The Dirt Late Model cars are...
The Dirt Late Model cars are more open in the area around the rearend making gear changes easier than with some other designs of circle track cars. It may be well worth the effort to match the gear ratios to track conditions.
The right time to consider making a gear change might include: 1) when the track conditions change. This may be true for dirt or asphalt tracks. On dirt, it's obvious when the track changes, and for asphalt, temperature changes affect bite and gear choices, 2) when the tire sizes change, 3) when we go to a different racetrack that might be longer or shorter and/or have different tire sizes.
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 power band, gear changes must be made.
On asphalt tracks, hot summer temperatures make some tracks slick. A lower gear might produce more wheel spin and slow down lap times. A higher gear would allow more throttle application without tire spin. For the cooler months, a lower gear in combination with the added grip the track provides could produce better gains off the corner whereas the hot summer months might require a higher gear.
Always calculate your gear needs when changing rear tire sizes. A change in gear ratio equal to our example above 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 set change.
This rack of gears for a quick...
This rack of gears for a quick change rearend is neatly placed out of the way inside a race trailer. All of the gearsets that would ever be needed from a short quarter-mile track to a long one-mile track are here. All of the boxes are clearly marked so any crewmember can easily find and retrieve a needed ratio.
When we travel around to different racetracks, we need to consider several factors when selecting a gear. Gear needs are influenced by: 1) track length, 2) track banking angle (speed through the turns), 3) turn radius and length of straight-aways (tighter turns equal less speed and rpm, long straights equal high-end speed and rpm), 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 usually 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 higher turn speeds, similar to what 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 shorter-length tracks with higher banking as well as longer, low-banked tracks. It will probably be more successful in this situation because with the higher banking and downforce created, traction off the corners will be less of a concern.
Gear selection and FDR maintenance are 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 best done during testing and with a stopwatch.
We have shown here that you can run different gear ratios and still end up with nearly the same beginning and ending rpm. So, shooting for just a rpm number may not lead us to the fastest gear. Don't neglect this tuning process that is a critical part of the overall performance package.