Classic Audi » Audi Sport / Competition » Rally chat » URQ rear axle caster setting.

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Old 10-02-18, 04:18 PM   #1
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Join Date: Oct 2010
Location: Vesterlyng/Föllenslev, Denmark
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Default URQ rear axle caster setting.

In the FIA homologation 671 documentation there is a picture 35 showing a wishbone with altered caster setting.

IIRC OEM caster is 1.25 and I suspect the illustrated wishbone modifies caster to 2.65 as on the Sport quattro.

Increasing caster on front axle will provide stability and to some extend improve handling at low speed on tarmac (I am told)...

However... A dude I know have also increaced caster on the rear to the extend that the rear wheel have a noticeable offset towards the rear of the car.

Front axle is positive caster, rear axle is negative caster.

I have been looking into what effect it would have on Toe-In/Out as a result of the increased caster on the rear. Increased negative caster with the control rod being offset to the wishbone pivot line produces "Toe-Out Steering" and should increase oversteer. Functionality is quite similar to "Bump Steer".

Now, this is a 1982 Quattro, 75 mm bearing housing which means the control rod is mounted in the pivot live on the underside of the subframe. Had it been a 1983 the car would have 82 mm bearing housings with the control rod mounted on the back edge of the subframe.

No matter how I look at it I stuggle to produce a caster trail big enough to have effect on Toe-In/Out...

Any of you guys out there got experience with this?
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