Tyre Pressures

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Post by roli on Wed Apr 11, 2018 7:31 am

I am another "pillar pressure driver" always seems to give a decent ride on all the vans

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Post by bolero boy on Wed Apr 11, 2018 7:47 am

...but have you compared your 'decent ride' to what you get by reducing them somewhat in line with Michelin/Continental recommendations?
you might find that better than 'decent'...

this is my info from Continental..

ContiVanco Camper 225/75 R16 (CP*) 116 R 

Front Axle: 1600 Kg - 3.0 bar/ 43.5 psi, am now trying 50 psi as a comparison
Rear Axle: 1820 Kg - 3.75 bar/ 54.3 psi am now trying 60 psi as a comparison

the original Conti pressures give a really good ride, but am just experimenting, will probably settle on 48 front, 58 rear.
either way, much lower than the pillar pressure....ouch

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Post by mikethebike on Wed Apr 11, 2018 10:33 am

bolero boy wrote:...but have you compared your 'decent ride' to what you get by reducing them somewhat in line with Michelin/Continental recommendations?
you might find that better than 'decent'...

this is my info from Continental..

ContiVanco Camper 225/75 R16 (CP*) 116 R 

Front Axle: 1600 Kg - 3.0 bar/ 43.5 psi, am now trying 50 psi as a comparison
Rear Axle: 1820 Kg - 3.75 bar/ 54.3 psi am now trying 60 psi as a comparison

the original Conti pressures give a really good ride, but am just experimenting, will probably settle on 48 front, 58 rear.
either way, much lower than the pillar pressure....ouch
Yes thats much better.Never go by pillar pressures. So many members going around with a small rubber footprint with tyres at 70 to 80 psi.If you had false teeth ,you would soon know.
Its come up so often that you need to weigh your own van.
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Post by Paulmold on Wed Apr 11, 2018 10:42 am

Michelin only recommend one pressure for CP rear tyres no matter what make of motorhome or weight. That pressure is 80psi.(5.5 bar). The Tyresafe website has been amended to the same pressure.
I quote from the tyresafe website

CP-type tyre construction enables the use of higher inflation pressures to provide resistance to the difficult conditions of use encountered on motorhomes. Therefore, when CP-type tyres are fitted on the rear axle in a single formation set the inflation pressures to 5.5 bar (80 psi) for all loads.

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Post by daisy mae on Wed Apr 11, 2018 10:46 am

I have rear 80psi ( 5.5 bar ) years ago never had all that faffing about.

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Post by MikeJJ on Wed Apr 11, 2018 10:51 am

Paul you beat me to it - Michelin give one pressure for CP tyres because that is what they are designed to operate at.  "C" tyres are different.

Another point of unclarity is the Mercedes Sprinter handbook pp 280-283.  The statement is ".....only the tyre pressure levels specified for laden vehicles apply to motor caravans...." But it does not clarify if that is the actual measured laden weight OR the max axle load capacity.

My rear axle is specified with a load rating of 2430kg, not that I am anywhere near that.
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Post by PLOUGHLIN on Wed Apr 11, 2018 11:02 am

The MB handbook for my 235/65 x 16 tyres says the same, but if your front axle is weighed at 1650kg though rated at 1800kg I don't see why you shouldn't use the 1650kg  bracket values ie 3.3 bar instead of 3.7 bar, similarly for the rear axle use the value for the actual weight interpolating if necessary.

The Continental Tyre Pressure book (in the Factsheet section) gives values for various actual axle weights and does state it covers ALL types of Conti tyres ie Camper tyres as well.

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Post by MikeJJ on Wed Apr 11, 2018 11:10 am

I have no issue with that and as I am using "C" tyres I feel confident that I am driving without causing any long term issues/damage.  But I just wish Mercedes and Continental would be clearer and consistent.  The tyre pressure plate is after all stuck on by Mercedes after having selected the appropriate Continental tyre (as specified in the CofC).
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Post by mikethebike on Wed Apr 11, 2018 12:30 pm

Paulmold wrote:Michelin only recommend one pressure for CP rear tyres no matter what make of motorhome or weight. That pressure is 80psi.(5.5 bar). The Tyresafe website has been amended to the same pressure.
I quote from the tyresafe website

CP-type tyre construction enables the use of higher inflation pressures to provide resistance to the difficult conditions of use encountered on motorhomes. Therefore, when CP-type tyres are fitted on the rear axle in a single formation set the inflation pressures to 5.5 bar (80 psi) for all loads.
Yes thats the maximum.Much too high for a lightly loaded van.Most of us dont have difficult conditions.
 thats 80.85psi  actually. very small contact patch and hard ride.
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Post by bolero boy on Thu Apr 12, 2018 7:57 am

I agree Michelin have changed their stance on this, but as far as I know (other forum interaction with Michelin) the front axle should be pressurised in line with the axle weight...

the quote above (again AFAIK) refers only to the rear axle...

plenty of discussion, correspondence from Michelin et al, on MMM forum.

fortunately, I now have Continentals..

80psi on the front axle must be rock hard....and a bit.....

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Post by MikeJJ on Thu Apr 12, 2018 8:10 am

The current stance of Michelin is to strictly follow the ETRTO recommendation for CP tyres whereas Continental take a more liberal view.  Of course that may all change.

The Michelin Safety and Utilisation Manual states the following - my italics merely to indicate it is a direct copy and not changed by me

"....
Motorhomes:

Motorhomes require tyres are that are adapted to their conditions of use.  In 2003, the ETRTO (European Tyre and Rim Technical Organisation) changed the standard ,as well as its recommendations relating to motorhome tyres, and now says  “CP-type tyres have been designed to cater for the higher loads imposed by motor-caravans”, and that “it is strongly recommended that motor-caravans are only fitted with CP-tyres”.   At replacement, Michelin strongly recommends the fitting of CP tyres to vehicles originally homologated and fitted with CP tyres. The load on the tyre must not exceed its maximum limit for any reason, i.e. the load rating must be respected. The ETRTO also states that where CP tyres are used on the rear axle (single fitment), they must be inflated to a pressure of 5.5 bar instead  of the normal pressure of 4.75 bar for example.

 MICHELIN CP marked tyres are therefore specially designed to be driven at an inflation pressure of 5.5 bar (550 kPa) This higher pressure improves road holding and increases resistance to the challenging driving and usage conditions encountered by motorhomes, especially with regard to loads (occasional static and/or dynamic overload associated with this type of vehicle;  considerable rear overhang, load imbalance, high centre of gravity due to highly positioned loads) and long-term periods of disuse.

Fitting tyres that are not adapted to this type of use could lead to: - poor handling (roll, pitch, yaw, difficulties in road holding) - in difficult or severe conditions, premature deterioration of tyre components, such as the crown, which could lead to a rapid deflation.

In use:  check and adjust if necessary tyre inflation pressures monthly and before any long journey.  Under-inflation can be dangerous: for example, for the tyre size 225/70R15 Camping CP, an under-inflation of 0.5 bar/7.2psi (11%) is equivalent to an overload of around 100 kg per tyre. Overloading (even temporarily) or poor vehicle load distribution can cause premature deterioration of vehicle components and/or tyres and thereby cause damage to persons or property.
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Post by bolero boy on Thu Apr 12, 2018 8:19 am

as I said, rear axle 'directive' only....

if I (felt I) had to run all four tyres at 80 psi, i wouldn't buy Michelin, I'd use Continental, which I have....

I would think telling folk who understand the difference between a rock hard ride and more compliant one to run at rock hard pressures, would steer more folk away from the brand....

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Post by mikethebike on Thu Apr 12, 2018 8:39 am

bolero boy wrote:as I said, rear axle 'directive' only....

if I (felt I) had to run all four tyres at 80 psi, i wouldn't buy Michelin, I'd use Continental, which I have....

I would think telling folk who understand the difference between a rock hard ride and more compliant one to run at rock hard pressures, would steer more folk away from the brand....
I dont agree with all the facts that Michelin quote. Is this tied in with the tyre moniting system that they sell? I think so.
I agree, would never buy Michelin.Have never liked thier tyre construction.Best for long life.However many motorhomers on this site like to change tyres after 5 years or so,so long life is not important.
each to his own.

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Post by Paulmold on Thu Apr 12, 2018 9:27 am

Where in any of the above does it say the fronts should be 80psi?

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Post by Jaytee on Thu Apr 12, 2018 9:37 am

I can't quite get my head around the statement ' difficult conditions of use encountered on motorhomes' scratch head.
Strooth, have these manufacturers watched white van man in a hurry?

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Post by daisy mae on Thu Apr 12, 2018 9:43 am

I reolaced  my tyres which were on originally, Michelin Agilis CP, NO WHERE IS IT STATED TO RUN 80 ON THE FRONT,.  
To my mind a lot of bumf is on about tyres, get them right and enjoy your vans, if you have a problem with them I could understand it. life is too short, be safe but not OTT. jmho, not wishing to upset anyone but really!.

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Post by Jaytee on Thu Apr 12, 2018 9:49 am

If you had a Merc based vehicle you would understand Daisy Mae hugegrins

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Post by daisy mae on Thu Apr 12, 2018 10:12 am

Are they that probmatic,? will stick to plain and simple  in that case.   hugegrins

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Post by BornAgain on Fri Apr 13, 2018 7:50 pm

I have 2016 Broadway with 215/70/R15 CP and Continental state 47psi front up to 1520kg and 76psi rear up to 1940kg. I could therefore reduce the front pressures significantly below the Boxer plate but then the tyre pressure warning would stay on! Can’t win can you.
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