As the MC moves to the right...
As the MC moves to the right to the eventual dynamic location, the effective moment arm becomes shorter because of the direction of the resultant force.
Control Arm Angles vs. MC location Control
Arm angles are measured in degrees from horizontal. Therefore level would be zero 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, static, and dynamic.
Excessive lower control arm angles cause the front MC to move a greater distance as the car goes through the turns. Increasing or decreasing one or both of the upper control arm angles moves the MC side to side. Low or reverse (the chassis mount being higher than the ball joint) angles in the upper control arms cause excessive camber change in the front wheels, especially in the right front wheel where it affects the handling the most.
With the newer setups such as the big bar and soft springs (BBSS), we need to re-address the issue of camber change versus upper control arm angles. These setups cause much more dive and much less roll. The upper control arm angles will need to be less within the possibilities of a good MC location. The initial cambers for both the left and right tires need to change due to the excessive camber change associated with a lot of dive. The RF static camber must decrease and the LF static camber must increase.
Measuring stagger and taking...
Measuring stagger and taking tire temps are important but will mean little if you don't know your moment center location. Photo by Todd Ridgeway
Rules About MC Location
As we begin to design our car's front suspension, we need to determine where the MC should be located according to our type of racing and what kind of racetrack we will run. Here are a few general rules that we 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 racetracks and dry slick dirt racetracks, and cars with a low CG.
2. The farther right the MC is located, the less efficient the front suspension will be meaning it will be stiffer and want to roll less. A MC that is located farther to the right of the centerline of the car will be good for all tracks that are high banked including dirt and asphalt tracks. The higher the banking, the farther right the dynamic MC should be located. Because of the higher amount of downforce caused by the banking, we need the front to be somewhat stiffer to resist excessive dive on entry and in the middle of the turns.
When the right upper control...
When the right upper control arm has more angle than the left upper control arm, the MC is usually located more to the right of the centerline of the car. The upper control arm angles tend to control the position, left and right, of the MC. The opposite is true if the upper angles are reversed with the left being more than the right.
3. The amount of MC movement from static to dynamic locations that the car needs depends on how the racetrack is constructed. A track that has consistent banking throughout the turns requires a 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 may require a MC design that incorporates a greater amount of movement of the MC from static to dynamic locations. This is common in dirt track racing where corner entry must be enhanced aided by a MC location farther left.
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. Then as the car moves through the middle where the banking has increased, the MC will then move 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 is dependant on the height of the CG of the racecar as well as the track width of the car. A modified asphalt stock car with its low CG can tolerate a MC that is farther left than say a stock class car where the ride height is above 5 inches and the CG is above 18 inches. The narrower the car, the greater the effect 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 a MC that is farther to the right than wider cars.