Tyre Pressures

[Alex_5041384]

my handbook says 175x13 = 55psi for a lunar astara. which i think could be to high, when a car weighting more has a pressure of 36front 44 rear.granted spread over 4 wheels not two.anybody help on this,I have a friend who used to tow a van says 40 psi is enough??

cheers alex (not the editor) lol

 

[Damian]

Alex, just one observation, if the handbook states a certain recommended tyre pressure, why do you consider it to be wrong?

As for your "mate who used to tow a van",does he work for the manufacturer? if not, then his input is totally irrelevant.

Manufacturers set recommended pressures to suit the van, taking into consideration the weight of the van, the load the user puts in it, and the suspension properties of the inflated tyre.

If the manufacturer says 55psi, then 55 psi it is!!

My Abbey GTS vogue has 56psi in its tyres, where did I get this information,,,,,,,,from the Handbook,,thats what its for,giving the RIGHT advice.

 

[sparkes]

Alex

two points

1, the manufacturer has calaculated the pressure based on loads, speeds and type of tyre. Your mate probably took a guess

2, if you run at 40psi and have an accident, your insurance will be in fits of giggles as they write the letter saying claim void!

Steve

 

[rayc]

Damian, the reason the pressures are so high is because they are commercial ( Light truck) tyres. They carry the weight of the van on two wheels whereas the car does it on four.

The 55 psi quoted is the pressure at their maximum weight and speed. When the load is doubled it would be or exceed the van MPTLM. I expect they have a speed / load rating of 94N or similar which equates to 670kg max load at,I think approx 80mph.

Check your tyre load rating and confirm the weight that two of them will carry. If it is in excess of the van MPTLM then the pressure can be reduced in accordance with the tyre manufacturers specification but I think a reduction to 40 psi may be wishful thinking. If in doubt stick to the 55psi.

 

[rayc]

Damian, the reason the pressures are so high is because they are commercial ( Light truck) tyres. They carry the weight of the van on two wheels whereas the car does it on four.

The 55 psi quoted is the pressure at their maximum weight and speed. When the load is doubled it would be or exceed the van MPTLM. I expect they have a speed / load rating of 94N or similar which equates to 670kg max load at,I think approx 80mph.

Check your tyre load rating and confirm the weight that two of them will carry. If it is in excess of the van MPTLM then the pressure can be reduced in accordance with the tyre manufacturers specification but I think a reduction to 40 psi may be wishful thinking. If in doubt stick to the 55psi.

Sorry Damian, I meant that to addressed to Alex.

 

[Alex_5041384]

Damian why do i think its wrong. i did'nt say they where wrong i said i think they are a high.havin read manuals etc mistakes can happen in print thats why i asked.

re:_ If the manufacturer says 55psi, then 55 psi it is!!

not always the case my friend my work shop manual (motorcycle)say semi synthetic oil but dealer and manufacturer say fully synthetic thanks for the response.

Sparkes cheers for reply.

Ray did'nt think about the commercial tyres theory

did think about weight spread between the 4 tyres and two

again thanks for the reply

 

[ProfJohnL]

Helo Alex,

You have raised a point about mistakes. Whilst I know from personal experience that sometimes errors do creep into documantation, but it is rare, and the way documentation has to be checked these days, a fundamental error such as the wrong tyre pressure would either have had a erratum notice securly fixed in the book or the book would have be withdrawn and republished.

If I had a question about tyre pressures on any given vehicle, I would have contacted the manufacture, rather than relying on the information gleaned from a forum, which is likely to be far more error prone than the original documentation.

 

[rayc]

Helo Alex,

You have raised a point about mistakes. Whilst I know from personal experience that sometimes errors do creep into documantation, but it is rare, and the way documentation has to be checked these days, a fundamental error such as the wrong tyre pressure would either have had a erratum notice securly fixed in the book or the book would have be withdrawn and republished.

If I had a question about tyre pressures on any given vehicle, I would have contacted the manufacture, rather than relying on the information gleaned from a forum, which is likely to be far more error prone than the original documentation.

Alex didn't say the information was wrong, all he did was ask if anybody could explain why a pressure of 55 psi was specified. I don't see any problem with that, we may as well close the forum down if it is deemed that this sort of request should be put only to caravan manufacturers. I beleive that the answer I gave would stand up in court i.e. they are commercial tyres and that is the pressure specified by the tyre manufacturer for the use at the maximum speed / load rating of the tyre. It is propably a better explanation than you will get from a caravan manufacturer.

 

[Alex_5041384]

Helo Alex,

You have raised a point about mistakes. Whilst I know from personal experience that sometimes errors do creep into documantation, but it is rare, and the way documentation has to be checked these days, a fundamental error such as the wrong tyre pressure would either have had a erratum notice securly fixed in the book or the book would have be withdrawn and republished.

If I had a question about tyre pressures on any given vehicle, I would have contacted the manufacture, rather than relying on the information gleaned from a forum, which is likely to be far more error prone than the original documentation.

Thanks for the response john noted what you say.

Thanks ray,

i read the forums for pleasure a laugh and information as do many others.i might need to put my questions in a different way so as not to be read as a statement.

Quote " we may as well close the forum down if it is deemed that this sort of request should be put only to caravan manufacturers" i hope not.

 

[lunar2000]

Hi Alex, My Luna LX2000 handbook states the 175 R13 94 tyre pressures can range between 42 and 54 psi depending on load. As I normally keep to the MTPLW (Max gross weight)I blow my tyres up to 54 psi.

When I take my van in for service, I let the tyres down to a lower pressure 45 psi because I take all the extras out of the van ( awning etc).When I collect the van from the service the tyres are always up to 60psi for some reason? Must ask why they do that....?????

Pop

 

[ProfJohnL]

Hello Ray c

Perhaps I have touched a raw nerve? not intentional.

Alex's question seems to have been trigged by the disbelief of the relatively high presure stated for his caravan tyres, in other words he has doubts about the accuracy of the manufactures information.

I can understand and agree with the replies above my own, they dealt with the probable reason for such high pressures, but as we should all know it is unwise to simply accept without question what is posted on the forum. I felt it was wise to add a note of caution, and to suggest the corrcet method of verifying the information.

I do not belive that manuafctures would have alowed a fundamental error such as tyre pressures to have been published.

Perhaps I did not express my reasons clearly, I shall restate:

Manufactures are tied up with quite a lot of red tape these days. Road vehicels incluing caravans have to go through a 'type approval' process which includes close scruitinee of documentation, for many specific points, and I would suggest that road tyre pressures are one such item. Because of this scruitinee it is far less likely that an error will get through.

Legally you must run your vehicle according to the manufcatures instructions and the road traffic acts, so the only source of information with authority is the manufacture rather than un verifiable and possibly ill-informed sources such as these forums. There is the possibility that a contributer may deliberatley set out to miss-inform.

A court defence relying on information gleaned soley from a forum would not stand up in court.

I think I recall that you have contributed to tyre pressure questions previously, and I am happy to accept that you have experienmce in these matters. But even with my own replies I encourage people to verify details though some traceable route.

 

[JohnI.Stephen]

My Bailey Senator requires 66psi (I believe); the problem is that my portable inflator takes HOURS to get to 60psi and never realy makes it beyond that; I usually give up at 60psi!!

Any ideas on a suitable tyre inflator ?!

John

 

[william_5122476]

Only thing I can suggest is to do it the old fashioned way..with a foot pump..as you say the electric inflators take forever..my old Kismet foot pump does the job just fine..about ten strokes of the pump per ten pounds of pressure...bit hard on the old knees tho...I then check the pressure with a Draper dial gauge which seems to be very accurate..

William