April, do you know if Audi's "Track-Stabilizing Scrub Radius" implies a negative scrub radius?
12-14-2002, 11:11 AM
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April, do you know if Audi's "Track-Stabilizing Scrub Radius" implies a negative scrub radius?
Many A6/allroad spec lists (on foreign Audi websites) lists this Track-Stabilizing Steering Scrub Radius as a front suspension feature. I'm assuming this to mean that our cars are designed with a negative Scrub Radius, but I'd be interested to know by how much - incase anyone happens to have that info. =)
12-14-2002, 11:56 AM
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Good question. The 4 link system makes it harder to visualize.
<center><img src="http://www.wet.hr/audi/slike/suspension3.JPG"></center><p>All my materials show 0 camber. Where the tire patch and primary thust point intersect, isn't shown.
From C&D.
"The suspension resembles a typical unequal-length control arm setup, but it uses four separate links instead, each with its own ball-joint attachment at the hub. With this setup, the tire is steered about a virtual axis that is well outboard of the ball joints themselves. As such, Audi has been able to achieve a small kingpin offset (the distance between the steering axis and the center of the tire contact patch) to minimize bump steer and toe-out on braking, without resorting to a large kingpin inclination angle (the angle that the steering axis inclines inboard from vertical), as is usually required with ordinary struts or control arms.
The small kingpin inclination angle gives the A4 delightfully low steering effort, but its big advantage is this: the virtual steering axis passes within just 10mm of the center of the wheel. This small spindle offset virtually eliminates any torque moment on the steering from the driving force. (For comparison, the previous 80/90 model's conventional steering axis was 66mm inboard of the wheel center.) The result is a new benchmark for front-drive suspension engineering."
From C&D.
"The suspension resembles a typical unequal-length control arm setup, but it uses four separate links instead, each with its own ball-joint attachment at the hub. With this setup, the tire is steered about a virtual axis that is well outboard of the ball joints themselves. As such, Audi has been able to achieve a small kingpin offset (the distance between the steering axis and the center of the tire contact patch) to minimize bump steer and toe-out on braking, without resorting to a large kingpin inclination angle (the angle that the steering axis inclines inboard from vertical), as is usually required with ordinary struts or control arms.
The small kingpin inclination angle gives the A4 delightfully low steering effort, but its big advantage is this: the virtual steering axis passes within just 10mm of the center of the wheel. This small spindle offset virtually eliminates any torque moment on the steering from the driving force. (For comparison, the previous 80/90 model's conventional steering axis was 66mm inboard of the wheel center.) The result is a new benchmark for front-drive suspension engineering."
12-14-2002, 12:20 PM
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Thanks! That's the best explanation I've seen yet...
It seems from the text, that the kingpinn offset is +10mm.
Since I was previously assuming a negative offset, I had thought that increasing the scrub radius slightly, (to make it a small positive distance), might help steering feedback some. But, it seems like it'll just make the torque steer too strong.
Since I was previously assuming a negative offset, I had thought that increasing the scrub radius slightly, (to make it a small positive distance), might help steering feedback some. But, it seems like it'll just make the torque steer too strong.
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