Joe Curry wrote:
>
> It's really not rocket science. If you raise the pressure to the extent
> that the tires round the tread, you lose traction because the amount of
> rubber on the ground is decreases.
Sometimes, on the front tires, a _little_ rounding of the tread is not a
bad thing. One old racer's trick I know of (for bias ply tires) was to
run tires meant for wider rims (on the legal limit of narrow rims). The
natural curvature (sp?) was a little like having some negative camber,
for the outside edge of the tire. This was in the days before high
performance (DOT-approved "racing" tires) being molded with asymetrical
tread and directional mounting. These days, BFG R1s (and I assume some
others) are molded to provide the equivalent of some negative camber.
> On the other hand, if you decrease the pressure so much that you cause
> the sidewalls to flex, you increase the lateral movement of the car and
> that is not helpful for handling. You also risk rolling the tread and
> lose traction that way.
I strongly agree, run enough pressure to keep the tread from rolling
over.
> So the trick is to find that happy point where the pressure is right in
> between those tow points.
>
> Joe Curry
>
> P.S. You never (as was pointed out) want to exceed the manufacturer's
> recommended inflation pressure. They obviously know more about their
> tires than we do.
On your P.S., I must disagree. It is considered safe to exceed the
manufacturer's maximum air pressure, when not on the street. I have
often found it necessary to run 35lb. (or even 45lb.) for autocross, to
keep the tread from rolling over, especially on the front. At the TRF
Summer Party last weekend, I believe they required 35lb. minimum air
pressure (unless you _really_ knew what you were doing) for safety
reasons.
For autocross, you might adjust your air pressure so that your tread
does not roll over in the front, then adjust your air pressure in the
rear to approach neutral handling.
> DANMAS@aol.com wrote:
> >
> > In a message dated 98-08-15 14:52:02 EDT, gernot.vonhoegen@stir.ac.uk
>writes:
> >
> > > while I agree with the thread on pressures, I disagree with the
> > > improvement in handling due to higher tyre pressure. Typically the
> > > improvement is a lower pressure. Higher pressure will give you a better
> > > fuel economy when you drive on motorways where you don't expect much
> > > cornering etc. If you want better handling, you will find that dropping
> > > the pressure by about 5 psi below the recommendet setting will improve
> > > matters. However, that depends on the individual tyre make due to
> > > different grip and wear qualities.
> >
> > Gernot,
> >
> > I'm no expert (not even close), but according to Fred Puhn, author of the
>book
> > "How to Make Your Car Handle," higher pressure will improve handling. I
>quote
> > from the caption to figure 4, page 19:
> >
> > "Notice that you lose more by a small amount of underinflation than a small
> > amount of overinflation. When in doubt, increase the pressure before you try
> > decreasing it."
> >
> > Figure 4 is a diagram plotting grip vs pressure. Grip drops off much more
> > sharply on the low pressure side of the curve than on the high pressure
>side,
> > using optimum pressure as a reference.
> >
> > In the few years I hung out with the SCCA showroom stock racers (as a
> > photographer for a local TV station), I was amazed at the high pressures
>they
> > used - often in excess of 45 psi, all on street tires.
> >
> > Dan Masters,
> > Alcoa, TN
Yes, I agree with Dan.
Keith Edwards
Suffolk, VA
2 TR3Bs
2 TR4As
1 Healey
1 Princess
1 Winnebago
4 Hondas
about 4 "fractional" cars
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