tougefactory
02-18-2011, 01:52 PM
What is caster? Caster is the angle measured where the steering pivot axis is tilted forward, from vertical.
http://www.intraxracing.nl/UserFiles/File/CamberCasterToe/caster.pos.neg.gif
Increasing positive caster angle adds straight line stability, self centering of the steering, and camber gain. For drifting, added caster is beneficial for its ability to counter steer quickly and for quick transitions. For Grip, straight line stability for high speed, and camber gained turning turn-in can be a big advantage.
So you ask, "I know all this stuff, what's the point of this thread?". Good question. There are problems caused by the way the caster angle is changed on 240sx's. Only way to change caster is to use adjustable tension rods, by shortening the TC rods, you pull the wheels forward and effectively changing the caster angle.
By pulling the front wheels forward, you have now changed the geometry of the steering rack to the spindle. Theoretically this will increase ackerman and reduce total steering angle, which is not desired effect you want for performance.
To test our theory we put a S13 240sx with adjustable caster arms, coilovers(ride height set 2" lower than stock), stock inner and outer tie rods on our alignment system. Our state of the art system can measure "maximum turn angle", "Measured Ackerman" which we will be using for this test.
( I know its not a 240sx, the picture is to show you our alignment system :) )
http://tougefactory.com/tfworks/autogallery/galleries/012-jackie_ap1/DSC00366.jpg
1st test - Stance GR+ with standard camber plates, Stance Tension rods, Stock inner and outer tie rods. Ride height was set to 2.5" lower than stock.
We set the initial alignment setting to what we typically set most of the s13's with street tires. Caster - 7.1 deg, camber 3.5 deg, toe - 0 .
Max turn angle : 34 deg
Measured ackerman : 58%
2nd test - Stance GR+ with camber/caster plates. Stance Tension rods, stock inner and outer tie rods. For this test, we adjusted the tension rods to get the tie rods to sit close to 90deg to the spindle, this also centered the wheel in the wheel well. Caster was around 6deg at this setting. We than installed the Stance camber/caster plates and adjusted the caster to 7.1 deg. Camber was set to 3.5 and toe was set to 0. This way we minimize any variables.
Max turn angle : 39 deg
Measured ackerman : 51%
What does this mean?
Ackerman geometry was developed for low speed maneuverability.
For racecars, less ackerman is desired. Decreased ackerman will result in better initial turn-in response. For high speed racecars, decreased ackerman geometry is used to compensate for the large difference in slip angle between the inner and outer tires while cornering. This can reduce tire temps and increase traction during cornering.
Conclusion :
Drifting: Caster/Camber plate will increase angle and faster counter steer for transitions. Also reduce the effect of steering overcenter. Increase in 5 degrees of angle with stock inner/outer tie rods, with spacers in conjunction with camber/caster plate, you should be able to gain 8-10 degrees. That's modified knuckle category...:)
High Speed Grip: Caster/Camber plate will get the benefits of increased caster angle without increasing ackerman.
Low speed Auto X : Caster/Camber plate will reduce caster for faster steering and increase ackerman for low speed maneuverability.
Stance Camber/Caster plate will +/- around 1.5 to 2 degrees of caster depending on your camber setting.
http://www.tougefactory.com/tfdave/st_camcas.jpg
http://www.tougefactory.com/tfdave/st_camcas2.jpg
http://www.intraxracing.nl/UserFiles/File/CamberCasterToe/caster.pos.neg.gif
Increasing positive caster angle adds straight line stability, self centering of the steering, and camber gain. For drifting, added caster is beneficial for its ability to counter steer quickly and for quick transitions. For Grip, straight line stability for high speed, and camber gained turning turn-in can be a big advantage.
So you ask, "I know all this stuff, what's the point of this thread?". Good question. There are problems caused by the way the caster angle is changed on 240sx's. Only way to change caster is to use adjustable tension rods, by shortening the TC rods, you pull the wheels forward and effectively changing the caster angle.
By pulling the front wheels forward, you have now changed the geometry of the steering rack to the spindle. Theoretically this will increase ackerman and reduce total steering angle, which is not desired effect you want for performance.
To test our theory we put a S13 240sx with adjustable caster arms, coilovers(ride height set 2" lower than stock), stock inner and outer tie rods on our alignment system. Our state of the art system can measure "maximum turn angle", "Measured Ackerman" which we will be using for this test.
( I know its not a 240sx, the picture is to show you our alignment system :) )
http://tougefactory.com/tfworks/autogallery/galleries/012-jackie_ap1/DSC00366.jpg
1st test - Stance GR+ with standard camber plates, Stance Tension rods, Stock inner and outer tie rods. Ride height was set to 2.5" lower than stock.
We set the initial alignment setting to what we typically set most of the s13's with street tires. Caster - 7.1 deg, camber 3.5 deg, toe - 0 .
Max turn angle : 34 deg
Measured ackerman : 58%
2nd test - Stance GR+ with camber/caster plates. Stance Tension rods, stock inner and outer tie rods. For this test, we adjusted the tension rods to get the tie rods to sit close to 90deg to the spindle, this also centered the wheel in the wheel well. Caster was around 6deg at this setting. We than installed the Stance camber/caster plates and adjusted the caster to 7.1 deg. Camber was set to 3.5 and toe was set to 0. This way we minimize any variables.
Max turn angle : 39 deg
Measured ackerman : 51%
What does this mean?
Ackerman geometry was developed for low speed maneuverability.
For racecars, less ackerman is desired. Decreased ackerman will result in better initial turn-in response. For high speed racecars, decreased ackerman geometry is used to compensate for the large difference in slip angle between the inner and outer tires while cornering. This can reduce tire temps and increase traction during cornering.
Conclusion :
Drifting: Caster/Camber plate will increase angle and faster counter steer for transitions. Also reduce the effect of steering overcenter. Increase in 5 degrees of angle with stock inner/outer tie rods, with spacers in conjunction with camber/caster plate, you should be able to gain 8-10 degrees. That's modified knuckle category...:)
High Speed Grip: Caster/Camber plate will get the benefits of increased caster angle without increasing ackerman.
Low speed Auto X : Caster/Camber plate will reduce caster for faster steering and increase ackerman for low speed maneuverability.
Stance Camber/Caster plate will +/- around 1.5 to 2 degrees of caster depending on your camber setting.
http://www.tougefactory.com/tfdave/st_camcas.jpg
http://www.tougefactory.com/tfdave/st_camcas2.jpg