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.

 

A good tune will take care of this for sure

 

I believe that even in race mode the power is limited exiting turns until the tire sensors indicate the tires are hot. Look under the performance menu on the DIC to display the calculated tire temperature range (cold, warm or hot will be displayed). Traction control is still active in race mode however active handling is not.

 

Your track tires may be part of the issue. First, the circumference difference between front and rear tires needs to be the same ratio as stock, or it will trick the computer into seeing greater yaw angles and slip than there actually is. And you have to keep in mind that the traction systems in the car (yaw sensors, wheel slip sensor, e-diff) are all closely calibrated to, and optimized for, the stock tires. That includes tire temperatures and known levels of grip at that operating temperature.

The heat ranges and available grip on the hoosiers, and in particular the A6 in an autocross setting, will differ significantly from the stock tire. The stock tire will never likely get hot enough at an AX to generate best grip, and the hoosiers will have more grip available anywhere, anyway. Therefore, the computer will pull power when your brain knows there is more grip there. Solution is to turn everything off, but then you may have a real beast on your hands.

 

That's a good point. In the case of yesterday, two of us ran the car for a total of 10 runs; we barely had time to check tires, let alone cool the tires down with water, which we did from run 4 on. They definitely got hot, although I didn't check the car's system and we didn't have time to stick the probe to it. It was the most hurried set of runs I've encountered....... not enough single driver cars. Thanks much. Jeff

 

Well, first off, the Hoosiers (A7) are 0.2" shorter on the front than the Pilot Sport Cup ZP's (25.6" vs 25.8"), while the rear Hoosiers are 0.2" taller (25.8" vs 26.6"). All that tells me is the car's system (probably) won't consider the rear tires spinning since the ratio is greater front to rear with the Hoosiers, and the rear Hoosiers are taller than the ZP's. All that said, I'll be the first to acknowledge these are speculative comments on my part and I'm sure there are many things the system is looking at, as you pointed out. Ah, but your last comment does have me interested. How do I turn everything off? I know what you mean about having a real beast on my hands, and I may be bullied by the car into going back to Race mode and glad to have the computerized assistance in spite of the loss of power, in some instances. Thanks very much for your in-depth comments. I look forward to your additional comments. Jeff

 

You may be right, Mike, but since the problem only occurs on corners and the car is injected (thank God we don't have to worry about slosh tubes and vent screens ), I'm wondering if some other things are playing a role? See some of the other comments, below yours. I won't deny that it might boil down to a tune, though. Thanks much, Jeff

 

Put your stock wheels & tires back on, so you can get a baseline....

You'll never know for sure if your Hoosiers are doing you any good or not, unless you know what your performance is in stock form.

Wormwood

 

Actually, I did run the stock wheels/tires for 5 - 7 Ax's before putting the Hoosiers on, but the performance level was so far below running Hoosiers that I was not able to really push to that level. That being said, I have no recollection of the issues I mentioned with the Hoosiers. My plan is to totally disconnect all overrides, now that I've been told how to. Could be Toad's Wild Ride, but we'll see if the problem goes away. I've gained a healthy respect for the car's potential and know it can BITE me if I use the right peddle carelessly. Thanks much. PS: I'm hoping someone else who has put Hoosiers on will comment. I definitely picked up 2 - 2.5 seconds on a 60 second course, in spite of the issues I've mentioned.

 

OK. I doubt .4 increased circumference delta would cause an issue, but I may be wrong. So it is then the higher levels of grip, and the grip-at-temperature that the system is not calibrated for.

Don't have my car yet, but there should be two ways to get what you want: (1) go to the Track menu and access the car's Dry PTM modes - I believe there are 5, with Sport 2 interfering the least among "assist" modes and Race essentially turning all assists off except the e-diff power distribution, (2) and more crude: pressing the button at the center of the selector roller with the car-skid icon once should disable the systems.

Hopefully someone who knows more will chime in.

 

I did run in PTM, Race last weekend, so that isn't my solution. Will try the "crude" method when I run the weekend of 8/22 & 8/23. Thanks for the input and good luck with your car when it arrives. Color and options? Mine is DSOM with base brakes and a couple of other cosmetic things.

 

I've had my best luck running the car in Sport mode with both traction control and stability control off. Autocrossing it in Track mode no matter what 5 modes you set it in you always have some sort of assist. Which I did not like and got very frustrated with the engine holding back power and not letting you bring the rear end around when needed. There is a difference in Sport mode vs. Track mode. You do have less power when you are in Sport mode and it does not seem as fast acceleration wise but who really needs 650 hsp in an autocross car? If you think you need assist and some sort of help when autocrossing then I would recommend running it in Track mode without the traction control off. Leave the stability control ON tho and see how you like it. Do not try to set it in the individual modes of sport 1 sport 2 or race. Just only turn the traction control off and that's it. You will notice the computer still working and applying brake here and there when the car gets a little bent out of shape but if you give it more throttle you can overpower the computer and it will let you still get a little wild with it. But as for autocrossing and having all the assists off and having the least amount of help from the computer I would definitely try Sport mode with traction control off and stability control off. It makes a very big difference. Just remember to go easy on the throttle.


I run a 2015 Z06 A8

 

In Track mode the car knows how far the steering wheel is turned and compares it to the amount of gas you give it then calculates your speed as well and it judges how much gas you can give it with the maximum traction at that time coming out of a corner so therefore it cuts power to the engine and you hear the ****** noise that you have heard. I have had no problem at all since I switched to Sport mode with everything off. I do not believe that its holding you back due to cold tires. I have put on a lot of runs on every single mode and messed around with all the traction controls and never once has there been an issue starting out with cold tires. I have yet to run Hoosiers on the car. I will be running them this weekend so I am anxious to see how the car handles.


-Chad

 

Black, black wheels, 2LZ, iron brakes also. Did not get the comp seats because the uppers were too snug in the shoulder area and I did not feel I was sitting IN the seats so much as sitting ON them. Did get the suede inserts to help with grip. Hope I made the right seats choice and do not find myself flopping around in corners...

 

So, Chad, I'm on vacation wishing I were home and going to an AX this weekend, and trying the settings you suggested. I'm really, really excited about trying this!! You've explained so simply and articulately that I feel confident this is the solution I was hoping for. I do have two questions.

Once I go from "Tour" to "Sport", to turn off stability control and traction control, do I double tap the center console bottom or press and hold it for 5, or so seconds? Having run in "Sport" mode before, I didn't like it at all, BUT I was unaware I could turn SC and TC off. That should made a substantial performance difference.

With all the runs you've made, along with your testing, I assume you experienced what I did when you were in PTM's "Race" mode? Funny thing is that the autocross weekend prior to switching to Hoosiers, I had no issues with the car's performance when in PTM's "Race" mode. That course was more fluid, akin to a track. Last weekend's course was loaded with tight (25 mph - 35 mph) 90 & 180 degree corners....the kind I want to bring the power on before being straight. The car did its #%******%# at those times. Hope it was the setting I selected to run in and that the Hoosiers weren't a contributing factor. Please let me know how your car works with the Hoosiers..... I don't need to know how the Hoosiers perform, just if you get the #%******%#. I'm going to take the optimist's stance and assume your car will not have issues.

What size Hoosiers are you running? You've probably read my comments about the sizes (315's & 345's) I chose, which were what I ran on my C6 GS. Also what size rim (diameters and widths) are you running?

Chad, thanks again for taking the time to lay out the situation in detail. I next run 8/22 & 8/23, so look forward to hearing about this weekend's run you have planned. Good luck!

Jeff

 

I also chose the microfiber and, while I've only driven one other C7, a Z51 car without MF, I suspect the MF helps some. I also use Angel Wings, which I believe helps. I'm 5' 9" and 170, so they keep me from moving laterally. Haven't tried a racing seat, but have no complaints with the std ones.

 

When you put it in Sport mode you can hold the button down for 5 seconds or so and both lights will come off. If they don't then resort to pushing the button down twice. Yes I did run into the problem of the car having the same problems you did. I learned at Spring Nationals in Lincoln, it was the second race I took it to. It was not fun at all. The first autocross I took it to the car handled great. It was a local event and I messed around with some of the traction controls and absolutely loved the car. Then when I took it to Spring Nats for the second race I had all kinds of problems. Then when we switched to Sport mode it made night and day difference. Don't forget to use that PDR in your car. It will be very useful!


Front wheels are 18x11 on 315/30R18 A7
Rear wheels are 18x12 on 345/35R18 A7


Thanks! I'll let you know how it goes.


-Chad

 

Chad-

Are you running SSP? Would you be willing to share some PDR vids w/ us? ;-)

I'm upgrading to a Z06/Z07 & it will see a lot of duty in Super Street.

Sorry for the hijack, Jeff!

 

Seems like we had similar experiences early on.

I like your choice of tires and rims. I suspect I'll eventually go to at least a wider front rim.

I always run the PDR. In fact, it was what "pointed" to a "little" problem I had. There were a few times at one AX that the car felt like it was trying to accelerate when I was braking. I knew there was an issue, but couldn't believe the car was adding power. The PDR clearly showed that my new tennis shoes were hitting the go peddle while I was braking. One pair of racing shoes later the problem was gone! It's also helped with my lines.

Have a good AX weekend.

Jeff

 

No worries.