Car Control: The Basics

Smoothly controlling the shifting weight of your car as you accelerate, brake, and corner is the key to success on the racetrack.As the driver, your goal is to effectively manage your car's shifting weight to take full advantage of all available traction.

When standing at a dead stop, your car's weight is evenly distributed, with a predictable and stationary center of gravity. The moment you accelerate, however, everything changes rapidly. Under acceleration, the weight of your car shifts to the rear tires. When you brake or get off the gas, the weight of your car shifts to the front tires. When you execute a corner, the weight shifts to the outside tires. As the weight of your car shifts from front to rear or side to side, so does its center of gravity.

When you race, be keenly aware of your car's shifting weight and how it affects the amount of available traction in your tires. When weight transfers from one pair of tires to another, the tires that take on the weight also gain traction, and the tires that lose the weight also lose traction.

Tire Contact Patches

CLICK FOR VIDEO (10212 KB)

The effects of weight transfer on your car's capacity for traction can be seen clearly in each tire's contact patch. A contact patch is the portion of the tire that is in direct contact with the road surface. The more downward force you apply to a tire, the bigger the contact patch. The bigger the contact patch, the more available traction for that tire. This force on the tire's contact patch is also referred to as "vertical load."

When cornering, the contact patches of your four tires are where all the action is. In addition to the vertical load, cornering also involves the lateral force generated by turning. The result of these two forces acting on the contact patch is called "slip angle."

Slip Angles and Cornering Force

CLICK FOR VIDEO (10337 KB)

The slip angle of a tire is defined as the angular difference between the direction in which the wheel rim points and the actual path that the rolling tire takes over the surface of the road. Slip angle is a component of the elasticity, pliability, and "stickiness" of the tire at the contact patch. When a tire turns, the portion of the tire that is in contact with the road surface resists the turning motion, twisting and distorting the tread, and causing it to not turn as far as the wheel rim.

Up to the absolute limit of traction, cornering force increases as the slip angle increases. Once it's reached the limit of traction, however, the rubber at the contact patch begins to lose its elasticity and actually starts to loosen its grip, and slides. It's important to keep in mind, however, that even at the limit of traction, the tire still retains some cornering force. Often, if you can reduce the slip angle, you can regain control of the car.

As a race car driver, your challenge is to find the most desirable slip angle, the one that will give you maximum cornering force through a turn without losing traction and without using up your tires. Finding the limit of tire adhesion requires testing and practice. You should take to the track for testing sessions to explore the outer edges of your car's handling capabilities.

Smoothness and Balance

Mastering the art of smoothly balancing weight transfer while maximizing traction is a major goal of any serious race car driver.

Asking your car to do more than one thing at a time-turn and brake, for example-greatly affects the balance of your vehicle. The most skilled race drivers in the world spend years mastering this delicate balancing act to achieve three things-get around the track as quickly as possible, squeeze the most out of the car, and do so without asking the car for "too much."

Your goal is to achieve a perfect balance of the car at its limits. Understanding the relationship between weight transfer and traction is an essential part of achieving that balance.