tyre pressure

[supercav]

(?) (?) (?) Please excuse my ignorance as a newcomer since I guess that this subject will have been covered many times before. I have recently bought a new motorhome based on a Ducato with a MTPLM of 3400Kg and on receipt the tyres were at 75psi. I have loaded the van as for a holiday with driver, passenger, full tank of diesel, full tank of water and loads of gear and then taken it to a weighbridge where it registered 3050Kg. Do the tyres need to be at such a high pressure or is there a ratio for tyre pressure to weight? Thanks in anticipation.

[lizken]

I asked this question of my tyre specialist who recommended 55psi at 3100kilos. I am running at this pressure, but ould suggest that you seek advice from your local specialist Ken

[Derek Uzzell]

There is a ratio, but it's axle-load related not overall weight-related. It also depends on the exact make/type/size of tyre fitted. Did obtain the axle loadings when you visited the weighbridge, because those data are what you really need? It would also be useful to know the weight-limit figures on your motorhome's VIN plate (see recent "engine plate" posting).

[enodreven]

Hi, Supercav If you have Michelin tyres fitted you can contact them with the tyre details from the side wall and the axle weights front and rear from your visit to the weightbridge and they will provide you with the tyre pressures. It may be worth carring the reply with you just to show why the tyre pressures may be differnet from the MH manufactures recommendations ? I sent an email to this address:- Webtyreauto@uk.michelin.com but it may be quicker if you go direct to the Michelin web site which i think is www.michelin.co.uk hope this helps Brian

[Yorkshire Tyke]

Look carefully round the tyre wall. You will find a moulded section which will give the tyre pressure for the maximum load On our 3500 kg the max load for the tyres is about 2400kg at a pressure of 65LBS The van manufacturer quotes 62.5 lb front and 65.5 lb rear at max load If you are running empty then you may get a bumpy ride this is lessened as the load is increased Remember you are driving a vehicle designed to carry a greater load than a car and most motorhomes are at almost full load when you have put nothing into them Most motor homes have a payload (the amount of goods that you can put into them before overloading) is only about 400kg at the best While the same chasis used for a van would have in excess of 1000kg Running the tyres under inflated:- Increases tyre wear and heating Increases fuel consumption Causes rolling on corners/roundabouts This reduces the handling Can be attributed to the cause of an accident should one occurr Gives a softer ride I have only been driving vans for 46+ years, but have experienced the effects of soft tyres in that short time

[RonB]

Enodreven is right. The only specialist who can provide you with correct tyre pressures (given the correct axle loadings) is the actual tyre manufacturer. Motorhome constructors invariably quote figures that are the maximum - but don't say so. The CORRECT presures can be way below this.

[Brambles]

A lot of work has gone into collecting this information so I hope someone here finds it useful. It is of course only a guide and is information collected by myself regarding tyre pressures given to people enquiring about pressures from Michelin. The 1st column is the axle weight and then the recommended pressure and grouped by tyre sizes and front or rear. AS MENTIONED THIS IS ONLY A GUIDE and is no substitute for contacting tyre manufactures with your own details and axle weights for a recommended pressure. (trying to avoid any liability here for info or for forum owners..bla bla bla.) If you look up your handbook for the maximum permissable weights for axles (not tyres) then you will see you should be no where near the 80psi (5.5bar) given on tyres or rating lables etc. More like 60 to 65psi. Michelin 215/70 R15C XC front ( + michelin recommended adding 10% to given values) 1220kg 44psi + 1280 45 + 1400 46 + 1500 50 1650 51 rear 1600 52 1750 54 1750 56 1800 57 1900 60 2500 75 3300 80 Michelin 215/75C16 XC Front ( + michelin recommended adding 10% to given values) 1400 45 + 1660 49 + 1700 54 1750 55 1820 50 + 1850 52 + 1850 57 1850 60 Rear 1900 57 1900 60 1950 60 2100 63 2120 62 2120 64 Michelin Agilis 81 185R14C102R 1140 46 1700 65 (max permissable load 850kg per tyre at 65psi) Michelin Agilis 225/70C 16 Fr 1610 50 Rr 2240 60 Vanco 215/70R15 8 ply Fr 1460 45 Rr 1750 55

[Derek Uzzell]

Brambles: Historically, Warners have taken a dim view of specific tyre pressure data being given on this forum, so I expect this thread will get the chop shortly. I note how you have assembled your data but it needs to be said that many of your figures conflict with those given in Michelins's Technical Handbook for the tyres you mention. (I can't say I've checked all your figures and I've no data to hand for the Continental's 15" Vanco 8.) A particularly glaring discrepancy relates to the information you've provided for the Michelin 215/70 R15C XC Camping tyre. This tyre pattern has a load index of 109, indicating a maximum design per-tyre load of 1030kg (maximum 'single-wheel' axle load of 2060kg) at a pressure of 65psi. Even if we assume that this tyre has an unofficial 'undisclosed' capability of tolerating higher axlle loads, it's a big step up from 2060kg at 65psi to your 2500kg at 75psi and the rise to 3300kg at 80psi is, frankly, ridiculous. The latter capability would imply a load index of 125 that is way beyond that of any light commercial vehicle tyre whether 15" or 16" diameter, or 8- or 10-ply rated. Sorry, I appreciate you are trying to be helpful, but tyres are a safety-related subject and already enough of a mystery for many motorcaravanners without adding further confusion.

[Yorkshire Tyke]

Hi I dont know about any figures except the Agillis Rear (which are close to our front wheel figures) Those seem to be about correct our rear tyres are several KG above those figures (2800 & 65psi)

[Brambles]

Hi Derek, Well spotted, it does appear to be way of the mark. These are figures collected from people who have iether posted on Forums, emailed me the info or I have obtained from Michelin or verbally from fellow Motorhomers. Many of the figures are actually repetative figures from diffrent people but I have only listed once. The spirit of my post is to show that many motohomers are way over inflated by using the 5 or 5.5 bar shown in handbook or on sticker on vehicle. I cannot reinforce enough the weighing of axles and contacting tyre manufacturer. It is also important to note that if you have a tag axle on rear then pressures are quite different from single axles and above lists for rear have no tag axle pressures listed. Also when contacting Michelin some technicians make allowance for braking but don't say, some don't allow, and others mention 10% more for braking....all very confusing. If Warner don't like the post, fine, they are welcome to chop it. As I said it is a list of pressures people have been given that i have compiled - thats all it is a ...A LIST. A guide. No guarantee to it's accuracy. Yorkshire - If you can confirm your rear pressures are for Agilis size mentioned and from manufacturer I will add to my 'unofficial list'.

[Derek Uzzell]

Branbles: If you offer people a long list of axle-weight/tyre pressure statistics then there's more than a sporting chance they will accept that you are an expert and that the data are valid. Essentially, they will do exactly as you suggest and use the information for guidance. This might be OK if the data were 100% accurate but, in this case, it's evident they aren't. After I had highlighted the 2500kg/3300kg discrepancies, it's a cop-out in my book to say "Well spotted, it does appear to be way of the mark". Surely you should have recognised the anomaly yourself and investigated it before publishing your list? Because I'm aware I'm not infallible (though my wife must think I am as she regularly calls me a know-all) I can't guarantee that everything I write is totally accurate, but I do try my best that it should be so. I'm also doubtful of your "Michelin Agilis 225/70C 16" as Agilis has never been available in this profile/diameter combination. I'm guessing this should be Agilis 81 225/70 R15 C (a size commonly used on Mercedes Sprinter and pre-2000 Transit chassis), but even then your load/pressure data diverge somewhat from Michelin's handbook data. Searching this forum using "tyre" will reveal how extensively the subject has been aired previously (and remember that the threads retrieved only go back to January 2005 - there were tons more before that). If you are reluctant to wade through the lot, the threads of 4/4/2005 and 19/2/2006 would be good examples of the in-depth discussions that have taken place. (You might also be entertained by the "Tag-axle" posting of 8/3/2005 - sometimes this forum becomes Geek Heaven!) You must have spent much time compiling your list, but (forgive me for saying this) it seems a hell of a lot of effort to obtain questionable information when the Real McCoy is available in the tyre manufacturers' own guides.

[Brambles]

As I said. it is a list of information given to me by other people - all I have done is list it. As in the previous threads it highlights the total confusion people get over tyre pressures. Confusion between lbs and psi, Tyre sizes, bars and psi. Not to mention manufacture giving out conflicting values and errors.

[RonB]

I say again. The only 'people, expert, specialist' or whatever, who can give you the correct answer on this important subject is the tyre manufacturer.

[Brambles]

Well! all I can say is it is forum debates and dicussions like this one that have raised the awareness of correct tyre pressures and inflating to the Maximums given in handbooks and door pillar stickers is wrong. With out these constant postings, whether people agree or not, then many many Motorhomers would still be running at too high a pressure, equally some too low as my dealer said 35psi to me when I bought new.