195/50/15... Recommendations for air pressure front and rear?

[amalventano1 at tds.net (Allyn)]

> (Three of the four on Tire Rack are rated @ 44 psi Max, the fourth is 
> rated @ 51 psi Max.)
>
> I'm thinking Higher is Better.
>
> TBerk

i totally agree here. the few times i've autocrossed the rieger (kumho 712), 
i've noticed that lowering tire pressure only seems to give an advantage in 
slow speed tight cornering. i believe this is due to the uneven contact 
patch that results in stock caster, low roll rate, and high steering angle 
(outside front tire - inner part of tread has greater contact than outer).

in all other situations (higher speed cornering), the advantage is had when 
the front tire pressure is closer to the rated sidewall marking. the higher 
pressure causes far less give in the sidewall area, which also helps reduce 
the slip angle of the tire (due to less tread section compliance around the 
contact patch area).

i came to these conclusions when i did the g-tech pro runs on the rieger. i 
spent an afternoon experimenting with different tire pressures / speeds. i 
found that tight/slow cornering was best at ~30 psi, while higher speed 
cornering was best at the sidewall rating (44 psi). also, pressure had a 
greater impact on the slow than the fast (so if you were trying to dial in 
for both situations on the same course, it would probably be better to be on 
the low side). for example, i generally run the rieger at 30-32 at the 
autocross (i bump the rear up to 45-50 to help get some more lift throttle 
oversteer in tight cornering). any other time (daily driving) i run 45 front 
/ 40 rear.

other pros/cons of higher tire pressure:
pro: less risk of wheel damage on rough roads / less rolling resistance -> 
better mileage
con: slightly less ride comfort / greater chance of wheel hop on a worn out 
suspension

note: this info was gathered with treaded street tires that had nearly full 
tread. other tires (lower tread, autox prepped tires, slicks) will have 
different charactersitics and work best with different pressures.

hth
Al