>Barry Fox wrote:
>>
>>
>> Whilst perusing the owner's manual for my 65 TR4A, I came upon
>> the Tyre Pressure Data table. I was quite surprised to see
>> Front 17 psi, Rear 25 psi for Michelin 165-15 radials. This
>> is the tire I more or less have on my TR (actually XZX). Are
>> these values realistic?
And Jerry Kaidor replied:
>**** Yes. Most recommendations I've seen tell you to run the fronts
>lower than the rears. Within reason, lower tire pressure = more rubber
>on the road = more stick. The idea is that when you push it too hard,
>the rear end should break free first.
Just for the sake of a gentlemanly counterpoint, a gross simplification of
the procedure for setting tire pressure in Fred Puhn's book "How to Make Your
Car Handle" is to increase tire pressure on the end you want to stick
relative to the end you care less about. Again, this assumes that the
pressures are reasonable. The significant factor in this balance is tread
distortion, that is, higher pressure allows less tread distortion, which
allows the tire to generate more grip.
I'm all in favor of a car which will oversteer if properly provoked, but I
believe mild understeer at the limit is somewhat safer than oversteer. Car
and tire manufacturers are likely to specify settings which promote safety
(and avoid litigation); in this country, "safe" cars are usually very prone
to understeer.
Confusion might arise over the fact that most cars (either front engine with
rear wheel drive or front engine/FWD) spec higher pressures in front than in
rear... but most cars have plenty of understeer designed into the suspension
geometry, so front tire pressure is spec'd higher to equalize wear patterns
front-to-rear. Tire pressure differential can not overcome suspension
geometry, but it can make a foul handling car a little more manageable, and
is useful as a fine tuning device for well balanced cars (like a TR4A or an
MGA :-).
Ernest Davis <wily1@aol.com> 8/16/94, 09:05
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