Tandem Axle - different tyre pressures front and rear
vince56 said
01:50 PM Oct 23, 2020
Hi All,
I was reading with interest on a car forum that some use higher pressures on the rear tyres on their dual axle vans, for instance one person ran 50 front and 55 rear.
The explanation was that this would aid in a sway situation as the rear would have control of the sway further from the pivot point.
Any thoughts?
yobarr said
02:19 PM Oct 23, 2020
vince56 wrote:
Hi All,
I was reading with interest on a car forum that some use higher pressures on the rear tyres on their dual axle vans, for instance one person ran 50 front and 55 rear.
The explanation was that this would aid in a sway situation as the rear would have control of the sway further from the pivot point.
Any thoughts?
Hi Vince....first off,I will say that it must be a very heavy van to need those pressures.Holy Moley! I run the rear axle on my car at 2300kg,and find that the ideal tyre pressure is around 60 psi....maybe a little less.Like the person to whom you refer,I run slightly more pressure in my van's rear-axle tyres than I do in the front.My GTM (weight on van wheels) is 3150kg,so I run 40psi in the front axle,and 42psi in the rear.Doing this reduces the tendency for the van to "pivot" on it's front axle,which can cause the rear axle to be the one that sways,as your friend suggests.When I turn sharply,it is very easy to see that the front axle moves sideways,rather than the van pivoting on that axle,and the rear axle of the van moving sideways.This obviously is a pointless exercise with load-sharing suspension.Cheers
Peter_n_Margaret said
02:30 PM Oct 23, 2020
The lower pressure tyres will have the greater grip (assuming identical loads). Cheers, Peter
-- Edited by Peter_n_Margaret on Friday 23rd of October 2020 02:32:02 PM
Whenarewethere said
02:39 PM Oct 23, 2020
Lower pressure will reduce the stress & everything been knocked to pieces.
It's why I have 3 compressors in the car so I can reinflate the tyres extremely quickly.
Rod Mac said
02:46 PM Oct 23, 2020
When I collected my van 4 years ago I was informed to run the tyres at 50 PSI (older Tandem roller rocker) so after one broken spring in the first year and then a bent axle in the second year, I checked an online tyre pressure calculator and now run 38 PSI all round, sits and tows nicely and nothing has broken.
I believe the high pressure was transferring to much load and shock from rough roads and potholes to the suspension and not absorbing some of it in the sidewalls of the tyres.
As for more pressure in the back axle theory, my thoughts are if you have a slightly nose down attitude of the van (not on purpose but just how it sits) then you are likely to have slightly less load on the rear axle with more load on the front one so you are negating the higher pressure in the rear set up.
I know that raises this question, if you have a slightly nose up attitude then what happens, you have then loaded up the rear axle more than the front one.
Good reason to have the van sit level or close as possible to level.
Will be interested in other people's thoughts.
yobarr said
02:50 PM Oct 23, 2020
Peter_n_Margaret wrote:
The lower pressure tyres will have the greater grip (assuming identical loads). Cheers, Peter-- Edited by Peter_n_Margaret on Friday 23rd of October 2020 02:32:02 PM
Hi Peter.... don't think that that is true,provided the tyre pressures are within their operating perameters.Think sidewall flex.You surely are not suggesting that a tyre at 20psi will have a better grip than would a tyre at 40psi,assuming no load-sharing axles and a level van? Cheers
Peter_n_Margaret said
02:59 PM Oct 23, 2020
yobarr wrote:
Peter_n_Margaret wrote:
The lower pressure tyres will have the greater grip (assuming identical loads). Cheers, Peter-- Edited by Peter_n_Margaret on Friday 23rd of October 2020 02:32:02 PM
Hi Peter.... don't think that that is true,provided the tyre pressures are within their operating perameters.Think sidewall flex.You surely are not suggesting that a tyre at 20psi will have a better grip than would a tyre at 40psi,assuming no load-sharing axles and a level van? Cheers
Ask any drag racer...... tyre pressures are as low as they can go without destroying the tyre.
Same with rock crawling.
Cheers,
Peter
Radar said
09:09 PM Oct 23, 2020
I did read read this article by a Journalist, supposedly expert in everything motoring about 3 years ago, tried a couple of test with varying pressures on the caravan.
Decided, juno had very little to do on a day and put this story together with out really testing in real life travels. After I wasted several hours of testing. First test was Toowoomba to Brisbane, some high speed then some lone speed. Second test was Brisbane to Grafton.
I used the 4psi rule. Just about drove my lady mad jumping ojt of the car to test the tyre pressures.
Grafton to Gosford I went back to tow vehicle specs pressures front 34psi,, rear 36psi when loaded and dual axle caravan is run with 40psi. It sèems to be happy at that.
Theory is believe about 25% of what you read.
Jaahn said
08:58 AM Oct 24, 2020
Radar wrote:
I did read read this article by a Journalist, supposedly expert in everything motoring about 3 years ago, --------------
Theory is believe about 25% of what you read.
Ha
But which 25% is the real problem ??????
Jaahn
kesa32 said
09:05 AM Oct 24, 2020
This is a topic Collyn Rivers brought up ( years ago ) as a helpful aid to sway issues on tandems , found it helpful and worthwhile..... and it's free
yobarr said
10:16 AM Oct 24, 2020
kesa32 wrote:
This is a topic Collyn Rivers brought up ( years ago ) as a helpful aid to sway issues on tandems , found it helpful and worthwhile..... and it's free
Hi Ken....Thanks for that.I had decided to make no further contribution to this topic,but your mention of Collyn Rivers changes my mind! Anyone who knows of Collyn will understand that he is a well respected expert on weights and dynamics,with over 50 years experience in this field.His advice is,I believe,to run 5psi lower pressure in the front axle of a tandem van.This allows the softer tyres to scrub across the ground when the van turns or sways,which increases sway resistance.To make a point,this example may help some to understand, although the difference in pressures is extreme? Try running 10psi in the rear axle,and 50psi in the front.You now will find that the front axle is very much in control,as it has become the 'pivot',and the effective drawbar length has been reduced.Next,try running 50psi in the rear axle,and 10psi in the front.The rear axle now is the 'pivot',effective drawbar length has increased,and the ball weight has also been increased.Hard to argue with simple physics.Cheers
Hi Peter....Sorry,can't help there as I am not at all computer literate,and have no idea how to do "links" etc.A while back I bought some of Collyn's books,and made lots of notes from them into my diary.(Old school). Once we had made the decision to live permanently on the road,we gave away many of our possessions,TVs,fridges,washer and dryer,beds,cabinets etc,and Collyn's books were among the hundreds of things we gave to various charities. When I get a minute I will try to source the relevant details.Cheers
outlaw40 said
10:46 AM Oct 24, 2020
Peter i think Collyns theories were discussed extensively on the caravanners forum . i had a van a few years ago that was , for want of a better term unsettled and i did find that collyns idea of running the front axle 5 psi lower than the rear helped somewhat .
darjak said
04:35 PM Oct 25, 2020
We have been full time since 07 covered 300+Ks.
Depending on which suspension you have and tyres.
My van 3200kg fully loaded, Simplicity Suspension, tyres 265/75/16 LT @ 38psi bitumen, 20 > 25 dirt & 14>18 sand.
Toyota 100 series 300L fuel, boat on top same tyres only pressure different 41psi bitumen, 25 rear for dirt.
Tyres are a part of your suspension if running them too hard you will only shake everything to pieces.
Pulled up once for a person on the Birdsville Hwy said it was his third puncher and asked me what
pressure I was running as his were 60psi when I told 25psi with no problems he soon let them down.
Never had anything to do with single axle vans or camper trailers so cant comment there.
yobarr said
07:27 PM Oct 25, 2020
darjak wrote:
We have been full time since 07 covered 300+Ks. Depending on which suspension you have and tyres. My van 3200kg fully loaded, Simplicity Suspension, tyres 265/75/16 LT @ 38psi bitumen, 20 > 25 dirt & 14>18 sand. Toyota 100 series 300L fuel, boat on top same tyres only pressure different 41psi bitumen, 25 rear for dirt. Tyres are a part of your suspension if running them too hard you will only shake everything to pieces.
Pulled up once for a person on the Birdsville Hwy said it was his third puncher and asked me what pressure I was running as his were 60psi when I told 25psi with no problems he soon let them down.
Never had anything to do with single axle vans or camper trailers so cant comment there.
Hi Darrell...those pressures look great in all conditions,for that size of tyre,with one exception.Working backwards,the figures show that your car's rear axle weight would be only 1600kg? Have you ever weighed that axle? Cheers
Aus-Kiwi said
09:33 PM Oct 25, 2020
Tyre pressures cold is much higher when hot . Drag racers surprisingly only travel 1/4 mile at a time and straight too ! Race cars start at 16-17 Lb . I look at tyre deflection . Ive found on my duel axle rear .6.5 ton motorhome . 55lb inside 65lb outside , 65 to 75 front . As a truck with much heavier load . Tyre pressures are around 90lb . Distance, road conditions, weight and speed all add up . See many tow vans at speeds way too high things falling apart inside !!
travelyounger said
05:51 AM Oct 26, 2020
vince56 wrote:
Hi All,
I was reading with interest on a car forum that some use higher pressures on the rear tyres on their dual axle vans, for instance one person ran 50 front and 55 rear.
The explanation was that this would aid in a sway situation as the rear would have control of the sway further from the pivot point.
Any thoughts?
I tow a 3500 ton van with the tug just under 3500 ton and on the van have cruise master suspension and have dropped the tyre pressure from 55 psi to 45 psi and have noticed a lot less things are thrown in around the van.
Have never had sway issues even with my old van which had leaf springs .I always travel with my water tanks full to keep the weight down low and correct me if I'm wrong I always thought swaying or the tail wagging the dog was more to do with incorrect tow ball weight and poor distribution of load in van or a trailer which has not been set up correctly and of course speed we should have a rule like they do in WA when towing a trailer a speed limit of 100 km pH .
Cheers
Peter_n_Margaret said
08:54 AM Oct 26, 2020
https://www.youtube.com/watch?v=zwlgZG55QWk
Cheers, Peter
Aus-Kiwi said
10:16 AM Oct 26, 2020
The foils are for dirt ,dust prevention sucking up the back ! Other than looks .
Hi Peter...tried to send thus as PM,but seems photos cannot be sent that way? You no doubt will recognise where it is from? This is the best I can do to provide the source of my information,but it really is only simple physics. Cheers
Cheers
-- Edited by yobarr on Tuesday 27th of October 2020 10:23:16 AM
My Caravan tyre pressures are at 44psi front and rear for my Toyo HO8 225/75 R15C.
I like many others followed the advice that was being suggested of the front tyres pressure should be lower than the rear, I lowered fronts to 39psi and the kept rears at 44psi, well that was an absolute disaster the mear hint of a semi overtaking created sway, rather than write it off as being wrong at the next servo I increased the fronts to 44psi and inflated the rears to 49psi, well I had to fight to regain control of the sway when being overtaken by large vehicles.
I considered the advice as totally unsuitable for my combination, considering I am required to use a weight distribution hitch as setout in my owners manual for towed loads over 1800kg, following the instructions for setting up my WDH both the Ute and Caravan are level, thus the lower front tyre pressure must create some instability factor.
I could go through the whole reset of the WDH with the different tyre pressures, but at the end of the day my combination is very stable in it origional setup, therefore if it aint broke dont try and fix it.
Hi All,
I was reading with interest on a car forum that some use higher pressures on the rear tyres on their dual axle vans, for instance one person ran 50 front and 55 rear.
The explanation was that this would aid in a sway situation as the rear would have control of the sway further from the pivot point.
Any thoughts?
Hi Vince....first off,I will say that it must be a very heavy van to need those pressures.Holy Moley! I run the rear axle on my car at 2300kg,and find that the ideal tyre pressure is around 60 psi....maybe a little less.Like the person to whom you refer,I run slightly more pressure in my van's rear-axle tyres than I do in the front.My GTM (weight on van wheels) is 3150kg,so I run 40psi in the front axle,and 42psi in the rear.Doing this reduces the tendency for the van to "pivot" on it's front axle,which can cause the rear axle to be the one that sways,as your friend suggests.When I turn sharply,it is very easy to see that the front axle moves sideways,rather than the van pivoting on that axle,and the rear axle of the van moving sideways.This obviously is a pointless exercise with load-sharing suspension.Cheers
The lower pressure tyres will have the greater grip (assuming identical loads).
Cheers,
Peter
-- Edited by Peter_n_Margaret on Friday 23rd of October 2020 02:32:02 PM
Lower pressure will reduce the stress & everything been knocked to pieces.
It's why I have 3 compressors in the car so I can reinflate the tyres extremely quickly.
When I collected my van 4 years ago I was informed to run the tyres at 50 PSI (older Tandem roller rocker) so after one broken spring in the first year and then a bent axle in the second year, I checked an online tyre pressure calculator and now run 38 PSI all round, sits and tows nicely and nothing has broken.
I believe the high pressure was transferring to much load and shock from rough roads and potholes to the suspension and not absorbing some of it in the sidewalls of the tyres.
As for more pressure in the back axle theory, my thoughts are if you have a slightly nose down attitude of the van (not on purpose but just how it sits) then you are likely to have slightly less load on the rear axle with more load on the front one so you are negating the higher pressure in the rear set up.
I know that raises this question, if you have a slightly nose up attitude then what happens, you have then loaded up the rear axle more than the front one.
Good reason to have the van sit level or close as possible to level.
Will be interested in other people's thoughts.
Hi Peter.... don't think that that is true,provided the tyre pressures are within their operating perameters.Think sidewall flex.You surely are not suggesting that a tyre at 20psi will have a better grip than would a tyre at 40psi,assuming no load-sharing axles and a level van? Cheers
Ask any drag racer...... tyre pressures are as low as they can go without destroying the tyre.
Same with rock crawling.
Cheers,
Peter
I did read read this article by a Journalist, supposedly expert in everything motoring about 3 years ago, tried a couple of test with varying pressures on the caravan.
Decided, juno had very little to do on a day and put this story together with out really testing in real life travels. After I wasted several hours of testing. First test was Toowoomba to Brisbane, some high speed then some lone speed. Second test was Brisbane to Grafton.
I used the 4psi rule. Just about drove my lady mad jumping ojt of the car to test the tyre pressures.
Grafton to Gosford I went back to tow vehicle specs pressures front 34psi,, rear 36psi when loaded and dual axle caravan is run with 40psi. It sèems to be happy at that.
Theory is believe about 25% of what you read.
Ha
But which 25% is the real problem ??????
Jaahn
Hi Ken....Thanks for that.I had decided to make no further contribution to this topic,but your mention of Collyn Rivers changes my mind! Anyone who knows of Collyn will understand that he is a well respected expert on weights and dynamics,with over 50 years experience in this field.His advice is,I believe,to run 5psi lower pressure in the front axle of a tandem van.This allows the softer tyres to scrub across the ground when the van turns or sways,which increases sway resistance.To make a point,this example may help some to understand, although the difference in pressures is extreme? Try running 10psi in the rear axle,and 50psi in the front.You now will find that the front axle is very much in control,as it has become the 'pivot',and the effective drawbar length has been reduced.Next,try running 50psi in the rear axle,and 10psi in the front.The rear axle now is the 'pivot',effective drawbar length has increased,and the ball weight has also been increased.Hard to argue with simple physics.Cheers
I did find these, but they do not mention different pressures for each axle..
rvbooks.com.au/caravan-and-motorhome-tyres/
rvbooks.com.au/caravan-and-tow-vehicle-dynamics/
Cheers,
Peter
Hi Peter....Sorry,can't help there as I am not at all computer literate,and have no idea how to do "links" etc.A while back I bought some of Collyn's books,and made lots of notes from them into my diary.(Old school). Once we had made the decision to live permanently on the road,we gave away many of our possessions,TVs,fridges,washer and dryer,beds,cabinets etc,and Collyn's books were among the hundreds of things we gave to various charities. When I get a minute I will try to source the relevant details.Cheers
Depending on which suspension you have and tyres.
My van 3200kg fully loaded, Simplicity Suspension, tyres 265/75/16 LT @ 38psi bitumen, 20 > 25 dirt & 14>18 sand.
Toyota 100 series 300L fuel, boat on top same tyres only pressure different 41psi bitumen, 25 rear for dirt.
Tyres are a part of your suspension if running them too hard you will only shake everything to pieces.
Pulled up once for a person on the Birdsville Hwy said it was his third puncher and asked me what
pressure I was running as his were 60psi when I told 25psi with no problems he soon let them down.
Never had anything to do with single axle vans or camper trailers so cant comment there.
Hi Darrell...those pressures look great in all conditions,for that size of tyre,with one exception.Working backwards,the figures show that your car's rear axle weight would be only 1600kg? Have you ever weighed that axle? Cheers
I tow a 3500 ton van with the tug just under 3500 ton and on the van have cruise master suspension and have dropped the tyre pressure from 55 psi to 45 psi and have noticed a lot less things are thrown in around the van.
Have never had sway issues even with my old van which had leaf springs .I always travel with my water tanks full to keep the weight down low and correct me if I'm wrong I always thought swaying or the tail wagging the dog was more to do with incorrect tow ball weight and poor distribution of load in van or a trailer which has not been set up correctly and of course speed we should have a rule like they do in WA when towing a trailer a speed limit of 100 km pH .
Cheers
https://www.youtube.com/watch?v=zwlgZG55QWk
Cheers,
Peter
Hi Peter...tried to send thus as PM,but seems photos cannot be sent that way? You no doubt will recognise where it is from? This is the best I can do to provide the source of my information,but it really is only simple physics. Cheers
-- Edited by yobarr on Tuesday 27th of October 2020 10:23:16 AM
www.caravanersforum.com/viewtopic.php
Cheers,
Peter
My Caravan tyre pressures are at 44psi front and rear for my Toyo HO8 225/75 R15C.
I like many others followed the advice that was being suggested of the front tyres pressure should be lower than the rear, I lowered fronts to 39psi and the kept rears at 44psi, well that was an absolute disaster the mear hint of a semi overtaking created sway, rather than write it off as being wrong at the next servo I increased the fronts to 44psi and inflated the rears to 49psi, well I had to fight to regain control of the sway when being overtaken by large vehicles.
I considered the advice as totally unsuitable for my combination, considering I am required to use a weight distribution hitch as setout in my owners manual for towed loads over 1800kg, following the instructions for setting up my WDH both the Ute and Caravan are level, thus the lower front tyre pressure must create some instability factor.
I could go through the whole reset of the WDH with the different tyre pressures, but at the end of the day my combination is very stable in it origional setup, therefore if it aint broke dont try and fix it.