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Tyre Pressures

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Post by Caraman Wed Jan 12, 2022 10:55 am

Yes the Peugeot TPMS is a blessed nuisance.  This is what got me so involved with tyre pressures in 2020.  Eventually I got Peugeot to adjust it with A-S covering the cost as a gesture of goodwill.  The A-S website doesn't say if the M-B conversions have a TPMS but someone on the Forum will know and if they do have a TPMS how it is set.
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Post by PLOUGHLIN Wed Jan 12, 2022 11:22 am

BornAgain wrote:I reduced the front pressures on my Broadway to 3.25 bar which was correct for my axle weights. That meant living with a low Tyre pressure warning (unable to reset) but at  considerably improved ride quality. Sold the van so was unable to try it out on a long run. Awaiting arrival of a new Bourton when, no doubt, I’ll have the same dilemma but maybe the TPMS is easier to recalibrate on the Merc.

TPMS on the Sprinter can be reset through the dashboard computer.

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Post by BornAgain Wed Jan 12, 2022 5:27 pm

PLOUGHLIN wrote:
BornAgain wrote:I reduced the front pressures on my Broadway to 3.25 bar which was correct for my axle weights. That meant living with a low Tyre pressure warning (unable to reset) but at  considerably improved ride quality. Sold the van so was unable to try it out on a long run. Awaiting arrival of a new Bourton when, no doubt, I’ll have the same dilemma but maybe the TPMS is easier to recalibrate on the Merc.

TPMS on the Sprinter can be reset through the dashboard computer.

[You must be registered and logged in to see this link.]
That’s helpful thanks. I kind of expected the Merc. to be better. Expecting delivery in March but whether it will actually turn up is another matter!
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Post by Caraman Wed Feb 09, 2022 11:51 am

Caraman wrote:
Suppersready wrote:I use the up to date tyresafe guide, only I put the actual laden rear axle weight of my van into the front tyre pressure section. This gives a tyre pressure of 66 psi, with this being a satisfactory pressure for the front axle I cannot see why it would not be so for the rear especially given that the front tyres are under a lot more stress than the rear ( steering, driven wheels, higher breaking force )
I then input the actual weight of the front axle into the front tyre section to obtain the recommended tyre pressure for that axle.
This seems logical to me … however I’m open to be challenged as I certainly do not want to be unsafe.



Niall
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I don't know if you have Continental Tyres but if you don't it doesn't matter.  Their Databook:

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shows the ETRTO figures used by all tyre manufacturers and TyreSafe even though they appear to be Continental figures.  Conveniently it shows the ETRTO's rear CP tyres pressures before the ETRTO stipulated that all rear CP tyres should be inflated to 5.5 bar.  This shows that rear CP tyres should have higher cold pressures than front CP tyres of the same size.  In 2020 Continental explained to me why this is so but I can't find their e-mail.  Can I suggest you contact Continental to find out the reason.  If you are using front CP tyre pressures on your rear CP tyres they will be under-inflated.  You could also ask Continental about the ETRTO's recommendation to use 5.5 bar which is reflected in TyreSafe's on-line calculator and the TyreSafe recommendation to set a cold tyre pressure for an axle mass that is 10% higher.  I discussed this on the phone with Continental's technical director in 2020.  He was very helpful and supported TyreSafe's 10% recommendation but not the ETRTO's recommendation that all rear CP tyres should be inflated to 5.5 bar regardless of axle mass.
Niall,

I don't know if you have spoken to Continental but I have now found their reasoning for having higher pressures on the rear tyres:

"Experience shows that due to the weight distribution of vehicles in the leisure industry such as motor homes the likelihood of overloading or uneven weight distribution tends to put a greater load on the rear axle rather than on the front axles, where the weight tends to remain more consistent. It is true that when braking occurs the weight transference is to the front, but this only tends to be for short periods, whereas overloading on the rear axle can be present over long periods, when the tyres are rotating at high speed. 
This is the main reason that with CP Camper type tyres the inflation pressures at the rear is deliberately set higher. Although this also has a bearing on the contact area when negotiating grassy parking areas and also to the sidewall deflection, which influences the body roll."
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Post by Suppersready Thu Feb 10, 2022 10:44 am

Caraman wrote:
Caraman wrote:
Suppersready wrote:I use the up to date tyresafe guide, only I put the actual laden rear axle weight of my van into the front tyre pressure section. This gives a tyre pressure of 66 psi, with this being a satisfactory pressure for the front axle I cannot see why it would not be so for the rear especially given that the front tyres are under a lot more stress than the rear ( steering, driven wheels, higher breaking force )
I then input the actual weight of the front axle into the front tyre section to obtain the recommended tyre pressure for that axle.
This seems logical to me … however I’m open to be challenged as I certainly do not want to be unsafe.



Niall
Niall,

I don't know if you have Continental Tyres but if you don't it doesn't matter.  Their Databook:

[You must be registered and logged in to see this link.]

shows the ETRTO figures used by all tyre manufacturers and TyreSafe even though they appear to be Continental figures.  Conveniently it shows the ETRTO's rear CP tyres pressures before the ETRTO stipulated that all rear CP tyres should be inflated to 5.5 bar.  This shows that rear CP tyres should have higher cold pressures than front CP tyres of the same size.  In 2020 Continental explained to me why this is so but I can't find their e-mail.  Can I suggest you contact Continental to find out the reason.  If you are using front CP tyre pressures on your rear CP tyres they will be under-inflated.  You could also ask Continental about the ETRTO's recommendation to use 5.5 bar which is reflected in TyreSafe's on-line calculator and the TyreSafe recommendation to set a cold tyre pressure for an axle mass that is 10% higher.  I discussed this on the phone with Continental's technical director in 2020.  He was very helpful and supported TyreSafe's 10% recommendation but not the ETRTO's recommendation that all rear CP tyres should be inflated to 5.5 bar regardless of axle mass.
Niall,

I don't know if you have spoken to Continental but I have now found their reasoning for having higher pressures on the rear tyres:

"Experience shows that due to the weight distribution of vehicles in the leisure industry such as motor homes the likelihood of overloading or uneven weight distribution tends to put a greater load on the rear axle rather than on the front axles, where the weight tends to remain more consistent. It is true that when braking occurs the weight transference is to the front, but this only tends to be for short periods, whereas overloading on the rear axle can be present over long periods, when the tyres are rotating at high speed. 
This is the main reason that with CP Camper type tyres the inflation pressures at the rear is deliberately set higher. Although this also has a bearing on the contact area when negotiating grassy parking areas and also to the sidewall deflection, which influences the body roll."

Caraman,

With the correct management of load and storage plus an understanding of the fulcrum effect ( especially given the long rear overhang of the Corinium ) it should be perfectly safe to run CP tyres at pressure based on their actual load. 
I may be best just moving to C type tyres of the correct load rating but I am unsure as to which would be the better option, either way I will need to have the TPMS system reset if I can.

I do appreciate you following up with this information, thank you.



Niall

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Post by Suppersready Thu Feb 10, 2022 5:08 pm

Duplication …. scratch head

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Post by Caraman Fri Feb 11, 2022 7:20 am

Suppersready wrote:



Caraman,

With the correct management of load and storage plus an understanding of the fulcrum effect ( especially given the long rear overhang of the Corinium ) it should be perfectly safe to run CP tyres at pressure based on their actual load. 
I may be best just moving to C type tyres of the correct load rating but I am unsure as to which would be the better option, either way I will need to have the TPMS system reset if I can.
Niall,

I agree that 'it should be perfectly safe to run CP tyres at the pressure based on their actual load' and that this should apply to the rear axle just as it applies to the front axle.  Continental also agree this but the point I was making is that the CP pressures Continental recommend in their data book for the rear axle are all about 0.5 bar higher than the front axle for a given load.  

I would only consider downgrading from CP to C to have an all season M+S tyre but now that Continental has brought out an all season M+S CP tyre there is no need to do this:  

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The safety benefits of having CP tyres (with the correct pressures) on a coachbuilt are significant in my opinion.
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