ADVANCED TIRE PRESSURE TUNING

Once you have found the optimal pressure for a large contact patch, you can
throw the large patch out the window to alter how your car handles. Under
heavy steering, there are three possible handling characteristics that you can
encounter.
1) Understeer - This is very common for factory cars. Understeer is generally
considered safer for normal driving. If your car is understeering you will notice
that the front tires will lose their grip and you will slide instead of turning
into a corner. Moving the steering wheel even further into the turn will not
effect the direction you are going, you will just continue to slide.
2) Oversteer - This is where the rear tires loose their grip and your back
end will slide out behind you.
3) Neutural handling - This is where all tires loose their grip at the same
time. When this happens, you will end up in a four-wheel drift around the corner.
This is often the characteristic most people try and achieve.
Which characteristic you wants depends on what you are doing, but you can tweak
how your car handles by adjusting your tire pressure.
Modifying front or rear tire pressure allows you to alter when the front or
rear tires loose their grip. If you have the factory understeer (where your
front tires lose grip, but your back do not), and you want to move more towards
neutral handling, you would alter the pressure in your rear tires so they lose
grip sooner. On the other hand, if you had neutral handling and wanted some
oversteer you could change the pressure in your rear tires so they lose grip
sooner. This would be good for autocross so you could whip your back end around
a sharp corner quickly.
Which way to alter your pressure in this case depends on driver preference.
Both increasing and decreasing pressure will cause the tires to loose grip sooner.
By decreasing the pressure, the tires will get soft and mushy and it will roll
over on the sidewall and lift the opposite tread off the ground-decreasing grip.
Increasing the pressure you decrease the footprint creating less grip. This
also results in a stiffer sidewall, which can increase the steering response.
The advantage to decreasing the pressure is it will have a gentle transition
and it won't lose grip as quickly as over-inflated tires.
Doing these adjustments should be made very gradually, and should only be done
in .5 - 1psi increments.
Once you have found your optimal tire pressure for your goals, you can easily
revert back to it whenever you need to focus purely on handling, and can forget
about tire wear and ride quality.