Post by Lawton70 on Dec 11, 2011 10:00:38 GMT -5
Here are some tips when setting up your car or building a new one. The length and angle of the tie rods can have a great deal of influence on the handling of your car. A completely neutral setup is the tie rod the exact same length as the a-arm and the tie rod parallel with the rod. Any other length and angle causes changes through the range of the suspension.
At the rear (assuming a simple A-arm with an upper link):
The rear is a great place to start to understand how the angle and length of the upper link changes handling, because the rear is fairly simple.
Angle = roll center
- The angle is when you compare the upper link to the a-arm. the upper link parallel with the A-arm is neutral.
- If the angle of the upper link is lower inboard in the chassis than it is outboard at the wheel the car will resist rolling when cornering (high roll center).
- Conversely, if the upper link is higher inboard than it is outboard at the wheel the car will roll easier when cornering (low roll center).
Length - Camber gain
- the length of the upper link controls the automatic camber gain. which means how much the tires will lean in/out as the suspension is compressed. The upper link equal length as the a-arm is neutral, or no gain.
- the upper link shorter than the a-arm = the top of the tire will lean in toward the chassis more as the suspension is compressed (more side grip in corners, less forward traction).
- the upper link longer than the a-arm = the top of the tire will lean away from the chassis as the suspension is compressed (not typically a setting used).
At the Front (assuming a simple setup with an a-arm, and upper link and a steering tie rod.):
The front is a bit more complicated. The rules for the upper link length and angle are the same. The steering tie-rod length and angle is a bit more complex.
Up&down Angle = Bump Steer
- the steering tie-rod parallel with the A-arm, when viewed from the back, is neutral for bump-steer.
- if the tie rod is higher in at the chassis and lower out at the wheel, when compared to the a-arm, then the front wheels will toe-in when the suspension is compressed.
- if the tie-rod is lower at the chassis and higher at the wheel, when compared to the a-arm, the front wheels will toe out as the suspension is compressed.
Tie-rod shorter/longer = Ackermann angle
Ackermann is a subject all on its own. In short it means trying to get the inside wheel to steer more than the outside while cornering.
- tie-rods that are the same length as the a-arm will not produce any ackermann.
- tie-rods shorter than the a-arm length will increase the steering angle of the inside wheel during cornering.
- tie-rods that are longer than the a-arm will decrease the steering angle of the inside wheel during cornering.
Tie-rod angle front to back.(when viewed from the top)
There is an additional angle to consider with the front tie-rods, and that is the angle when viewed down from the top. This initial angle will change how much Ackermann effect is available.
- the tie-rods parallel with the a-arm is neutral.
- the tie rods at an angle toward the back of the car will reduce the effect of Ackermann.
- the tie rods at an angle toward the front of the car will maximize the affect of Ackermann.
At the rear (assuming a simple A-arm with an upper link):
The rear is a great place to start to understand how the angle and length of the upper link changes handling, because the rear is fairly simple.
Angle = roll center
- The angle is when you compare the upper link to the a-arm. the upper link parallel with the A-arm is neutral.
- If the angle of the upper link is lower inboard in the chassis than it is outboard at the wheel the car will resist rolling when cornering (high roll center).
- Conversely, if the upper link is higher inboard than it is outboard at the wheel the car will roll easier when cornering (low roll center).
Length - Camber gain
- the length of the upper link controls the automatic camber gain. which means how much the tires will lean in/out as the suspension is compressed. The upper link equal length as the a-arm is neutral, or no gain.
- the upper link shorter than the a-arm = the top of the tire will lean in toward the chassis more as the suspension is compressed (more side grip in corners, less forward traction).
- the upper link longer than the a-arm = the top of the tire will lean away from the chassis as the suspension is compressed (not typically a setting used).
At the Front (assuming a simple setup with an a-arm, and upper link and a steering tie rod.):
The front is a bit more complicated. The rules for the upper link length and angle are the same. The steering tie-rod length and angle is a bit more complex.
Up&down Angle = Bump Steer
- the steering tie-rod parallel with the A-arm, when viewed from the back, is neutral for bump-steer.
- if the tie rod is higher in at the chassis and lower out at the wheel, when compared to the a-arm, then the front wheels will toe-in when the suspension is compressed.
- if the tie-rod is lower at the chassis and higher at the wheel, when compared to the a-arm, the front wheels will toe out as the suspension is compressed.
Tie-rod shorter/longer = Ackermann angle
Ackermann is a subject all on its own. In short it means trying to get the inside wheel to steer more than the outside while cornering.
- tie-rods that are the same length as the a-arm will not produce any ackermann.
- tie-rods shorter than the a-arm length will increase the steering angle of the inside wheel during cornering.
- tie-rods that are longer than the a-arm will decrease the steering angle of the inside wheel during cornering.
Tie-rod angle front to back.(when viewed from the top)
There is an additional angle to consider with the front tie-rods, and that is the angle when viewed down from the top. This initial angle will change how much Ackermann effect is available.
- the tie-rods parallel with the a-arm is neutral.
- the tie rods at an angle toward the back of the car will reduce the effect of Ackermann.
- the tie rods at an angle toward the front of the car will maximize the affect of Ackermann.