taken19

Hey guys,

At the track yesterday I struggled with traction/ AH issues all day. Here's a quick rundown.

Last month ran my best times with used R6's (3-4 heat cycles on them). The very next track day, AH was engaging in EVERY turn (yes I know most of you run with AH off, but I'm not ready for that quite yet). It engaged at turn in and worked to control the car through the entire turn, past track out. The car didn't feel like it was pushing at all, just "sloppy" if you will. My turn in speeds were 5-10% slower than normal and AH still engaged. The front tires seemed to lock up (ABS engaged) sooner than normal as well.

The only thing different between the two track days is a pFadt camber kit. Previous day front camber at -2.5, yesterday I started at -3.3. During the day I dropped to -3.0, then -2.7 with no significant change. Pyrometer readings showed inside of tire 10-20F hotter than outside, this trend decreased as camber was reduced. Car currently has pFadt poly bushings DRM Bilstiens and stock Z51 springs (2005 Z51 M6 car).

The tires are still soft (can push my fingernail into them). They have about 13-15 total heat cycles on them now. Could they be heat cycled out? They aren't corded and 3 of 4 haven't even worn down to the grooves yet. I'm struggling to figure out what may have changed to make such a significant change. My times yesterday were 4 sec slower than last track day, same weather conditions. As the sessions progressed I was losing 1-2 seconds on my laps per session.

I will inspect the front and rear suspension to look for something out of whack or broken. The only things I can think of are heat cycled tires, something in the suspension is broken, worn/damaged/broken spring, wheel sensor going flakey (but no AH/TC/ABS messages). I did notice my PS pump leaking at the shaft seal, but it's not bad at all and I can't imagine that causing the issues. It's only a few drops per session and the steering feels smooth and predictable (reservoir still has plenty of fluid).

Thoughts?

JDIllon

Where did you run yesterday?? If you ran Sebring? It was very slippery. I caught the car several times in the morning. I talked to a couple of other instructors. And they said the same thing, turns 3,5 10 were particularly bad. ?????????? JD

taken19

Ran at Homestead. Nobody else complained about grip. My old instructor on Nitto Invo's was out cornering me on R6's! Last track day I destroyed him. He has a C6Z with 590 rwhp to my 407 and I put a half lap on him in 15 min during the last track day. Yesterday, I could only hold him off for 2 laps and I think he was being generous. He shouldn't be able to keep up with me in the corners on street tires...

Could a damaged stock spring or sway bay end link do that? I'm gonna take a look this morning for anything obvious.

sperkins

Yeah tires fall off, but not 4 seconds a lap (unless your car really sucks or is literally bone stock).

You said the only difference was the camber kit like it shouldn't be that big of a deal, but it's actually a huge deal if everything wasn't set back up properly.

Are you adjusting for toe after changing your camber? That's a alot of work to be doing at the track and get it right.

taken19

Motor is stock, but I'm slowly getting brakes and suspension up to snuff. What really bothers me is the last session of the last track day the car ran a 1:43 and I think it had another 1-2 seconds in it. Very first session yesterday the best I could do was 1:47. Fell off to 1:50 by the end of the day.

Yes, I did adjust toe. I can usually dial it in with 2-3 iterations - measure, adjust, drive car around to settle suspension and measure again. And believe me, I used every bit of the hour I had between sessions. I set toe to 1/32" toe out before I went back out there. I even went from -1/8" to -3/16 toe in rear to see if it would help.

Another thought... Could the camber kit have drastically impacted caster or bump steer? I'm pretty weak on how both of those work but I haven't heard the camber kit affecting those negatively. I guess I can put the wheels back on and measure all three and post up results for opinion.

msracing

Sean ,, the track grip felt pretty good for me and the vette .. even in turn one were i saw a 911 spill some oil all the way thru 3.. but after a few laps it cleared up.. ,, i did take out my buddy's GTR after lunch and notice that you were a little slow coming off the corners.. ..the GTR was also loose in the rear and it was also on r6 also.. the front of the grt was awesome but the rear felt like the tires just gave up... maybe something to do with the r6 homestead..

well it still was a great day....

Manny

taken19

Manny, thanks for chiming in. It was a victory for me because the motor held together for the first time since March and I got home with all body panels intact. I'm really struggling to figure out what is so different here. I've never had the AH kick in at turn in unless I made a serious mistake. I was doing my warmup laps and AH was still engaging. I had to slow down SIGNIFICANTLY at turn in to avoid AH, slower than if I was on street tires. There's no way a C6Z on Invo's should be eating my rear bumper in the corners. I was crushing him in the corners last month and literally one session later I was getting hammered.

The thing that suprises me is that is was engaged the entire turn, not just for a second to correct a mistake. In addition, I can usually feel the car sliding before I feel AH, especially in comp mode. Yesterday the AH would engage before I felt anything with the car - strange. the front end did feel a little sloppy, almost like the sidewalls were flexing more than normal. It took a bit more than normal for the car to set in the corner. Tire pressures were set for 38 psi hot (26-27 cold). As the tires heated up, it made no change in the way the car or AH behaved.

Something is definately not right. I looked at the suspension, nothing it rattling, missing or broken. There's no leaks on the shocks. The only thing I found was steering fluid on the spring and undercarriage (which I expected since the pump shaft seal is leaking a bit). Pyromoter temps were showing me hotter inside tire temps than outside so I kept lowering camber to counteract. It helped but didn't completely correct it, I was still 10-12F hotter in the inside with -2.5 camber.

geerookie

By itself, not really.

But, I've never seen a Corvette C5 or C6 get -3.3 degrees of camber without it being significantly lowered! Unless it is -3.3 on one side and -1.0 because the frame is bent or someone missed the pins when they mounted the cradle.
And lowering a Corvette enough to get those kind of numbers will have an impact on the bump steer and the camber gain and usually not in a good way.

As far as caster, who cares. These cars work well with anything between 4 and 8 degrees of caster and I'm sure you didn't change it that much. And if you had one side significantly off from the other you would have complained about a bad pull on the straights or under braking.

taken19

Car is lowered all the way on stock bolts, has been for over a year. I don't think that would be a significant contributor especially since that didn't change between events. Camber was -3.2 and -3.3 (left/right) to start and ended at -2.7 and -2.8 by the end of the day. I always try to keep them within 0.1 of each other.

To my knowledge, bump steer can be felt like bottoming out on something. This wasn't that feeling. It just felt a bit "floaty" on the front end, almost like going from thick sidewall runflats to non-runflats. I tried to keep everything else the same... tire pressure, toe, etc.

taken19

Some pics of the tires. They were all worn equally before yesterday. Fronts were just a bit more worn on the outsdie edge, just as you would expect.



Front tires. Worn pretty even.


Front inner wear pattern. Same on both sides.


Front outside wear pattern. Same on both sides.





Rear outside tire (right)-left handed track. Right tires take most of the abuse. Old camber setting was -1.6, this was -1.9. Both had -1/8 to -3/16 toe.

Outside wear pattern of above tire

Inside wear pattern



Rear INSIDE (left) tire. To my untrained eye, it looks like too much negative camber here, but it was within 0.1 of the outside tire. Significantly more wear on the inside.

Outside edge of above tire

Inside edge of above tire



It didn't feel like the rears were giving me any trouble, but the wear is different between the two. What gives?

froggy47

Don't take this the wrong way, but it takes me 4-6 hours to do my alignment correctly in my garage with slip plates smart camber & strings.

Maybe if you had a very competent helper you could do a good job in an hour, maybe.

Check your alignment once again at home & verify. I would suggest ZERO toe in the front, I toe out a bit for autox but never for track.

2.9 to 3.1 is a nice neg camber, varies with the track.

Camber kit should not affect bump steer, bump steer is a result of raise/lower ride height.

Caster doesn't matter much as geerookie said.

I think you are chasing your tail (like many NASCAR crew chiefs) doing all these rushed & on the fly adjustments.

The only thing I adjust at track is rear toe (sometimes).

Use a durometer & a probe pyrometer (not infared) if you are going to do this.


2 cents.

taken19

Good input. My first alignment took 6-7 hours. I have experimented with the camber kit over a couple days to see what different shims do. pFadt instructions say 1 mm is about 0.2 camber and they are right on the money. So here is what I did between sessions - tire off, loosen upper control arm stud bolts, slip in a spacer (1.75 mm was 0.3-0.4 camber change), take a rough guess ad toe and adjust (used 5 flats to start). Set car down, drive around and measure caster to confirm expected change (was accurate) and toe to see where I was at (got to within 3/32"). from there, it was a matter of a couple quick toe adjustments with drive in between to get toe where I want it. The camber kit takes all the guess and finesse out of camber adjustment - the eccentrics can slip while torquing, shims do not. Camber is right on the first time.

One hour is plenty of time for camber adjust (20 min) and 2-3 toe adjusts.

I only adjusted on the fly yesterday because I was have AH problems, which tells me that the car wasn't seeing what it was expecting and trying to correct. This only comes when the steering input doesn't match yaw of the car. Since I didn't feel the front slide or slip, I figured it was the front (that, coupled with the sloppy feel of the front end).

Could a leaking steering pump seal have anything to do with this? steering felt controllable and consistent. Im reaching for something to explain this.

froggy47

No it's not a small leak from the steering pump. I would still guess toe was off somewhere. The camber kit IS very accurate, I agree.

On my car I will spend a lot of time chasing .1 of a degree or 1/32 inch, I try to go to 1/64 but it's hard to read the lines that fine. Once I am done, it's spot on.

Best of luck sorting this out.

Is your tire height correct with rears being 1/2 to 3/4 taller (If I recall correctly - check the stock tire stagger to confirm)

taken19

OK so tires back on the car, drove around town for 10 minutes aiming for road imperfections to settle in the suspension and measured. Here's what I got...

Camber
Front Left -2.5
Front Right -2.6
Rear left -1.9
Rear right -1.9

Toe
Front 1/32" out
Rear 3/16' in

Right where I left it!

Now I did a castor measurement. I read to turn wheels 20 degrees both ways and measure camber each time. Here are the results...

20* left
Front Left +2.2
Front Right -5.1

20* right
Front left -5.1
Front right +2.3

total difference of 7.3 left and 7.4 right. I read to multiply by 1.4??? That would make 10+ on both sides!!! Am I doing something wrong?

taken19

No it's not the tire stagger. My last set of tires I had that issue (275 front/305 rear) and it would trigger AH/TC warnings at high speed (over 95 mph) in a straight line. This new issue is turns only. Turning TC off solves that problem. I tried running with TC off yesterday just to see if it made a difference - no changes.

geerookie

As I reread this thread I think I may know what is going on. I'm not sure but I'm going to take a big swing at it.......
I still know that by lowering your car as much as you have you will have issues with bump steer and camber gain but if you have been driving it this way and it now seems worse since you added the camber kit and did all this alignment testing I think I know where to look for the issue.

It's probably one of two things or a some skewed version of both.
The first is while you were doing all your toe adjustments and checking I'm guessing you haven't checked your thrust angle.
My guess is it is off and that will cause the car to "crab" as it goes down the track and will cause it to act and feel funny in one turn direction but not the other or maybe worse in one and fine in the other.

Then add GM's AH to the equation and you have another issue. The steering system has a potentiometer that in conjunction with the yaw sensor and accelerometer tells the AH/ABS what direction you are headed in relation to what position the steering wheel is in. You can get the potentiometer off center by adjusting toe to far in one direction as well as disconnecting the steering linkage and getting reinstalled 180 degrees or more out of position. You can do this while replacing inner tie rods or disconnecting the intermediate shaft or setting toe.
To a point the system should be able to go through its centering routine and then realign to its new position but if you go way far off it will start to throw codes.
My guess is you may have it far enough off that the "center" is skewed and then add to it the tires may not be exactly the right stagger (but still within tolerance) and all of this combined puts the calculations on the edge and the system kicks in too early.

Two ways to test my theory, first would be to try and run with all helps off and run at 90% which from what you are saying should be much better than you can do in the systems current state. If that doesn't make a difference or maybe only some difference then I would disconnect at least 1 wheel sensor which will 100% defeat AH and ABS then try running at 90% and see if it works like you are used too.

If either of these solve or improve the problem then I would reset your thrust angle but before you do it make sure that the rack is centered (same # of turns lock to lock) then reposition the steering wheel by physically disconnecting it from the rack and centering it. When you center the wheel you need to make sure the potentiometer is in the center of its range. You will need a voltmeter to do this. You may be able to do it with a Tech2 but I don't have the money for one them there fancy tools
I have had to recenter 2 or 3 cars recently due to being far enough off center to spit codes.

geerookie

Just saw this. Is TC off the same as AH off in your car? If so you will have to disconnect a wheel sensor to test my theory.

Nevermind, I see you have an '05.
Comp Mode = TC off but AH on

taken19

That's great advice! I didn't think of that but it makes perfect sense. To add to your theory, the steering was off center a bit yesterday as I was adjusting, maybe 2-3 flats to correct it. It's still off a hair after the last adjustment, maybe 1-1.5 flats. I didn't think much of other than being annoying...

In addition, I have never measured thrust angle so that could definitely play a part in this whole issue. This would relatively easy to check in the garage as well. I will buy some PVC pipes and setup with strings to check. I bet you're right with the aggregate impact of several small things.

Thanks, I now have a direction to point in!

Sean

taken19

In my car, comp mode does not turn off TC. It allows more yaw (5%) before turning on the nannies.

Measuring thrust angle would be the easiest thing to check - it's free! Couple that with the steering wheel being off center a bit, and the second I turn into a corner AH sees something it doesn't like and engages.

I'm keeping my fingers crossed...

taken19

Running some real quick math... Every 1 degree of thrust angle would measure 1.845" using the wheelbase as a reference.

I will buy some PVC and setup the strings tomorrow. Will post the results as soon as I can!