Date:         Tue, 13 Aug 2002 01:28:58 EDT
Reply-To:     KimBrennan@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Kim Brennan <KimBrennan@AOL.COM>
Subject:      Tire pressure
Content-Type: text/plain; charset="US-ASCII"

As I was putting my SA 15" wheels and 215/75 tires on the GoldBrick this
previous weekend, I got to thinking about tire pressures. Since I recall some
questions on this in the past, I figured I'd post my own meanderings....

First off, I've only got Syncros. Non-syncro pressures might be slightly
different (though I don't believe that is the case.)

With 185/80R14 tires, the recommended pressures are 40 psi in the front and
48 psi in the rear. With 205/70R14 the recommended pressures are 36 psi in
front and 40 psi in the rear. Now for some simple math and analysis.

Based on the weight of the vehicle we can figure out the AREA that each tire
covers on the road when loaded...because we know the pressure the tire
exerts. However, if we simply glance at the above numbers a simpler pattern
emerges. 36 psi is about 10% less than 40 psi (the front tires). the 185
(remembering that this number is the WIDTH of the tires) is about 10% less
than 205. Or to reverse this...the 205 is about 10% wider than the 185
tires...which is a nice correlation to the pressure.

Onto the rears...and the math isn't quite as close, but is still similar. 40
psi is about 18% less than 48, but the width is still only about 10% wider.

Going for Kentucky windage and I guesstimate that another 5% wider tire will
allow for about a 5% decrease in tire pressure...

So on my 215s I went for 35 psi in front, and 37 psi in the rear. The ride
feels just about right (perhaps a trifle stiffer, but reasonable).