Monday, May 18, 2015

So simple, yet so complex

In many ways, the structure of the go kart is simpler than that of a race car, but that constructive simplicity can make the tuning and optimization even more complex. While it may be possible to use advanced structural and aerodynamic analysis to improve your kart's performance, most karters will agree that is not necessary. 
Following general guidelines for assembly, seat mounting, and weight balancing should get you pretty far. The little tweaks that come after that will improve your performance. Some understanding of the forces on the kart will help the mechanic and driver predict what happens when a parameter changes.
When it comes to driving, the most impactful differences between a kart and a car are that the kart lacks a differential and it lacks any suspension components.

Inside wheel lift
The most important part to remember is that the kart must lift the inside wheel while cornering. Inside wheel lift is what allows the kart to corner in a controlled way
Because there is no differential on a kart, the two rear wheels are attached by a solid axle and must spin at the same speed. When you go around a corner, the inside wheel is traveling a shorter distance than the outside wheel. If it is correctly lifted, it can rotate without skidding against the track.

If the inner rear wheel is not lifted you may experience an initial understeer because the tire is dragging, and then as you correct for it, the wheel lifts and you go into a skid. This occurs because when the inner wheel lifted, you did not have enough traction on the outer wheel to overcome the centripetal (side) forces at the speed that you were going.

Monday, May 11, 2015

Back to the tires - karting dynamics

The first part of kart dynamics is your set of tires.

A kart does not have a suspension like a car, so what remains are the frame and the tires that make the kart grip the track. That makes the traction from the tires one of the greatest contributors to your ability to win the race. Traction is a combination of how grippy the track surface is with how grippy the kart tires are. Grip from the tires is a combination of the rubber used in the tires themselves and any treatment used on the tires, including chemicals or heating. This combination of surface frictions can vary throughout the day and the race with changes in temperature and humidity.

When a kart is going straight down the track with the wheels positioned straight ahead, the kart follows the wheels. As you turn the steering wheel, the kart will change direction, but not instantly to the same direction where the wheels are pointing. The kart follows an arc that is slightly larger than the place the front tires are pointing as it tries to adjust to the new direction. This creates a slight difference between the angle of the wheels and the angle of travel. According to Bob Bondurant of Bondurant SuperKart School, when angle is between 6 and 10 degrees, the tires are generating the maximum amount of grip. Managing the speed of your kart to maximize grip is the job of a good kart driver.