# Tyre pressures : Conflicting advice



## blindwatchertrev (Nov 4, 2011)

Hi guys, getting a bit more used to the Eldiss over the past week and as always I always check tyre pressures at least weekly. However, having just done so I've come across some conflicting advice as to the correct pressures and was hoping someone may be able to clarify things for me.
There is a manufacturers plate on the inside of the near side door which instructs to use 73 lb on the fronts and 80 lb on the rears. Contrast this with a comprehensive data sheet attached to the drivers visor which states that 60 for the fronts and 65 for the rears. Neither says anything about fully laden or light load etc so I'm puzzled by this fairly large discrepancy.
Can anyone enlighten me please. Regards Trev.


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## cabby (May 14, 2005)

The door plate is for the original Cab unit or van as it would have been, disregard that completely. The second set of pressures sounds about right,but if still too hard a ride take them down another 5psi.and you might find that it will not ride as good as the 60 and 65psi.

cabby


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## blindwatchertrev (Nov 4, 2011)

Thanks cabby.....you know your stuff! Trev


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## cabby (May 14, 2005)

Did not see what tyres you have, there should in amongst all the letters and numbers be a psi limit on the wall of the tyre.


cabby

Thank you for your comment, but I must admit I have been wrong on occasion, but fortunately other members have saved the day and corrected me. lol.


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## blindwatchertrev (Nov 4, 2011)

Cheers again. Will check the tyre walls forthwith.


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## TheNomad (Aug 12, 2013)

I see many motorhomes with obviously very over-inflated tyres.....looking like balloons on the rims

Converters suggested pressures will be just that; suggestions.
Disregard anything from the original factory chassis-cab manufacturer; they didn't know what body was going to be bolted on, nor how much kit and caboodle the owner would then chuck in.

The tyres need to be inflated until there is just a slight bulge in the sidewall at the contact point on the ground. If in doubt, google for pictures of correctly inflated tyres.

If there's no sidewall bulge, but there's a bulge across the face of the treads, then they are too highly inflated.

Always check the MAX pressures printed on the tyre sidewall; and don't inflate beyond that....usually to get correct inflation, but without a choppy hard ride, inflation maybe 10psi below that is a good starting point. 

Remember tyre pressures should always be taken when the tyres are cold.


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## Wizzo (Dec 3, 2007)

cabby said:


> Did not see what tyres you have, there should in amongst all the letters and numbers be a psi limit on the wall of the tyre


This figure can be ignored it is only for the North American market.

JohnW


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## Mrplodd (Mar 4, 2008)

Take your vehicle to a weighbridge in full "going away mode " including occupants) to get the ACTUAL weights that your vehicle runs at 

Then contact the maker of the tyres fitted. Give them the recorded weights along with the tyre details (the size and load rating off the side wall) and ask THEM what pressure you should run at. 

They make the things so are best placed to give you correct advice. 

Andy


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## ob1 (Sep 25, 2007)

Taken at face value that would be the correct advice Mr Plodd. Unfortunately, there is a trade wide agreement between tyre manufacturers to always quote 80psi for rear tyres on motorhomes as a safeguard against overloading at lower pressures. I was told this by non other than a nice guy at Michlin. I was also told the way round it to obtain the correct pressure, by anyone knowing their correct rear axle weight, was to quote their rear axle weight as for a front tyre and thereby get the correct pressure for the rear tyres. Are you with me? A right carry on I know, but there you go.

Ron


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## blindwatchertrev (Nov 4, 2011)

Thanks to all. As ever a proverbial mine of good info........Trev


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## powerplus (Oct 6, 2014)

i have a couple of pages from continental that gives me all the infirmation on there tyres

it gives things like rolling diameter and air pressure for a given weight

it also shows that a twin axle tyre will not carry the same weight as the same tyre on a single axle

i have just been down the route of weighbridge and was 120kg over 3500kg fully loaded

the rear axle was 2020kg just over the plated max of 2000kg and 40kg below the max of my tyres

as i need 2 new tyres i will put bigger tyres on the back and get the van re rated to 3850kg

barry


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## greygit (Apr 15, 2007)

ob1 said:


> Taken at face value that would be the correct advice Mr Plodd. Unfortunately, there is a trade wide agreement between tyre manufacturers to always quote 80psi for rear tyres on motorhomes as a safeguard against overloading at lower pressures. I was told this by non other than a nice guy at Michlin. I was also told the way round it to obtain the correct pressure, by anyone knowing their correct rear axle weight, was to quote their rear axle weight as for a front tyre and thereby get the correct pressure for the rear tyres. Are you with me? A right carry on I know, but there you go.
> 
> Ron


 After giving Continental my axle weights and tyre specs they recommended 70psi for the rear tyres not 80psi .


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## Pudsey_Bear (Sep 25, 2008)

Is there a guide to the physical measurement at the base of a tyre say 50mm from the road when it's at the right pressure for the weight being carried, usually if it looks right it probably is quite close, but something more accurate but better than a printed figure which is arbitrary anyway as the load changes all the time by anything up to 750kg, a visual aid would be great, but is there such a thing.

Experience tells us when a normal profile tyre is flat regardless of it's size, more difficult with low profiles.

Just wondrin


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## TheNomad (Aug 12, 2013)

Wizzo said:


> This figure can be ignored it is only for the North American market.
> 
> JohnW


I'd strongly suggest NOT ignoring it.

Although it is only a legal requirement in the North American market to actually print the MAXIMUM inflation figure on the tyre wall, the manufacturers haven't just guessed at what safe psi MAX figure to put there.


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## cabby (May 14, 2005)

As I have not seen you post it yet, what size wheels and tyres have you got on at the moment.At a guess I would think 215/70/15R.If you are going to be running at virtually top weight even when upgrading, I myself would opt for 16" wheels and tyres accordingly.

cabby


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## powerplus (Oct 6, 2014)

hi cabby

yes 215/70/15r

on a 2011 x250 can you put the 16" wheels on 

i thought the stud spacing was different 


barry


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## Wizzo (Dec 3, 2007)

TheNomad said:


> I'd strongly suggest NOT ignoring it.
> Although it is only a legal requirement in the North American market to actually print the MAXIMUM inflation figure on the tyre wall, the manufacturers haven't just guessed at what safe psi MAX figure to put there.


The Tyre Safe booklet says this "The loads and pressures moulded on the sidewalls of many tyres are a North American requirement and do not apply in the UK or Europe"

So they can be ignored.

JohnW


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## Wizzo (Dec 3, 2007)

powerplus said:


> hi cabby
> yes 215/70/15r on a 2011 x250 can you put the 16" wheels on i thought the stud spacing was different
> barry


No need to go to that extreme, you can fit 225/70/15. These have a higher load rating and can run at a slightly lower pressure for the same weight. They are slightly bigger so will affect the gearing slightly.

JohnW


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## powerplus (Oct 6, 2014)

hi john

yes i was thinking of the 225/70/15 they are rated at 112 so will be fine on the back

my speedo is a little high so would the 225 be worth putting on the front my van is geared low so the extra diamiter should help


barry


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## Wizzo (Dec 3, 2007)

powerplus said:


> my speedo is a little high so would the 225 be worth putting on the front my van is geared low so the extra diamiter should help
> barry


Very worthwhile having the same sized tyres all round even if only for the need to carry one size of spare (if you have such a thing). My speedo is more accurate now, particularly at lower speeds but still reads higher than actual.

JohnW


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## TheNomad (Aug 12, 2013)

Wizzo said:


> The Tyre Safe booklet says this "The loads and pressures moulded on the sidewalls of many tyres are a North American requirement and do not apply in the UK or Europe"
> 
> So they can be ignored.
> 
> JohnW


Going round in circles here (wink).

Just because it ain't a legal requirement in Europe to have those maximum limits printed on the sidewall, that doesn't alter the fact that they are the safe upper limits that the tyre manufacturer established when testing that tyre.

The laws of physics don't alter simply because the tyre is being used on a vehicle in the UK rather than the USA.


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## cabby (May 14, 2005)

I was thinking of making that alloy wheels, but forgot to put that bit in my last post. As to spacers,I am not aware that is required.But would be interested to hear from anyone who has done that size wheel change.


cabby


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## Wizzo (Dec 3, 2007)

TheNomad said:


> ... that doesn't alter the fact that they are the safe upper limits that the tyre manufacturer established when testing that tyre.


Are they though? If that were the case why does it not apply in the UK or EU? Why also can Fiat recommend an inflation figure which is much higher than the Max shown on the tyre wall? You and I obviously read different interpretations of the words "does not apply".

I see the loading and Max Pressure info on the tyre wall as a legal antidote to being sued in the USA.

JohnW


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## Wizzo (Dec 3, 2007)

cabby said:


> I was thinking of making that alloy wheels, but forgot to put that bit in my last post. As to spacers,I am not aware that is required.But would be interested to hear from anyone who has done that size wheel change.
> cabby


Going from 15" to 16" wheels would make a very significant alteration to the overall gearing. I would think you would need to alter the final drive ratio to accommodate it.

JohnW


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