Tyre Pressure advice

[Guest Alf W]

Could someone with the relevant info (why dont tyre companies publish tables on the web ?) suggest appropriate pressures for - Michelin Agelis 81's - 195/70 R15C with Front Axle weight 1500Kg and Rear at 1700Kg. Would the pressure be significantly different if each axle weight was 100Kg more ?

[Guest Brian Kirby]

Alf Go direct to Michelin technical. You probably already have tyre pressure recommendations from your vehicle manufacturer. If you intend to reject these, you may need to be able to demonstrate how/why you arrived at the alternative pressures. Otherwise you may be held to be running deliberately overinflated, or under inflated. Either could, under the wrong circumstances, cause legal/insurance problems. I have found the technical people at Michelin excellent and very helpful. Contact them via their website, giving the vehicle model, make, year and tyre type/size, plus overall and axle loads. They do respond. They'll probally ask you to ring to confirm details, but are prepared to confirm their recommendations in writing via e-mail, so you have all the necessary evidence should you ever need it. It also makes a useful reference note, as a reminder of the changed pressures! They also gave me a formula to calculate the correct pressures for other loads as well, but I think this is possibly tyre specific, so it would be inappropriate for me to pass it on. Also you need the info to have identifiably come from Michelin, otherwise it'll lack the necessary authority. Good luck Brian

[Guest Alf W]

Many thanks Brian. I'll take your advice and be in touch with Michelin direct. The Pressures given in the Manual relate to a total weight of 3500Kg. We tour at something like 3100Kg and I think the recommended pressure is giving us a less comfortable ride than might be.

[Guest Mike C]

Hello Alf, If the Agilis 81's are load indexed 104/102R then the pressures should be as follows. Front 1500 kg - 58psi Front 1600 kg - 58psi Rear 1700 kg - 65psi Rear 1800 kg - 65psi 65 psi is the maximum pressure for this tyre up to a maximum load of 900 kg per tyre equal to 1800 kg per single axle (2 wheels per axle). For a twin axle (ie. 4 wheels on same axle)the maximum pressure is still 65 psi but the maximum load per tyre is 850 kg equal to 3400 kg per axle. Hope this is of assistance. Regards, Mike C.

[Guest Mike C]

Hello Alf, Sorry typing error. The pressures should read. Front 1500 kg - 51psi Front 1600 kg - 58psi Rear 1700 kg - 58psi Rear 1800 kg - 65psi Sorry about that. Regards, Mike C

[Guest Brian Kirby]

Alf Notwithstanding Mike's comments I'd still recommend you get it direct from the (Michelin) horse's mouth. Mike's pressures are much higher (over 10 psi higher) than Michelin recommended for my 215/70R15XC Campings at similar loads. At the time, I gained the impression from them that pressures for Agilis of the same size would be about the same. I know yours are a bit narrower, so may run harder for the same loadings, but I am puzzled by the disparity. From Michelin's data I would have expected to see some difference in recommended pressures to account for each 100kg increment in load. For mine it's about 3psi, although, again, that is for a wider tyre. Our original, Fiat/Burstner, recommended pressures were 65psi all round and that was very hard. After taking Michelin's advice I now get to keep all my stoppings! I hope you also get a satisfactory reply. Brian

[Guest Brian Kirby]

Alf I case of confusion, I was still writing my previous comment while Mike was correcting his typos! He beat me to the the draw, so my comments about differences in pressures are no longer relevant. I'd still get the confirmation direct from Michelin, though, for reasons already stated. Brian

[Guest Alf W]

Thank you Brian and Mike. I'm waiting a response from Michelin. My Autosleeper Ravenna also recommends 65psi all round which is most uncomfortable - hence the query. I will try revised pressures this weekend.

[Guest Brian]

You might have a long wait I emailed Pirreli and Michelin giving all the rel info on my M/H to establish what the correct tyre pressures should be Pirreli came back whin a couple of days but6 weeks later I'm still waiting on Michelin!!!

[Guest Mike C]

Hello Alf and Brian, The discrepancy between Agilis 81 and XC Camping is explained by firstly the ply rating of 8 for Agilis 81 and 10 for XC and the load index of 104/102R for Agilis and 109/107Q for the XC. On the XC the pressures are quoted by Michelin as <1460kg 43 psi, 1660 kg 51 psi, 1880 kg 58 psi and 2060 kg 65 psi. Maximum pressure for the XC Camping is 80 psi against 65 psi for the Agilis 81. It is good to see that you realise the importance of getting the tyre pressures correct. Regards, Mike C

[Guest Derek Uzzell]

Michelin's van-tyre technical data handbook gives the following axle-load/inflation-pressure figures when Agilis 81 195/70 R15 is used on a 'single wheel' axle: 1800 kg - 65psi 1640 kg - 58psi 1480 kg - 51psi 1300 kg - 43psi Between these figures the load/pressure relationship is linear, so a simple 4-point straight-line graph allows extrapolation of the inflation pressures for intermediate axle-loads. Alf: Michelin will normally provide tyre-pressure recommendations based on a vehicle's 'plated' maximum axle-loads (which you'll find on your motorhome's VIN data-plate) or on 'real' axle-load figures obtained via a weighbridge. In the latter case Michelin's normal policy is to suggest that the inflation pressure relating to the vehicle's 'static' front axle-load be increased by 10% to deal with weight transfer to the front wheels during braking. As there seem to be only two logical options on which to base pressure recommendations - plated weights or weighbridge weights - I'm a bit wary of your "100kg more" query. Perhaps this is just curiosity? Why don't tyre manufacturers publish this sort of information on the web? Come now - to appreciate why they don't you only have to look back through archive postings on this forum and see the confusion that reigns over what's essentially a common-sense subject.

[Guest Alf W]

Does not confusion reign because of the lack of information ? I have figures from the weighbridge, my original figures.The additional 100Kg was curiosity in part related to additional weight that might be carried with a second passenger - not weighing a full 100 Kg I better add ! (and possibly as case or two of liquid refreshment on the annual expedition). Thanks for the further info.

[Guest Peter Sharpe]

Please note that I have previously been instructed to remove any posts advocating particular tyre pressures, as there are legal reasons for doing so. As you will have seen, there has been a typing error, which if it had gone uncorrected, might have led someone to inflate their tyre incorrectly. In this thread, the general consensus has been that you should always contact the tyre manufacturer for advice, which we endorse wholeheartedly. Please understand though, that there are sound reasons for us to remove similar posts in future. Thanking you.

[Guest Alf W]

In that case I wont respond with Michelin's advised pressures received today.

[Guest Mike C]

Hello Peter, Quite happy for you to remove the information I gave on this thread and totally agree with your advice not to quote specific tyre pressures. I will not in future. May I suggest that you add this to the Forum rules. How does this leave giving any other specific technical information that could lead to legal action either on this forum or in the MMM magazine? Regards, Mike C.

[Guest Brian Kirby]

Mike, Peter, Alf et Al I do think this is now getting a bit "sticky". There are legal connotations to having the wrong tyre pressures, not just for MMM if the recommendation came from that source, but also for the driver af a vehicle that appears to have incorrectly inflated tyres. The chassis manufacturer and the converter both give written recommendations for tyre pressures for a specific tyre type and size. That is in black and white and is in the handbook. Mine is a Burstner, and both Fiat (chassis) and Burstner (converter), say 5.5 bar. However, that results in a very harsh ride. Acting upon various recommendations (mainly in MMM)) I contacted Michelin technical, and got their own reccommended pressures based upon actual axle loads for the loaded vehicle. This, they were prepared to put in writing. Thus, should I have an accident, or just be stopped by the police at a roadside check, I now have the Michelim e-mail to back the pressures at which I run my van. To do otherwise would, in my opinion, be unwise and could lead to legal complications - particularly following an accident where tyre pressures were found to differ from the chassis manufacturer's and converter's written pressures, but without any proper evidence as to why. Just saying "I got these alternative tyre pressures from MMM forum" would hardly hold up in a court of law! I can only repeat, give all of the relevant information to the tyre manufacturer - whatever he wants - get his recommended pressures confirmed in writing, carry them with you, and then go your various ways in peace! Kind regards to all Brian

[Guest Alf W]

The final twist in the tail from my point of view is that, in the light of figures quoted earlier in this discussion,I was suspicious of one of the pressures I got from Michelin by email yesterday. I queried it. They confirmed this morning that they had mis-printed. It seems clear to me that the MMM forum could not be held to be an authoritative source for tyre pressure info and that the law would still come down on the owner/driver. The ability to have open discussion and so in my case cross-check the "official" Michelin version was invaluable.

[Guest Brian Kirby]

Just one for Brian, if he's still listening!! If you've waited six weeks for a reply from Michelin, I suspect your e-mail never got to the right person, or was accidentally deleted along with all the others someone had when they got back from their hols. May I suggest you re-submit? I had no problems, and clearly Alf has also had a response. May we assume Alf liked his reply? Cheers Brian

[Guest Mike C]

Hello Brian Kirby, Not sure exactly what you meant when you said "I do think this is now getting a bit sticky" but I assume rightly or wrongly that you mean it is getting controversial. I personally do not think that any of us posting on this thread so far disagree with Peter Sharpe, he is the site moderator and is quite within his rights to specify reasonable and sensible rules of which not quoting specific Tyre Pressures is an example. I fully support him in this. My question was intended seriously, if tyre pressures are not to be quoted where does this leave others posting to this site in response to technical questions (eg. Service Intervals, Electrical Safety etc., etc.,) or technical answers in MMM. Michelin and other tyre manufacturers publish technical booklets and leaflets giving the correct tyre pressures for all their current tyres. In Michelin's case "Van Tyre Fitments Pressures and Technical Data". If one has this book why is there a need to write to Michelin to get a "legal confirmation"? Incidentally the Michelin book also has extensive sections on advice including Construction and Use Regulations. In so far as tyre information from the coachbuilders and vehicle manufacturers this is often incorrect. On my previous vehicle two different pressures were given 44 psi and 65 psi both incorrect for the type of tyre and load. My existing vehicle quotes 80 psi and 65 psi and the coachbuilders manual specifies "For tyre pressures refer to the base vehicle manufacturer". Fiat's 80 psi puts the vehicle outside the Construction and Use regulations. If it was not for my extensive knowledge in the tyre industry I could be driving the vehicle in an unsafe condition. Regarding the forum. One of the problems with this forum is that having made a posting one cannot either delete or edit it to correct errors, which we all make on occasions. Peter, are there any plans to include either item delete or edit facilities in the near future? Regards, Mike C.

[Guest Brian Kirby]

Hello Mike I think our biggest general problem is that none of us really knows the other, or with what authority he/she speaks. I too have the info from Michelin. It is technical information and has safety connotations. However, Michelin is its author, not me. I cannot know if there is additional or revised advice Michelin might add to their published information to suit someone else's particular circumstances. I therefore think, on balance, that such critical advice should come from, and be confirmed by, technical author. After all, to their great credit, they seem happy to provide confirmation, so why not obtain it? On the more general issues, I think it is a quite a difficult balance. A forum query is, by its nature, somewhat general. In responding to such queries one can surely point others in the right direction, provide contact names and addresses, express opinions and recommend courses of action. However, I, personally, would be uneasy providing detailed technical advice to someone I don't know, mainly because I wouldn't know what he/she might then do with it and whether they had properly understood it. For similar reasons I'd also be a bit chary about acting on advice so given. I'd be very grateful for it, but I'd still have a good sniff around it before going ahead. I think that is Peter's concern: that someone, somewhere, may be inadvertantly misled into acting upon a technically convincing answer, given in good faith, that turns out to have been erroneous because of fundamental misunderstanding between questioner and respondent. To some extent the answer to your question may lie in the desire to re-edit information given. How long afterwards? Suppose someone was quick off the mark and had acted in the meantime? I think the guideline must be to couch technical replies in a general vein, but guide questioners to the fountainhead for the final answer to their problem. I wonder what other think, if they're still awake? Brian

[Guest Mike C]

Hello Brian, Fullly agree with what you say especially about checking before going ahead and I apply this also to magazine articles and even vehicle handbooks, a belt and braces approach. I notice that Dave Newell has made a comment in a similar vein in reply to Clive in the Electrical Problem thread. This type of exchange is what makes this a good forum but I would still like to see the Delete and Edit facility provided. Regards, Mike C.

[Guest Derek Uzzell]

Mike: How would you define the logic that would drive your Delete/Edit facility? If you allow the author of an original posting to delete it, what are you going to do with any 'orphan' replies that related to it? Or would you anticipate author-deletion of the original posting also killing off responses to it? Or are you going to limit Delete/Edit just to replies? Retrospective editing of a posting or replies also has knock-on implications. If a posting author is allowed to change the original radically then replies to the earlier unedited version may be rendered nonsensical. Similarly, for replies relating to replies. I'm not convinced people would use the enhancement you're suggesting enough to make its addition worthwhile. (Incidentally, when I took delivery of my Hobby motorhome, I had the choice of five different sets of tyre pressures. Four of these were clearly wrong (like 15 to 20psi wrong) and the fifth set applied to a different chassis with similar maximum axle loadings. What price the information provided by dealer, chassis manufacturer or converter?!)

[Guest Mike C]

Hello Derek, I have used other forums which allow both delete and edit and the audit trail is left intact by the creation of an Item Deleted posting in place of the original posting. For edit the original posting is marked as editted with the date and in some cases the before and after image. In both cases only the originator would be allowed to delete his/her posting (also the site moderator obviously). The purpose is to allow either correction of an incorrect posting or to remove a posting of the "I wish I had not posted this now" variety. I cannot see any real problems with either of these but the rule could be set that a delete will only be allowed if no further postings exist. I quite see your point but surely this will also apply to a situation where the moderator removes a posting and not the entire thread. I assume that if one felt strongly enough about removing or editting a posting made in error the moderator could be asked to remove it with the same result. At present the only option appears to be to make another posting correcting the one in error but as Peter mentions any reader may act on the first posting before the correction is read. The real advantage of this forum over some others is that the postings do not have to wait until a moderator allows them to be posted. This allows an answer to a technical question to be received as soon as the answer is posted and not when the moderator has read and agreed the content then allowed posting. This is several days on some forums and makes the forum next to useless for getting quick solutions. Perhaps other changes such as Spell Checking should be of a greater priority. Concerning the information supplied by dealers, manufacturers and coachbuilders, it is not just on tyre pressures. When I was tugging, the UK handbook of our VW Passat gave a +300kg inaccuracy in the vehicle kerb weight(measured on a weighbridge)and a +20 kg inaccuracy in the maximum allowed noseweight for our model. When questioned we were told that these weights referred to a German Spec Passat and must under no circumstances be used for a UK spec vehicle. On checking the specifications the only difference was that the German Spec vehicle was LHD. I often wonder what would have happened if an accident had occurred directly as a result of towing using the incorrect weights. Regards, Mike C.

[Guest Derek Uzzell]

Mike: I believe what your're talking about would involve a total software rethink rather than just a tweak. Not sure when (or even if) Warners have any plans to alter the present forum structure as it seems to function OK most of the time. I think Peter S. once told me that, with the present system, he can delete a complete thread but not just an element (or elements) within a thread. Perhaps that's why the Malcolm Johns posting of 23/10 still exists!