I agree with Steve...
This is a critical factor in dirt circle track cars primarily, and greatly affects the "Moment Center" of the car.
There is an excellent feature article all about this in the February 2010 Circle Track Magazine (yes I said February 2010... I get them early)starting on page 52 called "Race Car Design Basics".
Even though you don't have a circle track chassis, you might grab this issue and read the article anyways before you get started, as it gives a lot of insight about chassis static and dynamic characteristics, and how to manipulate them.
Jim