Tyre Pressure

[4petedaniel]

I have just taken procession of a Autosleeper Amethyst Motor home and was checking out the tyre pressure And found them at 60 lbs PSI now I am properly wrong but it seems a bit high to me does any one know what is the correct pressure?

Petedaniel

[Brambles]

The straight answer to your question is ...no one knows the correct pressures for your tyres. The only realway to find out is to have the axles weighed on a weighbridge and get in touch with tyre manufacturer for recommended pressures. However 60 sounds about right as a maximum tyre pressure. Not trying to be awkward but this has been asked many many times and getting axle weights is the safest way because every Motorhome has different build weights depending on layout and how much stuff you pack in.

Jon.

[panagah]

as brambles says, try doing a forum search. There was a good thread with some helpful info on recently.

 

60 psi IMO is not too high, it is lower than what I run mine on.

[4petedaniel]

The last Autosleeper camper I had a Clubman. Had the tyre pressure printed on the inside of the drivers door and it was only 28 lbs the replacement is only 2 foot longer and more than twice the pressure seem a bit excessive to me.

Pete

 

[colin]

28lbs for your earlier van sounds very low, more like that should have been 2.8bar 48psi

[rupert123]

4petedaniel - 2008-09-22 9:37 AM

 

The last Autosleeper camper I had a Clubman. Had the tyre pressure printed on the inside of the drivers door and it was only 28 lbs the replacement is only 2 foot longer and more than twice the pressure seem a bit excessive to me.

Pete

 

Pete, take note of what you are being told. With my Swift Sundance neither Swift or Fiat could give me correct tyre pressure only a starting point. I had to go to a weighbridge get the axles weighed and contact tyre company. My pressures are 50lbs front 70lbs rear, high rear pressure is probably because kitchen is all at rear and I carry a scooter on a rack. This is the only way as nobody except you has any idea of the loads you will carry. Probably the 60lbs in your tyres is a good starting point and will be ok for a time but to make sure get it weighed.

[cronkle]

If you get the vehicle weighed it may be a good idea to e-mail the tyre manufacturer for the correct pressure and if it is different to what you have in your documentation keep a copy of their reply with your vehicle documents as evidence if the police/VOSA/insurance company ever query it.

[Derek Uzzell]

Petedaniel:

 

Amethyst was normally constructed on a Ford Transit Mk 5 FT-150 3300kg long-wheelbase chassis with (as original equipment) 225/70R15C 6-ply-rated tyres. This was the same base-vehicle as that used for my 1996-built Herald Templar and the recommended tyre pressures for that chassis were 41psi(front) and 53psi(rear).

 

If your Amethyst is a late model (say Year-2000), there's a small chance that Auto-Sleepers used the FT-190 3500kg chassis with 8-ply-rated tyres instead, in which case the recommended rear-tyre pressure would increase from 53psi to 61psi to handle the FT-190 rear-axle's upgraded load capacity. However, whether the FT-150 or the FT-190 chassis was employed for your vehicle, front-tyre pressures should be significantly lower than the rear-tyre ones. It does need emphasising that, as your motorhome is at least 8 years old and is quite likely no longer on its original tyres, it's impossible to be specific without more details of the vehicle and confirmation as to what tyres are currently fitted.

 

As Brambles suggests, the wisest thing for you to do would be to obtain 'fully loaded' axle weights and then seek pressure recommendations from the tyre manufacturer.

 

Personally, I found that, with my Herald Templar, weighbridge-provided data would have allowed me to have lowered Ford's 41/53 pressure recommendations safely based on Michelin's (the manufacturer of the tyres that were fitted) advice. In fact, as the Mk 5 Transit is softly sprung, I chose to leave the pressures unchanged from Ford's axle-loading maxima recommendations and never found that this compromised the ride quality.

 

Weighing my Herald also proved that, although it would have been virtually impossible to exceed its maximum permitted axle-loads, it wasn't that difficult to approach its 3300kg maximum permitted overall weight when the motorhome was full to the brim with fuel, water, passengers, luggage, etc.

 

The Templar was the smallest of the Transit Mk 5-based Heralds and it was obvious that the bigger versions would be heavier. Received wisdom at the time was that contemporary Transit-based coachbuilt Auto-Sleepers models, (Amethyst, Legend, etc.), due to their hefty GRP monocoque body-shell, were even heavier than the Herald equivalents and that their 'genuine' user-payload was pretty limited. So a secondary benefit of you weighing your Amethyst would be to discover how much spare payload you've got.

[4petedaniel]

Thank you all for your information I have now discoverd the last weighbridge certificate and it would seem the tyre pressure should be 54psi front and 58 psi back so they are not to far out.

Pete

[Derek Uzzell]

Unless you've got peculiar tyres on your motorhome, or you've somehow got a helluva lot of weight on its front axle, the figures you've quoted conflict with what I'd anticipate would be appropriate for the vehicle (particularly for the front tyres) and also vary from Michelin's recommendations for the tyres that one would normally expect to find fitted to an Amethyst's Ford chassis. Anyway, as long as you are happy that's the main thing.

[Derek Uzzell]

I've copied below a tyre-related piece I wrote in 2001 for the Herald Owners Club. It has some relevance to this thread as the Ford base-vehicle and tyre options are what one might resonably expect to find on a typical Auto-Sleepers Amethyst. It shows how unreliable advice on tyre-pressures can be when offered by internet forums, non-specialists and even by motorhome manufacturers themselves.

 

Unsuitable Tyre Pressures: A Cautionary Tale.

 

Ever wondered why your motorhome’s tyre pressures are what they are? Neither had I until recently.

 

On a French website Pierre asks for advice. He owns a camping-car based on a Ford Transit 150 lwb chassis. It has Michelin 225/70R15C tyres that he has always inflated to 41psi (Front) and 53psi (Rear) because that’s what his handbook says. But the MOT inspector tells him these pressures are too low and recommends 59psi F&R. Who is right, Pierre asks, handbook or inspector? (Europeans use ‘bars’ rather than ‘psi’, but I’ll stick with English terminology. 1 bar is about 14.7psi)

 

Pierre’s ‘van/tyre specification seems to matches my Herald Templar’s. 41F/53R are as given in my Ford Owner’s Handbook (and my Haynes Manual) for this chassis/tyre combination and I have been happily using such pressures for 3 years. I reply confidently that the MOT inspector is mistaken.

 

But then come comments from Thierry (similar chassis/similar tyres, he says) who now inflates the tyres on his Pilote to 59F/62R after two blow-outs at the ‘standard’ pressures. From Alain, who is using 66 F&R following advice from Laika. From Guy, who employs 59 F&R but whose ‘van, it transpires, has a Transit 190 chassis, twin rear wheels and 185-width Firestone tyres. And it gets worse when Pierre asks his local camping-car main dealer and is told 66F/71R. (That’s respectively 60% and 34% above Ford’s 41/53 figures.)

 

Rather odd this, so I e-mail Firestone, Michelin, Pilote and Rapido (because they are French and built ‘vans on the FT 150L base) for advice. No help from the first, Michelin confirm Ford’s 41F/53R pressures and provide lots more useful data. Pilote says 66F/71R, but when I challenge this, quoting Michelin, I get no reply. A belated reply from Rapido (I'm talking months not days) also advises 66F/71R. I also consult my local tyre specialist who says 41F sounds low, 53R sounds high and heavier construction tyres would be better for an over 3 ton motorcaravan.

 

Lots of feedback from motorhome owners and ‘professionals’ and much of it conflicting. So let’s start again, with my Herald Templar II as guinea-pig.

 

Firstly, we need to be specific about vehicle and tyre details. My Herald is diesel-powered, built on a 1996 model-year Ford Transit 150 (long) chassis-cab and shod with ‘original equipment’ tyres showing Michelin 225/70R15C PR6 XC4S on the sidewalls. The VIN plate in the Herald’s nearside cab foot-well indicates that the vehicle’s Maximum Authorised Mass is 3300kg and the Maximum Axle Carrying Capacities are 1600kg (front axle) and 2000kg (rear axle). I had copied these data to Pierre for comparison: he had replied that his ‘van matched exactly on both vehicle and tyres. (So two of us at least were not talking at cross purposes!)

 

I had also relayed these details to Michelin and I’ll summarise their response:-

 

“Michelin require individual axle weights (not overall vehicle weight) in order to supply pressure recommendations for the quoted load conditions. These can be presented in the form of values stated on the 'VIN plate' (maximum axle carrying capacity) or, much better for motorhomes, from actual weigh-bridge readings. The latter would be preferred, due to readings being taken in the actual vehicle 'running' condition - that is to say, with all water/fuel/baggage and passengers etc. onboard and may result in better comfort if the vehicle is running well below maximum capacity.

 

The Ford Transit 150 LWB chassis-cab is listed as having pressures Front 41 psi / Rear 53 psi, however, the weight change due to the motorhome conversion may make these figures irrelevant.

 

The tyres stated: “XC4S” 225/70R15C PR6, are able to run at the following axle loads/pressures (with linear scaled values in between each listing):-

 

Single fitment axle --- Pressure

(Kgs) ------------------ (psi)

1460 ------------------- 36

1660 ------------------- 44

2060 ------------------- 55

(Where 'single fitment axle' = one tyre fitted each end of axle).

 

We would not recommend using this tyre at above 55 psi. Where an axle load is listed/measured as being over 2060 Kgs (single fitment) then 8 ply (8PR) should be used, rather than trying to compensate by over-inflating the 6 ply (6PR) tyres.”

 

A simple graph based on Michelin’s figures reveals that the pressures needed to support axle loads of 1600kg and 2000kg are about 41psi and 53psi. But let’s be very clear, these are maximum axle loads for Pierre’s ‘van and mine, so the 41F/53R are maxima too, as a need for higher pressures would imply axle overloading. In addition, if the axles were both maximum loaded, the vehicle would weigh 3600kg and thus be 300kg overweight.

 

Michelin has two 8-ply 225/70R15C tyres, the “XCA” and the “Agilis 81”, and the single fitment axle loads/pressures for these are 1540kg/44psi, 2020kg/58psi and 2240kg/65psi. The recommended maximum pressure for both 8-ply tyre types is 65psi, while the pressures needed to support axle loads of 1600kg and 2000kg are 4-5psi higher than for the 6-ply XC4S at about 46psi and 57psi respectively.

 

There is nothing subtle then about the tyre pressures shown in your handbook - they are worst-case figures. They are not written in stone and they can be varied to suit real-world conditions. In fact, 41F/53R seem to work well for my Templar: empty, the ‘van’s ride is decidedly choppy, but it’s quite comfortable in its normal holiday mode and tread wear shows no evidence of under or over inflation.

 

Based on the ‘French Experience’ I have described, I suspect many ‘vans are being driven with quite unsuitable tyre pressures. While under-inflation of tyres must be avoided absolutely, the hard ride that results from over-inflation stresses humans, tyres and vehicle alike. If driving your motorhome is shaking your fillings loose don’t just accept it as normal. Get the ‘van weighed in fully loaded condition and if the axle loads are well below their permitted maxima seek advice from the tyre manufacturer. Resolution of the ride problem may just be a matter of adjusting the tyre pressures appropriately.

 

[4petedaniel]

THis subject is far more complicated than I had Imagined The motor home builders should be forced to fit a plate. With the required tyre pressure on each motorhome. with unloaded and fullload to the 3300 maximum On my last VW motor home there was a plate on the inside of the drivers door with the tyre pressure settings, But they seem to be very low compaired to the pressures mentioned. and it did seem to Bounce about a bit.

Pete

 

[Don Madge]

I think this has been posted before but it might help some.

 

http://www.tyresafe.org/data/files/motorhome%2008.pdf

 

Don

[Derek Uzzell]

Pete:

 

The vast majority of motorhomes are built on basic light commercial vehicle chassis and, when sold new, will come with an owners' handbook produced by the manufacturer of that chassis. This handbook will invariably include tyre-pressure recommendations. There will also be a handbook provided by the motorhome manufacturer and this normally will include tyre-pressure recommendations too. (Some motorhomes (like my Ford-based Hobby) do, in fact carry a 'plate' specifying tyre-pressures: unfortunately - in my Hobby's case - the recommendations are wrong!)

 

Makers of light commercial vehicles will always specify as original equipment tyres that are capable of dealing with the maximum permitted axle loadings that the chassis are designed to cope with. As the manufacturer plainly cannot know whether the end-user will run a vehicle lightly or heavily loaded, for safety's sake tyre pressure recommendations will normally relate directly to maximum permitted axle loadings. And these recommendations will usually just be copied into the motorhome manufacturers' handbooks. The Ford handbook for my 1996 Herald recommended 41/53 front/rear tyre pressures and the same data appeared in the Herald Templar handbook.

 

Now, everything is fine and dandy as long as the motorhome, in fully loaded state, has axle-loadings somewhere near their design maxima. However, if the motorhome has axle-loadings that are a lot lighter than those maxima, then the recommended tyre pressures can produce a distinctly uncomfortable ride and that's when weighing the motorhome and seeking advice from the tyre manufacturer can be helpful.

 

I don't want to be unkind, but your original question was rather like someone going to their GP and saying "Doctor, I've want some advice about my daughter's leg" and expecting a useful response.

 

I've still no clue as to when your Amethyst was built and, although there will be a VIN-plate on your motorhome (in the passenger-door foot-well if my memory serves me right) that gives the vehicle's maximum permitted overall weight and individual axle weights, you've not provided those data. I've assumed your tyres are 225/70 R15C size, but you haven't confirmed this. That tyre-size comes in various 'flavours' regarding load-carrying capability (for a while Michelin even made a camping-car version that could be inflated to 80psi) and, without you revealing exactly what tyres your Amethyst wears currently, based on the markings on their side-walls (eg. Michelin Agilis 81 225/70 R15C 112R), it's just rough guesswork as to whether the 54psi/58psi pressures you quoted are appropriate or otherwise. For all I know you've got tyres from 5 different manufacturers and with varying load-carrying capabilities. Knowing your Amethyst's weighbridge-obtained axle weights would also be valuable as, if 54psi is indeed right for your front-tyre pressures, your motorhome's front axle loading must be close to (or beyond) its permitted maximum, which would be rather strange.

 

When a motorhome is new, it should be possible to say, with reasonable certainty, what the recommended tyre-pressures for the vehicle are. After the vehicle has gained some years of use, and some or all of the tyres have been replaced, things become less clear. And the pressures themselves recommended by the base-vehicle and/or motorhome manufacturer very definitely won't be optimum for every motorhome. This is an idea that many motorcaravanners appear to find uncomfortable, but few people would have trouble accepting that, if you've got a wheel-barrow with one brick in it and a 5psi tyre pressure, you can trundle that barrow around with perfect ease. But, for an identical barrow loaded with 100 bricks, you'll need a much higher pressure than 5psi to cope with the extra weight. Motorhomes are little different - essentially a heavy axle-load demands a higher tyre pressure than a light one.

[rupert123]

Pete, their is nothing complicated about it and although Derek has come up with loads of information no one can tell you what they should be except the tyre people. Knowing what your m/h is or any other details does not matter, it is simple. Get it weighed email or telephone the tyre manufacturer, give them the details, weights, tyre type and size, they will give you pressures. What is complicated about that. If you are going to query what they give you then their is no hope and you may as well just guess.