RV.Net Open Roads Forum: Class A Motorhomes: Checking tire pressure with jacks down...


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fourfurz

Memphis

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Joined: 03/23/2008

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Posted: 10/09/08 08:09pm

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Home Skillet wrote:

fourfurz wrote:

Remember PV=nRT

Shucks........you got me.

I think the issue is "tire deflection" with added weight.
Not enought to compress the air in the tire. The rubber casing in the tire would bulge out, so the volume remains the same. No?

I'm no tire geometry expert but I'm going to test this theory in a couple of days. I hope it makes no difference. I've been going through a lot of extra trouble to check my tires if it doesn't matter.

2007 Mountain Aire 4528
2006 CRV SE
Based in Memphis area

Jim&Peg

Central Ohio

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Posted: 10/09/08 08:11pm

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If there is a difference, it would take a gauge capable of reading to several decimal places to detect it. You are not going to see any difference with a normal gauge.

Dutch_12078

Upstate NY

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Posted: 10/09/08 08:18pm

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I had occasion to test this just the other day. I had a new tire for my Coachmen mounted on a rim at our truck shop, with instructions to inflate it to 80 PSI, which was done while I watched. After I installed it on the coach and let the jack down, I checked it again to make sure the pressure had held. It read 81 PSI, a minor variance attributable to either temperature or gauge differences.

Dutch
'95 Coachmen Catalina 322XL 33 ft. F-53 chassis
Great Sacandaga Lake, NY

zsr22

Atlanta, GA

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Posted: 10/09/08 08:20pm

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What gauge is everyone using?

Zack
1998 Holiday Rambler Endeavor 36WGS

Front Row Talladega Infield | ol' Kegerator | Our UGA Tailgate

wilanddij

CA Desert

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Posted: 10/09/08 08:21pm

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The next time you buy new tires, watch the installer and see where the tire is when he inflates it to pressure. My guess is that the tire will be on the changer or the balance machine.

Will & Di
2004 Southwind 32VS
Workhorse/8.1
Jeep Wrangler/Blue Ox
"We have met the enemy, and he is us" Pogo

dirtengineer

Alaska

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Posted: 10/09/08 08:36pm

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The load changes the shape of the tire in contact with the ground, not the pressure in the tire to any significant amount. That is why over-inflated tires wear in the middle.

Dutch_12078

Upstate NY

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Posted: 10/09/08 08:43pm

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zsr22 wrote:

What gauge is everyone using?

I use a Milton dual-foot 0-160 PSI "stick" gauge at home. In the shop, we use Accutire digital gauges.

Hookum

Tucson, Ariz.

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Posted: 10/09/08 08:49pm

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I think there are a bunch of rocket scientists on this site.

Those are the kind of questions NASA would have. They would appoint a committee of 12 people to study the problem.

gperry

Tennessee

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Posted: 10/09/08 09:13pm

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I recently had a slow leak fixed and have been watching the tire carefully. The patch is holding well but there is consistently about a one pound difference between on the levelers and off. I was surprised by that as I would have expected no difference. It's possible it could be due to other factors also.