Tire Pressures (1 Viewer)

madbluemad

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Jan 26, 2008
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Hi Folks

I had a new tire fitted about four weeks ago. I asked the fitter to check all of the tires at the time.

He checked them and they were all at 70 psi. The information printed on the tire says 80 psi cold. I asked the fitter to take them to 80 psi but he said that 80 was to high and that 70 was the optimum pressure.

I have just checked my tire pressures and they vary from 70 psi to 55 psi. This may be because its very hot on one side of the van and relatively cool on the other side.

Whats your opinion and what pressure should my tires be inflated to.

Cheers

Jim :Sad:
 
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OP
OP
M

madbluemad

Banned
Jan 26, 2008
3,327
239
spain
Funster No
1,335
MH
just looking
Exp
since 1980
Hi Folks

I had a new tire fitted about four weeks ago. I asked the fitter to check all of the tires at the time.

He checked them and they were all at 70 psi. The information printed on the tire says 80 psi cold. I asked the fitter to take them to 80 psi but he said that 80 was to high and that 70 was the optimum pressure.

I have just checked my tire pressures and they vary from 70 psi to 55 psi. This may be because its very hot on one side of the van and relatively cool on the other side.

Whats your opinion and what pressure should my tires be inflated to.

Cheers
Jim :Sad:

Please delete post, I have the answer. Unless of course its of any use to others.

Jim :thumb:
 
T

TJ-RV

Deleted User
For the benefit of others who might see this in future, the tyre pressure on the wall of a tyre is the maximum pressure. Correct tyre inflation pressure is best determined by separately weighing the four corners, or at least weighing each axle, and using the load/inflation tables on the tyre manufacturer's web site.

I have the answer

Care to share that for the benefit of others?

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L

landau

Deleted User
Tyre Pressure

I work in the workshop of a motorhome dealer (American and European) and 10psi under the cold pressure which is marked on the tyre is the rule of thumb, hope this helps .
 

haganap

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Dec 5, 2007
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Mine are set at 70psi, exactly 10psi undr the maximum.
 
T

TJ-RV

Deleted User
Some fixed number below the maximum makes little sense. If the tyres are replaced somewhere down the road by some with a different maximum pressure, do you then adjust the inflation pressure down or up even though the load on the tyres hasn't changed?

Check the load/inflation tables on the tyre manufacturer's web site to determine the correct pressure for a given load. Here, as an example, is GoodYear's load/inflation table. Note that, in addition to the required pressure varying by load on the inidividual tyre, it also varies depending on whether the tyre is mounted single or as one of a pair (aka duallies).

Underinflation is a recipe for a blowout, while overinflation will likely result in unexpected wear patterns in addition to poor ride and handling characteristics.

With due respect to dealers and repair shops, I've yet to come across one that has any clue what load is being carried by tyres or, for that matter, who have heard of the load/inflation tables.

When we bought our coach from a dealer, there was a truck weigh scale next door, although the dealer had obviously never used it. The PDI tech assured me he had checked and correctly inflated the tyres to 120 psi. I checked them (cold) and found they were inflated to 140 psi, which was higher than the rating on the rims. After weighing the coach and consulting the tyre manufacturer's table, I found the correct inflation pressures to be 90 psi in the front and 95 psi in the rear.
 
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Tony Santara

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Jul 26, 2007
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Care to share that for the benefit of others?[/QUOTE]

Hi tom
Looks like Jim (madbluemad) doesn't want to share :Smile:

Oh well maybe he'll want us to share info with him next time :winky:
 
T

TJ-RV

Deleted User
Tony,

Given the nature and intent of forums such as this (i.e. sharing of knowledge, information and experience for the mutual benefit of the members), I don't understand why anyone would ask questions but not share answers. I understand even less a request to remove their question after they have their answer.

OTOH I've been around forums many years and nothing surprises me anymore.

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T

TJ-RV

Deleted User
Tony,

We don't worry about tyre pressures on our other RV ::bigsmile:

Weight isn't an issue either; She'll carry more than I could think of loading on board. Plenty of spare HP too, and no brakes to worry about.

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OP
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madbluemad

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Jan 26, 2008
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since 1980
For the benefit of others who might see this in future, the tyre pressure on the wall of a tyre is the maximum pressure. Correct tyre inflation pressure is best determined by separately weighing the four corners, or at least weighing each axle, and using the load/inflation tables on the tyre manufacturer's web site.



Care to share that for the benefit of others?

Care to share that for the benefit of others?

Hi Tom
Its simple, the tire pressures are printed on a label inside the coach, this is a federal ID tag that must be inside the coach.

Ive had a lot to do with tires recently and you are correct in saying that the most accurate way to identify the correct inflation pressures is to weigh the vehicle.

Different loads require different inflation pressures. The problems start when you have an American tire on your coach, you try to replace it and find that the US system of identification is different to the UK one.

I spoke to the CC&C, two local tire dealers, kwik Fit, Michelin, Ford, Hankook, Gulfstream and a host of others. None of them new what the equivalent UK specification was to the US one. PATHETIC

In the end it came down to taking some of the info from the US tire and then making reference to the coach weights which again are posted on the inside of the coach.

Whats more disturbing for me is why did my tire pressures change by such a varying degree after only about five weeks.

Ive invested into a good quality tire pressure Gauge so that I can now check more often.

Cheers

Jim :thumb:
 
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madbluemad

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I work in the workshop of a motorhome dealer (American and European) and 10psi under the cold pressure which is marked on the tyre is the rule of thumb, hope this helps .

That would account for all of the tires being at 70 psi when they are marked 80 psi cold. :thumb:
 
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madbluemad

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Care to share that for the benefit of others?

Hi tom
Looks like Jim (madbluemad) doesn't want to share :Smile:

Oh well maybe he'll want us to share info with him next time :winky:[/QUOTE]

What seems to be your problem then. As it happens Ive been logged off and only just seen the posts, the first one I read was from TJ and I responded immediatley. Then I read your not to pleasant piece of graffiti.

Grow Up

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madbluemad

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Tony,

Given the nature and intent of forums such as this (i.e. sharing of knowledge, information and experience for the mutual benefit of the members), I don't understand why anyone would ask questions but not share answers. I understand even less a request to remove their question after they have their answer.

OTOH I've been around forums many years and nothing surprises me anymore.

SAD Try get your facts right before engaging the mouth
 
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madbluemad

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OOPS looks like we touched a nerve ...::bigsmile:

You got that one right. I will help anybody at anytime and they dont need to be a member of an internet forum

Had you read my initial post you would have seen that I said " Leave it on if its of interest to others"

I then left my computer. Upon my next visit to the forum I find that you have incorrectley accused me of being unhelpful and unwilling to help people or share my knowledge/information.

This could not be further from the truth. You then led TJ by the nose and he joined in the attampted character assaination.

Big Grins dont do it son, you can be as arrogant and as nasty as you like but not with me.

Like I said Grow Up

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Tony Santara

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Jul 26, 2007
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I'm not getting into it on the forum with you it's not the place for personal arguements .

Ill feeling could have been avoided if you had explained the answer you had found at the time you said you'd found it ...simple
 

haganap

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Dec 5, 2007
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You got that one right. I will help anybody at anytime and they dont need to be a member of an internet forum

Had you read my initial post you would have seen that I said " Leave it on if its of interest to others"

I then left my computer. Upon my next visit to the forum I find that you have incorrectley accused me of being unhelpful and unwilling to help people or share my knowledge/information.

This could not be further from the truth. You then led TJ by the nose and he joined in the attampted character assaination.

Big Grins dont do it son, you can be as arrogant and as nasty as you like but not with me.


a lads,,,
calm down calm down:Doh:


could of been that mad and blue was just not logged in.
please don't trade insults, it makes us funsters :Sad:

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T

TJ-RV

Deleted User
OK guys, time to cool it. I probably helped to (inadvertently) stir the pot here, but didn't mean to catalyze ill feelings. Apologies if I started WWIII.

Let's all take an aspirin (or couple of pints), get a good might's sleep, and things will look and feel better in the morning.
 
T

TJ-RV

Deleted User
Its simple, the tire pressures are printed on a label inside the coach ....

Hi Jim,

Any chance you could scan a copy of it, or maybe just snap a photo? It would certainly help my/our understanding.

...this is a federal ID tag that must be inside the coach.

There seems to be some misunderstanding here. In the case of cars, there is usually a tag on the doorpost &/or a label in the glove compartment stating the recommended tyre pressures, although I honestly don't know if it's Federally mandated or not. But, even this typically gives a range of inflation pressures.

In the case of RVs, they typically carry a Federal Certification Tag such as the one in the attachment. However, if you read it carefully, you'll see that the tag is for the chassis, aka incomplete vehicle. The tyre pressures shown are for the maximum gross axle weight ratings (GAWR front and GAWR rear), whereas actual weights vary a lot because of floorplans and options ordered by the customer &/or the dealer. As a result, it's impossible for the chassis manufacturer to determine the correct tyre pressure; He (the chassis manufacturer) really has no clue what the actual weight will be when the coach is delivered to the customer, so he specifies inflation pressures for the maximum rated axle loads (weights).

The problems start when you have an American tire on your coach, you try to replace it and find that the US system of identification is different to the UK one.

One of my pet subjects. Some years ago I headed a US standards-making body (not for tyres), comprised of 50 technical committees, each comprised of from 30 to 150 representatives. Achieving international standardization was nigh impossible, although we sent delegates to international standardization meetings. A relatively simple thing like metrication was a hard slog at that time. So, I'm not surprised that you'd have difficulty finding equivalent tyres.

Whats more disturbing for me is why did my tire pressures change by such a varying degree after only about five weeks.

I'm assuming that they were initially inflated to 70 psi cold and that you checked them cold. Did you possibly lose air from one or more tyres? As for differences between the "hot side" and "cold side", the GoodYear RV Tire Guide says that:

A 10 degree F (5.6C) temperature change will result in a 2% change in pressure (higher temperature = higher pressure).

This could have a significant effect here in the California sun, but I have no idea about the UK. Definitely not on the Western side of the Severn Bridge in what I affectionately call "not-so sunny South Wales".

Ive invested into a good quality tire pressure Gauge so that I can now check more often.

Smart move. Another couple of options that I use are:

  • Wireless pressure sensors on each tyre valve to continually monitor and relay pressures to a unit on the dash. There are several out there, but I happen to use PressurePro.
  • An infrared thermometer. Whenever I stop for lunch or a potty break, I walk around the coach and the toad, pointing the IR thermometer at each tyre. Loss of tyre pressure will show very quickly as an increase in temperature. I mentally have to compensate for the inside tyre of duallies running hotter than the outside, and tyres on the sunny side of the coach running hotter than the shady side. But, after doing this a few times, you get a relative feel for what to expect, and an anomaly will jump out at you.

P.S. apologies for the angle/quality of the attached image; It was taken by a friend of mine on his prior coach. I'll try to remember to snap a photo of the equivalent tag on my coach next time I'm over at the remote storage lot.
 

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