CAMBER, CASTER, TOE-IN/TOE-OUT EXPLAINED
Camber, caster, toe-in/toe-out explained
Camber is the angle of the wheels in relation to the road, when viewed from the front (in front of the car). Try to imagine a vertical line through the centre of the tyre tread. (We will call this the ‘centre line’). At 0º, this line will be perpendicular to the road. (Black). If these ‘centre lines’ form a ‘V’-shape, we call this ‘positive camber’ (red line). ‘Negative camber’ occurs when these lines form an ‘A’-shape (blue line).
This is where we look at the car from the side. Now imagine a line that runs through the steering axis. That is the axis around which the front wheels will turn when steering. It usually runs through the upper and lower knuckle balls or through the centre line of the MacPherson pivot points. The green line indicates ‘positive caster', so the top of this line tilts toward the rear of the car. The red line shows ‘negative caster'. Positive caster is responsible for the self-centring effect that provides stability when driving in a straight line. This is similar to the front wheels of a shopping cart.
Toe-in & toe-out, also known as positive toe & negative toe
Now, we look at the car from above. Imagine lines in the driving direction, running through the centre of the tyre tread. (This refers to the position of the wheels). The red lines show ‘positive toe', which means the lines cross in front of the wheels (‘A’-shape). The green lines show ‘negative toe’, where the lines cross behind the wheels (‘V’-shape).
Part 2: How do camber, caster, positive and negative toe influence the driving behaviour?
Camber is usually from 0 degrees to 6 degrees (negative). When cornering, the body work of the car will start to roll/tilt. This can lead to more positive camber on the wheels (depending on the wheel geometry). Negative camber will compensate for this effect, causing a bigger contact surface between the tyres and the road ('footprint’). This results in more grip and stability during cornering. Furthermore, negative camber causes a force to be applied to the wheels that we call ‘camber-thrust'. This force wants to push the wheels toward the centre of the car.
Seen from ride height, more and more negative camber will occur during the compression of the suspension (depending on the wheel geometry). Tyres will wear more evenly when the camber is properly adjusted.
Question Is negative camber always a positive phenomenon?
Why It causes more wear on the inside of the tyres while driving in a straight line. In case of extreme negative camber, the tyres’ grip on the road surface could be reduced. This is due to the contact surface becoming smaller.
Ideally, the tyres should always be at right angles (perpendicular) to the road, under all circumstances. This will be more difficult for a passenger car than for a race car. The reason is that the passenger car has more suspension travel, a softer suspension and more body roll. We also want the tyres to last as long as possible, but for a race car, they only need to last long enough to reach the finish flag. Depending on the type of race, qualification, sprint race or endurance race, different settings can be chosen. This means that for street / track day cars, a compromise must be found. This usually results in -½ to -2 degrees of camber (negative).
For most street cars, there is limited room to adjust the camber. The ‘settings range’ is often no more than +0.5 and -1.5 degrees.
CASTER (or CASTOR)
This will usually be in the range of 1 to 10 degrees positive.
Generally speaking, caster only applies to the front (i.e. steering) wheels.
Caster is, among other things, necessary for straight line stability, also called ‘self-steering effect'. To better understand caster, we illustrate it using the front (i.e. steering) wheels of the shopping cart. If you were to turn around these wheels by 180 degrees, then they would have negative caster. The cart is now a lot more difficult to push (and could even lock up). It has suddenly become unpredictable and unstable. Positive caster also affects the camber while steering. The outer wheel will get more negative camber, while the inner wheel will get less negative camber. This obviously benefits the grip.
More positive caster provides more ‘feedback’ while driving, especially without power steering. You might think: the more positive caster, the better. That is, however, not the case. As caster increases, steering becomes heavier. And there is another disadvantage. While cornering, positive caster causes the following effect. If there is more positive caster, the dynamic wheel pressure will remain on the inner wheel, thus increasing grip at the front of the car.
Normally speaking, setting caster is very difficult, if not impossible. Applying the Intrax camber/caster plates allows you to set caster as well as camber in an instant.
Toe-in/toe-out (positive toe & negative toe)
This influences 3 important driving characteristics.
1. Tyre wear.
2. Straight line stability.
3. Moment of cornering.
For minimum tyre wear, it would be ideal if tyres were parallel while driving. In other words, no positive or negative toe, so 0 degrees.
With a front-wheel drive car, this can be achieved by having a little negative toe-in static conditions. A rear-wheel drive car should actually have slightly positive toe-in such conditions. This is particularly applied for street use. For racing, it depends on the type of car, tyre and wheel geometry. For a rear-wheel drive car, negative toe at the front wheels and positive toe at the rear wheels is quite usual.
There is a difference between ‘static’ and ‘dynamic’ tracking. We see this mostly with front-wheel drive cars, but it is also found with rear-wheel drive cars with independent wheel suspension. When releasing the driving forces, the momentum of the drive shafts causes the suspension, as well as its joints and connecting components, to be subjected to a high load. This will lead to distortion of the suspension's construction. The driving wheels want to go forward and will get positive toe. This especially applies to street cars. By applying flexible rubbers for the purpose of comfort and noise reduction, there is a lot more movement in these types of suspension. Which is why static tracking often starts with some negative toe.
High toe-out values will lead to the inner edges of the tyres being 'eaten', which will lead to additional wear and tear. A lot of toe-in will especially subject the outermost part of the tyres to a high load.
Negative toe will mainly improve the steering response. Positive toe will mainly increase the straight line stability.
Sometimes toe-in or toe-out is applied for a different effect: tyre temperatures. It is very important for racing tyres to reach a proper operating temperature, in order to ensure maximum grip and performance. When tyres remain too cold, the so-called scrub effect of tracking may provide a solution. This scrub effect also has a cleansing effect on the tyre tread. This means the brakes can be applied more forcefully and there will be more grip available in the corners.
Passenger cars are mostly set up with toe-in (positive toe), as the steering behaviour is then sacrificed for straight line stability. For race cars, steering behaviour is more important than straight line stability, so toe-out (negative toe) is preferred here.
In case of independent wheel suspension at the rear wheels, toe-in and toe-out also apply. Roughly speaking, the effects are the same as with the front wheels.
All of the above is of great importance to handling and other matters, such as tyre wear, and let us not forget driver satisfaction. Our advice is therefore: only use default factory settings or values that have been tested and proven correct as the starting point for a good set-up of your chassis. When replacing springs, entire dampers and/or camber plates, it is essential to adjust the wheel alignment again. Do not try to save money by not using professional wheel alignment services with up-to-date equipment. This could potentially completely ruin your investment in improving your chassis. The driving characteristics could worsen to such an extent that you might not even notice the improvement of the new suspension. Suddenly, worn tyres can present you with unpleasant surprises. For example, dangerous situations could occur because of instability in a straight line/in turns and/or during braking.
With the information we’ve provided on this page, we hope to have broadened your understanding of car chassis and made you aware of its importance. We hope you will enjoy driving your car safely and responsibly!