Dennis K

Interesting . . . I thought the roll center would not only be above ground, it'd be above the C of G (your hanging roller coaster example).

Also those NASCAR boys change the rear roll center height during pitstops by adjusting the height of the Panhard bar connection. A lot of crafty engineering goes into those stock cars.

mark kibort

Along this thread, i was really concerned with the suspension angles when i lowered my street 928 and started calling it a race car. its so low, the tie rods just sitting there, are at 20degree angles! however, i talked myself out of thinking i had a problem as i figured my only problem was the inside tire, which would then be at a funky toe and camber based on the roll of the car and droop of the wheel on the inside, but since it was barely touching, i thought that at worst it would be scrubbing while the outside tire did all the control and steering. I havent seen too much tire wear and it seems to be handling well, except for a nasty push lately turing 70mph turns

Good stuff. really interesting about the roll center attributes. good puzzle!

MK

SundayDriver

Thanks. Sounds like your car is in pretty good shape - most cars take lowering without too much suspension upset but with a lot of height change and certain suspension designs, it can go crazy.

The first thing is bump steer, but that is fairly easy to fix. Camber gain can be way off and it is hard to fix unless you are able to change suspension pickup points. Finally you are changing the roll centers - it gets really weird if they move through bround or wander much side-to-side. That is really hard to fix.

The point is that the suspension is being operated in a travel region where it was never intended to operate. Tie rods, at an extreme angle, are messing with bump steer and can be dealt with. If the suspension parts (A arms, struts, etc) have had big changes in angle, it is much harder to fix.

mark kibort

Thanks! not any huge problems yet, but id say the biggest issue is all the rubber stock bushings i still have vs real race cars with h-joints. Im not too worried about my disparate camber and toe (and its substantial) on the droop wheel (inside turn side) as i said, i think my only draw back here is tire scrub on the inside edge of the inside tire. (at willow springs, probalby due to turn 8-9, i remember one day roasting the inside tire to the cords on the inside edge, where usually i get a few weekends out of a set) One interesting problem that hasnt been a real problem yet, is that part of my suspension is the bump stops. i smack them down the corkscrew, but fortunately, they get unloaded just enough before i start to turn so that i dont have the push associated with such an event.

i think Ive been lucky on most of the set up issues that would yeild most other cars undrivable. as the car gets a little faster, im sure im going to grow out of a lot of my set up configurations and its going to cost $$$ to get it back in line.

Mark