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Wow, that is worse than I have seen -- although the corner does look like it is significantly off camber. It looks like you bounced the brakes - on hard, off, back on semi-hard, and then off as the car entered the off-camber section. It looks like it started to rotate when the brakes were applied the second time. Does this sound right, and/or do you think that contributed?
No, I was trail braking a tad prior but was off them completely and on SLIGHT maintenance when it let go. I almost think if I had been harder on the throttle it would have weighted the rear enough to prevent.
Corner is off camber but not as bad as it looks on video. Of course it was a combination of factors but poor alignment was the real culprit. I was on the brakes hard prior as it was a blind corner and I didn't know if there was going to be a cow or car on the other side of it.
A number of pros have analyzed the event and agree it wasn't induced by driver error.
Only good part is it resulted in only cosmetic damage. Nothing mechanical was damaged.
I hope this video post doesn't take off and detract away from the intent of this thread which is about setting up the car properly...
Mike, if you read this you might confirm my comments and/or offer your thoughts.
No, I was trail braking a tad prior but was off them completely and on SLIGHT maintenance when it let go. I almost think if I had been harder on the throttle it would have weighted the rear enough to prevent.
Corner is off camber but not as bad as it looks on video. Of course it was a combination of factors but poor alignment was the real culprit. I was on the brakes hard prior as it was a blind corner and I didn't know if there was going to be a cow or car on the other side of it.
A number of pros have analyzed the event and agree it wasn't induced by driver error.
Only good part is it resulted in only cosmetic damage. Nothing mechanical was damaged.
I hope this video post doesn't take off and detract away from the intent of this thread which is about setting up the car properly...
Mike, if you read this you might confirm my comments and/or offer your thoughts.
Rick
Was not a criticism - the brake input was subtle I was just wondering how you felt about it. It definitely did rotate abruptly.
Was not a criticism - the brake input was subtle I was just wondering how you felt about it. It definitely did rotate abruptly.
I did not take your post as negative or critical in any way at all. Very valid question and a good observation. These types of comments are what helps everybody. I get frustrated with the people who post saying that's what you get for driving over 65 mph.
Rick,
I agree... you did nothing wrong to cause such a response.
I don't have any videos, but this is the same sort of thing that happens to me
on an autocross with my Z51. A little too strong coming out of a corner, and spin city.
I agree that was totally unexpected from what I see in the video. However, I have never had that happen where I wasn't the cause of the spin or there wasn't something lubricating the surface. It is hard to believe a change of rear toe would cause that much loss of rear grip. Especially at a speed that doesn't look like it challenged the road surface or the tires. Even the curve looks fairly benign. Your entry speed into the curve wasn't all that high and plenty of us have done similar things without a butt cinching moment like that. The light tap on the brakes just scrubbed off some speed and shifted some weight forward giving a little more grip on the front tires but I can't see that causing the car to pivot like it did. Could something else have caused that to happen? Did a control arm cam slip? What kind of road surface was it? One of those low cost tar and stone type of surfaces?
I feel ya. My first trip to the track in my C7Z on cold tires and the factory alignment. I lost it exiting pit lane and put it in the tire wall backwards. Right in front of the track motorsports manager and many of my instructor colleagues. Trust me, it snapped so quick there was no catching it.
I agree that was totally unexpected from what I see in the video. However, I have never had that happen where I wasn't the cause of the spin or there wasn't something lubricating the surface. It is hard to believe a change of rear toe would cause that much loss of rear grip. Especially at a speed that doesn't look like it challenged the road surface or the tires. Even the curve looks fairly benign. Your entry speed into the curve wasn't all that high and plenty of us have done similar things without a butt cinching moment like that. The light tap on the brakes just scrubbed off some speed and shifted some weight forward giving a little more grip on the front tires but I can't see that causing the car to pivot like it did. Could something else have caused that to happen? Did a control arm cam slip? What kind of road surface was it? One of those low cost tar and stone type of surfaces?
Bill
Bill,
Knowing you track your car I want to make sure I'm communicating the issue with these cars is improper rear caster setting from the factory.
I agree, positive, negative or zero toe would be a mostly insignificant contributing cause of the snap oversteer I experienced.
The main contributing factor was IMPROPER REAR CASTER. This is also the main lesson to be learned from this thread
Go back and reread Mike's/DSC post about how the engineers screwed the pooch on their factory setup/alignment. As Mike states he doesn't understand what they were dreaming of and they got the geometry wrong. I'm not smart enough to make that statement with conviction but I'm confident Mike is. GM should hire him but I don't think they could afford him.
Remember the Road and Track test with Randy Pobst at I think Big Willow where he said something was wrong with the car? He said he couldn't, and wouldn''t, drive the car as he was scared of wrecking it due to a twitchy rear end? GM was there and checked it out and said the rear caster was all out of whack. They set it and I believe he ran some pretty good laps and said it wasn't the same car. Someone correct me if my memory is wrong. I do know this is what Randy told me directly.
I'd say the reason this is not discussed in forum discussions is maybe only 10% of owners drive the car in a manner that would "allow" them the opportunity to experience this phenomena. Setup doesn't matter to 90% of owners due to the way they use their cars. All I can imagine is "most" of these 90%'s are more concerned with getting maximum tire life instead of performance. As such, the factory sets it up for these people. These are the guys who are surprised when I tell them I'm thrilled if I get 5,000 miles out of a set of tires. They think I'm nuts.
Looks like you drove through an oil slick on the road at 17s which might have lost your traction as you turned into the bend a second or two later.
Guys, I parked the car down the road and walked back to the turn. I spent a good period of time there checking out every aspect of the road looking for an explanation to what happened. My thoughts before walking back to check it out was someone oiled the road and I just didn't see it. It wasn't.
As much as I'd like to blame the surface I can't. There wasn't nuthin' there. No oil, gravel, lane paint, etc. It is definitely off camber enough that it was a contributing factor but not near the top of the list.
That's pretty crazy. What driving/PTM mode were you in?
**nevermind. Sport 2. So no active handling.
It gave you a small hint of oversteer...a couple of degrees kind of slowly at first. Then it snapped and was gone. I've only experienced that on freshly paved asphalt in an autocross. It was like ice skating. Every spin was a 360.
Last edited by spearfish25; 08-05-2016 at 08:36 PM.
PTM can't really save this because there was very little throttle application.
The 5 PTM modes all have varying factors such as suspension damping, traction control and active handling. In Sport 2, dampers are on track and active handling is off.
Ok frame by frame in the video, the right side painted white line is intermittent right where you spin. Was there gravel or dirt on the road side there? Your right tires are on the line it looks like but tough to judge the true width from video.
Knowing you track your car I want to make sure I'm communicating the issue with these cars is improper rear caster setting from the factory.
I agree, positive, negative or zero toe would be a mostly insignificant contributing cause of the snap oversteer I experienced.
The main contributing factor was IMPROPER REAR CASTER. This is also the main lesson to be learned from this thread
Go back and reread Mike's/DSC post about how the engineers screwed the pooch on their factory setup/alignment. As Mike states he doesn't understand what they were dreaming of and they got the geometry wrong. I'm not smart enough to make that statement with conviction but I'm confident Mike is. GM should hire him but I don't think they could afford him.
Remember the Road and Track test with Randy Pobst at I think Big Willow where he said something was wrong with the car? He said he couldn't, and wouldn''t, drive the car as he was scared of wrecking it due to a twitchy rear end? GM was there and checked it out and said the rear caster was all out of whack. They set it and I believe he ran some pretty good laps and said it wasn't the same car. Someone correct me if my memory is wrong. I do know this is what Randy told me directly.
I'd say the reason this is not discussed in forum discussions is maybe only 10% of owners drive the car in a manner that would "allow" them the opportunity to experience this phenomena. Setup doesn't matter to 90% of owners due to the way they use their cars. All I can imagine is "most" of these 90%'s are more concerned with getting maximum tire life instead of performance. As such, the factory sets it up for these people. These are the guys who are surprised when I tell them I'm thrilled if I get 5,000 miles out of a set of tires. They think I'm nuts.
Rick
Rick,
I have no idea what the rear caster is on my car at this time. The track alignment was done except for the caster since none of the dealers in the area had the proper equipment. Since then I obtained the tools but haven't had a chance to get it on a rack to check it.So far I haven't had any indications of a snap oversteer. Compared to my C6Z the backend of the car is planted.
Something else I saw at the 24 second mark of the spin video. Look at what's painted on the tree directly in front of the car right below the PDR display of 1 mph. Not a "direct" contributing factor but definitely some bad juju.
Me thinks mine was not the first time there's been something bad happen at this corner.....
Not necessarily anything similar to my event. Hell, could have been an incident where some drunk just drove through the turn. Never the less, that's some bad chit.
OK, now that's creepy. The boogyman gave your rear end a flick at that corner. I wonder what that guy was driving if a Z06 moving at a good clip didn't make it to that tree.
Last edited by spearfish25; 08-05-2016 at 09:38 PM.
Rick,
I have no idea what the rear caster is on my car at this time. The track alignment was done except for the caster since none of the dealers in the area had the proper equipment. Since then I obtained the tools but haven't had a chance to get it on a rack to check it.So far I haven't had any indications of a snap oversteer. Compared to my C6Z the backend of the car is planted.
Bill
Luckily I'm in the same position as you Bill. I had the track alignment done, except for rear caster, prior to my first HPDE with the car, and the rear just feels so planted. I can really get into the throttle even in Sport 2 without the car snapping around. Granted I tend to run in a higher gear than many others here to control temps, (mine's an A8), so I can only guess that I have a car with somewhat accurate rear caster from the factory.
Also my car is a Z07, so perhaps the stiffer spring rates also help?
How will this affect daily driving and tire wear? Or is this set up just for track use?
I have a couple race cars so I use my car mostly on the street. I too am concerned about tire wear and asked Mike/DSC Sport to comment. His response:
"Nah, with the stability you gain in the back you'll not use up the front tires any more than with the factory alignment. Plus, negative toe helps a lot. If you keep the dampers soft with DSC its all the better. Car handles too good with this setup to mess with it. I'll not change mine"
08-05-2016, 04:55 PM
