Tyre Pressures

[Tanskavan]

Hi,

 

Recently I have had a slow puncture, to which I took to 2 different places. The first suggested that it was the valve that was faulty and replaced it for a minimal charge. The tyre went down again, the second place could not find damage to the tyre and suggested to replace the valve again. So far the tyre has held the pressure, however both were amazed that the pressure required in the tyres were 80psiand suggested that the high pressure could contribute to the pressure loss?. Can anyone confirm that the pressure I have in my tyres is correct? (Fiat Ducato - Bessacarr E760). I took the information from inside the door on the drivers side

[spartan3956]

seems a bit high i run an Auto trail of similar size on 65 psi

 

Pete

[Terrytraveller]

Hi Tony,

 

If you are using Michelin Camper tyres the max pressure is 80 psi, but no one ever runs them so hard. Check that you have Steel valves fitted not rubber valves, rubber valves are only good to around 69 psi, and will blow out at pressures above.

 

I have a 3300 Kg MH and run the front tyres at 45 psi and rear at 55 psi, these are pressures recommended for my MH at the actual axle loading on my MH.

 

If you load up your MH for touring, go to a weighbridge and obtain a certificate, email Michelin or whomever manufactured your tyres and ask them the pressures for given axle loads.

 

Incidently - the little sticker on my door frames advises a pressure of 72 psi all round. I have been running at the Michelin recomended pressures for three years and 22000 miles, tyres are worn evenly and are about half worn.

 

Regards Terry

[Tanskavan]

Hi Terry,

 

Thanks for this info, I am running on Mitchelin Camping tyres. As we are new to this we have not been using the vehicle fully laden in fact we do travel quite light. I have noticed that we seem to feel every bump, but I put this down to us being new to the MH.

I may reduce the pressures to 65PSI and see how we go

 

Thanks Again

 

Tony

[Keith T]

Our Rapdio 710F (3400kg) was factory set at a recommended 80 psi on Michelin Camping tyres, but we found this a trifle uncomfortable, and after checking it out with the Fiat garage, they reduced to 74psi. This wasa far better, and basically we never adjusted them from that setting in the 5 years we had the motorhome.

[George]

Hi Terry, your advice regarding steel valves is very important. Our van was two years old when we bought it,and we discovered that it had been fitted with rubber valves from new when one of them failed. Fortunately we were parked on our drive when the valve 'exploded'. Swift subsequently caried out a recall and replaced the rubber valves with steel ones. I hope other forum members check their valves and don't simply assume that steel ones have been fitted.

Cheers, George

[Brian Kirby]

Before you do anything with your tyre pressures, look back to page 2 of this forum, and look down for a post entitled "Tyres" on 20 April.  This is just to save re-stating advice on obtaining instruction from the tyre maker before changing from recommended pressures.  Lots of other tyre related information in that post.

The point about the valves is absolutely critical.  Do make sure you have the steel barrelled "clamp in" type valves fitted to all wheels, including the spare.  This is highly desirable even if running at reduced pressures, since the tyres are suitable for pressures above 65psi and may be set to those higher pressures during servicing, or by someone else after you've sold the van.  The consequences, if the wrong valves are fitted, could be catastrophic!

If your tyre valves are fully shrouded in rubber they are standard "snap in" valves, suitable only for cars, completely unsuitable for fitting with Michelin XC Camping tyres, and should not have been fitted. 

If they are part shrouded in rubber with a portion of the metal barrel clearly visible between the rubber shroud and the base of the valve cap, they may be of a type called "high pressure snap in" valves.  If this is the case they are capable of sustaining higher pressures than the standard snap in type but, from memory, are unsuitable for 80psi, so, again, should not have been fitted.  There is some indication these valves may suffer accelerated ageing so treat with suspicion if over 4 years old.

If your tyre fitters haven't come across 80psi tyres, I'd strongly recommend going elsewhere!  They have inadequate experience and training to work with motorhome tyres, or with the high pressure clamp in valves that should be fitted with them!

[tonyishuk]

Drop Michelin an email;.

 

I sent of details of my Rapido 709F and received the following by return.

 

++++++++++++++++++++++

 

Subject: Ref XXXXXXX-2 Pressures for motor home

 

 

Dear

 

 

 

Thank you for your recent e-mail.

 

 

Based on the loads given for your Rapido 709F fitted with 215/70 R15 XC Camping we would recommend the following pressures; -

 

Front axle at 1750kg = 58psi

 

Rear axle at 1900kg = 60psi

 

 

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.

 

 

++++++++++++++++++

 

The weights I quoted were the max front and rear axle loadings ( On the assumption that they would never be exceeded ) So in all probability the tyre pressures could be dropped a bit.

 

Sticky label on the door says 75 PSI.

 

As I understand it, the pressure is as much to do with the shape of the foot print on the road, as much as how much pressure is required to keep the shape of the tyre. ( I think I know what I mean )

 

Rgds

 

[Brian Kirby]

Tony

Yes, your pressures could be dropped a bit.  At present you have quoted, as you say, the axle maxima.  However, you can't legally load your van to these maxima, since your MAM is, I think 3,500Kg - probably a bit less. 

If you fully load your van, including passengers, and take it to a weighbridge, you can get the actual laden axle weights.  This is preferable to assuming neither axle is overloaded, and that the axle maxima are, therefore, the "safe" default. 

If you give these actual axle loads to Michelin in lieu of the maxima, they'll give you the pressures that are truly appropriate.  If you then reduce pressures accordingly, you are likely to find both ride comfort, adhesion/traction and directional stability are somewhat improved.  The differences probably won't be that great, but you should find your van benefits overall from feeling just that bit "taughter" on the road.

However, it would be unwise for anyone else to assume they can adopt the pressures you have quoted above.  Such is the paucity of payload, and particularly rear axle load margin, on many vans, it is all too probable one axle will be overloaded.  It is vital to sort this out, and proceed from factual information, before adjusting tyre pressures.  In addition, if one were stopped at a roadside check, or possibly following an accident, and the tyres found "underinflated", how else could one prove one's tyres pressures were correct for ones van?  Quoting someone else's tyre pressures would hardly be accepted.

[tonyishuk]

Brian,

 

Thanks for your observations.

 

The only thing I would add is that I have a copy of Michelins email (with their reference number) in case I am questioned about the pressures.

 

Rgds

[Vernon B]

This thread coincided with my annual service and MOT arising from which I have used the Michelin online helpdesk to get some advice. Although this corroborates other entries here several additional points have come out which may be of general interest. My own interpretation of what Michelin have to say is:-

 

1. The tyre pressures given in your handbook are most likely to be unreliable! Get advice from the tyre manufacturer. (A frightening fact when you consider the safety implications!!)

2. Don't assume that when you are replacing a pair of tyres these should go on the front wheels.

3. It may be safe to run your spare for six years from the time it is first put into service and not from the date of purchase. (I think - please see rather ambiguous reply below)

 

What follows is a copy of the exchange of e-mails:

 

My Question:-

I have Michelin XC Camping tyres fitted to my 4 year old Fiat motorhome - size 215/75 R16C. The front treads are down to 4mm the rear are a healthy 7mm; the spare has not been used. I'm told by my garage that in parts of Europe the legal limit is 3mm. As the front are approaching this limit it would it be a good idea to replace them with one new tyre and the spare, and retain one of those front tyres as a spare? I'm told that irrespective of tread wear tyres have a safe working life of five years so is my idea soundly based or will I have to consider two new tyres on the front and the replacement of the rear next year when they're five years old. And what about that unused spare? Many thanks B Baker

 

Michelin's reply:

 

The 3mm rule applies to winter tyres so you will be OK to run your current set up. When you do need to change then we would advise moving the two rears to the front and fitting one new tyre with the spare and retaining the better of the current front tyres as a spare. We do advise that the tyres are changed once they have been in use for six yrears.

 

 

My follow-up question:

 

Many thanks for your prompt and informative reply. I will be following your advice but would welcome clarification on one point and advice on an associated matter.

 

Clarification. In your reply you say "we advise that tyres are changed once they have been in use for six years" . Does the term "in use" include been held as a spare, in a carrier underneath the motorhome, ie has my spare been "in use" for four years to date?

 

Associated matter. The recommendation in my vehicle handbook is that the tyre pressure should be 80 psi but I have found this produces a very harsh ride and I have been running them at 75 psi. A recent thread on a motorhome website says that the 80psi pressure is a maximum and the tyres can be run at a much reduced pressure depending upon the axle loads. My motorhome has a maximum gross weight of 3850kg and is built on an Alko chassis. When fully loaded the load on the front axle is typically 1620kg and 2100 kg on the rear. I would be most grateful if you could suggest optimum tyre pressures for this set up.

Many thanks again for your help

 

And Michelin's reply:

 

If you have had the spare tyre through out its life then you are aware of its history and if there are no signs of degredation then its use should be OK. To be absolutely sure we would advise that the tyre is removed from the rim and fully inspected before prolonged use.

 

The pressures that we would advise for your motor home fitted with 215/75 R16 XC Camping tyres are as follows; -

 

Front axle at 1620kg = 51psi

Rear axle at 2100kg = 63psi

 

end

 

I shall be adopting these recommended pressures on my next outing and will be interested to see how they affect ride and handling - they are of course substantially different to those adviced by the motorhome manufacturer.

 

What I'm unclear about is whether I would have got more mileage out of my front tyres if I had adopted Michelin's tyre pressure advice from the outset.

 

 

 

Vernon B

 

 

[Roamer]

I totally agree with all the above regarding the setting of on the road tyre pressures based on axle loads. I would however like to add that I understood that the 80 psi setting was to reduce the chance of the tyres creating flat spots when parked up for long periods. I would recommend that if you lay up your van for the winter to set the pressure to 80 psi and then reset to the recommended pressure when it is back in use.

 

[Keith T]

Vernon B - 2007-05-03 7:24 PM

 

The pressures that we would advise for your motor home fitted with 215/75 R16 XC Camping tyres are as follows; -

 

Front axle at 1620kg = 51psi

Rear axle at 2100kg = 63psi

 

end

 

I shall be adopting these recommended pressures on my next outing and will be interested to see how they affect ride and handling - they are of course substantially different to those adviced by the motorhome manufacturer.

 

What I'm unclear about is whether I would have got more mileage out of my front tyres if I had adopted Michelin's tyre pressure advice from the outset.

 

 

 

Vernon B

 

 

Hi Vernon

I'm interesetd in your comments, since as stated in my earlier posting we ran our's at 74psi, although Rapido/Fiat had suggested 80psi, and did not suggest that simply as 'maximum'. but by implication, the normal running pressure. So perhaps you can post your views in due course on the lower pressure results.

Also, what mileage have you got from those tyres - I changed ours, as the front ones were down to probably about 3-4mm, but I was doing a long trip in France and wanted to make sure they were OK. They had done something like 30k miles.

I then had a slow puncture in France on one of the rear tyres, so had the spare (unused after over 4 years) put on. However when I got home, and asked the local tyre depot to sort out the puncture, they were unable to repair as there was signs of deterioration on the side walls, which equates with the 5 year rule, I guess. The treads were fine however, at 32k miles, and would have gone on a lot longer.

The spare was Ok, so I bought two new ones and returned the spare as it was then the 'oldest' one to its place under the motorhome.