I would really appreciate anyone's response that knows if the following front-to-rear tire diameters are electronically (ABS, TC, and etc.) compatible on a C7-Z51 Stingray:

Front = 25.3"______Rear = 27"_____Difference = 1.7"

OR

Front = 26"_______Rear = 27"______Difference = 1"

For reference, the O.E. tire diameters (Super Sports) are:

Front = 25.8"______Rear = 26.5"____Difference = .7"

My concern is that if the diameter difference between the front and the rears is too great, my electronics (ABS, TC, and etc.) will protest.

From experience, I do know that the following difference IS COMPATIBLE, as it should be, because it is the same difference as the O.E. diameters:

Front = 26.3"______Rear = 27"_____Difference = 0.7"

Thank you!

Joe

 

I'm running Toyo's and they are 25 front and 26 rear with no issues other than having to adjust the speedo.

 

Thank you, RottenII! Your information is helpful. Hopefully someone else will let me know if the 1.7" is compatible.

One more thing please, when you said "adjust the speedo", is there a method to physically do that to the car, or are you referring to calculating in your head?

 

Computer adjustment with HP Tuners.

 

The difference in diameter isn't what counts it is the ratio between front and back. The stock ratio of rear/front is 1.04. Another way to look at it is the rear is about 4% larger than the front. Typically ABS systems can handle a max change of about a 4%. TC sometimes can work with that much but some Electronic Brake Control Modules (EBCM's) are less tolerant than others. Same goes for engine drag control where the rear tire gets too big in relationship to the front.

Changing the tire diameter affects ABS and Stability Control by changing the reaction of the system to an activation. The brakes will be pulsed like a stock system but the tire reaction will be different which can lead to changes in how the system reacts overall. You won't get an error code but you may notice a difference in how the car works.

TC will react sooner with ratios smaller than 1.04 but you may not get an error from the EBCM until it gets down to 1.1 or less.

Engine drag control is used to keep the rear wheels from slipping in low grip situations when the driver takes their foot off the gas pedal. When the system detects the rear wheels turning to soon it adds throttle. Keep the ratios between 1.02 and 1.06 and you will probably be fine.

Bill

 

Hello, Bill,

Thank you very much for your thorough explanation! And just to be sure I'm calculating the ratios correctly (up vs. down), are the following examples correct:

27/26.3 = 1.026...therefore acceptable

26.5/25.8 = 1.027...therefore acceptable (this is O.E. sizing)

27/25.3 = 1.067...therefore unacceptable

27/26 = 1.038...therefore acceptable

Thanks again!

Joe

 

C7 seems to be much less sensitive to diameter changes. Even when you install too different diameters causing stability control warning messages, it was reported that the message later cleared, suggesting it learns and recalibrates. Just like TPMS, looks like C7 takes care of it itself when it comes to the obvious.

My latest setup is 315/30/18F, 325/30/29R, and I have no issues. It's 25.35"F, 26.73"R; ratio is 1.0544378698224 and never any issues.

 

Thank you, X25!

I'm tempted to try the 25.3'F with 27"R = 1.067 however I'm sure there must be a limit. Bill Dearborn indicates the 1.06 may be the maximum.

 

I'd say don't try for C6, but for C7, I would try and see if it adapts. After all, mathematically speaking, all that the car needs to do is to monitor tire speeds during cruise for a while to come up with the actual ratio : )

That said, 27" is the limit of what you can put in without hitting the bumper side of rear fender liner. I changed my control arms as well when I switched to 26.73" diameter tires, and it was literally almost touching before I got the alignment (toe) fixed. 27" would be my limit, and I'd never install anything taller for sure, no matter the ratio.

 

More great input, X25...thank you!

 

I just put winter tires on my Z51:

Fronts:
245/40R19 Pirelli Winter Sottozero Serie II Run Flat

26.7" diameter

Winters by Daniel Toombs, on Flickr


Rears:
275/35R20 Pirelli Winter Sottozero Serie II

27.7" diameter

Winters by Daniel Toombs, on Flickr

No rubbing that I can tell. No issues with traction control.

 

Thank you, Daniel! So yours is a 1.037 ratio, and except for rubbing in the rear (especially if you lower the car on its O.E. adjusters), everything else should be okay.

 

I was wondering about this issue as well for my snow tires. I will be running the same size tires/wheels at all 4 corners. Just have to see what happens but I'm hoping it will be fine.

FWIW on my 15 mustang GT, the car came with a square setup and I installed staggered 20"s with a difference of an 1" frt/rear and there were no problems. I'm hoping the c7 can do the same.

 

I posted a similar question on the Z06 board help for drag radial and mostly I got guys telling me to not be cheap and buy new wheels and in 18" for a better selection. A couple guys actually tried to offer some info that was anecdotal and good but still not as good as here. But...I still need some real experience or good recommendations. I especially appreciate the info that some of you had or have some TC or stabilitrac warnings that went out but didn't actually apply the brake like on another C7 my tire guy tried to upsize and locked up as pulled off the hoist.
I've also heard that by running in Track mode which minimizes TC and stabilitrac, that it "fixed" the problem. I don't want to do that all the time but if only needed when I drag race is necessary, I could live with it.

Tire guy still thinks even an inch is too much and doesn't know if car will electronically adjust. I called Tire Racket where I've purchased tires for 20 years and was only told "we dont sell Nittos" and there is no recommended drag radial for c7 Z06. He was a bit of an *** offering no suggestions other than to try and sell me the Michelins they do carry.Never mentioned the small print (below)

Now I can pretty much afford to buy any tire solution be it even 4 wheels and 4 tires but I choose to keep my machined edge OEM wheel because I like them and thats why I speced them when I ordered the Z06. The stock Michelin 335 25 20 is 25.3 inches in diameter (tall). the front 285/30R19 is 25.8. In small writing Tireracket add "Match with 325/30-19 to downsize the rear." which even the CS guy didn't mention. (must be a Mustang owner).That tire is 26.7 diameter almost 2.4 inches different (larger) in diameter than the OEM 20" which by most of the postings here is likely to big a difference.

I had wanted to try the Nitto N05r which is 28.74 and the 555R is 28.58 but were a big 3+ inches difference.
The Toyo 888R in 325/30ZR20 is 27.7 and 27.5 in 315/30ZR20 but both Nitto and Toyo are about 3/4 to an inch narrower in tread width.

Only the P305/35R20 MT is same or larger at 13" OEM tread vs 13.2 MT but is 28..4 diameter.
So I'd welcome some suggestions or experience that may have happened since the last post or even before that you didn't post. Thanks in advance.

 

The car doesn't know what diameter tire is installed. It only knows the stock difference in wheel speeds when going down the road in a straight line at a steady speed. Use a ratio to set your tire diameters for the C7 it is the ratio of rear diameter divided by front diameter. For stock C7s that ratio is 1.039 or 1.04 rounded. Vary front and rear diameters to keep close to that ratio and you should be fine. I wouldn't let it vary from 1.02 to 1.06 to keep things happy. Simple to calculate and simple to remember.

Bill

 

Bill or anyone that is more knowledgeable on the C7 finicky nature than I, which would probably be everyone, lol.

What happens if the car detects a ratio that it doesn't like? I have a set of NT05's (305/35/19's) that only have a couple of passes on them (used on my blown S550 Mustang), and mounted them on a set of knock of 19x10 Z51 rims. The calculation on the ratio take it just above the 1.06 mark at 1.064. Will this be a real problem? I haven't put them on the car yet as they would be strictly for the track and all its done is rain since the A&A, meth kit and tune were done. Thanks in advance.