04:02 PM Jan 16, 2024
Gundog wrote:
dogbox wrote:
The weight of the tow vehicle and caravan stay the same (total, except for weight of WDH) but the distribution of weight changes, from rear axle of tug to front axle of tug and trailer axle(s) by the WDH trying to lift back of tug
Sorry but only a fool would weigh their tow vehicle to establish axle weights and GVM without the hitch head and bars, and the brackets fitted to the caravan.
When the WDH is engaged yes it lifts the back of the tug and front of the van thus distributing weight across all axles, not even HR has proven that weight has changed on the towball, because there is no load cell placed under the tow hitch to display the actual weight.
Unfortunately this is circular argument because the anti WDH people will use stupid unsupported statements and their version of physics to pooha those who support the use of a WDH. Whilst Allen defend his position with passion, but there is far too much credence placed on towball weight, after you establish your static towball weight, when its connected to the tug it means SFA because its all part of the combination.
i do confess that i maybe some what slow and FOOLISH but why would you buy a WDH before you determine if you need one or if there could be a better way to fix the issue you are trying to resolve or do you think joe down the road has one I got to get one after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth? assuming you are trying to level your rig? you may have to much weight on tow ball or in back of tug move some stuff /get rid of some stuff maybe a extra leaf in rear spring will fix the issue as shown in posted pictures a WDH can impose loads on places that may not be able to handle them and may cause more problems than they solve
-- Edited by dogbox on Tuesday 16th of January 2024 04:05:38 PM
Gundog said
07:07 PM Jan 16, 2024
dogbox wrote:
Gundog wrote:
dogbox wrote:
The weight of the tow vehicle and caravan stay the same (total, except for weight of WDH) but the distribution of weight changes, from rear axle of tug to front axle of tug and trailer axle(s) by the WDH trying to lift back of tug
Sorry but only a fool would weigh their tow vehicle to establish axle weights and GVM without the hitch head and bars, and the brackets fitted to the caravan.
When the WDH is engaged yes it lifts the back of the tug and front of the van thus distributing weight across all axles, not even HR has proven that weight has changed on the towball, because there is no load cell placed under the tow hitch to display the actual weight.
Unfortunately this is circular argument because the anti WDH people will use stupid unsupported statements and their version of physics to pooha those who support the use of a WDH. Whilst Allen defend his position with passion, but there is far too much credence placed on towball weight, after you establish your static towball weight, when its connected to the tug it means SFA because its all part of the combination.
i do confess that i maybe some what slow and FOOLISH but why would you buy a WDH before you determine if you need one or if there could be a better way to fix the issue you are trying to resolve or do you think joe down the road has one I got to get one after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth? assuming you are trying to level your rig? you may have to much weight on tow ball or in back of tug move some stuff /get rid of some stuff maybe a extra leaf in rear spring will fix the issue as shown in posted pictures a WDH can impose loads on places that may not be able to handle them and may cause more problems than they solve
-- Edited by dogbox on Tuesday 16th of January 2024 04:05:38 PM
Whilist I support the use of a WDH where it is needed, I don't advocate that everyone should.
I guess some caravan salesmen see a WDH as an upsell accessory, like other junk that is not needed foisted on to unsuspecting customer.
If you are required to use one, then comply. Some quibble over the weight of the WDH choosing to use a helper springs and sir bags, but these item cannot transfer weight to the front axle.
If its not a required item then everything starts with getting the ball height to match the coupling height, then its a case of moving weight around your vehicles to get both vehicles level to a degree, generally +/- 25 mm at the rear axle is a good starting point, unfortunatly most punters do this before both units are fully laden as if you are leaving on your journey. now its time to get to a weighbridge and make sure everything is correct, unfortunatly this is another task that many ignore.
Its only now will you find out if a WDH is maybe needed, if you cannot get weight on your front axle.
BarneyBDB said
07:43 PM Jan 16, 2024
I think I found a pic that may help some of you visualize how a WDH actually works....
I still have a problem with the statement that tow ball load does not change.
The weight of the car on the weighbridge is constant regardless of other load imposed by the caravan. So it follows the tow ball load is reduced when a WDH is tensioned.
Alan
Are We Lost said
08:22 PM Jan 16, 2024
Alan, It is only you and Yobarr that are arguing this issue. It is a pointless argument because it can only be answered in theory and once the van is connected, can not be actually measured to prove it one way or another. It makes no difference in the function of a WDH and I don't think anyone is disputing how the weights on the different axles change. It is arguing about the internals of how the result is achieved, and who cares anyway?
I suggest both you and Yobarr stop flogging a dead horse. You will never agree and Yobarr will never give any explanation other than "because I have said it before, and expert x says it is so."
The fact that he will never give an explanation shows he can't. Let's avoid yet another WDH thread going downhill over this constantly repeating but unimportant issue.
-- Edited by Are We Lost on Tuesday 16th of January 2024 08:24:51 PM
Are We Lost said
09:19 PM Jan 16, 2024
dogbox wrote:i do confess that i maybe some what slow and FOOLISH but why would you buy a WDH before you determine if you need one or if there could be a better way to fix the issue you are trying to resolve or do you think joe down the road has one I got to get one after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth?
assuming you are trying to level your rig? you may have to much weight on tow ball or in back of tug move some stuff /get rid of some stuff maybe a extra leaf in rear spring will fix the issue as shown in posted pictures a WDH can impose loads on places that may not be able to handle them and may cause more problems than they solve
... after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth?
Technically it is possible for most utes to tow 3500kg but not realistically so unless it is a dog trailer. Most have 6000kg GCM, so the tug can only weigh 2500kg .... dangerously underweight, and often only enough allowance for the driver and a toothbrush. But if they market it as 3000kg while a similar vehicle is marketed as 3500kg how many sales would they lose? And yes, it can tow a dog trailer OK, albeit subject to that restrictive 2500kg maximum vehicle weight.
... assuming you are trying to level your rig? That should not be the goal to aim for. Level or not is just a symptom. The primary goal is to get more weight on the front wheels (and hence road grip). As a result, the symptom of not being level is addressed. A secondary goal is to reduce porposing and this is where a WDH shines because it dynamically increases tension the more it is needed, and reduces to zero when not needed.
....maybe a extra leaf in rear spring will fix the issue
For someone who is towing most of the time it could be a good idea, although at the expense of ride comfort. It would have some effect on reducing porpoising but would do nothing to restore lost road grip. It would hide the symptom so everything looks OK but is not OK. Done in combination with a WDH ... sure.
..... a WDH can impose loads on places that may not be able to handle them
Yes, quite true, but usually if the vehicle does not support a WDH it will have a warning against their use. Of course some people will misadjust them or use them in situations they should not. When used conservatively on a towing capable vehicle and a strong enough van, the risk of problems is miniscule.
Gundog, I agree with most of what you say but disagree on needing to see the result to know if a WDH is required. Imagine a vehicle with very stiff suspension vs one with soft suspension. One will show no visible need for a WDH while the other will be very obvious. I believe it can be decided by knowing towball load and the ratio between wheelbase and towball overhang.
For example, assuming a typical ute or SUV with laden weight of 2500kg or more. A 300kg towball weight will put around 425-440kg load on the rear axle and lift the front by about 125-140kg. More weight in the back of the tow vehicle increases that disparity. To me, it is obvious that such a rig would benefit by the use of a WDH. A starting point for adjustment would be to restore about 50% of the sag at the rear, followed up with confirmation at a weighbridge, and then adjust as needed after some driving time.
RAvanner raised the interesting point on understeer (caused mainly by insufficient load on the front axle vs rear axle) but has not progressed further. From driving, the increase in understeer without a WDH is very obvious. I would be interested in how much the weight difference front to back is considered best.
One other point. While I am an advocate for WDH, I don't believe one is always required. If the van is light for the tow vehicle or the towball load/weight in the rear of the vehicle is not great, then one is probably not needed. Weighbridge measurements are the prime determinant, and tension should never be so high as to induce oversteer.
-- Edited by Are We Lost on Tuesday 16th of January 2024 09:27:24 PM
yobarr said
09:44 PM Jan 16, 2024
Are We Lost wrote:
Alan, It is only you and Yobarr are arguing this issue. It is a pointless argument because it can only be answered in theory and once the van is connected, can not be actually measured to prove it one way or another. It makes no difference in the function of a WDH and I don't think anyone is disputing how the weights on the different axles change. It is arguing about the internals of how the result is achieved, and who cares anyway?
I suggest both you and Yobarr stop flogging a dead horse. You will never agree and Yobarr will never give any explanation other than "because I have said it before, and expert x says it is so."
The fact that he will never give an explanation shows he can't. Let's avoid yet another WDH thread going downhill over this constantly repeating but unimportant issue.
Hi Stephen, as I am about over talking to a brick wall who either does not, will not, or cannot understand facts I had decided to stay away from this thread, but your post has made me rethink.
Please note that I am not arguing, but merely stating indesputable facts.
Also please know that I know a lot more about this topic, and that a WDH DOES NOT change towball weight, than I am prepared to post here.
If people like Alan cannot understand what already has been posted, any further revelations that I might make would cause absolute mayhem. Alan's totally incorrect assertions do not bother me at all, as everybody is entitled to an opinion, no matter how misguided they may be, but my major concern is that newbies, and even current members keen to learn, will be negatively impacted by his ramblings, to their detriment.
Believe me, I have delved right into this, but any further revelations would cause total mayhem. Cheers
-- Edited by yobarr on Tuesday 16th of January 2024 09:55:48 PM
yobarr said
09:53 PM Jan 16, 2024
Are We Lost wrote:
Gundog, I agree with most of what you say but disagree on needing to see the result to know if a WDH is required. Imagine a vehicle with very stiff suspension vs one with soft suspension. One will show no visible need for a WDH while the other will be very obvious. I believe it can be decided by knowing towball load and the ratio between wheelbase and towball overhang.
Thanks for this paragraph Stephen, and its indesputable truths. Previously, several times, I have pointed out exactly this to Graham, but it has either been ignored, misunderstood, or went right over the top of his head.
Perhaps your post will do better? Cheers
yobarr said
10:02 PM Jan 16, 2024
Brenda and Alan wrote:
Ron
I still have a problem with the statement that tow ball load does not change.
The weight of the car on the weighbridge is constant regardless of other load imposed by the caravan. So it follows the tow ball load is reduced when a WDH is tensioned.
Alan
Alan, again, for the 73rd time (approximately!) I suggest that you take your fully loaded car and van, along with the adored WDH, to a weighbridge and conduct the weighing exercises that I have outlined many times.
Provided that you don't fiddle the figures to suit yourself you will see that what I have been saying for ever is indesputably correct.
The weight of the car on the weighbridge will change, as will the weight of the caravan.
k
watsea said
10:23 PM Jan 16, 2024
When my van is hitched to my vehicle and I tension the bars of my WDH, I get 40kg extra weight onto the axles of my van and 40kg less for the total of the weight the axles of my vehicle. So I guess no one would argue with that type of outcome.
For a WDH that uses bars from an arrangement on the hitch near the towball, and then tensioned to locations usually about 30 inches from the tow ball, the tension in the bars lifts and applies uplift to the tow hitch and tow bar, not the towball. So the lift force does not happen at the towball.
The forces in the tension bars that provide the lift to the hitch and tow bar are located at the tension points. These forces are downwards onto the drawbar A frame. The forces downwards on the drawbar increase the overall load to the van and that is why the axles loads of the van increase when the bars are tensioned.
I would expect that actually there would be an increased downwards load on the actual towball when the bars are tensioned, but meanwhile the hitch and towbar are being lifted which reduces the load on the vehicle ands changes its axle loads.
Sorry, too late at night to try some actual numbers in an example.
yobarr said
07:26 AM Jan 17, 2024
watsea wrote:
When my van is hitched to my vehicle and I tension the bars of my WDH, I get 40kg extra weight onto the axles of my van and 40kg less for the total of the weight the axles of my vehicle. So I guess no one would argue with that type of outcome.
For a WDH that uses bars from an arrangement on the hitch near the towball, and then tensioned to locations usually about 30 inches from the tow ball, the tension in the bars lifts and applies uplift to the tow hitch and tow bar, not the towball. So the lift force does not happen at the towball.
The forces in the tension bars that provide the lift to the hitch and tow bar are located at the tension points. These forces are downwards onto the drawbar A frame. The forces downwards on the drawbar increase the overall load to the van and that is why the axles loads of the van increase when the bars are tensioned.
I would expect that actually there would be an increased downwards load on the actual towball when the bars are tensioned, but meanwhile the hitch and towbar are being lifted which reduces the load on the vehicle ands changes its axle loads. Sorry, too late at night to try some actual numbers in an example.
You're onto it Ted. Previously I have posted the results from my actual weighing exercise, but it's 4.30am here and I've justed started the Roadtrain, so off to work we go! Maybe I'll find time later to look for them. Cheers
dogbox said
09:30 AM Jan 17, 2024
Brenda and Alan wrote:
Ron
I still have a problem with the statement that tow ball load does not change.
The weight of the car on the weighbridge is constant regardless of other load imposed by the caravan. So it follows the tow ball load is reduced when a WDH is tensioned.
Alan
try to think of it as a clamp ,the downward forces are neutralized by the upward forces so no change in actual weigh of set up other than clamp. which as i mentioned earlier an was told i must be a fool, but a WDH can vary in price from a couple of hundred dollars to over a thousand an add up to 40 kilos of weight and if you are going off road it is recommended to disconnect anyways, better to fix the problem if possible than try an patch it up
Are We Lost said
09:32 AM Jan 17, 2024
watsea wrote:
I would expect that actually there would be an increased downwards load on the actual towball when the bars are tensioned, but meanwhile the hitch and towbar are being lifted which reduces the load on the vehicle ands changes its axle loads.
Yes. Due to the differing lever principles, the uplift from the bars is greater than the load from them onto the drawbar. So the net effect is a lifting of the rear, resulting in weight being transferred from the rear axle to be shared between the front axle and the van axle.
dogbox wrote:try to think of it as a clamp ,the downward forces are neutralized by the upward forces so no change in actual weigh of set up other than clamp.
.......
better to fix the problem if possible than try an patch it up
Not quite. As per my response to Watsea, the forces are not neutralised. There is a net upwards force. That is why the rear end rises back up, and the basis for how the system functions.
If by fixing the problem you are referring to suspension modification in preference to a WDH, you are not fixing the problem at all. You are hiding it from view. See more detail in my response last night.
-- Edited by Are We Lost on Wednesday 17th of January 2024 09:46:31 AM
dogbox said
10:31 AM Jan 17, 2024
Are We Lost wrote:
watsea wrote:
I would expect that actually there would be an increased downwards load on the actual towball when the bars are tensioned, but meanwhile the hitch and towbar are being lifted which reduces the load on the vehicle ands changes its axle loads.
Yes. Due to the differing lever principles, the uplift from the bars is greater than the load from them onto the drawbar. So the net effect is a lifting of the rear, resulting in weight being transferred from the rear axle to be shared between the front axle and the van axle.
dogbox wrote:try to think of it as a clamp ,the downward forces are neutralized by the upward forces so no change in actual weigh of set up other than clamp.
.......
better to fix the problem if possible than try an patch it up
Not quite. As per my response to Watsea, the forces are not neutralised. There is a net upwards force. That is why the rear end rises back up, and the basis for how the system functions.
If by fixing the problem you are referring to suspension modification in preference to a WDH, you are not fixing the problem at all. You are hiding it from view. See more detail in my response last night.
-- Edited by Are We Lost on Wednesday 17th of January 2024 09:46:31 AM
I was referring to the idea of doing a bit of research and buying a balanced rig with some minor adjustments not trying to fix a problem of buying a caravan that does not suit the tow vehicle then have to buy/use add on to fix the problems. look on you tube an see the amount of money spent on upgrading vehicles and caravans to make them legal then some one comes along an thinks they can achieve the same result without spending the dollars loading up the ute putting boat on roof outboard motor 3500 kilo plus caravan then go out an share the road with the rest of us
the "net upward force" is transferred to the chassis of tug transferring weight from rear axle to front axle and caravan axle(s) via downward pressure on caravan chassis ,other than the clamping effect on the tow ball no additional weight is applied to tow ball
-- Edited by dogbox on Wednesday 17th of January 2024 10:34:51 AM
Are We Lost said
10:49 AM Jan 17, 2024
dogbox wrote:.... other than the clamping effect on the tow ball no additional weight is applied to tow ball
It is the net upwards vs downwards force (clamping effect) at the towball/coupling that causes the rear end to rise. The upwards effect is greater than the downwards one. That is as close as I am going to the never ending argument.
dogbox said
11:26 AM Jan 17, 2024
it puts pressure on the tow ball coupling but no more or less weight on tow ball the upward effect of applying WDH is transferred to rear chassis of tow vehicle with downward pressure on caravan chassis an front axle of tug
RAvanner said
03:15 PM Jan 17, 2024
A WDH has as far as the operator is concerned it only has one purpose, that is to achieve some degree of front axle load restoration. If this is the reason for the use of said WDH then the internal physics is of no real use. If users are curious about the internal workings, then the following applies.
It was stated that the force imposed on the ball by the van does not change. Absolutely correct. Further that that the WDH acts to provide a clamping force to the ball which is equal to the force from the load bars once again correct. However, the clamping force is usually 762 mm from the ball hence is less than the full load from the spring bars. Think of a painter on a plank If he/she is in the centre of the two supports each support sees the same force. If the painter moves left or right the forces at the supports are different, a WDH is the same. The total force on the ball is:
BL in kg + (1-762/ball to van axle distance) * LL in kg.
Any analysis must consider this and the load levelling force at there respective distance from any fixed point but the simplest is the front axle of the vehicle.
Example say 285 kg ball force, ball to van axle 4.4 m and the load from the spring bars to be 220 kg. Which is usually an unknown value.
Then:
Total force on the ball with the WDH is 285+(1-762/4400) *220 which equals 466 kg. the sum of the vertical forces at the ball is 466 220 = 246 which means that 39 kg has been transferred to the vans axles.
As I do not have access to Hayman Reeses files, I cannot comment whether they have proven this or not, nor can any one else. I can suggest that Hayman Reese has proven this. I can also advise that the Safe weigh hitch with its inbuilt pressure / load gauge offers proof of concept.
Perhaps uncharitably I am unwilling to accept speculation as to how a caravan chassis may have cracked. It may be for any number of reasons; it may have been exacerbated by the WDH. But the reason for the failure it cannot be determined from a photograph.
I think it was Yobarr who suggested he has information which would cause mayhem, a little mayhem never hurt anyone and probably should be provided to be discussed and or debated or accepted or rejected.
Sorry people Heavy stuff ahead!
With regards understeer and understeer gradient the following are calculated results utilizing Pacejka or equivalent equations for a specific set up.
These are mathematically correct; they are consistent with what experimental researchers and theoretical researchers report. They will never be absolutely correct but they illustrate what occurs.
Vehicle alone critical speed > 180 kph, static understeer gradient +0.0045, damping ratio at 100 kph 0.9.
Vehicle +BL critical speed 162 kph, lateral acceleration at which US/gradient is zero 0.51, U/S gradient -0.01384, damping at 100 kph 0.1.
Vehicle +BL+ 50% LL critical speed 137 kph, lateral acceleration at which U/S gradient falls to zero 0.355, US gradient -0.0197, damping 0.13.
Vehicle +BL+ 100% LL critical speed 120kph, lateral acceleration at which U/S gradient falls to zero 0.072, US gradient -0.0256, damping 0.16.
The SAE J2807 values previously advised are recommended minimums. Almost certainly with a level of safety incorporated.
Road designers I believe employ a value of 0.15 to 0.2 g for the design of curves at the design speed. Hence the 0.3 and 0.45 of lateral acceleration at which the understeer gradient falls below zero values are conservative.
But this is essential given the potential of less than perfect road surfaces, tyre condition and pressure, ambient weather conditions etc.
I am not going to attempt to discuss the solution of quartic equations (which Pacejkas formula reduce to), imaginary numbers or the magic tyre formula all of which contribute to the answers above.
End of heavy stuff.
But a WDH does have an impact, hence the opening comment A WDH has as far as the operator is concerned only has one purpose. It does lots of things!
Trusting that everyone has fun with this and stays safe throughout the year
yobarr said
06:55 PM Jan 17, 2024
RAvanner wrote:
A WDH has as far as the operator is concerned it only has one purpose, that is to achieve some degree of front axle load restoration. If this is the reason for the use of said WDH then the internal physics is of no real use. If users are curious about the internal workings, then the following applies.
It was stated that the force imposed on the ball by the van does not change. Absolutely correct. Further that that the WDH acts to provide a clamping force to the ball which is equal to the force from the load bars once again correct. However, the clamping force is usually 762 mm from the ball hence is less than the full load from the spring bars. Think of a painter on a plank If he/she is in the centre of the two supports each support sees the same force. If the painter moves left or right the forces at the supports are different, a WDH is the same. The total force on the ball is:
BL in kg + (1-762/ball to van axle distance) * LL in kg.
Any analysis must consider this and the load levelling force at there respective distance from any fixed point but the simplest is the front axle of the vehicle.
Example say 285 kg ball force, ball to van axle 4.4 m and the load from the spring bars to be 220 kg. Which is usually an unknown value.
Then:
Total force on the ball with the WDH is 285+(1-762/4400) *220 which equals 466 kg. the sum of the vertical forces at the ball is 466 220 = 246 which means that 39 kg has been transferred to the vans axles.
As I do not have access to Hayman Reeses files, I cannot comment whether they have proven this or not, nor can any one else. I can suggest that Hayman Reese has proven this. I can also advise that the Safe weigh hitch with its inbuilt pressure / load gauge offers proof of concept.
Perhaps uncharitably I am unwilling to accept speculation as to how a caravan chassis may have cracked. It may be for any number of reasons; it may have been exacerbated by the WDH. But the reason for the failure it cannot be determined from a photograph.
I think it was Yobarr who suggested he has information which would cause mayhem, a little mayhem never hurt anyone and probably should be provided to be discussed and or debated or accepted or rejected.
Sorry people Heavy stuff ahead!
With regards understeer and understeer gradient the following are calculated results utilizing Pacejka or equivalent equations for a specific set up.
These are mathematically correct; they are consistent with what experimental researchers and theoretical researchers report. They will never be absolutely correct but they illustrate what occurs.
Vehicle alone critical speed > 180 kph, static understeer gradient +0.0045, damping ratio at 100 kph 0.9.
Vehicle +BL critical speed 162 kph, lateral acceleration at which US/gradient is zero 0.51, U/S gradient -0.01384, damping at 100 kph 0.1.
Vehicle +BL+ 50% LL critical speed 137 kph, lateral acceleration at which U/S gradient falls to zero 0.355, US gradient -0.0197, damping 0.13.
Vehicle +BL+ 100% LL critical speed 120kph, lateral acceleration at which U/S gradient falls to zero 0.072, US gradient -0.0256, damping 0.16.
The SAE J2807 values previously advised are recommended minimums. Almost certainly with a level of safety incorporated.
Road designers I believe employ a value of 0.15 to 0.2 g for the design of curves at the design speed. Hence the 0.3 and 0.45 of lateral acceleration at which the understeer gradient falls below zero values are conservative.
But this is essential given the potential of less than perfect road surfaces, tyre condition and pressure, ambient weather conditions etc.
I am not going to attempt to discuss the solution of quartic equations (which Pacejkas formula reduce to), imaginary numbers or the magic tyre formula all of which contribute to the answers above.
End of heavy stuff.
But a WDH does have an impact, hence the opening comment A WDH has as far as the operator is concerned only has one purpose. It does lots of things!
Trusting that everyone has fun with this and stays safe throughout the year
Thanks Ron, for this detailed and accurate workings if a WDH, which should quieten those who seem not to understand simple physics, and peresevere with their seemingly endless streams of waffle that invariably causes friction (no pun intended) whenever a question is asked about WDHs.
Thank you sincerely, and I will put this post among my recordes so any further discussion can quickly be squashed. Cheers
P.S Despite your kind offer I will not further "Rock the Boat"
A WDH does NOT change towball weight.
Never has done.
Never will do.
Peter_n_Margaret said
07:48 PM Jan 17, 2024
First problem I see with this "debate" is that some very verbal participants confuse weight and mass.
These terms are not interchangeable and both the sprukers and the readers need to understand the difference and get them correct.
Not doing so makes this whole thing a pointless mess.
Cheers,
Peter
Are We Lost said
08:12 PM Jan 17, 2024
RAvanner wrote:
The total force on the ball is:
BL in kg + (1-762/ball to van axle distance) * LL in kg.
Any analysis must consider this and the load levelling force at there respective distance from any fixed point but the simplest is the front axle of the vehicle.
Example say 285 kg ball force, ball to van axle 4.4 m and the load from the spring bars to be 220 kg. Which is usually an unknown value.
Then:
Total force on the ball with the WDH is 285+(1-762/4400) *220 which equals 466 kg. the sum of the vertical forces at the ball is 466 220 = 246 which means that 39 kg has been transferred to the vans axles.
A slightly shorter and simpler formula to calculate the effect of the bars on the van axle is just to use ratios and not include the original towball load because it needs to be subtracted again in a second calculation and has no bearing on the change to the weight on the van wheels. So:
Load applied by bars (kg) to drawbar X (load point distance to axle / towball to axle distance). Using your 762mm as the load point, the distance from there to the axle is 3638mm.
220 x (3638 / 4400) = 38.1kg. To calculate the load added at the towball is 220 x (762 / 4400) = 181.9kg. Add original towball load if you wish.
RAvanner, as I said before you provide a lot of information but little to help the typical vanner.
For example:
"Vehicle +BL+ 100% LL critical speed 120kph, lateral acceleration at which U/S gradient falls to zero 0.072, US gradient -0.0256, damping 0.16."
I picked the lowest critical speed from your list. Ignoring the fact that it is faster than any sensible caravanner would travel, how should this information be applied in a practial sense? With the descending list of speeds can any meaningful interpretation be made for someone who travels under 100kph?
"Road designers I believe employ a value of 0.15 to 0.2 g for the design of curves at the design speed. Hence the 0.3 and 0.45 of lateral acceleration at which the understeer gradient falls below zero values are conservative."
What does this tell me in relation to what I should be considering or aware of with my rig or when driving?
-- Edited by Are We Lost on Thursday 18th of January 2024 01:13:40 AM
Brenda and Alan said
09:52 AM Jan 18, 2024
Ron
Still no response re Newtons laws and unchanging tow ball weight.
Your calculations show that tow ball loading is reduced by 39 Kg wt, and axle weight increased by said amount.
This obeys Newtons law.
jegog said
02:27 PM Jan 18, 2024
yobarr wrote:
Brenda and Alan wrote:
Ron
I see flaws in your argument.
You state that a WDH does not change the tow ball download.
If a WDH obeys the laws of physics then the WDH must reduce the loading that the drawbar of a caravan imposes on car. This is so because these laws tell us that the weight of the car can't increase or decrease unless the force of gravity or the cars mass is altered. neither of these things can be done by a WDH.
1st weighing car 2460 kgwt
2nd car 2460 kgw - tow ball load 320 kgwt - total 2780 kgwt
3rd car 2460 kgwt - tow ball load 280 kgwt - total 2740 kgwt
Yobarr
You still don't understand the difference between Mass ( the amount of material ) and weight ( force ). They are two entirely different things and are NOT interchangeable. As an example the amount of mass converted to energy in the Hiroshima atomic bomb was equivalent to the mass of a common paper clip, about 1 gm. Just think of the destruction of a 40 Kg change to the cars mass.
Alan
Alan, do you not think that it is time to cease throwing your convoluted, incorrect and confusing 'theories' into every WDH thread that is created? All that your contributed rubbish does is thoroughly confuse everyday members who simply are trying to learn about WDHs.
The fact that a WDH is only ever used, whether mandated by manufacturers or not, in an attempt to make a car do things for which it never was designed has been extensively covered on this forum over some years, but still you waffle-on with your own theories, totally at odds with advice from many engineers, and indeed Hayman Reese themselves.
You are, of course, entitled to your opinion, no matter how wrong it is, but I despair the confusion you're causing among beginners, as well as the possible danger taking your advice would create.
Just in case you've forgotten, A WDH does NOT change towball weight.
Never has. Never will.
.. Cheers
P.S You will, of course, have noticed that this particular thread is almost a year old?
-- Edited by yobarr on Sunday 14th of January 2024 01:55:43 PM
Note it is a force, and on a theoretical 3000kg. caravan:
The wheels are exerting a downward force of aprox. 2700N(Newtons) and the tow ball is exerting a downwards force of apron. 300N.
When we install a WDH it(the WDH) creates a torque on the vehicle which exerts a downwards force on the vehicle's front wheels and an upward force on the rear wheels and tow bar. This torque rotates the vehicle about the vehicle's centre of mass forcing the front of the vehicle down and the rear of the vehicle up.
If we measure the weight of the vehicle it will confirm that the weight on the front wheels increase and the weight of the rear wheels decrease.
Or to put it another way the WDH torque is added to the front wheels and subtracted from the rear wheels.
There is also WDH torque on the tow ball and because it is in the opposite direction to the tow ball force it is subtracted from the tow ball force. This increases the force on the caravan wheels. And when weighed the van wheels show increased weight.
If the weight of the caravan wheels change then there must be a corresponding change in the tow ball weight.
When we measure weight we are really measuring the force exerted on the vehicle and van by gravity
That the rear of the vehicle rises indicates that the tow ball weight has decreased.
But does it really matter? Only for explaining why disasters happen when the vehicle and the caravan relative angle change while negating a culvert or creek bank.
Brenda and Alan said
08:52 AM Jan 19, 2024
Jegog
I get the drift of your arguments, but you are out by a factor of 9.807 on your weights expressed in newtons.
What you have is weight in Kg wt.
My concerns with the use of a WDH is Yobarr insists that the van becomes heavier overall and thus could exceed it's ATM rating.
As this discussion progresses it become more complicated.
Rons analyses confirms that simple arithmetic achieves the same result.
Cars hitched weight minus cars weight equals tow ball download with or with out aWDH.
Alan
watsea said
10:29 PM Jan 19, 2024
In this forum, under the thread "WDH again", on May 13 and 14, 2023, I presented some WDH calculations where I had modelled the WDH to be a simple torque application device. Please refer to those previous posts if you are interested.
Attached is a sheet of calculations where I have modelled a WDH as a tension bar type.
I used the same vehicle and van dimensions as my May 2023 calculations but assumed the vehicle and van had no mass. This gave values of forces involved, just from the bar tensions. I used a distance of 650mm from the towball coupling to the bar tension mounts. This is a little more accurate that 760mm because that 760mm is along the A frame rails rather the centreline of the van.
As I expected, the changes in weights of all the axles, due to the WDH using bar tension are the same as my May 2023 calculations. The January 2024 values and the May 2023 are essentially the same if one takes calculator rounding errors into account. The January 2024 calculations show the increased load on the towball coupling when using a bar type WDH, but into the tow hitch the bars are counteracting that extra coupling load.
I wasn't going to comment on this as I have said it all before and I am sick of arguing with yobarr on the merits of WDH's.
However, a misconception has been brought up in a recent post.
The ATM of the van does not change and will not change with the use of a WDH.
A WDH is not some miraculous gravity defying device.
The ATM is the total weight of the van and it's load, measured with the van off the vehicle standing on it's jockey wheel.
A WDH, as it's name suggests, redistributes how the total GCM of car and van is supported across the various axle groups of the rig.
That is it takes some load off the rear axle of the tow vehicle and redistributes that to primarily the front axle and some to the van axle group.
The GTM of the van may rise slightly but the ATM and the GCM figures will always remain the same unless load is added or subtracted. The laws of Gravity hadn't changed the last time I looked.
Think of a bridge with the abutments each end and a pylon in the middle.
We have 1000 tons of load sat in the middle of the bridge over the centre pylon.
So whilst the abutments will be sharing the load to some extent, the centre pylon is supporting the most.
So now we move the load to out near the abutments with 500 tonnes at each end.
The abutments are now supporting most of the load and the centre pylon not very much.
The load amount hasn't changed. The weight of the bridge hasn't changed, just we have now changed how the overall load is supported.
This is exact what a WDH does. You can experiment with a plank and some chairs to replicate our bridge if you wish.
Tow ball down load does not change as the gravitational load from the van pushing down through the drawbar on the car is the same, just the WDH has spread that load a little differently.
Theoretically if you are flying very close to the wind in terms of your weights, you might exceed your GTM on the scales by using a WDH but never your ATM or your GCM.
The GTM is the measured load on the vans axle group with the van connected to the car. The ball download is being supported by the car and therefore is included in the cars GVM.
And just to add I have been using and am an advocate of WDH's since the mid 1970's and have done 100,000's of kilometres with them. I do not use them as some sort of magic fix for an incorrectly loaded rig but rather as a tuning device to improve steering and braking response that is lost when sticking a van on the back. In that role I can attest they work very well despite the BS expressed here by some.
yobarr said
09:34 PM Jan 20, 2024
Not again, Greg? Tomorrow, if I can find time, I will respond to this post. Of course ATM doesn't change. It's a rating, but the Weight on wheels (GTM?) increases while towball weight stays the same.
Clearly the van weighs more, using the generally accepted meaning of weight.
It is pointless discussing mass when all we're trying to do is help others understand.
Again I will say that a WDH is used only by people who are trying to make a car do things for which it was not designed.
the weight of the tow vehicle and caravan stay the same (total, except for weight of WDH) but the distribution of weight changes, from rear axle of tug to front axle of tug and trailer axle(s) by the WDH trying to lift back of tug
Alan, have you ever considered that you could become a mukti-millionaire, maybe even move from Flowerdale, were you to prove to HR that for 50 years their design team, manufacturing team, and their marketing team have been giving incorrect advice to their customers. No, didn't think so.
You are totalling misinterpreting and cherry-picking points in my posts, whether intentionally or not, and this helps nobody.
-- Edited by yobarr on Tuesday 16th of January 2024 10:35:07 AM
Sorry but only a fool would weigh their tow vehicle to establish axle weights and GVM without the hitch head and bars, and the brackets fitted to the caravan.
When the WDH is engaged yes it lifts the back of the tug and front of the van thus distributing weight across all axles, not even HR has proven that weight has changed on the towball, because there is no load cell placed under the tow hitch to display the actual weight.
Unfortunately this is circular argument because the anti WDH people will use stupid unsupported statements and their version of physics to pooha those who support the use of a WDH. Whilst Allen defend his position with passion, but there is far too much credence placed on towball weight, after you establish your static towball weight, when its connected to the tug it means SFA because its all part of the combination.
A WDH does not violate Newtons laws;
A WDH obeys the laws of statics in that the sum of the forces acting on the system is zero. Also, that the sum of the moments acting on the system is zero;
There is no movement of mass;
Reaction forces change because of where the weight distribution acts on the caravan chassis and the resultant moments that this reaction generates;
The ball load does not change; added see below
The solution to Kleins equations requires that the ball load apparently increases. Again, in truth it does not change. added see below
The following results appeared very much scrambled originally so are repeated here.
Vehicle only front axle 1160 kg, rear axle 1300 kg for a total of 2460 kg.
With ball load of 320 kg front axle 1020 kg, rear axle 1760 kg total 2780 kg
With load levelling front axle 1140 kg, rear axle 1600 kg total 2740 kg. To van axle 40 kg
Since the post there have been several comments/questions.
One related to the use of SAE J 2807 and how this had been extrapolated to a WDH. SAE J 2807 make numerous mentions of WDHs. Clause 4.4.3 sets out a number of conditions and gives values for FALR. The target value is 50% and the range 40 to 60 %. I have quoted the average value of a 40 to 60% range. This is a direct quote and is perfectly reasonable. There is also a whole appendix which describes the set-up
The reference is not a statement that anyone should use this value, it is a starting point to consider.
If manufacturers information for the vehicle or the hitch is available the best advice is to follow the information.
In Klein's original works he carries out experiments with what is quoted as being 0% and ??% and 25% load front axle load restoration (FALR) in his original work the definition of FALR is different from that of SAE.
The SAE 50% is very close to Kleins 25% value.
Further Hayman Reese were once advocates of 100% FALR but now suggest a value of approximately 50%. Safe Weigh hitches (please check website) offer a pressure/load gauge on their hitch and advise what the load should. The recommended load equates to an approximate 50% FALR. So now manufacturers of hitches who make money from their product and do not want to get sued also suggest a 50% FALR.
Which is equal to the value stated in SAE J 2708 the standard, albeit without the conditions of the standard.
Another comment has suggested that there is some inference that there would need to change the gravitational constant. It changes enough on its own, but the commonly accepted value is 9.807 m/sec/sec. and is not used in the solution anyway. A WDH does not violate the first two dot points above and does not change the gravitational constant. Commentator has provided a theory as to how the WDH should be calculated, but fails to achieve the load levelling axle loads above described as being from a check weigh at Yarragon. A theory which fails to give answers that are close to the actual figures is probably incorrect.
The fourth dot point explains how a WDH works. But let me add a clarification. The ball load which results from the caravan being hitched to the vehicle is a constant value but it is not the total of the forces which act at the ball. The total force which must be used is BL in kg + (1-762/ball to van axle distance) * LL in kg. For a standard 30-inch spring bar. It is then a moment calculation.
The additional force to the caravan axles is (762/ball to van axle distance) * LL in kg. for proof of this please check the Weigh Safe website and have a play with their calculator.
Yet another comment questions whether it is correct that a ball load reduces the understeer gradient and a WDH reduces it further. It is correct. Reference any of Klein, Rivers, Pacejka.
Another question relates to the recommended values of lateral acceleration at which the understeer gradient falls to zero. I have advised the minimum value from SAE J2807 of 0.3 g which is at 100% load levelling SAE J 2807 also identifies another value of 0.4 g at 50 % load levelling. The latter value is difficult to achieve.
I have probably missed some comments so I apologize to those with unanswered questions.
As well, after reading a comment on LC 200s yesterday, what is the real question? How it works, the FALR, the ball load, the distribution to the caravan, or a contest between good and evil?
One last point. A WDH does not change the mass of the car. The results above defined at a weighbridge or equal illustrate that the axle weights are different. This occurs through the lever system that creates moments.
Trusting that everyone has fun with this and stays safe throughout the year
i do confess that i maybe some what slow and FOOLISH but why would you buy a WDH before you determine if you need one or if there could be a better way to fix the issue you are trying to resolve or do you think joe down the road has one I got to get one after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth?
assuming you are trying to level your rig?
you may have to much weight on tow ball or in back of tug move some stuff /get rid of some stuff
maybe a extra leaf in rear spring will fix the issue
as shown in posted pictures a WDH can impose loads on places that may not be able to handle them and may cause more problems than they solve
-- Edited by dogbox on Tuesday 16th of January 2024 04:05:38 PM
Whilist I support the use of a WDH where it is needed, I don't advocate that everyone should.
I guess some caravan salesmen see a WDH as an upsell accessory, like other junk that is not needed foisted on to unsuspecting customer.
If you are required to use one, then comply. Some quibble over the weight of the WDH choosing to use a helper springs and sir bags, but these item cannot transfer weight to the front axle.
If its not a required item then everything starts with getting the ball height to match the coupling height, then its a case of moving weight around your vehicles to get both vehicles level to a degree, generally +/- 25 mm at the rear axle is a good starting point, unfortunatly most punters do this before both units are fully laden as if you are leaving on your journey. now its time to get to a weighbridge and make sure everything is correct, unfortunatly this is another task that many ignore.
Its only now will you find out if a WDH is maybe needed, if you cannot get weight on your front axle.
I think I found a pic that may help some of you visualize how a WDH actually works....
Ron
I still have a problem with the statement that tow ball load does not change.
The weight of the car on the weighbridge is constant regardless of other load imposed by the caravan. So it follows the tow ball load is reduced when a WDH is tensioned.
Alan
Alan, It is only you and Yobarr that are arguing this issue. It is a pointless argument because it can only be answered in theory and once the van is connected, can not be actually measured to prove it one way or another. It makes no difference in the function of a WDH and I don't think anyone is disputing how the weights on the different axles change. It is arguing about the internals of how the result is achieved, and who cares anyway?
I suggest both you and Yobarr stop flogging a dead horse. You will never agree and Yobarr will never give any explanation other than "because I have said it before, and expert x says it is so."
The fact that he will never give an explanation shows he can't. Let's avoid yet another WDH thread going downhill over this constantly repeating but unimportant issue.
-- Edited by Are We Lost on Tuesday 16th of January 2024 08:24:51 PM
... after all these tugs we are buying are advertised to tow 3500 kg so it must be true why would they twist the truth?
Technically it is possible for most utes to tow 3500kg but not realistically so unless it is a dog trailer. Most have 6000kg GCM, so the tug can only weigh 2500kg .... dangerously underweight, and often only enough allowance for the driver and a toothbrush. But if they market it as 3000kg while a similar vehicle is marketed as 3500kg how many sales would they lose? And yes, it can tow a dog trailer OK, albeit subject to that restrictive 2500kg maximum vehicle weight.
... assuming you are trying to level your rig?
That should not be the goal to aim for. Level or not is just a symptom. The primary goal is to get more weight on the front wheels (and hence road grip). As a result, the symptom of not being level is addressed. A secondary goal is to reduce porposing and this is where a WDH shines because it dynamically increases tension the more it is needed, and reduces to zero when not needed.
....maybe a extra leaf in rear spring will fix the issue
For someone who is towing most of the time it could be a good idea, although at the expense of ride comfort. It would have some effect on reducing porpoising but would do nothing to restore lost road grip. It would hide the symptom so everything looks OK but is not OK. Done in combination with a WDH ... sure.
..... a WDH can impose loads on places that may not be able to handle them
Yes, quite true, but usually if the vehicle does not support a WDH it will have a warning against their use. Of course some people will misadjust them or use them in situations they should not. When used conservatively on a towing capable vehicle and a strong enough van, the risk of problems is miniscule.
Gundog, I agree with most of what you say but disagree on needing to see the result to know if a WDH is required. Imagine a vehicle with very stiff suspension vs one with soft suspension. One will show no visible need for a WDH while the other will be very obvious. I believe it can be decided by knowing towball load and the ratio between wheelbase and towball overhang.
For example, assuming a typical ute or SUV with laden weight of 2500kg or more. A 300kg towball weight will put around 425-440kg load on the rear axle and lift the front by about 125-140kg. More weight in the back of the tow vehicle increases that disparity. To me, it is obvious that such a rig would benefit by the use of a WDH. A starting point for adjustment would be to restore about 50% of the sag at the rear, followed up with confirmation at a weighbridge, and then adjust as needed after some driving time.
RAvanner raised the interesting point on understeer (caused mainly by insufficient load on the front axle vs rear axle) but has not progressed further. From driving, the increase in understeer without a WDH is very obvious. I would be interested in how much the weight difference front to back is considered best.
One other point. While I am an advocate for WDH, I don't believe one is always required. If the van is light for the tow vehicle or the towball load/weight in the rear of the vehicle is not great, then one is probably not needed. Weighbridge measurements are the prime determinant, and tension should never be so high as to induce oversteer.
-- Edited by Are We Lost on Tuesday 16th of January 2024 09:27:24 PM
Hi Stephen, as I am about over talking to a brick wall who either does not, will not, or cannot understand facts I had decided to stay away from this thread, but your post has made me rethink.
Please note that I am not arguing, but merely stating indesputable facts.
Also please know that I know a lot more about this topic, and that a WDH DOES NOT change towball weight, than I am prepared to post here.
If people like Alan cannot understand what already has been posted, any further revelations that I might make would cause absolute mayhem. Alan's totally incorrect assertions do not bother me at all, as everybody is entitled to an opinion, no matter how misguided they may be, but my major concern is that newbies, and even current members keen to learn, will be negatively impacted by his ramblings, to their detriment.
Believe me, I have delved right into this, but any further revelations would cause total mayhem. Cheers
-- Edited by yobarr on Tuesday 16th of January 2024 09:55:48 PM
Thanks for this paragraph Stephen, and its indesputable truths. Previously, several times, I have pointed out exactly this to Graham, but it has either been ignored, misunderstood, or went right over the top of his head.
Perhaps your post will do better? Cheers
Alan, again, for the 73rd time (approximately!) I suggest that you take your fully loaded car and van, along with the adored WDH, to a weighbridge and conduct the weighing exercises that I have outlined many times.
Provided that you don't fiddle the figures to suit yourself you will see that what I have been saying for ever is indesputably correct.
The weight of the car on the weighbridge will change, as will the weight of the caravan.
k
For a WDH that uses bars from an arrangement on the hitch near the towball, and then tensioned to locations usually about 30 inches from the tow ball, the tension in the bars lifts and applies uplift to the tow hitch and tow bar, not the towball. So the lift force does not happen at the towball.
The forces in the tension bars that provide the lift to the hitch and tow bar are located at the tension points. These forces are downwards onto the drawbar A frame. The forces downwards on the drawbar increase the overall load to the van and that is why the axles loads of the van increase when the bars are tensioned.
I would expect that actually there would be an increased downwards load on the actual towball when the bars are tensioned, but meanwhile the hitch and towbar are being lifted which reduces the load on the vehicle ands changes its axle loads.
Sorry, too late at night to try some actual numbers in an example.
You're onto it Ted. Previously I have posted the results from my actual weighing exercise, but it's 4.30am here and I've justed started the Roadtrain, so off to work we go! Maybe I'll find time later to look for them. Cheers
try to think of it as a clamp ,the downward forces are neutralized by the upward forces so no change in actual weigh of set up other than clamp. which as i mentioned earlier an was told i must be a fool, but a WDH can vary in price from a couple of hundred dollars to over a thousand an add up to 40 kilos of weight and if you are going off road it is recommended to disconnect anyways, better to fix the problem if possible than try an patch it up
Yes. Due to the differing lever principles, the uplift from the bars is greater than the load from them onto the drawbar. So the net effect is a lifting of the rear, resulting in weight being transferred from the rear axle to be shared between the front axle and the van axle.
Not quite. As per my response to Watsea, the forces are not neutralised. There is a net upwards force. That is why the rear end rises back up, and the basis for how the system functions.
If by fixing the problem you are referring to suspension modification in preference to a WDH, you are not fixing the problem at all. You are hiding it from view. See more detail in my response last night.
-- Edited by Are We Lost on Wednesday 17th of January 2024 09:46:31 AM
I was referring to the idea of doing a bit of research and buying a balanced rig with some minor adjustments not trying to fix a problem of buying a caravan that does not suit the tow vehicle then have to buy/use add on to fix the problems.
look on you tube an see the amount of money spent on upgrading vehicles and caravans to make them legal then some one comes along an thinks they can achieve the same result without spending the dollars loading up the ute putting boat on roof outboard motor 3500 kilo plus caravan then go out an share the road with the rest of us
the "net upward force" is transferred to the chassis of tug transferring weight from rear axle to front axle and caravan axle(s) via downward pressure on caravan chassis ,other than the clamping effect on the tow ball no additional weight is applied to tow ball
-- Edited by dogbox on Wednesday 17th of January 2024 10:34:51 AM
It is the net upwards vs downwards force (clamping effect) at the towball/coupling that causes the rear end to rise. The upwards effect is greater than the downwards one. That is as close as I am going to the never ending argument.
It was stated that the force imposed on the ball by the van does not change. Absolutely correct. Further that that the WDH acts to provide a clamping force to the ball which is equal to the force from the load bars once again correct. However, the clamping force is usually 762 mm from the ball hence is less than the full load from the spring bars. Think of a painter on a plank If he/she is in the centre of the two supports each support sees the same force. If the painter moves left or right the forces at the supports are different, a WDH is the same. The total force on the ball is:
BL in kg + (1-762/ball to van axle distance) * LL in kg.
Any analysis must consider this and the load levelling force at there respective distance from any fixed point but the simplest is the front axle of the vehicle.
Example say 285 kg ball force, ball to van axle 4.4 m and the load from the spring bars to be 220 kg. Which is usually an unknown value.
Then:
Total force on the ball with the WDH is 285+(1-762/4400) *220 which equals 466 kg. the sum of the vertical forces at the ball is 466 220 = 246 which means that 39 kg has been transferred to the vans axles.
As I do not have access to Hayman Reeses files, I cannot comment whether they have proven this or not, nor can any one else. I can suggest that Hayman Reese has proven this. I can also advise that the Safe weigh hitch with its inbuilt pressure / load gauge offers proof of concept.
Perhaps uncharitably I am unwilling to accept speculation as to how a caravan chassis may have cracked. It may be for any number of reasons; it may have been exacerbated by the WDH. But the reason for the failure it cannot be determined from a photograph.
I think it was Yobarr who suggested he has information which would cause mayhem, a little mayhem never hurt anyone and probably should be provided to be discussed and or debated or accepted or rejected.
Sorry people Heavy stuff ahead!
With regards understeer and understeer gradient the following are calculated results utilizing Pacejka or equivalent equations for a specific set up.
These are mathematically correct; they are consistent with what experimental researchers and theoretical researchers report. They will never be absolutely correct but they illustrate what occurs.
Vehicle alone critical speed > 180 kph, static understeer gradient +0.0045, damping ratio at 100 kph 0.9.
Vehicle +BL critical speed 162 kph, lateral acceleration at which US/gradient is zero 0.51, U/S gradient -0.01384, damping at 100 kph 0.1.
Vehicle +BL+ 50% LL critical speed 137 kph, lateral acceleration at which U/S gradient falls to zero 0.355, US gradient -0.0197, damping 0.13.
Vehicle +BL+ 100% LL critical speed 120kph, lateral acceleration at which U/S gradient falls to zero 0.072, US gradient -0.0256, damping 0.16.
The SAE J2807 values previously advised are recommended minimums. Almost certainly with a level of safety incorporated.
Road designers I believe employ a value of 0.15 to 0.2 g for the design of curves at the design speed. Hence the 0.3 and 0.45 of lateral acceleration at which the understeer gradient falls below zero values are conservative.
But this is essential given the potential of less than perfect road surfaces, tyre condition and pressure, ambient weather conditions etc.
I am not going to attempt to discuss the solution of quartic equations (which Pacejkas formula reduce to), imaginary numbers or the magic tyre formula all of which contribute to the answers above.
End of heavy stuff.
But a WDH does have an impact, hence the opening comment A WDH has as far as the operator is concerned only has one purpose. It does lots of things!
Trusting that everyone has fun with this and stays safe throughout the year
Thanks Ron, for this detailed and accurate workings if a WDH, which should quieten those who seem not to understand simple physics, and peresevere with their seemingly endless streams of waffle that invariably causes friction (no pun intended) whenever a question is asked about WDHs.
Thank you sincerely, and I will put this post among my recordes so any further discussion can quickly be squashed. Cheers
P.S Despite your kind offer I will not further "Rock the Boat"
A WDH does NOT change towball weight.
Never has done.
Never will do.
These terms are not interchangeable and both the sprukers and the readers need to understand the difference and get them correct.
Not doing so makes this whole thing a pointless mess.
Cheers,
Peter
A slightly shorter and simpler formula to calculate the effect of the bars on the van axle is just to use ratios and not include the original towball load because it needs to be subtracted again in a second calculation and has no bearing on the change to the weight on the van wheels. So:
Load applied by bars (kg) to drawbar X (load point distance to axle / towball to axle distance). Using your 762mm as the load point, the distance from there to the axle is 3638mm.
220 x (3638 / 4400) = 38.1kg. To calculate the load added at the towball is 220 x (762 / 4400) = 181.9kg. Add original towball load if you wish.
RAvanner, as I said before you provide a lot of information but little to help the typical vanner.
For example:
"Vehicle +BL+ 100% LL critical speed 120kph, lateral acceleration at which U/S gradient falls to zero 0.072, US gradient -0.0256, damping 0.16."
I picked the lowest critical speed from your list. Ignoring the fact that it is faster than any sensible caravanner would travel, how should this information be applied in a practial sense? With the descending list of speeds can any meaningful interpretation be made for someone who travels under 100kph?
"Road designers I believe employ a value of 0.15 to 0.2 g for the design of curves at the design speed. Hence the 0.3 and 0.45 of lateral acceleration at which the understeer gradient falls below zero values are conservative."
What does this tell me in relation to what I should be considering or aware of with my rig or when driving?
-- Edited by Are We Lost on Thursday 18th of January 2024 01:13:40 AM
Ron
Still no response re Newtons laws and unchanging tow ball weight.
Your calculations show that tow ball loading is reduced by 39 Kg wt, and axle weight increased by said amount.
This obeys Newtons law.
Jobarr needs to define what he means by weight.
The weight of an object is the force acting on the object due to acceleration or gravity.
We are on ly interested in gravity on earth.
Note it is a force, and on a theoretical 3000kg. caravan:
The wheels are exerting a downward force of aprox. 2700N(Newtons) and the tow ball is exerting a downwards force of apron. 300N.
When we install a WDH it(the WDH) creates a torque on the vehicle which exerts a downwards force on the vehicle's front wheels and an upward force on the rear wheels and tow bar. This torque rotates the vehicle about the vehicle's centre of mass forcing the front of the vehicle down and the rear of the vehicle up.
If we measure the weight of the vehicle it will confirm that the weight on the front wheels increase and the weight of the rear wheels decrease.
Or to put it another way the WDH torque is added to the front wheels and subtracted from the rear wheels.
There is also WDH torque on the tow ball and because it is in the opposite direction to the tow ball force it is subtracted from the tow ball force. This increases the force on the caravan wheels. And when weighed the van wheels show increased weight.
If the weight of the caravan wheels change then there must be a corresponding change in the tow ball weight.
When we measure weight we are really measuring the force exerted on the vehicle and van by gravity
That the rear of the vehicle rises indicates that the tow ball weight has decreased.
But does it really matter? Only for explaining why disasters happen when the vehicle and the caravan relative angle change while negating a culvert or creek bank.
Jegog
I get the drift of your arguments, but you are out by a factor of 9.807 on your weights expressed in newtons.
What you have is weight in Kg wt.
My concerns with the use of a WDH is Yobarr insists that the van becomes heavier overall and thus could exceed it's ATM rating.
As this discussion progresses it become more complicated.
Rons analyses confirms that simple arithmetic achieves the same result.
Cars hitched weight minus cars weight equals tow ball download with or with out aWDH.
Alan
In this forum, under the thread "WDH again", on May 13 and 14, 2023, I presented some WDH calculations where I had modelled the WDH to be a simple torque application device. Please refer to those previous posts if you are interested.
Attached is a sheet of calculations where I have modelled a WDH as a tension bar type.
I used the same vehicle and van dimensions as my May 2023 calculations but assumed the vehicle and van had no mass. This gave values of forces involved, just from the bar tensions. I used a distance of 650mm from the towball coupling to the bar tension mounts. This is a little more accurate that 760mm because that 760mm is along the A frame rails rather the centreline of the van.
As I expected, the changes in weights of all the axles, due to the WDH using bar tension are the same as my May 2023 calculations. The January 2024 values and the May 2023 are essentially the same if one takes calculator rounding errors into account. The January 2024 calculations show the increased load on the towball coupling when using a bar type WDH, but into the tow hitch the bars are counteracting that extra coupling load.
Not again, Greg? Tomorrow, if I can find time, I will respond to this post. Of course ATM doesn't change. It's a rating, but the Weight on wheels (GTM?) increases while towball weight stays the same.
Clearly the van weighs more, using the generally accepted meaning of weight.
It is pointless discussing mass when all we're trying to do is help others understand.
Again I will say that a WDH is used only by people who are trying to make a car do things for which it was not designed.
Indesputable, inconvenient truth.