Anti-Lift Calculator

When a car brakes or accelerates the weight distribution between the axles shifts and the vehicle body tilts. When braking, the front of the vehicle dips while the rear is lifted up. When accelerating, the rear of the vehicle dips while the front is lifted up.

Anti-pitch geometry uses the angles of the suspension links to counteract this pitching motion. This tool will calculate the amount of anti-lift, anti-squat and anti-dive effect based on the conditions selected when you input arm angle, wheelbase and center of gravity location.

What are anti-lifts, anti-squats and anti-dives?

The braking and acceleration forces all act through the center of gravity which is the point about which the vehicle body rotates. When braking, the vehicle leans forward causing the front to drop down and the rear to lengthen. When accelerating it's the opposite.

Anti-pitch geometry does not change the total amount of weight transfer between axles. That total is determined by braking or accelerating forces, wheelbase and center of gravity location. What it changes is how much of that weight is transferred through the springs and how much is transferred through the suspension links, and the degree to which the vehicle body pitches.

These different constructions are classified by axle and function. Anti-squat acts on the rear axle during acceleration. Anti-dive acts on the front wheels when braking. Anti-lift aims to reduce both the extension of the rear part while braking (rear anti-lift) as well as the lifting of the front part when accelerating in front-wheel drive and all-wheel drive vehicles (front anti-lift).

Arms and moment centers in a side view.

The anti-geometry measurement is based on the lengths of the arms in a side view. In suspension, the connecting links are extended until they intersect. The point of intersection is the moment center. For double wishbone suspensions, the lines of the upper and lower wishbones are extended until they intersect. For MacPherson strut suspensions, one line goes through the lower wishbone and another line is perpendicular to the strut axis.

A line is drawn from the point of contact of the tire to the center of moments. This line is the lever length in side view and the angle it makes with the road surface is the arm angle as referred to by this calculator. The steeper this line, the more anti-geometry effect the suspension has.

How to use this calculator:

Select the type of analysis: Anti-Squat, Anti-Dive, Front-Anti-Lift or Rear-Anti-Lift. Then enter any three of four values: Arm Angle, Wheelbase, Center of Gravity Location or Percentage of Anti-Geometry and leave the fourth value blank. The calculator will automatically fill in the blank value. Many users input geometry parameters to determine percentage but it is just as easy to convert: for example, calculate an angle that results in a given percentage of 25%.

For braking conditions ie Anti-Dive and Rear-Anti-Lift you set the front wheel brake bias. Only a certain percentage of the braking force is taken into account so the effective values will be reduced depending on the bias percentage. Each length field has a toggle between metric and imperial units while angles can be given in degrees or radians.

About the calculation equations

All four scenarios use the same ratio between the arm angle, wheelbase and center of gravity position.

Theta is the arm angle, L is the wheelbase and h is the center of gravity height. The factor f represents the proportion of force acting on the axle; for accelerating the drive it's 1 while in braking conditions it represents the brake distribution of that axle. If f is set to 1 you get a geometric ratio which is shown in the results view and doesn't take into account the brake distribution.

A rear-wheel drive car brakes with a center of gravity position of 0.5 meters, wheelbase of 2.6 meters and the hitch angle is 3 degrees. The front axle carries 60 percent of the braking power.

The geometric values are calculated: The tangent of 3 degrees is approximately 0.0524. The wheelbase divided by the center of gravity position results in 2.6, divided by 0.5, which leads to 5.2, multiplied by 100. The result is the geometric rear downforce, which is about 27 percent.

Now the brake distribution is taken into account. If the front axle carries 60 percent of the braking force, then the rear axle carries 40 percent, so that the effective rear lift is about 27 percent, multiplied by 0.4, which gives about 11 percent. The geometry compensates for about 11 percent of the lift effect at the rear, while the rest is absorbed by the springs and dampers.

The table below shows each symbol and example values.

Comparison of anti-squat, anti-dive and anti-lift.

Although the geometry is calculated, in practice each condition affects one another. The link angle that produces good anti-squat for the rear axle will typically also affect the rear axle's anti-lift when braking because these two modes of operation put different loads on the suspension. So in actual design a compromise is made to suit the intended use of the vehicle.

Brake bias only affects braking conditions. Anti-dive refers to the front wheel brake proportion while anti-lift uses rear wheel brake proportion. In contrast, typical street or race car brake force distribution is about 60 percent for the front wheels. Under acceleration conditions all of the drive train power is used so anti-squat and front anti-lift do not affect bias.

Typical values and fields of application:

Most street vehicles use values between 15 and 30 percent. This allows good handling while still providing useful body control. Racing cars increase this to 30-50 percent for a more responsive feel, but must also accept a harsher ride and greater sensitivity to road imperfections. Off-road conversions use lower values so that the suspension can work freely over rough terrain.

In motorsport teams adjust the link angles to stabilise the contact patch of the tyres when braking and exiting corners which improves stability and grip. On front wheel drive or all-wheel drive cars, front anti-lift is important. When the driven wheels, i.e. the front ones in a front wheel drive car, lift up during acceleration, the car loses traction leading to understeer. This problem also occurs when moving the original mounting points or designing a completely new suspension from scratch.

Chassis geometry tips:

When the value exceeds a certain percentage (50), the suspension begins to become stiffer under load and feels very hard. This can cause the wheels to hop over uneven surfaces or increase traction loss. As shown in the table, even small changes in mounting position can significantly affect the percentage, so you should carefully measure the values before cutting or moving parts. Make sure that the vehicle is at its normal ride height and the suspension is in its intended position before measuring the angles.