Suspension Geometry question, What cause a car to wander under heavy braking? Options

[nine14cats]

I have a question for the suspension gurus out there. I am experiencing some wandering in my car during heavy braking out of high speed sections into sharp corners. Visualize turn 7 at Sears, turn 14 (CCW) at Thunderhill, turn 2 at Laguna Seca. When I get on the brakes hard, the car wanders and "twitches" a bit. The car doesn't jump and it's not out of control, but it keeps you busy, busier than I'd like. I'd like to refine the car to not exhibit this trait.

My thought (and others) is that under heavy braking the front squats and the toe out becomes excessive, allowing the car to follow the undulations in the track pavement.

What are possible causes of this as the front suspension goes through it's travel?

One possibility could be linked to my front strut steering arms on my car. I have coil over RSR style struts with "custom" bends in the arms. The shop that built the car put a custom bend in the arms when they fabricated the raised spindle. Can a non uniform bend to the arms contribute to excessive toe out under hard braking?

Thanks,

Bill P.

[smdubovsky]

Bill, if this is in the 911 - its something I know (a little) about. Its rear toe change. When the ass end lifts under braking it will start toeing out. I believe lowered cars make it worse. If you start w/ very little toe, it will eventually get to zero or even full toe out. My 911 will move 1 car width side to side under heavy braking over the bumps. Not uncontrollable but 'busier' than you like. Rear monoballs helped. I think the ultimate solution is to relocate the pickup points w/ boxes like smartracing sells and the 935-type rear spring plates (but I haven't done that yet). You can play w/ geometry more and it eliminates all compliance.

SMD

[nine14cats]

Bill, if this is in the 911 - its something I know (a little) about. Its rear toe change. When the ass end lifts under braking it will start toeing out. I believe lowered cars make it worse. If you start w/ very little toe, it will eventually get to zero or even full toe out. My 911 will move 1 car width side to side under heavy braking over the bumps. Not uncontrollable but 'busier' than you like. Rear monoballs helped. I think the ultimate solution is to relocate the pickup points w/ boxes like smartracing sells and the 935-type rear spring plates (but I haven't done that yet). You can play w/ geometry more and it eliminates all compliance.

SMD

When we get it up on the rack we'll have to take the car through it's suspension settngs. On Fritz (our 911 track car) we have RSR coil overs all around. In back I have the ERP 935 adjustable spring plates and Smart Racing Products 930 to 911 chassis Rear Control Arm Pivot Boxes. I also have 930 swing arms. But I can't recall if the inner control arm bushings are monoballs or not. They probably are, since the previous owner put this stuff on, but you never know.

I'm not moving over a car width under heavy braking, but it's busy. I'll probably run the car as is through August and maybe until the end of September depending on what events I run. this winter, I plan on a few upgrades such as checking the toe settings, monoballs in the rear if I don't have them on the control arms, and maybe popping for the adjustable Smart Racing Shocks. And while I'm in there...maybe I should put that ERP front suspension that was earmarked for The Beast into Fritz.....

Someone hold me back..... (IMG:style_emoticons/default/slap.gif)

Bill P.