[vtirocz]

Originally Posted by Captrob

This post came up just in time. I am ordering the MRR M017’s on Monday. The one thing I was still uncertain on was to try and keep the same heights 40/35 or go with 30’s all the way around.

Keep in mind that 40 and 35 are not the height, but the aspect ratio.

If you're planning for a 285 width front tire and 305 width rear tire, the closest size both front and rear (to the stock SS diameter), would be 285/35/20 (front) and 305/30/20 rear.

I'm not sure if that's better or worse overall (from a system standpoint) than just the stock SS 1LE sizes 285/30/20 and 305/30/20.

[Captrob]

Originally Posted by vtirocz

Keep in mind that 40 and 35 are not the height, but the aspect ratio.

If you're planning for a 285 width front tire and 305 width rear tire, the closest size both front and rear (to the stock SS diameter), would be 285/35/20 (front) and 305/30/20 rear.

I'm not sure if that's better or worse overall (from a system standpoint) than just the stock SS 1LE sizes 285/30/20 and 305/30/20.

Thanks!! The guy at the tire store told me wrong and about had me ordering the wrong tires. I want to order the size that closest matches my stock tire heights.

[Shawnqa800720]

So had some great offline discussions with some folks and wanted to post thoughts on this.

One of the things I was thinking about is that overall diameter is only going to impact the speedo, which most of us don't care about. BUT the ratio of front to back diameter needs to remain as close as possible to stock so the system can operate as intended. The stabilitrack system won't necessarily know/care how fast you're going, but it will know if the tires are spinning at different rates than intended.

If this is true, I assume Chevy considered this, and that the SS 1LE tires are the correct ratio to not cause any issues. But when I did a quick calculation, it doesn't appear to be too close. One of the replies I got from Alpha1BC (feel free to post your feedback as replies - it was helpful to me, but didn't want to take the liberty of quoting a PM) was that the allowable ratio is pretty wide, but he was going to see if he could track down the actuals.

Here are my rudimentary calculations, including some alternate options I am considering for tire sizes.

Stock SS
Size; Diameter; tread width
Front;245/40-20; 27.7; 9.6"
Rear;275/35-20; 27.6; 10.8"
Diameter Ratio: 0.99638

SS 1LE
Size; Diameter; tread width
Front ;85/30-20; 26.7; 11.2"
Rear;305/30-20; 27.2; 12"
Diameter Ratio: 1.01872 (within 2.2% of stock)


Alternate size 1:
Size; Diameter; tread width
Front ;265/35-20; 27.3; 10.4"
Rear; 305/30-20: 27.2; 12"
Diameter Ratio: 0.99633 (within 0.005% of stock)

Alternate Size 2:
Size; Diameter; tread width
Front; 275/35-20;27.6; 10.8"
Rear: 305/30-20;27.2; 12"
Diameter Ratio: 0.985507246 (within 1.1% of stock)



Alternate 1 gets the closest to stock diameter ratio (nearly a perfect match), but alternative 1 is almost an inch narrower, while Alternate 2 is second closest and keeps the front width closer to the 1LE. Do you think I am on to anything here for the folks who don't want to do a tune? My wife often says I overthink things, but as a biochemist and Project Manager, it is part of my DNA

[LT4Greg]

I put 285/35s instead of the stock rear 275/35s on my SS. Those 2 sizes are real close. The speedometer is about 1 mph off. I used the tire size website.

[wrankin]

Originally Posted by Shawnqa800720

One of the things I was thinking about is that overall diameter is only going to impact the speedo, which most of us don't care about. BUT the ratio of front to back diameter needs to remain as close as possible to stock so the system can operate as intended. The stabilitrack system won't necessarily know/care how fast you're going, but it will know if the tires are spinning at different rates than intended.

@Shawnqa800720 - thanks for putting this together. To follow along with your theme, this is what I am considering:


Size; Diameter; tread width; revs / mile; revs / mile
Option A:
Front;285/35-20; 27.9; 11.2"; 724; 746
Rear;305/35-20; 28.4; 12.0"; 717; 733
Diameter Ratio: 1.01792

Option B:
Size; Diameter; tread width
Front;285/35-20; 27.9; 11.2"; 724; 746
Rear;295/35-20; 28.1; 11.6"; 710; 740
Diameter Ratio: 1.000716

One thing I noticed is that the revs per mile from the tire size website (https://tiresize.com/comparison/) is very different from Tire Rack's website.

At this point, I'm trying to decide between Michelin PS4 and Continental Extreme Contact Sports. The Michelin's are not available in Option A sizes

Bill

[vtirocz]

Here's information straight from GM on this topic. I reached out to Jordan Garwood (Product and Marketing Manager: Performance Parts – All Vehicles
Performance Vehicles, Accessories, & Motorsports) on what it would take to put SS 1LE wheels/tires on my SS and calibrate for the different diameters:

"Unfortunately we (GM) don’t have a way for a dealer to do this [calibrate tire size or rev/mile] so it would require an aftermarket handheld tuner. Vehicle calibrations are specific to VINs and a dealer cannot put the cal from 1 VIN (1LE) into another VIN (SS). I can’t really say since these aren’t “manufacturer approved” vehicle calibration updates. I bounced the cal question to another Engineer I know, who was a Camaro test driver previously, and his reply is below:

“Confirmed that we do have two different cals (SS & 1LE) for the speedo. We will have different cals for the ABS/TC/ESC for the different vehicles as well due to the tire and suspension differences. The lowering kit for the SS is meant to work with the SS tires. Should a customer choose to put the 1LE tires on the vehicle, the vehicle will have speed and odometer errors along with less optimized Chassis Control Cals. They may even risk voiding the vehicle warranty with this change.”

Of course the Performance Suspension Kit is designed to integrate perfectly with your stock SS vehicle and cals, but it sounds like the 1LE wheel and tire change is more challenging than even I would have anticipated since there is no “factory” calibration solution available and you would therefore need to find a tuner for more than one of your vehicle calibrations.

I agree the wheels would look great but it sounds difficult to get the exact calibrations needed to realize the desired performance benefits you are seeking.

So, even though this may not be the answer you wanted, hopefully it points you in the right direction should you decide to pursue.

Thanks again for your passion for your Camaro and all your interest in the Performance Suspension kit.

Hope this helps!"

With that said, take it for what it's worth. I've summarized the % difference in revs/mile in this table. The SS 1LE wheel/tire combo still provided a performance benefit based on GM's testing in the Ask Al section.

[jacekpuzio]

I replaced stock R18 with aftermarker R19. Do I need to program it to BCM somehow?