Car actively trying to swap ends on track?

[RussMcB]

Here's a quick, free thing you can do. Are you familiar with checking toe alignment using strings? It is often done by using four jack stands to create a rectangle around the car. The two side strings should be parallel with the car's centerline. Then you can measure the distances between the string and the front and rear of the rims. By comparing the gaps you should be able to tell if a rear wheel is excessively toed in or out.

This method is very good at identifying a single rear wheel that is out of alignment.

An easier, quicker (and much less accurate) method I often do is to tie a string end to something on the rear of the car, like a tail pipe, then pull it around to the side of the car, touching the rear tire's rear sidewall and the rear tire's front sidewall, then seeing where it is relative to, say, the "ZR-1" badge on the front fender. If it is a foot away from the car, that rear tire has a ton of toe out. If the string hits the middle of the door, that rear tire has a lot of toe in.

Hope that makes sense. maybe I could make a drawing or find something on the web to better describe it. Maybe Google "sting alignment".


https://www.hotrod.com/articles/ctrp...ring-your-car/

[d15b7]

hi again! Mark is asking really good questions. I'm leaning more and more towards 'broken or failing suspension component combined with alignment way out of wack'.

on a previous racecar I had a lower control arm bushing disintegrate during a race and the toe would radically change during braking and acceleration and the car became almost totally undrivable near the end of the race. I wrestled/limped it to the checkered flag but the last 3 laps were hair raising. visually looking at the car after the race revealed nothing, but once I got it home and up on stands and prying on the suspension and control arms revealed a totally failed lower control arm bushing which allowed tons of movement of the wheel during braking and acceleration allowing that wheel to toe in and out radically.

look carefully with the car up on a rack and pull/push/pry very hard on all components. and of course check the alignment too. good luck man!

[cbaclawski]

Originally Posted by Vette Guy

Puzzling, but we’ll get there! Does the car roll in corners or does it remain fairly stiff? Do you get any sensation of weight transfer as you add power through turns? Or can you not add enough power? By chance, does your shifter jump up in the console?
Wondering if C-Beam is flexing at attachment points, binding in control arms or issue with sway bar mismatch/end link issue.


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Very little roll, better there than I expected, and can definitely feel the weight transfer, though it's slight due to light throttle...


The shifter feels great, Best feeling shifter I have...

[cbaclawski]

Originally Posted by RussMcB

Here's a quick, free thing you can do. Are you familiar with checking toe alignment using strings? It is often done by using four jack stands to create a rectangle around the car. The two side strings should be parallel with the car's centerline. Then you can measure the distances between the string and the front and rear of the rims. By comparing the gaps you should be able to tell if a rear wheel is excessively toed in or out.

This method is very good at identifying a single rear wheel that is out of alignment.

An easier, quicker (and much less accurate) method I often do is to tie a string end to something on the rear of the car, like a tail pipe, then pull it around to the side of the car, touching the rear tire's rear sidewall and the rear tire's front sidewall, then seeing where it is relative to, say, the "ZR-1" badge on the front fender. If it is a foot away from the car, that rear tire has a ton of toe out. If the string hits the middle of the door, that rear tire has a lot of toe in.

Hope that makes sense. maybe I could make a drawing or find something on the web to better describe it. Maybe Google "sting alignment".


https://www.hotrod.com/articles/ctrp...ring-your-car/

I'm somewhat familiar with the string alignment, and I might just do that just to see if there is an obvious issue. I have to get a new front tire mounted anyway, so was planning to have a professional alignment done at the same time, using the spec chart you posted...

Originally Posted by d15b7

hi again! Mark is asking really good questions. I'm leaning more and more towards 'broken or failing suspension component combined with alignment way out of wack'.

on a previous racecar I had a lower control arm bushing disintegrate during a race and the toe would radically change during braking and acceleration and the car became almost totally undrivable near the end of the race. I wrestled/limped it to the checkered flag but the last 3 laps were hair raising. visually looking at the car after the race revealed nothing, but once I got it home and up on stands and prying on the suspension and control arms revealed a totally failed lower control arm bushing which allowed tons of movement of the wheel during braking and acceleration allowing that wheel to toe in and out radically.

look carefully with the car up on a rack and pull/push/pry very hard on all components. and of course check the alignment too. good luck man!

"almost undriveable" sounds about right. I thoroughly teched the car and pulled by hand on the components, but just to check for obvious looseness, I didn't really "pry" or pull that hard...


I have a set of quickjacks so it'll be relatively easy to go over it more thoroughly...




Thanks to all, I really want to enjoy this car on track, and have invested a lot to do so. It is much appreciated

[cbaclawski]

So I had to get a tire replaced anyway, and while it was there I had them do an alignment. Not a race shop, so all they could do is try to get back to factory specs, but at least I could get a read on what it was.

Before:

Left Front +.01deg camber +7.0 caster -.04deg toe
right front +.01 camber +6.7 caster -.04deg toe
left rear 0.0 camber -0.37deg toe
right rear -0.7 camber +0.12deg toe
rear total toe/thrust angle -0.25deg

after:
LF +0.1 camber +5.9 caster -0.03 toe
RF +0.2 camber +5.7 caster -0.05 toe
LR +0.2 camber +0.07deg toe
RR +0.0 camber +0.06deg toe
rear total toe 0.12deg thrust angle 0.01deg

Not an alignment guru by any means, and clearly the "after" is not the ideal track alignment, but are the "before" #'s bad enough to account for my handling issues??

[RussMcB]

I notice you had some toe out on one rear tire. That's not good, but maybe not enough to cause bad handling. It will (or did) mean your car was "crabbing" slightly down the road. Probably not enough to notice.

I wonder if they were able to check for looseness that wouldn't show up in a simple, static alignment. For instance, (as mentioned by folks earlier), the problem could be bad bushings or C Beam allowing the rear alignment to go out of whack when power is applied, and when the suspension gets loaded when you start to turn in.

Do you have a suction cup Go-Pro mount you can put your camera facing a rear wheel and see if it does something crazy? Can you make it happen in an isolated parking lot or road?

I notice you have slight positive camber. That seems odd. But, if they are putting it to specs, I guess that's within range.

[RussMcB]

Originally Posted by RussMcB

Do you have a suction cup Go-Pro mount you can put your camera facing a rear wheel and see if it does something crazy? Can you make it happen in an isolated parking lot or road?

This suggestion came from my thought process whenever I have a problem I'm trying to figure out:
1. Can I reproduce the problem, predictably?
2. Can I gather some kind of data when it's happening to give me clues about the cause?

Maybe that will spark some thoughts.

It's often a challenge when you have a problem at the race track and need to diagnose it at home (or on public roads).

[cbaclawski]

Originally Posted by RussMcB

I notice you had some toe out on one rear tire. That's not good, but maybe not enough to cause bad handling. It will (or did) mean your car was "crabbing" slightly down the road. Probably not enough to notice.

I wonder if they were able to check for looseness that wouldn't show up in a simple, static alignment. For instance, (as mentioned by folks earlier), the problem could be bad bushings or C Beam allowing the rear alignment to go out of whack when power is applied, and when the suspension gets loaded when you start to turn in.

Do you have a suction cup Go-Pro mount you can put your camera facing a rear wheel and see if it does something crazy? Can you make it happen in an isolated parking lot or road?

I notice you have slight positive camber. That seems odd. But, if they are putting it to specs, I guess that's within range.

Yeah don't like the positive camber. On the rear toe, had toe out on one side(driver) and toe in on the other, which I interpret to mean that the wheels were pointed, albeit slightly, to the driver side. Considering that the majority of the loose back manifested in right handers, with the back coming out towards the driver's side, It kinda makes sense, I just don't know if it was enough to matter that much. Next step is to get it up in the air at home to check the bushings/beams...


Thanks,


Curt

[cbaclawski]

Originally Posted by RussMcB

This suggestion came from my thought process whenever I have a problem I'm trying to figure out:
1. Can I reproduce the problem, predictably?
2. Can I gather some kind of data when it's happening to give me clues about the cause?

Maybe that will spark some thoughts.

It's often a challenge when you have a problem at the race track and need to diagnose it at home (or on public roads).

I do have a camera I can attach if it comes to that, but there is really no data I can think of as it happens pretty much anytime the car is turning, more exaggerated in right hand turns (which is most of them when running clockwise)


You are totally right about being hard to diagnose track issues at home or on the roads. There really isn't anywhere I can simulate track conditions safely on the road, at least around here. I'd love to go test out the changed alignment and see if that helped, and if so, fine tune it some more. Short of a track day I just cant. Also, I have a TT event this coming weekend in the e46, so I'm spending most of my time teching/readying that car. Next event I have is June 23 weekend, and wasn't planning on bringing the Z, so it might be 2 months before I can even see if I'm on the right track.


Thanks again,


Curt

[Vette Guy]

Agree with Russ, as I don’t think it was enough to cause bad handling. That said, prior to running C-Beam plates (run them on all my cars) the back end would kick out to one side (I just can’t recall which side) when I spun tires. Again, doubt this is the cause, but could contribute to it.

A ‘96 GS ended touring laps at the Gathering this past weekend after encountering the same problem... he was running Sumis. Add the possibility of tires to the list, particularly as they were 315 rears. Doubt he had the track experience you have though.

The puzzle continues....


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