The MC has basically two locations-static and dynamic-that can be easily calculated. Static is where the MC is located when the car is at ride height and standing still. The dynamic location is where the MC moves as the car dives and rolls through the turns. Because the control arms move as the car rolls and dives, the instant centers also move. This causes the MC to move along with the instant centers and, in most cases, the MC moves to the right in a left-turning circle track race car.
Control Arm Angles vs. MC Location
Control arm angles are measured in degrees from horizontal. Therefore, level would be 0 degrees and straight up would be 90 degrees. The lower control arm angles largely control the amount of lateral movement of the front MC and the upper control arm angles mostly control the lateral location of the two MCs. Excessive lower control arm angles cause the front MC to move a greater amount as the car goes through the turns. Increasing or decreasing the upper control arm angles moves the MC side to side. Low angles in the upper control arms causes excessive camber change in the front wheels, especially in the right front wheel where it affects the handling the most.
Rules About MC Location
As you begin to design your car's front suspension, you need to determine where the MC should be located according to your type of racing and what kind of race track you will run. Here are a few general rules you need to follow:
1. The farther left the MC is located, the longer the effective moment arm and the more efficient the front suspension will be (meaning it will want to roll more). A more left location is proper for low-banked asphalt race tracks and dry slick dirt race tracks. 2. The farther right the MC is located, the less efficient the front suspension will be (meaning it will be stiffer). An MC that is located farther to the right will be good for all tracks banked beyond 10 degrees, including dirt and asphalt tracks. The higher the banking, the farther right the MC should be. Because of the higher amount of downforce caused by the banking, the front needs to be somewhat stiffer to resist excessive dive on entry and in the middle of the turns.
3. The amount of MC movement from static to dynamic locations that the car needs depends on how the race track is constructed. A track that has consistent banking throughout the turns requires an MC design where there is very little movement from the static to the dynamic location. Tracks that are constructed where the banking going in and coming off the corners is far less than the banking in the middle of the turns require an MC design that incorporates a greater amount of movement of the MC from static to dynamic locations. As the car turns into the corners, the MC can be designed to start out statically farther to the left and that is more suited to the lower banking. As the car moves through the middle where the banking has increased, the MC should move farther to the right, and that location is better suited to the higher amount of downforce caused by the high banking.
4. The lateral location of the MC range depends on the height of the center of gravity of the race car as well as the track width of the car. A modified stock car with its low CG can tolerate an MC that is farther left than a stock class car where the ride height is above 5 inches and the CG is above 18 inches. The narrower the car, the more effect there is on lateral location of the MC. A narrow track width (distance from center to center of the tires) results in a greater tendency for the front end to want to roll. Narrow stock cars should be designed with an MC that is farther to the right than wider cars.