In this example, we have a new tire size of 87 inches in circumference, up from the 85 inc
When to Make Gear Changes
The following are indicators that it may be time to make a gear change:
1) When the track changes, which may be true for dirt or asphalt tracks. On dirt, it is obvious when the track changes. For asphalt, temperature changes affect bite and gear choices.
2) When the rear tire sizes change.
3) When we go to a different racetrack.
For dirt tracks, you might need to make two or three changes to your gear ratio, depending on how much the track changes during the event. When the lap times change by 3-4 seconds, the lowest and highest speeds the car will attain will necessarily change. To keep the engine in the proper powerband, gear changes must be made.
Hot summer temperatures make some asphalt tracks slick. A lower gear might produce more wheelspin and slow down lap times. A higher gear would allow more throttle application without tire spin. For the cooler months, a lower gear combined with the added grip the track provides could produce better gains off the corner.
Always calculate your gear needs when changing rear tire sizes. A change in gear ratio equal to our example represents a 150 rpm difference at 6,000 rpm. If you have dialed in just what you need for optimum lap times, maintain the FDR by making the necessary QC gear change.
The dirt Late Model cars are more open in the area around the rearend, making gear changes
When we travel to different racetracks, we need to consider several factors when selecting a gear. Gear needs are influenced by the following: 1) track length, 2) track banking angle (speed through the turns), 3) turn radius and length of straightaways (tighter turns equal less speed and rpm, long straights equal high-end speed and rpm), and 4) surface bite availability, especially for dirt tracks.
For longer tracks, we are less concerned about acceleration off the corners because the exit speeds are much higher than on shorter tracks. We can tune our gear selection to the rpm desired at the end of the straights.
Tracks with high banking angles will allow more turn speeds, just as the longer tracks do. Therefore, our exit rpm will be higher and the added speed will be carried over the entire lap. The method of gearing slightly lower can be applied to short tracks with higher banking as well as low-banked tracks. It will probably be more successful in this situation because traction off the corners will be less of a concern with the higher banking and downforce created.
Gear selection and final drive ratio maintenance is very important and can improve your performance if done correctly. The math is simple, and the process of finding the correct gear that will produce the quickest acceleration is a process that is best done during testing.
We have shown where you can run different gear ratios and still end up with nearly the same beginning and ending rpm. Shooting for just an rpm number may not lead us to the fastest gear. Don't leave out this tuning process that is a critical part of the overall performance package.