Just a brief description of various suspension angles that I done for a college self assessment, so I thought I would whack it up on here.
1: Castor angle
Castor angle is the angle made between the pivot line and the perpendicular angle to the ground looking at the vehicle side on. The pivot line is taken between the top ball joint and the lower ball joint. If the pivot line meets the ground ahead of the contact patch of the tyre then the angle is considered negative. And if it meets behind it then the castor angle is positive. A negative angle is most common as this helps the wheels self centre and provides stability at speed. A positive angle will be highly unstable and will amplify any steering input in a given direction. And direction changes will be very hard and then very sudden. The faster the vehicle is travelling the greater this effect. Not good for a car. So the below will discuss negative castor angles.
This angle has a big influence on the steering characteristics of the vehicle as the more aggressive the angle the greater the wheels will want to centre themselves. This can be fine tuned to give the driver a higher level of feel through the steering system, but to great and the force needed to counteract the self centring force can lead to uncontrolled turns if the front wheels temporarily lose contact with the ground or the weight is taken off of them, after a bump for instance. This means that damping rates will need to be altered along with the castor angle depending on the track surface conditions or the undulations within the track. This symptom has been seen many times in the late stages of the Nurburgring 24 hr race. The track has many crests during corners and the above has happened, snapping the car into the corner resulting in a accident. The usual case in endurance racing is to reduce the castor angle to make the steering lighter and less sporadic. And the feel is not needed so much as the lap times are not going to be anywhere near 100%, whereas sprint racing for example will need lots of feel for a very short time to give the driver as much feedback as possible to produce the best lap time.
2: Camber angle
Camber angle is the angle between the vertical axis of the vehicle and the vertical axis of the wheel. If the top of the wheel is nearer the centreline of the vehicle than the bottom of the wheel then the angle is considered negative, and the reverse, positive.
Negative camber angle is the most common angle to use on road going and motorsport vehicles. This is because having a negative angle will run the tires on their inner portion of the contact patch when driving in a straight line. This is beneficial in a straight line as it reduces the amount of drag created by the friction of the contact patch as the contact patch is now far smaller. But the maximum tractive force that is able to be applied to the tire is far less as the contact patch is smaller, so acceleration off of the line will be reduced. In cornering the car will transfer weight to the inside of the vehicle an thus roll. As the car rolls the whole width of the contact patch is brought in contact with the road surface, giving lots of grip in the corners. With 0 camber the tire will be moved onto it’s outside edge. Running tires on a small contact patch will wear them far faster than running on the full contact patch however. So if there are lots of straights, lots of camber will wear your tires quickly but will give you higher straight line speed. If you have 0 camber and there are lots of corners you will wear your tires quickly. The amount of camber needed on a race car is a balancing act between the track, the tires, the strategy of the race and the suspension set up itself. If the roll bars are loosened then more camber needs to be run to take the extra tire roll into account. The tire pressures also affect how much the tires will roll onto their outside edge during cornering. The roll centre of the vehicle is very important when discussing camber. A vehicle with a high difference between roll centre and centre of gravity will need more camber to achieve optimum results, and will wear out tires quicker because of it. A pickup truck for example. A formula car on the other hand will not need as much camber to achieve optimum tire contact area during cornering and so will be much nicer on it’s tires comparatively. Tire temperatures are the easiest way to check camber setups for the given track. If the outside third of the tire is hotter than the inside third then too little camber is being run and visa versa. This and tire pressures are used together to create the best setup for tire maintenance.
3: KPI SAI
The KPI (King Pin Inclination) or SAI (Steering Axis Inclination) is a similar angle to to castor angle but in a differnet axis. Looking from the front or rear of the vehicle. It is between the vertical axis of the wheel and a line going through The upper and lower ball joint (in the case of SAI) or the angle of the king pin (in the case of KPI). King pins are very rarely seen nowadays but are still found in karting where there is no active suspension.
This angle tilts the steering axis. This has the affect, when turning, of changing the camber of the wheel and the height of the wheel centre. On a road vehicle this change in height is not a massive effect and is mostly taken up by the suspension. But with karts this change in ride height is key to the handling characteristics of the kart. As there is no suspension on a kart the tires are the only thing that all weight roll on. So by inclining this angle as the kart goes into a turn the inside front will increase in height to counteract this roll and the camber produced by this gives maximum traction as the full width of the tire is in contact with the road.
This subject could go on for pages and pages. This is the fundamentals.
1: Castor angle
Castor angle is the angle made between the pivot line and the perpendicular angle to the ground looking at the vehicle side on. The pivot line is taken between the top ball joint and the lower ball joint. If the pivot line meets the ground ahead of the contact patch of the tyre then the angle is considered negative. And if it meets behind it then the castor angle is positive. A negative angle is most common as this helps the wheels self centre and provides stability at speed. A positive angle will be highly unstable and will amplify any steering input in a given direction. And direction changes will be very hard and then very sudden. The faster the vehicle is travelling the greater this effect. Not good for a car. So the below will discuss negative castor angles.
This angle has a big influence on the steering characteristics of the vehicle as the more aggressive the angle the greater the wheels will want to centre themselves. This can be fine tuned to give the driver a higher level of feel through the steering system, but to great and the force needed to counteract the self centring force can lead to uncontrolled turns if the front wheels temporarily lose contact with the ground or the weight is taken off of them, after a bump for instance. This means that damping rates will need to be altered along with the castor angle depending on the track surface conditions or the undulations within the track. This symptom has been seen many times in the late stages of the Nurburgring 24 hr race. The track has many crests during corners and the above has happened, snapping the car into the corner resulting in a accident. The usual case in endurance racing is to reduce the castor angle to make the steering lighter and less sporadic. And the feel is not needed so much as the lap times are not going to be anywhere near 100%, whereas sprint racing for example will need lots of feel for a very short time to give the driver as much feedback as possible to produce the best lap time.
2: Camber angle
Camber angle is the angle between the vertical axis of the vehicle and the vertical axis of the wheel. If the top of the wheel is nearer the centreline of the vehicle than the bottom of the wheel then the angle is considered negative, and the reverse, positive.
Negative camber angle is the most common angle to use on road going and motorsport vehicles. This is because having a negative angle will run the tires on their inner portion of the contact patch when driving in a straight line. This is beneficial in a straight line as it reduces the amount of drag created by the friction of the contact patch as the contact patch is now far smaller. But the maximum tractive force that is able to be applied to the tire is far less as the contact patch is smaller, so acceleration off of the line will be reduced. In cornering the car will transfer weight to the inside of the vehicle an thus roll. As the car rolls the whole width of the contact patch is brought in contact with the road surface, giving lots of grip in the corners. With 0 camber the tire will be moved onto it’s outside edge. Running tires on a small contact patch will wear them far faster than running on the full contact patch however. So if there are lots of straights, lots of camber will wear your tires quickly but will give you higher straight line speed. If you have 0 camber and there are lots of corners you will wear your tires quickly. The amount of camber needed on a race car is a balancing act between the track, the tires, the strategy of the race and the suspension set up itself. If the roll bars are loosened then more camber needs to be run to take the extra tire roll into account. The tire pressures also affect how much the tires will roll onto their outside edge during cornering. The roll centre of the vehicle is very important when discussing camber. A vehicle with a high difference between roll centre and centre of gravity will need more camber to achieve optimum results, and will wear out tires quicker because of it. A pickup truck for example. A formula car on the other hand will not need as much camber to achieve optimum tire contact area during cornering and so will be much nicer on it’s tires comparatively. Tire temperatures are the easiest way to check camber setups for the given track. If the outside third of the tire is hotter than the inside third then too little camber is being run and visa versa. This and tire pressures are used together to create the best setup for tire maintenance.
3: KPI SAI
The KPI (King Pin Inclination) or SAI (Steering Axis Inclination) is a similar angle to to castor angle but in a differnet axis. Looking from the front or rear of the vehicle. It is between the vertical axis of the wheel and a line going through The upper and lower ball joint (in the case of SAI) or the angle of the king pin (in the case of KPI). King pins are very rarely seen nowadays but are still found in karting where there is no active suspension.
This angle tilts the steering axis. This has the affect, when turning, of changing the camber of the wheel and the height of the wheel centre. On a road vehicle this change in height is not a massive effect and is mostly taken up by the suspension. But with karts this change in ride height is key to the handling characteristics of the kart. As there is no suspension on a kart the tires are the only thing that all weight roll on. So by inclining this angle as the kart goes into a turn the inside front will increase in height to counteract this roll and the camber produced by this gives maximum traction as the full width of the tire is in contact with the road.
This subject could go on for pages and pages. This is the fundamentals.
