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Anti Dive and Anti Squat

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Anti Dive describes the amount the front of the vehicle dives under braking. When a car is decelerating due to braking there is a load transfer off the rear wheels and onto the front wheels proportional to the center of gravity height, the deceleration rate and inversely proportional to the wheelbase. If there is no anti-dive present, the vehicle suspension will deflect purely as a function of the wheel rate. This means only the spring rate is controlling this motion. As anti-dive is added, a portion of the load transfer is resisted by the suspension arms. The spring and the suspension arms are sharing the load in some proportion. If a point is reached called “100-percent anti-dive,” all of the load transfer is resisted by the suspension arms and none is carried through the springs. When this happens there is no suspension deflection due to braking and no visible brake dive. There is still load transfer onto the wheels, but the chassis does not pitch nose down.

Anti-dive percentage is always calculated with respect to a vertical plane that intersects the vehicle’s Center of Gravity. To find Anti-dive %,

Locate the front Centers of the suspension from the vehicle’s side view. Draw a line from the front tire contact patch through the Instantaneous Center. This is the tire force vector. Now draw a line straight down from the vehicle’s center of gravity. The Anti-dive is the ratio between the height of where the tire force vector crosses the center of gravity plane expressed as a percentage.

Squat is a term used to refer to the amount the car tips backwards under acceleration.  Over 100% of anti-squat (AS) means suspension will extend under acceleration. With 100% AS suspension won’t neither extend nor compress. Under 100% AS means tendency to compress under acceleration.

The calculation of anti-squat is similar to that of anti-dive. Locate the rear Centers of the suspension from the vehicle’s side view. Draw a line from the rear tire contact patch through the Instantaneous Center. This is the tire force vector. Now draw a line straight down from the vehicle’s center of gravity. The Anti-squat is the ratio between the height of where the tire force vector crosses the center of gravity plane expressed as a percentage.

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