Article: Installing a shorter lever arm is the best way to adapt a racer for speed. However, if the lever is too short, it will spin out. There is no precise formula for how long the lever should be. Experiment to see how short you can get the lever while maintaining control of the car. Longer lever arms will extend the time in which the axle is pulled, making it travel longer distances before the car reaches maximum speed. As a result, it will go slower, but move further. When you increase the size of the wheel, the amount of torque necessary to begin a rotation increases as well. A smaller wheel is easier to turn. So you should make sure that your driving (front) wheel is as small as possible. A good standard is approximately 3 inches (7.6 cm) in diameter.  Use materials that are as lightweight as possible. A larger wheel means more rotational inertia, which keeps the wheel moving once it gets going, but reduces acceleration. A smaller wheel is a trade-off between distance and speed. The overall distance traveled will decrease as you reduce the size of the driving wheel. Experiment to determine what the most functional design is. The greater the ratio of the diameter of the axle to the wheel, the less force will be required to accelerate the car. In other words, you should match a larger axle with a smaller wheel to increase acceleration.  Conversely, a mousetrap racer built for distance should have a smaller axle and a larger driving wheel.  One way to adapt the size of the axle is to wrap tape around the center of the axle, where it does not come into contact with the frame. This added weight will increase the torque of the axle.  Experiment to find the correct amount of torque by adding and removing layers of tape. For the wheel to pick up speed it needs to create pressure against the ground. For the wheel, use a material with a rough texture around the outside to give the wheel traction. Alternatively, cut something that has a rough surface such as a rubber balloon. Glue strips of this material to the outside of the wheel to give it traction. There are so many variables involved in the physics of a mousetrap racer that even similarly built cars operate differently. The only way to perfect your model is to experiment with small variations in design to determine what works best. Study mousetrap racers that have won competitions in the past. Learn from designs that you know work.

What is a summary?
Shorten the lever arm. Find smaller wheels. Increase the size of the axle. Increase traction. Keep on trying.