[smoyer]

A couple more hints (I have an entire PDF document on speeding up PWD cars).

1) You don't need 4 wheels (except to stay on the track). Lift one of them up slightly so the car is only resting on three wheels. Don't lift the forth wheel up high enough that it's not able to help guide the car along the guide rail.

2) Make sure the car rolls straight. There's a lot of friction against the guide rail if your car is constantly trying to turn into it.

3) Make sure the inside of your wheels are sanded smooth. You want any friction due to contact with the guide rail to be minimized.

4) Put as much weight as possible at the back of your car. Since that weight is higher up the launch hill, it will end up pushing the are longer. Think of it this way: Gravity will stop pulling a front-weighted car when it reaches the roll-out. With a rear weighted car, the back will continue to be pushed when the front wheels are on the roll-out. You get an extra car length worth of gravity.

Many PWD events mandate the use of the stock wheels and axles. The fastest car I ever saw used layers of teflon tubing inside the wheel hub and hypodermic needles for the axles - very smooth bearing surfaces. Beyond the tips above, the most important tip is to eliminate friction in the wheel-to-axle bearing.

Good luck!

[emerongi]

I think it's good to have the car not roll perfectly straight, but a little bit to one side. If it rolls too straight, it's going to bump from one side to the other and lose much more energy.

[ezl]

The energy you lose from lateral collisions has very small impact on the forward movement

rolling as straight as possible might bump from side to side, but between the left and right side the wheels will be rotating with as little friction as possible.

deliberately going to one side guarantees that the wheels will never reach max speed.

[smoyer]

Have you done A/B testing on that? I'm genuinely curious about which would win.

[krisneuharth]

Link?

[smoyer]

I paid for the PDF as a guide about 15 years ago and couldn't find a link to the same document. If I remember correctly, these were just four of the twenty-some tips. (We ended up with a second and third place car out of fields of about 80).