wrightcomputing wrote:
If the car suddenly lose rear grip you may be bottoming out or binding the suspension. That would explain why steady stater cornering has a little understeer but heavy cornering the car gets loose. Does it do the same thing on left and right hand turns. Sometimes it is worth watching a video to see if the car reacts the same in both directions.
Personally I would not add a sway bar. Standard things to reduce mid corner oversteer include adding camber (Static or dynamic), add a little toe in, softening the rear springs/shocks, lowering the rear of the car or adding downforce. You can also do the opposite to the front if you run out of adjustment in the rear or it makes more sense. Stiffening the front will have a similar effect to softening the rear.
Other things to check.
-Make sure you have a good alignment
-Optimize the tire pressures, ideally checking the temps across the tire and adjust the setup until you have inside, center and outside of the tire within a couple of degrees.
-Make sure all suspension components are tight and have no play
-Check the condition of the tires if the rears are older or have more runs on them they may be past their best )try swapping front to rear).
I would say it is not sudden enough to be bind. You can feel it starting before it actually breaks free. I've had a car that bottomed out the front in bump so know it's pretty sudden. I know my lower link bolts are close to my frame; I'll double check them to be sure. Solid axle so camber/toe are fixed. Rear springs and shocks are as soft as viable already. So yeah, to quote Metallica "back to the front!"
-alignment. I have no idea where good is yet for this car. iirc I'm around 0.10" toe, -1° camber, 5°ish Caster. It feels/looks good so far (I am experienced with alignments)
-tire pressures. Yeah I was going to make a better effort to play with pressures to try and diagnose next event. It should be a good testing course as it's after the autoX 101 course so will contain textbook sweepers, slaloms, offset gates.
-I will double check for play/flex. Due for that anyhow
-tires should be equal
Driven5 wrote:
My first thoughts would be front vs rear roll stiffness, or roll oversteer caused by the anti-squat. Got any calcs that you might have done for either?
Honestly, it took me so long to build this car that I have forgotten damn near everything about it. I know I have a LOT of antisquat. I will poke through my notebooks and see if I can find any notes. Do you know where/how antisquat will show up when cornering? I know brake hop is an issue but so far so good. On throttle it's great. Grips and pulls out of the oversteer. In terms of roll stiffness, I'd say from feel it is possible the rear has very little. It does feel like the rear is rolling more at times. Specifically over humps around curves while on power.
turbo_bird wrote:
You've got a fairly big engine in your car. When I first started driving mine I had pretty much the same problem, turns out it was caused by a loose but on the steering wheel. The amount of engine braking was reducing how much rear cornering clearance I had when I'd come completely off the throttle in a corner. I figured out to keep a bit of throttle through the corner and I can keep my cornering speeds up now. It was a big adjustment from the other cars I had autocrossed, mostly gutless fwd stuff. I'd be interested to hear if you find another solution to the issue too, I'm not a good enough driver to figure that stuff out though, so I pretty much just drive around any handling issues.
Kristian
Coming from the same gutless FWD background, I considered that as well and definitely think it may be a factor. The S/C tends to slap the throttle-plate closed very fast so mine could even be worse. Did you notice it while trying to finesse the throttle around a sweeper as well? As in, noticing understeer so touch throttle to sort it out then reduce throttle and surprise oversteer? I have been dealing with a sticky throttle (off idle) which was a real struggle to drive yesterday. That is high priority to get sorted (and make sure my S/C valves are working). My driving skills are not up to this car yet, but my experienced friend didn't think it was from engine braking. Though I'm not sure he's driven a car with this engine/weight ratio before. I'll ask.
Thanks again for the input so far. It helps.