Improving Driving Ability & Pleasure - Turning To Terms

Defining What Happens On The Road

Dan Dineson Mar 1, 2005 0 Comment(s)
Corp_0503_01_z Oversteer Diagram 1/1

The following introduces you to the world of high-performance driving. By reading this article, you're taking the first steps to improving your driving ability and pleasure.

Before we get into the hows and whys, it's important to define the terms used to describe the driving experience. To many, they're already familiar, but to others they may be confusing. All relate to cornering and/or traction.

Throttle SteerThrottle steer refers to the amount of throttle applied in a corner. The amount of throttle steer can induce oversteer or understeer with all configurations of engine and final drive layouts. Proper throttle steer is a balance of gas and traction regulated by the driver. The amount of throttle applied dictates the amount of steering to maximize traction. We steer the car with the throttle. Simply put, throttle steer is something you can use when you're entering freeway onramps or as you accelerate through any corner. The weight transfers to the rear tire patches, giving the rear end more traction, taking the weight off of the front tire patches some, and giving less front traction. So we steer the car with the throttle. For example, entering a freeway on-ramp, without stomping the gas, we smoothly accelerate, transferring the weight to the rear, taking it off the front, and steering the car outward onto the freeway. That same thing applies when you're coming out of a corner. Simply add gas, nice and smooth, and the throttle steers the car to the outside of the corner. The same is true on the racetrack or street.

Line/PathLine refers to the physical line of movement a car takes through any corner from entry, to apex area, to exit. A line can be either good or bad, right or wrong. The proper line or path through a corner always keeps the car stable and safe through any corner on the racetrack or street.

Apex AreaThe apex is the area of a corner where the car is in its most stable position, not just a clipping point, where the inside front wheel runs closest to the inside of the corner.

Where the apex area is in a corner directly relates to how the corner is entered and affects how and where it is exited. An apex area varies in length and location from corner to corner. It can be early, middle, late, long, short, or double.

Simply, the apex is where the inside front wheel comes closest to the inside edge of the corner, either early, middle, or late. If you've achieved proper apex when you exit the corner, you should be able to unwind the steering wheel gently by accelerating. If you have to add steering, you've apexed too early. If you didn't use up all the road and end up in the middle of the road, you've apexed too late.

DriftingDrifting is, or should be, a controlled function. It's directly opposed to sliding or skidding, which are out-of-control conditions.

Four-Wheel DriftingDrifting is a balance. The rear of the car can drift with throttle control, as can the front. The optimum condition one wants to create is an evenness that permits the entire car, front and rear, to drift in a balanced lateral motion on the border of maximum traction. This drifting effect utilizes gravity forces (inertia forces) on all aspects of the car, allowing it to travel its fastest at a speed just past the absolute limit of maximum adhesion.

Slip AngleSlip angle is the angle of drift of a car in a given corner. Ideally, the driver turns in properly while trail braking, accelerates through the apex area properly, and exits the corner at maximum velocity in a controlled drift.

Transition TimeTransition time is the time a driver spends in a corner between full brake and full throttle. Ideally, it optimizes the combined techniques of heavy braking, proper turn-in while trail braking, smooth transition from brake to throttle, using the optimum apex area, correct slip angle, and a controlled application of full throttle.

Weight TransferWeight transfer is the forward, back, and lateral movement of the loaded weight of a car under acceleration, braking, and cornering. The car's static weight transfers forward or rearward or side to side (laterally) during the time it is in motion. A stopped car has a determined weight balance, or bias. A moving car, because of suspension and movement, finds that weight balance or bias constantly shifting. For example, the moving weight of the car transfers forward under braking. Under acceleration, the weight transfers laterally. Simply put, the sprung weight of the car transfers to different areas of the car during movement. This in turn controls the tire contact patch (traction of the car) as it transitions through a corner.

To understand exactly what happens during driving, you have to know what happens at the point of contact-in this case, tire patch. Obviously, at rest all of the tire patches are the same. Upon acceleration, the tire patch up from level is diminished as weight is transferred to the back. In cornering, the tire patch changes dramatically again depending on weight transfer. Finally, on deceleration the tire patch is much larger in front than in back, justifying the need for larger-diameter rotors up front than in the rear.

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