Bill,
Your chart is a great help but I find the tire pressure part not compatible
with my experience.
When I increase the front tire pressure, my car (TR-4) will start to push
through the turns. Hence, my sense is that a softer tire has more traction
(but carries more drag in the straight-aways). Conversely, I figure that a
harder tire has less adhesion in the turns but less drag down the straights.
If higher tire pressure equates to higher adhesion in the turns and less
road friction in the straights, why are we all not running 45 psi?
My MO has always been to keep the tires as hard as I can until they slide
too much in the turns, then lower the pressure (forward or rear) until they
stick. I must admit that I have worked out my tire pressure program without
much outside support. If I'm wrong, it's not because anybody told me wrong.
It's simply because I figured it out wrong....and that won't be a first
either.
In fact, from your experience, what is the right way to set tire pressure?
I appreciate you help on this issue.
Richard Taylor
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Bill Babcock
Sent: Friday, March 18, 2005 12:29 AM
To: 'rob'; yellowandgreen@comcast.net; fot@autox.team.net
Subject: RE: sway bar
I assume you mean this:
INCREASE UNDERSTEER OVERSTEER
FRONT SPRINGS STIFFER SOFTER
REAR SPRINGS SOFTER STIFFER
FRONT SWAY BAR STIFFER SOFTER
REAR SWAY BAR SOFTER STIFFER
FRONT TIRE PSI LOWER HIGHER
REAR TIRE PSI HIGHER LOWER
FRONT CAMBER POSITIVE NEGATIVE
REAR CAMBER NEGATIVE POSITIVE
LBS. DISTRIBUTION FORWARD REARWARD
This is a standard chart I've seen a lot of places. It's generally correct
but it's a bit of an oversimplification. This is a small increase in detail
over Dave Talbot's rule of "soften the end that's sliding". For example,
Understeer means sliding the front end, so to decrease it you soften the
front springs or sway bar (increase oversteer), and/or stiffen the rear
springs or sway bar.
Camber and tire pressure are oversimplifications. For example, if your front
camber is already sufficiently negative, making it more negative will not
increase the contact patch size under cornering and so it will not reduce
understeer. Likewise, if you already have enough tire pressure, increasing
it will not make the tire flatter and will not reduce understeer--in fact
the tire will crown and overheat in the center. So there are upper limits.
Still, it's a handy chart.
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