# tyre pressures



## Jean-Luc (Jul 21, 2005)

Having read various posts on the subject of tyre pressures, this is my opinion on the issue. 
First off, tyres are but one component in the chain that cushions the vehicle from the roughness of the road, others include the spring system (air and/or metal) and the various rubber bushings which separate the suspension from the chassis. The compliancy of all these components added together dictate the harshness or otherwise of the ride. 
Lets talk about tyres. The pressure required to inflate a tyre so that it delivers its optimum roadholding and braking performance is determined by its size and the weight which it is bearing. the correct pressure will ensure that the full width of the thread is pressing evenly on the road surface and giving optimum grip with maximum wear life. 
If one inflates a tyre over its optimum pressure, from a grip point of view it looses pressure on the road on the outside of its thread with consequential reduced grip and also induces premature wearing of the outside of the tyre. 
As a tyre pressure gets harder it also increasing the harshenss in the ride quality and wear and tear of the vehicle suspension and internal fittings (remember the harder anything is pumped the more violently it will bounce). 
Now heres the rub, if you drive around with 5.5 bar pressure as found in many MH handbooks your vehicle will surely develope many rattles before it time and hasten its replacement date. Am I being cynical in thinking that manufacturers and dealers have latched on the the new high pressures which can be sustained by tyres like the Michelin XC as driving with such pressures will inevitably lead to shortening of the vehicles servicable life. 
In my opinion one should always be guided by recommendations from the product manufacturer after all if one requires info about the fridge, heating or other components is it not better to speak to the component manufacturer rather that the supplier who may or may not be correctly informed. 
I read in the Michelin blurb that the high pressure sustainable by their XC product helped maintain the tyres shape during long periods of lay up, but nowhere did I see a recommendation that driving with such pressure was advised. 
It requires only a simple phone call to the tyre manufacturers technical department, quoting the actual and/or maximum axel weights of your vehicle, to get the correct recommended pressure(s). In fact their advice to me was 3.5 bar for front axel(1700Kg) and 4.2 bar for rear axel(2080kg) 
Know your vehicle and drive with confidence


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## mgb (Dec 4, 2008)

*Rapido 7065+*

I have just had my Rapido 7065+ weighed to find out my axle loadings
Good job I did since my total laden weight of 3560 was over the limit of the plated weight of 3500 (but that's another story)
So I decide to confirm the tyre pressures that Michelin recommend for these weights
I rang the Michelin Stoke on Trent office
Michelin Tyre plc
Campbell Road, Stoke-on-Trent ST4 4EY
Tel: +44 (0)1782 402 000 Fax: +44 (0)1782 402 011
And here is the information straight from the horse's mouth as it were
Front Tyres
Michelin X Camper 215/70R15CP
Axle Load 1720Kg
Pressure recommended 70 psi or 4.8bar
Rear Tyres
Michelin X Camper 215/70R15CP
Axle Load 1840Kg
Pressure recommended 80 psi or 5.5bar


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## sallytrafic (Jan 17, 2006)

Goodyear won't tell you they just refer you to the vehicle manufacturer

Jean-Luc Shouldn't that be 'premature wearing of the *middle* of the tyre'. I think that under inflation leads to extra wear at the outside of the tyre.


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## ob1 (Sep 25, 2007)

Readers note that MGB and Jean-Luc are talking about different tyres, X and XC.

Ron


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## Jean-Luc (Jul 21, 2005)

Well spotted Frank, is should of course read middle.
Ron, you are of also right, and, mgb has 15" wheels and mine are 16" which would have a lower recommended pressure weight for weight. 
An extreme example of this is my bicycle tyres which have a recommended pressure of 85psi or 6bar to support my 80Kg.


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## scotsy (Feb 1, 2009)

*Michelin recommends......................*

....55psi for my Hymer but the Handbook says 70psi (5 BAR) :roll:

Being new to this malarky and seeing several posts about tyre pressures on this and other  relevant forums i decided to take the advice offered and send this Email to the tyre *manufacturer* last week:-

"Please could you advise me the correct 'cold' tyre pressure for use with my year 2000 (Fiat Ducato 2.8JTD based) Hymer B584 motorhome. Its MGVW is 3400kg, max front axle 1650kg, max rear axle 1750kg and is fitted with Michelin 215/70R15C (109q) tyres. Current pressures are 70psi and ride feels quite harsh. thankyou Ian"

I got a reply today which I can't seem to copy and paste (MS office trial version is playing up) but the main answer to my question is that they recommended *55psi* if i run to the MAX weight for each axle.

Now that explains to me why the ride is quite harsh at present, an extra 15psi and that is if we run to MAX weights, as there's only me and Margaret and a small dog with 2 days worth of food and water/clothes etc aboard i doubt we'll ever approach those max weights.

I am so glad you knowledgable folk take the time to help other 'less well informed' people to enjoy their new lifes as Motorhomers

I could still have been 'crash, bang and walloping' down every road with a minor imperfection if i hadn't taken your advice

Cheers to you all


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## Solwaybuggier (Mar 4, 2008)

Rather than ring Michelin why not email them? I emailed them on Saturday, got a reply this morning (next working day) with suggested pressures. When I get home I'll print out their reply, and keep a copy in the van in case I need it to show police etc etc - with a phone call you have no proof.


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## scotsy (Feb 1, 2009)

Solwaybuggier said:


> Rather than ring Michelin why not email them? I emailed them on Saturday, got a reply this morning (next working day) with suggested pressures. When I get home I'll print out their reply, and keep a copy in the van in case I need it to show police etc etc - with a phone call you have no proof.


*Exackerly *(in a peter kay type voice :lol: )


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## loughrigg (Nov 10, 2008)

I spoke to Vredestein UK and asked the pressure question. All they did was ask what the vehicle was and then said that it wasn't listed on their database (did they just not notice the introduction of the Peugeot Boxer a year or two back?).

The final comment was " our pressures are normally a bit less than Michelin, so just find out what they recommend for the same size tyre and knock it down a bit."

Just fills you with confidence........

Mike


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## ob1 (Sep 25, 2007)

It's often suggested that the reason that manufacturers/converters stipulate such high pressures is the belief that owners often overload their vans. By stipulating the high pressures that the Michelin Camper tyres can take they are playing safe.

Ron


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## Jean-Luc (Jul 21, 2005)

When I contacted Michelin I phoned, would any of you who used email successfully post the address you used here on the forum.

Thanks


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## scotsy (Feb 1, 2009)

My email was sent via their website but my reply has come from [email protected]

HTH
Ian


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## Solwaybuggier (Mar 4, 2008)

scotsy said:


> My email was sent via their website but my reply has come from [email protected]
> 
> HTH
> Ian


Yes, that's the email address I sent to and got a quick response - I found it in one of the many threads on this forum about tyre pressure - took a while to find it, mind, and as I'm currently on a slow connection it would take a while to get the link again.


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## zappy61 (May 1, 2005)

I sent an email for mine and got the following reply. They do add a disclaimer.

'Thank you for your recent e-mail.

If you could please supply further information such as the Tyre size, load and speed rating currently on your Motorhome as designated by the vehicle Manufacturer, we will be in a better position to answer your query. We can also supply tyre pressures if you follow the information detailed below:-

We suggest that individual axle weights from weigh scale readings are used, in order to calculate pressure recommendations for each quoted load condition. These would be preferred, due to readings being taken in the actual vehicle 'running' condition - that is to say, with all water/fuel/baggage & passengers etc. onboard - and may result in better comfort if the vehicle is running way below maximum capacity.

The results of roadside surveys indicate that some motor homes have been found to be over laden, especially the rear axle, with potential for subsequent tyre related problems.

The overall tyre industry, therefore, tries to build-in a safety factor by fitting strong tyres, inflated to high pressure, in order to remove the potential for consequences of overloading &/or under-inflating the tyres.

The drawback of this safety factor, at the corresponding high pressure, may be an extremely hard ride. The contents of the motor home may rattle, but the tyres will cope nicely.

One 'overall' weight is of no use in calculating tyre inflation pressure levels, since the vehicle may appear to be within the maximum permitted, but in reality may have the rear axle severely over laden & the front axle very lightly laden.

As a guideline from the axle weights that you have supplied on tyre size 215/75 R16 C if the XC Camping or Agilis Camping, the pressures for those weights are as follows:-

Front axle load of 1850kg the pressure should be – 70 psi (pounds per square inch)
Rear axle load of 2120kg the pressure should be – 80 psi (pounds per square inch)

We have allocated your message the reference number indicated above. If you need to contact us again regarding your message, we would be grateful if you could include the reference number.

Once again thank you for your interest in Michelin.

Yours sincerely
Michelin Tyre Public Limited Company'



Graham[


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## Broom (Oct 8, 2007)

Hi All

Just had the same reply as Graham

Best Regards
Adrian


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## scotsy (Feb 1, 2009)

*office now sorted so....*

this is a copy of the email i got back:-

Dear Mr Scotson

Thank you for your recent e-mail.

We suggest that individual axle weights from weigh scale readings are used, in order to calculate pressure recommendations for each quoted load condition. These would be preferred, due to readings being taken in the actual vehicle 'running' condition - that is to say, with all water/fuel/baggage & passengers etc. onboard - and may result in better comfort if the vehicle is running way below maximum capacity.

The results of roadside surveys indicate that some motor homes have been found to be over laden, especially the rear axle, with potential for subsequent tyre related problems.

The overall tyre industry, therefore, tries to build-in a safety factor by fitting strong tyres, inflated to high pressure, in order to remove the potential for consequences of overloading &/or under-inflating the tyres.

The drawback of this safety factor, at the corresponding high pressure, may be an extremely hard ride. The contents of the motor home may rattle, but the tyres will cope nicely.

One 'overall' weight is of no use in calculating tyre inflation pressure levels, since the vehicle may appear to be within the maximum permitted, but in reality may have the rear axle severely over laden & the front axle very lightly laden.

As a guideline from the axle weights that you have supplied and if on the Agilis Camping or XC Camping tyre size 215/70 R15 C 109Q, the pressures for those weights are as follows:-

Front axle load of 1650kg the pressure should be - 55 psi (pounds per square inch)
Rear axle load of 1750kg the pressure should be - 55 psi (pounds per square inch)

The Front axle pressure in this case may be the same as the Rear even though the axle loads are different. Therefore the slight increase in pressure which has been added to the front axle is due to the braking forces and shift in weight that's being exerted onto it.

We have allocated your message the reference number indicated above. If you need to contact us again regarding your message, we would be grateful if you could include the reference number.

Once again thank you for your interest in Michelin.

Yours sincerely
Michelin Tyre Public Limited Company

Attention is drawn to the following confidentiality and disclaimer notice:

This e-mail is intended only for the addressee named above and the contents should not be disclosed to any other person nor copies taken. If you are not the intended recipient and/or have received this message in error, kindly disregard the content and return it to the original sender. Any views or opinions presented are solely those of the sender and do not necessarily represent those of Michelin Tyre Public Limited Company unless otherwise specifically stated. As Internet communications are not secure we do not accept legal responsibility for the contents of this message nor responsibility for any change made to this message after the original sender sent it. Nothing in this e-mail is to be interpreted as an agreement on behalf of Michelin Tyre Public Limited Company. We advise you to carry out your own virus check before opening any attachment as we cannot accept liability for any damage sustained as a result of any software viruses. Michelin Tyre Public Limited Company reserves the right to monitor and record any e-mails addressed to any worker at Michelin Tyre Public Limited Company and the senders of messages shall be taken to have consented to such monitoring and recording.

Michelin Tyre Public Limited Company
Registered in England no.84559. Registered office Stoke-on-Trent ST4 4EY.

ian


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