Racing karts, we mean. While engineers for high-performance cars like Porsches and BMW M Series vehicles pore over active differential designs using advanced technology, racing karts have no differential to speak of. Yet, they can still corner like a minecart on rails.
How do they accomplish this razor-sharp turning without scrubbing the inside rear tire? Simple: they lift the inside rear tire for a split second.
What Is a Differential?
Just as a quick recap, a rear differential is a critical piece of equipment on rear and all-wheel drive vehicles that prevents jarring transitions into turns.
When a vehicle makes a turn, the outer tire has further to travel than the inner tire, meaning the inner tire must spin at a lower speed to allow the vehicle’s rear end to rotate smoothly. A differential device — or some other form of achieving a power ratio, such as active torque vectoring — can accomplish this goal.
Without a differential, two wheels on an axle will want to spin at the exact same speed. During a turn, the inside wheel will “scrub” by spinning over the surface of the asphalt while making sporadic contact. In a best-case scenario, the vehicle can turn while losing minimal tire tread to scrubbing. In a more realistic scenario, the tire catches throughout the turn, dangerously throwing off traction and making a controlled turn practically impossible.
How They Do It
There’s two major concepts that need to be equally understood in order to fully grasp how these karts actually perform such a feat. Firstly, karts do not have a suspension system, which means that every bump or jolt is directly felt by the frame. Kart frames are built to withstand this pressure by using metal that can flex just enough to prevent cracks or breaks. Again, the main point to understand from this first concept is that the tubing of the metal frame flexes on a kart to make up for the lack of suspension.
The second concept is building off of the one we’ve just gone over: the flexibility of the metal frame. Without a differential, karts need to find some other way to rotate the outside rear tire quicker than the inside tire in order to turn the kart without being forced to simply “drift” it. We only focus on the rear tires because all karts are rear wheel drive. Back to the original point though: in order to make up for the lack of a differential, karts simply lift the inside rear tire of the ground for a split second, which means that the outside rear tire is the sole tire powering the kart, known in the karting world as “jacking”. In doing so, they successful accomplish the same exact thing that a differential does.
Therefore, the “one weird trick” karts are capable of not only makes racing karts more fun and unique, but the karts themselves infinitely complex to work on. Very few car setup techniques or ideas translate to karting, and vice versa. This both adds to the allure of karting and provides a level playing field for those who have varying amounts of outside motorsports experience.
Finding the Right Amount of “Jack” Is a Fine Line
Finding the perfect setup means tinkering endlessly with the kart in order to precisely control how it will behave on the track. Even then, the track is never the same session to session. Too much rubber laid down could cause the kart to have too much grip, and the same could occur with extremely hot track temperatures or vice versa in low rubber and low temperature situations.
For this reason, kart drivers must become intimately familiar with both their competition track as well as how vehicle adjustments translate in real-world conditions. Through a long cycle of trial-and-error in conjunction with lots of experience, they can make smarter decisions and enjoy the hair’s breadth competitiveness that karting can offer.
If you want to learn more about karting, including how to race like a kart pro, you can sign up for public karting at Atlanta Motorsports Park or become a karting member to enjoy discounts and privileged access all year round.
Every minute you put in makes you a better kart racer, so book your next lesson or track time today!