You want to run the brake bias as far to the rear as you can. Go too far and you will get bad results in a hurry. What I do to run more rear bias once I have a decent setup under me is mess with power/coast/preload, and engine braking power. For engine braking the settings are 0-4. 0 gives you the most engine braking power, which will loosen you under braking/turn in. 4 gives you the least engine braking power. I usually run mine between 3-4.

Power, coast and preload. Power comes into play when on throttle, so I won't discuss it here. Coast comes into play while off throttle. Higher coast values make the car tighter/under steer, lower coast values makes the car looser/over steer.

Preload setting controls the response time of the power and coast settings. The higher the number the faster the response, the lower the number the slower the response. I have found that higher numbers tend to help tighten the car up.

My current power/coast/preload setting for Imola on the Corvette are 45/35/9. My brake bias is at 53/47. I have buttons mapped to change this during the race. Sometimes I find that the rear end gets a little too squirrelly when the car gets light on fuel. When this happens I bump the bias up more to the front.