# Geometry Explained

## Anti Squat, Dive and Lift Geometry

Anti-squat, anti-dive and anti-lift geometry which will be referred to as “anti-geometry” when discussing them as a whole is a form of geometry at the front and rear wheels that alters and controls the amount that a car will compress the springs due to acceleration, deceleration or braking conditions.

## Wheel Rate and Chassis Roll Stiffness

Wheel Rate Wheel rate is effectively the spring rate when measured at the wheel as opposed to at the spring. It is important to understand the wheel rate of a vehicle for calculating the spring rates and understanding the car dynamically. Coil Spring Wheel Rate In order to calculate wheel

## How to Calculate Installation Ratio

What is an Installation Ratio? An installation ratio is the ratio between how much the spring and damper moves in relation to how far the wheel and tyre move. In general, the wheel and tyre will move a further distance than the spring and damper. The installation ratio is vital

## Tyre Slip Angle

What Is Slip Angle? A slip angle is the difference between the steering angle and the direction in which the tyre footprint is taking. Tyre slip angles play a major part in steering systems and have a large effect on aspects of steering geometry such as Ackermann and toe. When a

## Toe

What Is Toe? Toe is the angle between each wheel with relation to the longitudinal axis of the vehicle. It is usually measured when the car is static and is measured either in degrees or in millimetres. If it is measured by distance then it is usually the difference in

What Is Scrub Radius? When viewing a wheel from front view, the scrub radius is the distance between where the extrapolated line of kingpin axis touches the road and the tyre contact patch centre point. If the extrapolated KPI is outboard of the contact patch then the scrub radius is

## King Pin Inclination

On current suspension systems, the kingpin is set at an angle to the vertical plane when viewed from the front or rear of the vehicle. This angle is known as the king pin inclination. The purpose of the KPI is to produce vertical displacement of the vehicle in during steering in an upward direction. The larger the KPI, the larger the effect. This lifting effect produces a self centering torque similar to that of caster. The KPI also generates scrub radius.

## Instantaneous Centre

What Is An Instant Centre? The word “instant” means at that particular position of the linkage. “Centre” refers to a projected imaginary point that is effectively the pivot point of the linkage at that instant. The instant centre is a point in space, governed by the position, angle and length

## Front View Swing Arm

What is Front View Swing Arm (FVSA)? The front view swing arm (FVSA) instant centre location controls the roll centre height, the camber change rate and the tyre lateral scrub. The instant centre can be located inboard of the wheel or outboard of the wheel. It can be above ground

## Caster

What Is Caster? Caster is the measure of how far forward or behind the steering axis is to the vertical axis, viewed from the side. This is measured by drawing a line between the top and bottom pivot points of the front upright. The angle between the drawn line and

## Camber Gain

What Is Camber Gain? Camber gain is the change in camber angle per amount of vertical displacement of the wheel. The most common situation is that camber will become more negative if the wheel is moved vertically upwards. Likewise, the wheel camber will become more positive if the wheel is

## Camber

What Is Camber & What’s Its Purpose? Camber angle is the angle between the plane of a wheel and the vertical. It is described as positive when the top of the wheel leans outward and negative when the top of the wheel leans inward. Camber angle alters the handling characteristics

## Bump Steer

What Is Bump Steer? Bump steer is a change in the steering angle of the wheel when the wheel is in bump or droop without turning of the steering wheel or lateral movement in the steering rack. This is due to the arc patterns of the wishbones and the steering

## Ackermann

Ackermann Steering Geometry In order for a car to turn smoothly, the inside wheel must travel on a smaller radii arc than the outer wheel. This is achieved by the inside wheel turning more than the outside wheel. This concept is known as Ackermann steering geometry. Perfect Ackermann geometry can