[T3] Tire inflation pressures

Daniel K. Du Vall dduvall at 1peter4-10.org
Fri Jul 15 14:28:50 PDT 2011

Thanks Jim this is very informative. 
Been one of them things I have thought about not just on my type3.
Rear tires on trucks always tend to be over inflated unless carrying a
load more than the bed and frame so I have always run much less in mine
on trucks. I can see how this would be opposite on rear engine
automobiles. I will let you know how thing go after I try your
recommendations. Always willing to experiment toward improving my VW
experience. :-)

Daniel Du Vall

-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim
Sent: Friday, July 15, 2011 3:15 PM
To: type3 at vwtype3.org
Subject: Re: [T3] Tire inflation pressures

On 15 Jul 2011 at 13:28, Daniel K. Du Vall wrote:

> Which brings up a question are you recommendations for radial or bias
> ply tires? Mine are radial and on 5.5X15 rims with p186/65 R15 tires.

The numbers I gave are for stock 165SR15 radial tires, although I 
think they would apply equally well to stock bias 165-15 tires. VW 
did indeed recommend a couple psi less for bias ply tires, but I 
never saw any good reason for this and haven't driven on bias ply 
tires since about 1970.

Larger tires, like yours, would do best with even less (yes, really) 

Think of it this way: Pressure is force per unit area. You're trying 
to support a certain amount of weight on a certain amount of ground 
contact area. The inflation pressure of the tire, times the area of 
the contact patch, needs to be about equal to the weight supported by 
the tire.   

So if you use a larger tire, with a larger contact patch, you need 
less pressure.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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