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Little physics:
A tire has 2 parameters in regards to handling balance. First, is the contact friction force with the road and second is the spring rate.
On a soft substance like rubber the amount of surface area does dictate the amount of friction force. Unlike hard surfaces, like steel on steel, where the amount of surface area touching doesn't matter.
So, by using air pressure settings that maximize the contact patch of the tire you are maximizing the grip of the tire on the road.
You can change the grip levels front rear by changing the tire pressure. So if the car understeers a lot you can increase the rear tire pressure so less of the outside of the tread touches the ground. Therefore, less contact patch, less grip and the rear will loss grip sooner...more oversteer. What pressures to use is completely dependent on the car, the climate and your preference. It's all trail and error.
The other aspect of tire pressure is the spring effect of the sidewall. A tire's sidewall has a spring rate that changes with tire pressure. The mechanism is different than the coil spring, but the tire sidewall has the same effect.
Increase tire pressure and you stiffen the sidewall of the tire. This decreases the overall spring rate of the car. It's the same as leaving the tire pressure the same and adding stiffer coil springs. Decreasing the tire pressure lowers the spring rate to a point. If you drop the pressure too much the sidewall will loss all stiffness and the spring rate of the tire will drop to zero, at this point the alloy is the sidewall. Again increasing rear tire pressure stiffens the rear tire sidewall and increases the rear's overall spring rate. This tends to cause the rear to oversteer sooner.
Basically, if your car is understeering you want to maximize the front tire pressure to get the most contact patch from the tire and then set the rear pressures to get a lower then optimal contact patch. With this the rear has less grip and the car oversteers more.
But it's all about optimization. The actual pressures to use depends on the car and the climate. There is no real formula that works, you have to try different pressures and see what you like.
But for a starting point, lower the front's 4 PSI from spec and increase the rear's 4 PSI above spec. Spec being the pressures on the door jamb plate. Then play with it until you like it.
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