Rear suspension that features anti-squat geometry optimizes a car's ability to apply acceleration force to the road surface. When this force is applied through suspension with 100% or greater anti-squat geometry the rear of a car pushes up rather than squatting down under power.
This is because the laws of physics state that for every force applied there is an equal and opposite reaction. Therefore, when accelerative forces are applied efficiently by a chassis to the road surface, the 'equal and opposite' reaction works back through the rear suspension geometry to actually push the chassis upward. In drag racing, a chassis that exhibits this has 100% or greater rear anti-squat suspension geometry.
Rear anti-squat is achieved when certain suspension geometry parameters are met. Determining the 'Center of Gravity' (CG) in a car is difficult, however it's generally accepted to be between 18 and 22 inches above ground level. Racing cars have a lower 'CG' - approximately 18 inches above ground level - and street cars have a 'CG' around 22 inches above ground level.
Rear anti-squat suspension geometry has implications for all-around performance, not simply drag racing
A combination of wheelbase, 'CG', and the point around which the rear axle rotates (Instant Center) determines the degree of rear anti-squat. One hundred percent rear anti-squat is achieved when the 'Instant Center' of the rear suspension falls on a line drawn from the rear tire's contact point with the road surface to the 'CG' directly above the front axle line. On a chassis that uses rear radius rods, the rear axle rotates around the point where the radius rods attach to the chassis.• Click here to see 100% rear anti-squat with radius rods
On a chassis using a 4-link rear suspension, the point of rotation is where the upper and lower links would theoretically intersect. An adjustable 4-link rear suspension allows the angle of the upper and lower links to be changed, thus changing their theoretical point of intersection, even to a position on a chassis that would be practically impossible.• Click here to see 100% rear anti-squat with four-link
Greater than 100% anti-squat exists when the line drawn from the rear tire's contact point through the 'Instant Center' is higher than the 'CG' directly above the front axle.• Click here to see more than 100% rear anti-squat with radius rods
Less than 100% anti-squat exists when the line drawn from the rear tire's contact point through the 'Instant Center' falls below the 'CG' directly above the front axle.• Click here to see less than 100% rear anti-squat with radius rods
Four-link rear suspension enables up to 100% or greater rear anti-squat to be dialed into a chassis with the benefit of compact dimensions due to much shorter link length than radius rod suspensions. Adjustable 4-link designs are important for optimizing suspension in a competition car, where track conditions and chassis configurations such as wheel and tire choice can change. However, by setting up a street car chassis within geometric parameters, up to or greater than 100% rear anti-squat can be achieved with a 4-link suspension that doesn't provide for adjustment.
Radius rod rear suspension can also deliver rear anti-squat geometry, however this can be difficult to achieve on modern vehicles as the long radius rods required usually limit suspension travel due to interference with the floor pan or rear sub-frame. However, custom tubular chassis for hot rods and street machines can be designed to accommodate rear radius rod suspensions that deliver excellent rear anti-squat characteristics.
Achieving rear anti-squat suspension geometry is a relatively simple matter of accurate chassis design and fabrication..........read more