Early tests revealed that using gear ratios gave the dragster greater speed than simply running the wheels directly off the motor. That led to adding as many gears as possible, but then the torque became too great for the motors to push the car off the line.
Other factors that came into play were a friction sled front end versus wheels. One Mindstorm uses the rechargeable battery pack while the other uses AA batteries, so power supply may have been a factor.
Steering became an issue, as both vehicles tended to veer to the side. Both racers used two motors to drive the axle, so mismatched motors may have delivered more torque to one side.
The programming wasn't overly complex. We used light sensors to identify when a bright light was flashed to start the race. While working through gear ratios, they did attempt to write code that would simulate shifting gears, applying less power at the start and increasing it accordingly.