Jeff Eikenberry

I autocross a C7 Z06, with an automatic and standard brakes. The only change I've made is that I run Hoosiers on a set of C6 Grand Sport rims. Tires sizes are 315x30x18 & 345x30x19. Using these rims doesn't appear to create issues with the car's electronics from what I can see (installed the C7 pressure sending units on the wheels, so no worries there). The car was within a few tenths of TTOD for Corvettes Sunday, at a local Corvette AX. Saturday, I was the 4th quickest Corvette. That speaks to the car's capabilities and not necessarily mine. However, all was not well. I ran with the car in RACE mode, so thought everything that limits performance was turned of. With one exception, it felt that way. My problem was when coming out of corners and applying more throttle, the car withheld additional power until I was almost going straight. The car made a loud rapping sound until the power came on. The PDR showed the tachometer didn't budge when the aforementioned occurred, verifying that power was being withheld. The problem occurred at speeds as low as 30 and up to a sweeper at 55 mph. My co-driver experienced the same problem. We both ran the car in manual mode and didn't bog from the wrong gear choices. In fact, when accelerating on a straight line all the power was available. Has anyone else experienced this and, if so, have you determined a solution? The car has incredible performance but this issue costs valuable tenths.

Poor-sha

That sounds like PTM. Even in Race it is still on and Andy Pilgrim commented on it after a few laps at Autobahn. I've found that I can work around it by smoothing out the throttle application. If your goal is to rotate the car it tends to work if you choose a lower gear or trail braking works really well with this car.

It sounds like yours is an FE6 car also (non-Z07). I like to run the starting pressures 1 psi higher in the rear to help the car rotate. Any issues with the 315 front's rubbing? I have a set in the garage but I rub on the stock 285's.

GTB/ZR-1

Hi Jeff-

I think Poor-sha hit the nail on the head... My C7 Z51 doesn't have MagRide/PTM, so I've not experienced it kicking in. I'd imagine you can turn it all off holding down the TC button for 5+ secs.

I'm upgrading to a Z06/Z07 & very interested to get your impression of the A8s level of control on course, compared to a manual. The A8 gearing is far superior for cone work (compared to the tall M7 gearing), but I'm concerned abt the control factor.

Can you pls share your PDR vids?

Thx in advance.

Jeff Eikenberry

You're right; I have the base Z06 brakes. I initially keyed in Z07 by mistake; I've since corrected that. I don't know this for a fact, but I doubt the Z07 package will fit with the C6 GS/Z06 18"/19" wheels. I'll be the first to admit that I do hit the right peddle a "tad" hard at times, so may be contributing to the problem. However, my co-driver is a very fluid driver and he suffered with the same problem I did. As for tire pressure, I ran 33/28 last weekend. Last year with the GS on Hoosiers, I ran between 31 & 33 front and 27 & 28 rear. I may go down on the front a little. I'll experiment with your suggestion. As for rubbing, my stock tires didn't and I didn't hear any issues this last weekend with the Hoosiers. Will pull them later this week and check. Since the Hoosiers are only 1/16" closer on the inside, but 0.2" smaller in diameter than the stock tires, I don't believe I'll see any rubbing. Since you rubbed with the stock tires, were you on different rims? What was your alignment (mine is -2.0) and did you lower the car (I haven't as yet)? Thanks much, Jeff

Jeff Eikenberry

Thanks for the input on how to disable the System. I'll try that.

As for the A8, I'm totally convinced I did the right thing ordering it, although I may find problems on course like Laguna Seca, Button Willow and Thunderhill, which I plan to run next year. I control shifts manually, as running in auto mode gave me a little problem a few times, so it's no issue running manual. My co-driver last weekend didn't have any issue, save one time when he couldn't find the paddle. It's a learning experience, so no worries.

I'll be glad to share the PDR if you can give me guidance on how to send that large of a file; I tried once and was denied. You can send me a private message.

Jeff

GTB/ZR-1

Hi Jeff-

I sent you a PM on how I get my vids loaded.

Thx for the response. I'm a bit worried abt road course cooling issues (I instruct for PCA & frequent Sebring, Roebling, Daytona--which can be hot!).

I'm glad the A8 sounds like it behaves like a M7 when in manual ;-)

Poor-sha

Stock wheels and either stock size MPSS or MPSC2. Track alignment per the book (-2.0 camber) I would rub right where the front fender spat meets the metal part of the fender. I've actually worn through two of them now.

The FE6 suspension is significantly softer than the FE7 (Z07) so it's not just the brakes but the suspension and that's why I worry about the wider tires and more roll on our cars. Good point about the slightly smaller diameter as well.

I'm hoping that with the rake change and smaller F/R tire width different it doesn't upset the balance too badly.

Jeff Eikenberry

I'm going to Spring Mountain for the GM sponsored, discounted 2 day course in Mid September. I asked for an A8 and was told they could provide one, but it would probably over heat on day two when we spend a lot of time on the track, requiring me to pit and hop into another A8, thereby losing track time....... bottom line: they were gracefully trying to steer me into a manual. Since I've got plenty of time with a C6 6 spd, I opted for the manual 7. So, what's that say when a GM affiliate is saying something like that? I'm sure you've heard the comments on the Forum re issues with the A8 over heating. My plan was to start doing some track days next year, but don't know if I'll be able to stay out long, as my preferred track is Laguna Seca which is exactly 1 hour from my home.

dvandentop

i am not having any issues with my 315 on 18x 11 ccw rubbing on my z07 while autocrossing at all stock ride height

Jeff Eikenberry

Wow! I didn't think the Z07 brakes would fit with 18" rims. Thanks for letting me know. Is most of your offset to the outside? With my 315's on the front, I'm 1/16" in closer than with the stock Michelin Pilot Sport ZP.

GTB/ZR-1

I saw the PDR vid--thanks for sharing. It *sounds* like some sort of TC. But not sure why it would happen in this case. Maybe it is the tire temp, since the stagger seems like it should be close enough front/rear.

Did you mean to start in 2nd? Also, you went to 3rd towards the end. Did you mean to select 3rd & if so, did you try to downshift back to 2nd, just before the finish?

Jeff Eikenberry

By my last run (10 for the car that day), we had hot tires and had been cooling them down for several runs, so don't believe that was an issue. It is a mystery, for now, why the car held power back at times.

Yes, I find starting in second works fine; there's gobs of torque, so no worries. I did mean to select 3rd on the next to last straight, as I would have exceeded second's top speed and bumped the rev limiter. However, if the car hadn't held me back on the last straight, I would have hit the limiter a few seconds before braking. Of course, it did hold me back. As for the finish, I really should have pulled it back to second and would have gotten a better response.

I plan to take the advise someone gave me on how to disconnect all of the controls, which may give me full power, too. Could be a wild ride, but we'll try it.

Thanks much, Jeff

froggy47

Please post how to turn everything off on a c7. I instruct in them from time to time & the owners always ask me that.

(Please don't post "warnings" guys)

Jeff Eikenberry

Just looked at the stock front tires and they show no rubbing, at all, on the inside or out. Also looked at the front fender wells and there is no rubbing anywhere, inside or out. Wonder why your car rubs? I'm not the most gentle in braking and turn in. You could probably add 1/4" spacers without adding new bolts....... and see what that does. I'm guessing on not needing new bolts.

I do plan to lower the car, but will be careful to make certain I end up with the same rake as stock to assure the system is happy. That'll be another alignment.

Best regards, Jeff

Jeff Eikenberry

That won't happen until 8/24, which is the Monday after a two day AX weekend. I just tried what I was told to do: Hold the TC button for 5 seconds. I did that in Track mode (not PTM) and the Stability control and Traction Control lights for "off" both came on. Hopefully, that will unleash the power, too. Wonder what the suspension, steering, etc. will be at?

GTB/ZR-1

I need to be schooled on that as well, since my C7 doesn't have PTM & not sure how systems interface w/ each other.

Great thread--informative for me on the A8s AutoX demeanor.

Jeff Eikenberry

Yes, between this thread and the one I posted in "C7 - tech/performance", I believe I now have the solution and will know in two weeks.

Yes, the A8 is Great for AX'ing. I had to make certain I had my hands positioned on the steering wheel in a manner that assured I could tap the paddles....... You'll see what I mean, I'm sure. Second thing is to "practice" using the paddles, until you no longer have to think about which is the up shift paddle and which is down. For some unknown reason, I had an issue sorting the two out, so used manual shift mode on the street until it became second nature.

GTB/ZR-1

I had the same learning curve w/ my old GT-R while in 'the heat of the moment'--so I know exactly what you mean. It did become second-nature after a while.

Pls keep us posted. I'm in hot pursuit of a Z06/Z07 now & eager to hear your progress.

Thx