[ASKED] What are the effects of a non-stock tire size on the sixth generation Camaro?
 

Al,

As you know, many people enjoy customizing their car with custom wheel and tire combinations. Also, dragstrip and road course enthusiasts often prefer specialty tires and wheels that aren’t always available, or optimal, in the stock size.

What are the effects of a non-stock tire size on the sixth generation Camaro?

Does the car detect and compensate for tire circumference changes (using GPS or some other mechanism)? If not, can a dealer provide the necessary calibration?

Thank You!

I know many guys who have already or are planning to put the SS 1LE, ZL1, or ZL1 1LE wheels on their car. Wouldn't be nice to know exactly how this might effect the car?

For me, I'm specifically interested in going from 20" to 19" wheels to open up a better track tire selection. The only thing holding me back is not knowing exactly how this might effect the software, e.g. Performance Traction Management, ABS, Stabilitrak, etc.

Most likely the speedometer will be off as it is in most cars, but wouldn't it be cool if we could have a dealer calibrate our cars correctly... or even better, if we could make the necessary adjustments ourselves without voiding our warranty (using HP Tuners or some other tool).

I really think this question has potential to get some truly helpful information back from Al and his team.

:popcorn:

The speedometer thing is really overblown for the type of changes that people are making here if not being radical with 22 inch wheels, slicks etc. For example, the stock RS 20 inch tire is a 245, going to a 275, means when your speedometer is reading 65, you’re actually going 64.7. Not enough to worry about ....do your calculations here:

https://www.discounttiredirect.com/l...xoC1KsQAvD_BwE

Your example is backwards, but your point is valid. (When you increase the circumference of your tire, the speedometer reads slower than your actual speed.)

Here's another good calculator:
https://tiresize.com/comparison/

An example of particular interest to me:
ZL1 front: 285/30ZR20 Goodyear Eagle F1 Supercar 3
ZL1 rear: 305/30ZR20 Goodyear Eagle F1 Supercar 3

ZL1 1LE front: 305/30R19 Goodyear Eagle F1 Supercar 3R
ZL1 1LE rear: 325/30R19 Goodyear Eagle F1 Supercar 3R

There is about -2% difference between the ZL1 and ZL1 1LE tire sizes. So not only will the speedometer be off, for every 1,000 miles there's going to be an extra 20 miles on the odometer due to the error. It's not a lot, but I think it's enough to annoy me.

Also, the ratio front to rear is changed ever so slightly.
Zl1 Front vs Rear: 1.85529% difference
Zl1 1LE Front vs Rear: 1.89036% difference

Most likely it isn't going to make a lot of difference, but I'm still interested in knowing exactly what might be impacted.

Changes to the circumference of the drive wheels can definitely affect mileage on the odometer. Since warranty is based on odometer readings, it would seem prudent to have a means of re-calibrating the speedometer/odometer. This would prevent extending or shortening the warranty and may also prevent owners from getting speeding tickets in strict enforcement areas.

As for your question on potential effect of tire size on automated systems, I can attest that neither my 27.8" tall Mickey Thompsons (345/35R18 ET Street S/S) nor the 25.9" Hoosiers (335/30R18 DR2 D.O.T. Slick) have triggered any warnings or intervention from Performance Traction Management, ABS, Stabilitrak, or any other systems.

When I first starting looking for replacement DRs I too was worried about intervention, having heard stories implying that some of our automated systems might complain and interfere. After comparing front to rear size difference between stock, MT's, and Hoosiers; and doing simple calculations and other research, I felt the risk was minimal. I was relieved after my road test when there were no negative effects whatsoever.

You can read about my initial search in "Help selecting replacement DRs" and my final selection and testing in "Hoosier DOT Slicks vs MT ET Street SS".

Individual posts from these threads with details and test results:

Rear wheel diameter comparison of stock to previous and prospective DRs

Wheel diameter front-to-rear comparison of stock to previous and prospective DRs

New Hoosiers Mounted, Balanced, Installed, and Tested

--Cal

Well if you want to get that picky. even the air pressure and for that matter the temperature in your tires will affect the circumference, thus will affect all your calculations.

It all depends on just how precise you want to be.

Unless you know for sure that your current odo/speedo calibration is dead-nuts on, how much could this matter? Having a speedometer that reads 2% faster than actual means you're that much better off, though it'd have to be a really tightly enforced zone for 1 mph @ 50 to make the difference between getting a ticket and not.

My track tires are a little over 4% shorter than OE, and all I noticed was slightly stronger throttle response and having to shift at slightly different places and sometimes another time or two on road courses. My current street tires are 3% shorter than OE and I'm unlikely to ever buy tires for this car that are any taller than those.


Norm

I'd like to see this question be on the next poll. I'm interested to understand if there's provisions in the software to enter in the correct tire diameter (or section width, aspect ratio, diameter), even on non-OEM size setups.

Excellent
 

Cal I love you posts. Perhaps we can have and "Ask Cal" forum :)

I have mixed feelings about forum members answering questions within Ask Al. When members post answers here, it's done with good intentions, but it can kill the interest for the question and the opportunity to get to some of the less obvious details from the Camaro team.

Perhaps the suggestions made in an Ask Al thread takes could be used to refine the way the question is actually submitted to the Ask Al team.


Norm

I'd really like to see this one on the next poll as I'm now considering to put SS 1LE tire/wheels on my SS. I'd really like to understand the best way to get the new tire size in the control module so vehicle speed and all stability/traction control algorithms have the correct speed feedback.

What does the timing look like for the next poll? I'd really like to see this one on it!