The Science of Straight

Launch Control
During launch, maximum power is applied to accelerate the vehicle in the most efficient manner. Thismeans you must be able to use all the power to accelerate forward, whilenot giving up traction and while maximizing all the variables, of whichthere are many, including track conditions, weather, horsepower andtorque output, launch rpm/converter stall speed, trans-mission and rearaxle gearing, suspen- sion type and adjustment, and tire size and type.And let's not forget about the weight of the vehicle, availabletraction, and driver skill.

In that first moment of launch, power istransferred from the engine to the transmission, either through a clutchor a torque converter. Torque is multiplied by the transmission gearing,and the flow of power is sent to the driveshaft and to the rearend. Thering-and-pinion gears further multiply torque. Then the differential orspool directs the torque to the axles in order to drive the wheels.Finally, the tires rotate and the car begins forward motion.

If the rearhousing was bolted or welded solidly to the chassis, as in a dragster,you would rely solely on the tires for traction. But in the case oflate-model Mustangs, the suspension allows the four wheels and tires tomove up and down independently of the chassis structure. And because thechassis is suspended, force applied to the sprung weight causes weighttransfer. Generally, when accelerating, the weight moves rear-ward; whenbraking, it transfers forward.

But what many don't realize is the act ofweight transfer is actually caused by engine torque and gearing. Becauseevery action has an opposite and equal reaction, the rear housing, whichis attached to the axles, will rotate in the opposite direction of thewheels. Because of this reaction, force is applied to the upper andlower control arms, which are attached to the housing.

Underacceleration, the upper arms are pulled rearward, while the lower armsare forced forward. This force is applied directly to the vehicle'schassis at the control-arm attachment points.

Since the control arms areattached directly to the chassis of the car, it is this force, ortorque, that causes the nose to rise and the weight to transferrearward. The upper control arms pull the chassis or unibody up and thelower arms drive it forward and up.

Meanwhile, the front springs, whichhave been compressed, possess stored energy. When the nose begins torise, the springs release this energy and force the nose up quicker thanit could be lifted on its own.

The sprung weight will be supported bythe springs. Springs separate the wheels and tires from the chassis andallow the tires to remain in compliance with the road or racing surface.Springs also allow the wheels and tires to absorb bumps and vibrationwithout transferring them fully to the vehicle's occupants.

If the carhas enough power or enough gearing, it will lift the nose off theground. This lifting can be further enhanced with front struts that havelittle resistance on extension. Naturally, a tighter strut will slow therise of the nose. Many racers use an adjustable strut to controlfront-end rise. A properly designed strut should also be engineered tobe stiffer on the compression side so the car doesn't slam down andbottom out the suspension.

Racers can also alter the rate or dampingeffect of the rear shocks to change the rate at which the rear housingreacts when acted upon. Ultimately, it is the tuning of these two areasthat make up a good suspension. Of course, you can alter the way yourcar launches by moving weight, or by changing the launch rpm, thegearing, and sometimes tire pressure, too.

As power is increased orstiffer gearing is installed, the load or force applied to the controlarms, the bushings, and the chassis is also increased. Therefore, itshould be noted that the first thing any Mustang owner does beforehitting the track is beef up the chassis, the suspension attachmentpoints, and the control arms and bushings.

As you can see, alteringanything relating to the engine, chassis, suspension, gearing, and so onwill affect how the car hooks and drives down the track. That's why it'simportant to understand what each part does and to buy only parts thatwill complement the entire package.