Tor,
I seem to recall that your wheels are 6" wide at the front and 7" in
the rear and that you are using street performance radials.
20 psi only sounds close for race tires but any street tires generally
require more than that. Or, if you are indeed using race tires and 20
is in the correct range, I wouldn't vary more than about 5 psi between
ends of the car (With maybe 22 as a top limit and about 17 as a bottom
limit). For street tires, about 40-25 range.
As for dialing in the handling with differential tire pressures,
ideally, the pressure should be near optimum for a given single
wheel/tire combination (which should, in turn, be chosen bearing in
mind the weight they'll be carrying) and adjustments made with springs
and anti-sway bars.
However, that said, most of us do use tire pressure to do a lot of
low-tech chassis tuning anyway, yours truly included. In fact, the
most extreme example I can remember is years ago, when I was very
restricted by the slalom rules as to what mods were acceptable on the
girlfriend's Spitfire and was forced to use 38 frt./17 rear in order
to combat the stock frt. positive camber and rear negative camber (i.
e., to get the car to turn), using wide tires. Won the championship
so it must have worked.
I would advise adjusting the front pressure so the car turns in the
way you want it, and then putting the rear pressure where it will have
the front-rear response that you feel comfortable with.
I like trailing throttle oversteer which can be converted to stability
with driver inputs. But not everyone likes that sort of handling.
Many prefer the "on rails" feel. For that, you go more towards the
same pressure all around. Since you have wider wheels on the back,
you may have to compensate for all the bite (which could overwhelm the
narrower front wheels/tires) by dropping the rear pressure.
I would guess that you'll end up with:
For race tires: Frt. 20, Rr. 18
For street tires: Frt. 36, Rr. 26 to 32 (see handling preferences
above).
Hope this helps.
Rod
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