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post #1 of 19 (permalink) Old 20-04-2019, 16:44 Thread Starter
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Tyre pressures

Afternoon all,
Loaded for a 2 hour drive ,noticed that van felt twitchy in straight lines and wallowed around corners , checked the tyre pressures and they were down , luckily only done 8 miles. The plate says 79.5 psi 5.5 barall round , the tyres on the front have max pressure of 65 psi rears say 60 psi ( 1050 kg per tyre) .
What pressures do I go to, plate say's one thing , tyres say another . Is over inflation as bad as under inflation.
I went to 79.5 psi on rears but the front I only went to 65 psi ..
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post #2 of 19 (permalink) Old 20-04-2019, 17:20
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Hi @Bigholty

Can't advise you what pressures you need as they vary between tyre manufacturers and the weights of your vehicle

Our Fiat based Dethleffs has Tyre pressures detailed on the Door frame which are much higher than those recommended by Continental whose tyres we have. I emailed Continental and they responded with their recommendations based on the Weights Overall, all Axle weights and the Tyres concerned. I guess the details on the door were put there by Fiat and not Dethleffs after they fitted it out. My pressures were down much nearer the 65psi you mentioned.

Doug

PS I emailed [email protected]

Last edited by Dougaitken; 20-04-2019 at 17:24.
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post #3 of 19 (permalink) Old 20-04-2019, 17:53
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I emailed Michelin with my front and rear axle weights and asked for their advice with Michelin Agilis. I got an answer very quickly, next day. I’d suggest you do the same.

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post #4 of 19 (permalink) Old 20-04-2019, 18:05
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There are many posts and threads on this matter if you search back. The pressures on the door frame (as Doug said) are most likely those from Fiat before the van was converted. The pressures shown on the tyres are the maximum pressure that the tyres can be inflated to and more and more tyre manufacturers are now advising motorhomers to inflate to the maximum even when that is often way beyond what is needed for the weight on the axles. A lot of motorhome converters are silent about what is the correct pressure.

The first thing you need to know is the individual axle weights. You can then contact the tyre manufacturer and ask them although, as I said, I think that some (Michelin and maybe others) are just giving the maximum.

Here are a couple of tables that Tyresafe published a few years ago. They no longer publish those tables - the big problem is that many motorhome owners overload their rear axles so it is best to play safe and advise maximums.
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post #5 of 19 (permalink) Old 20-04-2019, 18:34
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As a wild an unscientific guess, 55psi and see how it goes. Went well with my Hobby. If it's hard lower the pressure but if it wallows raise them.

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post #6 of 19 (permalink) Old 20-04-2019, 19:27
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Published tyre pressures are intended to be set when the tyres are cold.

As anyone with a TPMS will tell you, it is normal for the pressures to increase by 10psi as the tyres warm up while driving, so that needs to be taken into account.

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post #7 of 19 (permalink) Old 20-04-2019, 19:52
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There are so many things that can affect the ride. No one pressure fits all. It's trial and error to accommodate suspension, caster & camber, dampers, general geometry, load and loading, tyre tread, etc.

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post #8 of 19 (permalink) Old 20-04-2019, 20:54
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Quote:
Originally Posted by Bigholty View Post
Afternoon all,
Loaded for a 2 hour drive ,noticed that van felt twitchy in straight lines and wallowed around corners , checked the tyre pressures and they were down , luckily only done 8 miles. The plate says 79.5 psi 5.5 barall round , the tyres on the front have max pressure of 65 psi rears say 60 psi ( 1050 kg per tyre) .
What pressures do I go to, plate say's one thing , tyres say another . Is over inflation as bad as under inflation.
I went to 79.5 psi on rears but the front I only went to 65 psi ..
Do the rear tyres really say max 60psi? Seems very low. And did you really go to 79.5?? Sounds a recipe for disaster to me.

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post #9 of 19 (permalink) Old 21-04-2019, 07:59
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For the zillionth time, the pressures on the door are for the original van, not the conversion, Fiat has no idea what the final MoHo will become when they apply stickers.
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post #10 of 19 (permalink) Old 21-04-2019, 12:27
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You need to know the front and rear axle weights (around £5 to use a local weighbridge) and the size and type of tyres you have before adjusting your tyre pressures.

Any guesswork will mean your tyres probably won't last as long and may wear unevenly.

With the tyres I have fitted - Continental (225/70 R 15C 112/110) - on my Pilote on a Ducato base and with front axle 1560kg and rear axle 1940kg, confirmed fully laden by a weighbridge, the recommended pressures are 47psi (3.25 bar) front and 61psi (4.25 bar) rear.

Michelin have always recommended the maximum pressure in their tyres, and many of you will continue to take their advice, but those who have actually weighed their vehicles and reduced pressures will know what a big difference to ride and comfort is achieved.

I'm never sure why Motorhomes are run at the tyres maximum, usually 80psi, which gives a harsh ride and on many roads could dislodge your false teeth and certainly rattle the chassis with the hard tyres and no 'give'.

Everyone has an opinion on tyre pressures but my Pilote has run well with minimal tyre wear over 30.000 miles and there's no reason why yours shouldn't do the same with similar pressures.

Hope this helps.
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