Have you read through the Suspension/handling Articles sticky?
From http://www.wtrscca.org/tech.htm
"For Steady state understeer, All turns or low-speed turns only;
If front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).
If front tire pressures are optimum, decrease rear tire pressure. Increase if chunking occurs.
Improper front camber.
Too much body roll at front, causing excessive camber change.
For Steady state understeer, High-speed turns only
If front tire temps are OK, increase front downforce.
If front tire temps are too hot, reduce rear downforce."
etc.