A lot will depend upon the loading of the rear axle. When you put a load on your tow ball it lifts the front axle of the tug. The weight that comes off the front axle has to be added to the tow ball weight to ascertain the weight imposed in the tugs rear axle. This gives rise to the situation where the tug can be well within its GVM, but the extra load on the rear axle is greater than the maximum allowable for the vehicle. This means that the rear axle is overloaded. You then require a WDH to distribute some of that weight lost from the front wheels back onto the tugs front wheels.

You will need to load up your van and tug ready for travel plus all passengers and full fuel. Then head down to the nearest weighbridge and do some weighing.

Just to answer questions re weights / measures;

Current Model MU-X; build 10/22, Registered Nov 2022.

3500 braked towing capacity

140 Kw

450 Nm

2855mm wheelbase

2085 kerb weight

Total payload 615 kg

Axle loads; Front 1450kg ; Rear 1650 Kg

GVM 2700 Kg

Gcm 5900 KG

Maximum Towbar down load 350 Kg

Caravan GVM 2261 kg

Towball weight measured 235 KG

The hitch is as supplied by EazLift and the ball is 300mm from the front of the "socket" the hitch slides into.

I hope this assist, and I do thankyou all for you comments.

keiron wrote:

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Just to answer questions re weights / measures;

Current Model MU-X; build 10/22, Registered Nov 2022.

3500 braked towing capacity

140 Kw

450 Nm

2855mm wheelbase

2085 kerb weight

Total payload 615 kg

Axle loads; Front 1450kg ; Rear 1650 Kg

GVM 2700 Kg

Gcm 5900 KG

Maximum Towbar down load 350 Kg

Caravan GVM 2261 kg

Towball weight measured 235 KG

The hitch is as supplied by EazLift and the ball is 300mm from the front of the "socket" the hitch slides into.

I hope this assist, and I do thankyou all for you comments.

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 Looks OK Keiron,but you'll need to watch rearaxle load because your 235kg towball weight puts around 350kg onto that lightweight axle. Depending on model,a WDH usually increases towball overhang (TBO) or distance from rear axle to hitchpoint, thus adding even more weight to your lighweight rear axle,and increasing the effects of yaw,or the "tail wagging the dog" effect. This will be more severe than it is on many cars because of the short wheelbase. Despite having a tow rating of  3500kg,there is no way known your car could safely tow more than about 3000kg ATM as a PIG trailer.(Caravan) Cheers 

Dougwe wrote:

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 Ding Ding Round 1 of 15.

Oldbloke, I like the spreadsheet you attached, although I have not actually entered any values to confirm it all works.

As for the HR video you linked, I dont think they are saying the rear end sagged 15mm. That is the measurement after first fitting the bars. If you look closely at the video at 3:01, you can use the rear bumper sensor to estimate the sag. I would say about 30mm. Crazy that they dont show the before and after measurements.

You may know from previous threads I am a strong believer in using WDHs. But in the example with the black Ford Ranger (same model as mine) I don't see it as so clearcut. Rangers are a little light at the rear end so will benefit from a little extra weight. On that basis, if the weight on the rear end is small, it may not be an improvement. But, put much gear in the rear of the Ranger and the situation changes.

The other problem with the video is only using a tape measure to make the decision. What does 30mm sag mean in weight? What they should have focused on is measuring the actual weights before and after WDH setup. In real life the correct way to go about it would be to fully load both van and tow vehicle as if for travel and take it to a weighbridge. Then it will be clear how much weight is on each axle. The greater the difference front to back, the more the road grip differs.

On to Kieron's question. While your van is not in the heavier range it is getting close to the laden weight of your MU-X. Your payload of 615kg means 380kg remaining after you attach the 235kg onto the towball. That covers passengers, fuel and whatever else you carry. Its hard to say if this will still be within your rear axle limit. Remember that 235kg alone means around 350kg on the rear axle. But without doing a weighbridge trip you will not really know.

So your actual MU-X weight maxes out at 2465kg (2085 + 380). Its heavier than the van, but not by a huge margin about 7%. You already have the WDH so it will be easy to compare with and without. I suspect that you will much prefer the feel on the road with the WDH fitted.

Also, while the 2855 wheelbase is not bad, it falls well short of the better tow vehicles. You say the towing shank appears longer than necessary. I would put that as a priority to shorten it. That will help with rear axle load, and improve resistance to trailer sway.

From the specifications you posted you said the van GVM is 2261kg. Presumably this is from the VIN plate and is recorded on your registration papers (the maximum legal weight to be on the caravan wheels). This suggests the van ATM would be over 2300kg.

If you dont have time to load up and go to a weighbridge before your trip, I suggest planning for one on the way.

Are We Lost wrote:

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Oldbloke, I like the spreadsheet you attached, although I have not actually entered any values to confirm it all works.

As for the HR video you linked, I dont think they are saying the rear end sagged 15mm. That is the measurement after first fitting the bars. If you look closely at the video at 3:01, you can use the rear bumper sensor to estimate the sag. I would say about 30mm. Crazy that they dont show the before and after measurements. "

You may know from previous threads I am a strong believer in using WDHs. But in the example with the black Ford Ranger (same model as mine) I don't see it as so clearcut. Rangers are a little light at the rear end so will benefit from a little extra weight. On that basis, if the weight on the rear end is small, it may not be an improvement. But, put much gear in the rear of the Ranger and the situation changes.

One of the big disadvantages of the "cure it all" WDH,seemingly adored by many,is that too much weight can be removed from the car's rear axle so that oversteer easily occurs. The transferred weight also makes it much easier for the trailer to be affected by yaw,or the "tail wagging the Dog". 

The other problem with the video is only using a tape measure to make the decision. What does 30mm sag mean in weight?

It means nothing,because the sag is dependent on,among other things,the weight on towball,the TBO,the load carrying ability of the springs,how "tired" the springs are,and the wheelbase of the car. As well as being 8 years old,this video is "old school" thinking.Using a tape measure was a method last used by Noah when he drew plimsol lines on the Ark.

What they should have focused on is measuring the actual weights before and after WDH setup. In real life the correct way to go about it would be to fully load both van and tow vehicle as if for travel and take it to a weighbridge. Then it will be clear how much weight is on each axle. The greater the difference front to back, the more the road grip differs.

Measuring the actual weights is the only sensible way to find what effect the WDH has had,but even that can present problems because of the weighbridge increments.

On to Kieron's question. While your van is not in the heavier range it is getting close to the laden weight of your MU-X. Your payload of 615kg means 380kg remaining after you attach the 235kg onto the towball. That covers passengers, fuel and whatever else you carry.

If the car is carrying 1650kg maximum weight on the rear axle,with a GVM of 2700kg,there's only 1050kg left for the front axle. These cars have 1080kg rear axle weight at tare,to which we add 350kg for weight added by the towball,50kg (?) for towbar structure and you're already up to 1480kg,with no passenger,no luggage,no tools. The 300mm from the "socket" to your hitchpoint seems excessive,obviously increased by the WDH unit itself.That distance on my car is only 160mm and results in way less weight being added to the rear axle by towball weight.When I briefly fitted a WDH that weighed 33.60kg (HR figures) I also used a heavier adjustable drop shank which weighed  more than the standard shank,so total weight was over 35kg.Thus I increased the weight on the rear axle of my car by 55kg before I even hooked up the van! 

     It's hard to say if this will still be within your rear axle limit. Remember that 235kg alone means around 350kg on the rear axle. But without doing a weighbridge trip you will not really know.

So your actual MU-X weight maxes out at 2465kg (2085 + 380). Its heavier than the van, but not by a huge margin about 7%. You already have the WDH so it will be easy to compare with and without. I suspect that you will much prefer the feel on the road with the WDH fitted.

Also, while the 2855 wheelbase is not bad, it falls well short of the better tow vehicles. You say the towing shank appears longer than necessary. I would put that as a priority to shorten it. That will help with rear axle load, and improve resistance to trailer sway.

Excellent advice in this last paragraph.Short wheelbase and long TBO is asking for trouble. Cut the shank back as far as you can,unless the receiver has an open end,in which case the shank can be pushed fully in,and a new hole drilled for the retaining pin.Mind you,cutting the excess oength off the shank will help reduce weight!

From the specifications you posted you said the van GVM is 2261kg. Presumably this is from the VIN plate and is recorded on your registration papers (the maximum legal weight to be on the caravan wheels). This suggests the van ATM would be over 2300kg.

Unusual for caravans to have a GVM,I believe,with ATM being the generally used term.GVM is used when referring to powered vehicles,I believe. Perhaps the figure referred to as "GVM" is actually the GTM,or weight on trailer wheels? 

If you dont have time to load up and go to a weighbridge before your trip, I suggest planning for one on the way.

Good post Stephen,showing that you have a far better understanding of weights and physics than do some others! Cheers

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-- Edited by yobarr on Friday 4th of February 2022 05:27:58 PM

I believe I said

"A. About 5 minutes into the video attached is the answer.
If the rear of your mux sags (without a WDH) about 15mm you need to consider using a WDH."

I didn't say or suggest he must or that it would be unsafe.

At 4.00 min the bloke in the video says " do not place too much strain on the spring bars but they do need to be firmly in position" 

My interpretation of that the bars would have very little "effect" .

So I believe they are certainly suggesting 15mm sag is when you need to consider it's use. (Personally I think 30mm is a bit much. In any case each set up will be different.) And the HR video talks about a 12mm tolerance.

That is what HR is saying and I'm in no position to say they are wrong. I'm certainly not an engineer working as a transport specialist. And I'm not going to tell them what to say in their manuals or videos.

I think most would agree that you should weigh once you are loaded and set up to confirm all is well. They are talking about the initial "set up" after all. 

Just one thing that should be checked is: is the Eazlift WDH suitable his TBW? 

If you down load the spread sheet you can enter your own data. My weights are of no use to anyone else. That's why they were deleted.

keiron wrote:

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yobar.

Victorin Rego states; GVM 2261.

Not a missprint or typo.

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 The same for NSW. Tare is also shown, but no ATM.

Cheers.

keiron wrote:

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Hi again. I am ready (?) to do a short run around NSW, 6 days, with my new Isuzu NU-X, current model, towing my Jayco Starcraft weighing 23oo kg. Whilst I have not yet dropped the van onto the towball, I am expecting minimal, 30-40mm drop at the towbar. My first question is;

                 at what point is it felt essential / necessary to use WDH as opposed to relying simply on the towbar / ball without WDH? Towbar download allowed 600kg, Van ball weight is 230kg.

I have Eazlift WDH and Bars, with the centre-line of the towball being 300mm from the goose-neck receiver, which seems to be a long way, (although it worked fine on my old Patrol). My second question is:

                 What is the normal / accepted (?) distance from hitch to centre-line of ball, and is it possible to buy a shortened WDH hitch assembly?

Thank you as always for any assistance.

KB

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Can I make a suggestion.

The van is not on the heavy side.

Measure the height of your car at the guards as indicated in the video. Note them.

Ensure ball and coupling are same height,

Connect the van and remove the jockey.

Re-measure the height of guards and note again.

Go for a drive, perhaps 25k. Mix it up. Town, Hwy, perhaps a hill or two. Nothing crazy, sensible speed. If you can weigh everything. There are free weigh bridges in Vic, perhaps NSW also?

Now set up the WDH and make the car level or very close. (12mm)

Go for another drive. If you can weigh everything. Make a judgement.

Perhaps if you can, print out the form I uploaded to note the weights at the weigh bridge with pen and paper. It may help.

Attached from another forum. How to weigh the rig.

oldbloke wrote:

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Keiron,

Perhaps this will help. Been meaning to do this for a long time. Something practical that people can use rather than a lot a wordy & perhaps confusing information.

I'm sure if there is an error everyone here will tell me. :) 

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Whilst this chart is not entirely accurate,because of flawed methodology,it will at least be of some assistance to those members who are in the early stages of learning about weights and physics,and show some interest in having setups that are both safe and legal.Cheers