Race car physics: Sebring style

March 18, 2015

Race car physics: Sebring style

March 18, 2015

physicsGetting a race car well balanced and connected to the track for the entire 12 hours here at Sebring International Raceway requires a lot of good driver-team communication.

Fans can listen to team radios and follow the team as well as the Series telecasts, radio and team social media feeds to stay fully engaged. But if you listen in, you want to know what terms like “mid-corner understeer,” or “on-throttle oversteer,” and “high speed lift,” mean.

Generally, these driver descriptions have their basis in the laws of physics and performance characteristics that govern race cars.

Center of Gravity
One of the more critical areas in design and set-up. Generally, the lower the center of gravity is to the track, the better. All the accelerating, braking and cornering forces work through the center of gravity and that, along with today’s underbody designs, means more downforce and better stability, unless, of course, they go too low.
Race engineers like to run cars as low to the track as possible. That is why you may see sparks when the car touches the ground. There are sacrificial planks made of a wood material called jabroc (and sometimes titanium) to prevent damage to the car. A low center of gravity means less weight transfer, less roll, and less squat and dive – but watch out for the bumps.

ferrari_rigon1Aerodynamic Balance
Also called center of pressure – it defines when the downforce or aerodynamic pressure on the front wheels and the downforce on the rear wheels is equal. Too much pressure on the front causes oversteer (the back end of the car wants to slide out) and too much on the rear results in understeer (the car doesn’t want to turn). Downforce is a function of the car’s overall shape, underbody and wing design. The center of pressure is usually close to where the center of gravity is.

Aerodynamic Grip
The result of the downforce from the car’s bodywork, wings and the underside of the car. The faster you go, the more aero grip there is. In fact, a modern prototype race car will produce so much downforce that it could run upside down “on the ceiling” at speeds above 120 mph. Aero grip complements mechanical grip. If you miss the aero grip set up, the car will be nervous at speed and if you miss mechanical grip, it will be slow in low speed corners.

tiresMechanical Grip
This is the grip between the tires and the track produced by the suspension and tires. A good race car will maximize both aero grip and mechanical grip. Drivers like lots of grip and they have to manage the car if the tires start to overheat or lose grip. A lack of mechanical grip contributes to both understeer and oversteer and makes the car slow and difficult to handle.

Weight Transfer
How smoothly the weight is transferred and where it goes is critical. Under acceleration, weight is transferred to the rear tires, while under braking, the front tires get the weight, and during cornering, the load is put on the right or left tires. Weight transfer is used to maximize mechanical grip. Smooth is good. Drivers who are more abrupt in their throttle and steering inputs aggravate weight transfer.

rolex_podium_gal 15The Winning Formula
To win the race here, drivers and engineers want a well-balanced, drivable car with good aerodynamic and mechanical grip, consistent handling, the ability to handle the bumps, braking and turn in stability, adaptable to the changing track conditions and something that photographs well in victory circle.

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