This chapter is like the last chapter except it discusses tire traction on dirt rather than asphalt. On a true "dirt" track everything works backwards from what is explained in the last chapter. A True Dirt Track is a "Soft" Dirt Track. Ninety five percent of the time the tires do operate as explained in the last chapter. But if the track surface is a true dirt racing surface, the tire coefficients change differently, and a tire can "dig in" or "grab" if it is heavily loaded.

Tire Loads and Cornering Power on Dirt

The dirt condition can be so radically different that a new graph is required. We'll call it the Ct vs. Tire Load on Dirt graph. Notice that the curves are totally different from the Ct vs. Tire Load on Asphalt, Graph 2. This would be on a soft Dirt track, where the tire literally digs in and grips.

• Graph 4: Ct vs. Tire Load on Dirt

A core concept behind all race car handling, changing the values of the tire loads in Equation 5 (because of cornering loads) will always make the Cornering Power be less, does not work with Ct vs. Tire Load on Dirt *-Graph 4. The graph is not a straight line and is curved up.

This guide is written mainly for asphalt conditions. Dirt can be challenging because track conditions can and do change quickly, but much of the time dirt tracks are within the scope of asphalt (a hard racing surface) tracks.

Dirt Track Driving

On a dirt oval the driving line can radically change because of the racing surface variations. Here is a list of variations.

There could be loose dirt next to the inside fence.

There could be a small reverse bank of the track next to the inside fence. This will change the tire loads of your car, more than likely making it spin out.

There may be a cushion (a brim of loose dirt around the outside of the groove) where huge amounts of traction can be found.

There could be dry, slick spot where there is no traction.

The bank may not be consistent, and you have found the steepest and fastest groove in it.