. . . whatever you call it, a derby race is a lot of fun, and it's a great opportunity for learning and for making memories.

This document describes ways to make a derby car faster.

I must begin this document with a disclaimer: My experience building fast derby cars is limited. I typically invest most (if not all) of my effort in the appearance of my derby cars. However, I believe that my background in physics and engineering has enabled me to evaluate accurately the information I have accumulated from those who do have experience building fast derby cars.
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No amount of work can guarantee a winning car; I have seen many carefully optimized cars that didn't do well on race day. On the other hand, I have seen derbies won by cars that were built haphazardly, so it seems that a minimal effort does not assure a losing car either.

With that said, here are some ways you may be able to improve the speed of your derby car.

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This is the most important advice I can offer. If you break one of your derby's rules and your car is disqualified, it doesn't matter how fast it is. Some of the suggestions that follow are illegal in many derbies, including derbies that I have helped organize. Ignore any speed tips that violate the rules for your derby.

Make Sure Your Car Fits the Track Building masking

Two common sources of trouble are (1) wheels that are too close together, and (2) too little clearance under the car for the center guide rail. If its wheels pinch the center guide rail, or if its bottom drags on the center guide rail, then your car may not even reach the finish line. The original kit dimensions should fit the track; don't reduce them!

Unusual designs can encounter other track-fit problems. As a rule, if the basic shape of your design is unusual, check with whoever sponsors the race to see if it will work with the track's starting gate, finish gate, guide rail, etc.

Friction is Your Enemy Building masking

Yes, aerodynamics can make a difference. Yes, getting your car as close as possible to the weight limit can make a difference. Yes, other things can make a difference too. But friction is the most significant force slowing your car down, so reducing friction is the most important thing you can do if you want a faster car. Friction occurs between the wheels and axles, between the wheels and car body, and between the wheels and center guide rail. This is where you need to reduce friction.

Experiment Together

Don't forget that the derby is supposed to be a father-son (or adult-child) activity. Set up a long board on a slight incline and experiment together until the car rolls straight down the board as quickly and as smoothly as possible.

You can also test axle alignment this way. With perfect axle alignment, you can start the car with its wheels pushed in (against the car body) or with its wheels pushed out (against the axle heads) and they'll stay that way as the car rolls down the incline.

Keep Wheels & Axles Straight Building masking

Crooked axles will cause your car to ride the center guide rail, or will cause the wheels to slide in addition to rolling. In either case, the extra friction will slow your car down. Keeping your wheels and axles straight is probably the most important step in building a faster car.

The time to think about keeping your axles straight is before you start shaping your car. It is much easier to create straight holes for your axles when the sides of the block of wood are still square, than after you have shaped your car. Later, when you've finished shaping and painting your car, the axles will fit easily into these holes, and your wheels and axles will be straight.

One obvious technique for creating straight axle holes is to pre-drill them with a drill press. If you use a bit that is slightly smaller than the axle nails in your kit, then you may not need glue to hold your axles in place and you won't have to worry about the axles wobbling in oversized holes. Building masking

In our derby workshops, we use a variation of this technique. Instead of a drill bit, we use an axle nail with the head sawn off. Without turning on the drill press, lower the axle nail straight into the block of wood. If you don't have access to a drill press, you can clamp an axle nail in a pair of pressure pliars (e.g., Vice-Grips), and carefully insert the axle nail straight into the pre-cut axle slots.