track growth

[BRETT GRIFFITHS]

when setting up a-arm suspension how critical is it to stop your track width from altering as the arms cycle from top to bottom and what amount is acceptable

[therail]

I don't believe it's possible to stop the track width from changing during the cycling of an a-arm setup. The way to minimize it is with longer arms and to keep them as close to parallel to the ground as possible.

[scottm]

Thats called tire scrub, and you can control it to some extent. Watch your dezert people videos carefully and you will notice puffs of dust blowing out sideways from the front tires of some vehicles. Some have 3-4 inches of scrub per side, which is excessive. That horizontal push is hard on tires and suspension, and causes a squirrely feel similar to bump steer. It is affected by upper arm angle and length, and upright (spindle) hieght, and coincides with proper camber. You want 0-2° negative camber at ride height, and 5°+ negative at full bump and again at full droop. The changing camber reduces horizontal movement of the tire contact patch, reducing scrub. And proper negative camber in bump is crucial for proper cornering - ever notice in pictures how most dez race vehicles the tires lean out in corners? The tread rolls under, putting cornering forces on the sidewall of the tire. Obviously thats bad for many reasons, yet many, if not most desert vehicles do it. The secret (not a secret to racers outside of dezert) is to shorten the upper arm a little and lower the inboard pivot (or raise the outboard pivot) until you get enough negative camber at bump and droop.