Obviously, handling is extremely important in any racing car. In an autocross car, it is critical. A poorly handling car with lots of power will not do well at all on the typical autocross course. A Miata or CRX can usually beat a 60's muscle car like a Pontiac GTO even though the Goat may have four or five times the power. Those cars, while magnificently powerful, were designed for straight-line acceleration at the expense of cornering.

This month, we examine one aspect of handling, that of handling transient or short-lived forces. Usually, in motor sports contexts, the word "transient" means short-lived cornering forces as opposed to braking and accelerating forces. In broader contexts, it means any short-lived forces.

Transients figure prominently in autocross. Perhaps the epitome of a transient-producing autocross feature is slalom, which requires a car and driver to flick quickly from left to right and back again. Many courses also feature esses, lane changes, chicanes (dual lane changes), alternating gates, and other variations on the theme. All of these require quick cornering response to transients. Some sports cars, like Elans, MR2's and X1/9's, are designed specifically to have such quick response. The general rule is that these kinds of cars get you into a corner more quickly than do other kinds. They achieve their response with low weight and low polar moment of inertia (PMI). A chief goal of this article is to explain PMI.