more scrub radius

[Ervin]

I know scrub has been discussed many times but,,,,,,  Has anyone ever changed/improved thier handleing by changing the scrub radius?


   Thanks,  Ervin

[Glen]

Ask Sparky

[hotschue]

Correct scrub radius should prevent the front end from "hunting".  I incorporated 0 scrub with my new build through spindle modification and wheel offset, car tracked absolutely straight.   

[SPARKY]

ABSOLUTELY!!! 

[RICK]

I might have screwed up. I never measured or took into account 'scrub radius'. I took Mustang II spindles and put S-10 hubs on them with the rotor portion cut off. Later on I wanted front brakes, so I slid some Wilwood hat/rotors on top. Then to make things worse, I changed my spindles to, Two inch drop spindles,,, compounding some bad 'scrub radius'. And now that think about it,,,,,  My handleing seems to be deteriorating. What kind of 'scrub number' should I be looking for?

Sparky, What was yours? What did you change it to? How did you change it? And how much better did it make the car feel? At what speed?


         Thanks, ILLHANDELINRICK

[racergeo]

  I'll tell you Rick, I had improved handling from correcting my scrub. My front wheel drive car had WAY to much and I got to with in a 1/2 " and now it goes straight. So its well worth the effort!!!

[SPARKY]

I had 3.4" + and got it down to 3/8" + with special hubs and wheels.  It was a handfull before and not always controlable. Afterward 2 rookie drivers got AA lisc. with no handling issues at all.

[Blue]

So I'm reading here that less is better.  Although it's mechanically inconvenient, is negative scrub radius also bad?  is there a limit to how close to zero we need to get before it's "OK"?

[Peter Jack]

Generally the closest to 0" is best. Some small amount is probably not going to hurt. It will depend on the other alignment parameters and the vehicle itself.

Blue, in the case of tandem front wheels I think it's probably rather important that it be 0" because even if the offset is symmetrical the difference in distance from the center of the turning point could cause issues.

Pete

[racergeo]

 Peter,what would you say about a little negative scrub radius on a front wheel drive car?? I read that the FWD imports run neg. to help eliminate torque steer. I am talking about 1/2 to 3/4 of an inch. Any thoughts? thanks George PS FWD drag cars.

[SPARKY]

I think I recall Higginbotham telling me he got his inline car to really settle down when he eliminated some scrub radius issues---I only drove it after the fact---he said it loads in the trailer much easier now also.

[Peter Jack]

0" is best because it eliminates any steering effect caused by the offset. Negative may have less effect than positive simply because it is closer to the centerline of the car and may have less leverage. Have to do a little more thinking on that one. The problem comes when one wheel is loaded more than the other. At that point the heavier loaded wheel will affect the steering.

The real problem comes when there is some sort of side to side oscillation which will then cause the car to weave.

The interesting part of this whole thing is that negative offset will cause the car to go in the opposite direction to positive offset.

Pete

[SPARKY]

On my new wheels I have a slight amount of neg---MY GUESS at what tire growth will be---tire growth will move it toward zero at speed.

[SPARKY]

This month of Hot Rod has "Suspension Demystified"  has lots of good illustrations of various suspension terms!  Has some information also on how some interact with the others.  Thanks HR