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- - Tyres - - Suspension - - Driving - -

Suspension - Page 1


Toe is the angle of the wheels in relation to the body when viewed from above; toe in refers to when the wheels point towards the front of the vehicle when viewed from above (so the fronts of the tyres are closer together than the rears), and toe out is when the wheels point towards the rear. It can be measured in mm or degrees/minutes (1 minute is 1/60th of a degree).

Changing the toe in/out adds an amount of scrub to the tyres which can change the characteristics of the vehicles transient handling and also helps improve straight line stability, however the trade off in this stability is that extra drag can result. The increase in tyre scrub can also help to increase tyre temperatures. It is typically adjustable on the front of all cars by adjusting the length of the track rods that are attached to the steering arms. Cars with the ability to change the toe on the rear often have dedicated toe links which can be adjusted in the same way as the track rods on the front. Race cars should have adjustability on front and rear.

Toe in (on the front) generally results in understeer upon initial turn into a corner, whereas front toe out results in initial oversteer. When the suspension moves, the toe setting tends to change, so it is important to set up the toe when the car is in race trim (driver on board, correct fuel load etc) as extra weight will affect the ride height and so will affect the toe. Since either toe in or out is creating a certain amount of slip angle, when the suspension loads or unloads whilst driving, the slip angle changes, which results in steering inputs being induced. This is called bump steer if caused by independent suspension movement or roll steer if caused by body roll (when cornering). Generally this is undesirable for a racing car as the effects can be unpredictable.



Camber is the angle of the wheels when viewed from the front, or the angle from vertical. When the wheels are closer at the top than they are at the ground, then they are said to have negative camber. Camber forces the tyre into a slight conical shape, which in turn generates camber thrust, which is a lateral force, similar to the effect of leaning a bicycle when riding. The force tends to pull the tyre in the direction of the lean. Negative camber increases the amount of cornering force available (and so ultimate grip), however increased levels can lead to reduced straight line performance due to extra drag being induced, as well as increased tyre wear. Camber, when adjustable, is generally adjusted by way of shims or adjustable tie rods of rose joints.

Camber will change with suspension movement (bumps and body roll), and indeed will generally tend to reduce during body roll, hence the need for a certain amount of static camber for optimum tyre performance. A tyre generates optimum grip at a certain camber angle, so the camber should be adjusted so that during suspension movements, the tyre is at its optimum point for as long as possible. A good way to tell if you have set the camber up to the optimum angle is to check the tyre temperatures after being out on track with an infra red thermometer or tyre probe; at the optimum camber angle, the temperatures should be even across the width of the tyre, with an absolute maximum of 10 deg C differential across the width. If the temperature is higher on the inside of the tyre, reduce the level of camber and vica versa. Please note: a high level of camber is not suitable for road use as this will result in reduced tyre life.



Castor is defined as the angle that the stub axle pivot line (the kingpin) makes with the vertical when viewed from the side. Increased castor will increase straight line stability and increase the self centering force of the steering wheel, thus making the steering feel stiffer. This is because increasing the angle increases the distance between the centre of the tyre contact patch and the effective axis of rotation, so an increased steering torque is required to generate the same amount of force as the distance is larger. Clearly castor is applicable to the front wheels only.

An increased castor angle also causes an increase in camber angle when the wheels are turned. This is beneficial in race cars, as it allows an increase camber angle to be generated (therefore more grip) without having to run as much static camber, thus reducing tyre scrub and bump steer. The downside is that it is difficult to calculate the amount of extra camber that is being created due to the complex geometry involved.


Ride Height

The ride height is exactly what it says on the tin – the height at which the car rides! It is measured from the cars undertray to the floor, or, on cars without an undertray, should be measured from the floorpan to the floor. It is not the same as the ground clearance, which is measured from lowest point, usually the exhaust or differential housing.

Ride height should be measured at the front and back of the car, and should be equal or have a slightly higher value at the rear, which creates chassis rake. Rake refers to the angle of the car in relation to the floor when viewed from the side. A car should never have a higher ride height at the front than at the back, as this causes dangerous aerodynamic effects. When measuring the ride height, as with the other suspension settings, make sure that the car is in race trim, as extra weight on board could change the reading significantly, especially on lighter cars where fuel and the driver are a significant proportion of the total weight.

Having a lower ride height reduces the height of the cars centre of gravity (CG) which results in less weight transfer and more overall grip. (See tyres section, here for an explanation). When setting the ride height, it is important to make sure you do not set it too low, as this will result in body damage when the tyres rub on the wings, or damage to the underside of your car when the car ‘grounds out’ as the minimum ground clearance is too low.

One thing to take into account when modifying the ride height is the effect it has on the suspension geometry. Many racing cars have double wishbone suspension, and significantly dropping the ride height from its intended design purpose could have a significant knock on effect on the height of the roll centre as the suspension geometry changes. It could indeed have the effect of actually raising the roll centre height, which could negate any effects of reducing the cars ride height. However, most race cars should have this designed into them, so slight alterations should not have any drastic undesirable effects such as this.

There are also significant aerodynamic effects in altering the ride height and rake too. Most road cars generate lift at high speeds; dedicated race cars with wings and spoilers and other aero devices should create downforce at high speeds; reducing ride height reduces the amount of airflow under the car, and so reduces the lift (or increases the downforce) generated at high speeds. Chassis rake helps to reduce the pressure under the car and so helps with this effect too.

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