[h018871]

Not sure if this should be in the wheel/tire section or not, I'll start here.

We run open road races and will be switching tire sizes this year and I'd like to know if anyone runs a 305/30ZR19 GY supercar 3R square setup?

It should be easy by entering the published diameter into the wizard, but it doesn't seem that straight forward. The OE diameters for both a standard ZL1 and SS 1LE are 26.83" which is not the published diameter of a 305/30ZR20 GY supercar 3, it is 27.2"
Oddly enough the 26.83" number is pretty much what the published number for the 285/30ZR20 is.

BTW the OE number of 26.83" is exactly correct for speedometer and distance traveled on a stock tired ZL1, although it shouldn't be.


1). Does anyone know what GM uses for the number in the OE file for the ZLE?
2). Any educated guesses as to what I should at least start with for a car with 305/30-19 square setup? Making corrections on the fly could be problematic.

[wnta1ss]

Originally Posted by h018871

1). Does anyone know what GM uses for the number in the OE file for the ZLE?

Never used that wizard, but the 2018 ZL1-1LE has 2061mm for the rolling circumference of the 305/30-19 SC3R front tire in the tune. Table [ECM] 9056 Non-Driven Tire Circumference.

[h018871]

Thx for the reply

Is this the screen you got 2061mm from?

What does 9056 refer to?

[wnta1ss]

Originally Posted by h018871

Thx for the reply

Is this the screen you got 2061mm from?

What does 9056 refer to?

Yes, that screen is where the number came from.

[ECM] 9056 is what my HPT says for the Non-Driven Tire Circumference section when you hover over it, the tune file was from a 2018 model ZL1-1LE. See pic below, the table number at the bottom of the screen.

[h018871]

Gotcha, thx.

I input 25.83 into the gear tire wizard and got 2061mm for both driven and non driven tire circumference. That looks to be a great place to start if not the exact number needed.

Thx a bunch for your help wnta1ss