Well here a chassis for a chevelle

[XcYZ]

If the car is tight, regardless of tire sizes, basic chassis changes like a lower front spring rate, higher rear spring rate, less sway bar and raising the panhard bar would help, if not correct the problem. These are basic principles of race car chassis setups (not counting tire pressures, shock settings, etc), but they should also be the basics when setting up a street car.

I know this post doesn't add much to what the original thread was about, but the topic of tire sizes and understeer comes up from time to time and I wanted to add my two cents.