more understeer with aftermarket tires?

BrianMSmith

Yes, tires do have a big effect on a car. Different sizing front to rear on our cars is a big contributor. The tire contributes a huge amount to the overall damping of the suspension, which effects tire loading and therefore traction. Try lowering your front tire pressure, which will increase loading on the front tire, and typically helps understeer. You could also try an alignment adjustment, add some -camber to the front.