Basic Diff Ratio

Diff Ratios for NOS SPRINT

Small tight Track
Ratio 7.05

Simpson/Avalon/ Ballarat
Medium Race Tracks
Ratio 6.86

Banked and open
Ratio 6.70

For a new driver it is suggested to go up about 0.2 to start with and once he hits the limiter change down

Remember a diff ratio is calculated by the number of turns the input shaft of the differential does compared to the output shaft or in this case the axle.

If the ratio of the Crown Wheel and pinion are 4 to 1 then you multiply this by the ratio of the quick change gear set to get the final drive ratio.

The tricky part to remember is that the higher the number the lower the ratio is, ie 3 to 1 is a high ratio used at Bathurst, 7.2 to 1 is a low ratio used at a tight Speedway track.

Another helpful hint for the new racer is which gear goes to the bottom in the back of the quick change, the big gear always goes to the top, just think of “Dolly Parton”