Date:         Sun, 31 Oct 2004 21:08:10 -0500
Reply-To:     Dennis <guskersthecat@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis <guskersthecat@YAHOO.COM>
Subject:      Re: Largest diameter wheel.
Comments: To: John Rodgers <inua@CHARTER.NET>

John I would agree in some situations with your comments on tire width.  In
some cases, wider is not better.  However, there are several more issues to
consider.

1.  I posted this earlier on the increase in torque required to accelerate
a larger wheel/tire combination.

http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind0409D&L=vanagon&P=R6602

No secret there, I just tried to quantify the difference.

2.  Traction is derived from the combination of rubber/asphalt friction
coefficient + the tire's footprint + the weight on the tire.  On dry
pavement, increasing any of the variables, increases traction.  This means
that a wider tire on dry pavement will increase traction, improve cornering
grip, and reduce braking distances.  Providing the wider tire can channel
rain adequately, it will also work better in wet conditions.  Having
autocrossed for ten years or so in dry and wet conditions...I'm very
comfortable with the above statement.  Additionally, there are volumes of
evidence out there to support what I am suggesting.

3.  Now add in rim width, tire compound, surface type, load index,
temperature, snow, tire pressures etc. and you end up altering the
relationships inherent in the traction equation.  In snow and ice, point 2
is thrown out the window.

So I think the real question is how and where do you use your van?  What
are the compromises you are willing to accept?  A 200PSI bike tire on a
vanagon would give outstanding mileage, but be otherwise lethal.  225/60
16's (with adequate water dispersion) would be a huge improvement in
traction for folks in dry or wet weather, but would decrease the van's
acceleration noticeably due to the change in rotational mass, and decrease
fuel mileage.  Take the same tire in snow, and now you're very unhappy
again.

My van is stored winters, but my daily driver car sees 205/50/ 15's in
summer and skinny 175/70 13's in winter.  My next set of winter tires for
this car will be 155/80R 13's ... even narrower.  Both rim tire
combinations have similar rolling diameters, but vastly different
performance in the conditions at hand.