Date:         Thu, 28 Feb 2002 19:10:00 -0500
Reply-To:     80 Westy Pokey <pokey@VANAGON.ORG>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         80 Westy Pokey <pokey@VANAGON.ORG>
Subject:      Re: 15" Wheels/Tire Pressures
Comments: To: George.Becker@SCE.COM
Content-Type: text/plain; charset=us-ascii

Do you mean 215/65/15's? What kind or tires are they?

Thanks,
Chris

---- Original message ----
>Date: Thu, 28 Feb 2002 07:35:58 -0800
>From: George Becker <George.Becker@SCE.COM>
>Subject: 15" Wheels/Tire Pressures
>To: vanagon@GERRY.VANAGON.COM
>
>What tire pressures are correct for 15" wheels?
>I've been running 215/60/15's on my '87 Westy for a number
of years, but
>I've never been positive about the correct tire pressures.
I've recently
>lowered the pressures to be F29 R34 based on an assumed
F45/R55 weight
>distribution and some trust in the archive post below.
According to the
>formula, I could even lower the pressure some, but I'm
skeptical.
>
>>>> Posting number 72406, dated 22 Oct 1998 12:02:31
>Date:         Thu, 22 Oct 1998 12:02:31 -0700
>Reply-To:     YauMan Chan <YauMan@CCHEM.BERKELEY.EDU>
>Sender:       Vanagon Mailing List <vanagon@vanagon.com>
>From:         YauMan Chan <YauMan@CCHEM.BERKELEY.EDU>
>Subject:      Re: tire pressure - How to calculate
>Comments: To: vanagon@VANAGON.COM, vanagon@VOLKSWAGEN.ORG
>Mime-Version: 1.0
>Content-Type: text/plain; charset=US-ASCII
>Content-Transfer-Encoding: quoted-printable
>
>The correct tire pressure has nothing to do with the
diameter of the =
>wheel.. It can be determined by the Width of the tire and
the weight of =
>the van (+load).  Here is a sample calculation:
>
>The typical 2WD Vanagon (non-camper) is about 4400 lb wet!
The weight =
>distribution of most rear engine vehicle is 45/55 (45%
weight carried by =
>front wheels, 55% by rear)  I guess it's probably 50/50 for
synchros.
>
>Assume you carry a load of 1000 lb (7 passengers at ~ 150 lb
each - =
>1050lb)  So the total weight carried by the tires is 5400 lb
with 2430 lb =
>in front and 2970 lb rear (45%/55%)  So EACH front wheel
carries 1215 lb =
>(2430/2) and  EACH rear wheel 1485 lb (2970/2) (see why
reinforced side =
>wall tires are recommended!!)
>
>Now for the stock 207/xx-14 tires, the WIDTH of the tire is
205 mm which =
>is about 8 inches (205/25.4)  The typical tire make
a "footprint" of about
>=
>5 inches long This means that the area of surface contact is
about 40 sq =
>inch (8x5)  so the tire pressure for the front wheels is
1215/40 =3D 30 =
>psi  and for the read is 1485/40 =3D 37 psi (hey pretty
close to vanagon's
>=
>manual of 32psi front and 36 psi rear - they must be using a
different =
>weight distribution ratio!) =20
>
>So for your tires which are 225mm (8.9in) wide, your contact
surface is =
>close to 45 sq inch.  So the front is 1215/45=3D27psi and
rear is =
>1485/45=3D33psi.
>
>From this calculation you realised that the pressure formula
is self =
>correcting.  If you put less pressure in the tire, it will
flatten out and
>=
>increase the contact surface area...until the area is big
enough to hold =
>up the van.  Thus, the more pressure the lest contact
surface (more =
>slipping but better gas mileage) and the less pressure the
more road =
>contact!)  That's why big Catapillaf earth moving truck with
24" wide tire
>=
>requires only 6psi and skinny bicycle tires requires 100-
90psi.
>
>Yau-Man Chan
>87 GL
>
>George Becker
>e-mail: George.Becker@sce.com