ZL1 A10 Transmission tunning
 

So i have been wondering what are the gains and if its worth it or not to unlock the transmission and get it tuned, also if it has to do something with changing the wheels to aftermarket wheels because i just got myself a rear only set of 18x10.5 race stars and when i got them on the car it got weird and started to slow down by itself when ever I exceed 30 mph.

I can't speak to the transmission tuning as I have a manual, but if your rear tire size happens to be quite a bit different than what you took off it may be slowing you down because it thinks your spinning (traction control/stabilitrak is freaking out). I'd just hold down the traction control button for 10 seconds to disable everything and see if that eliminates the slowing down issue. That would at least point you in the right direction as far as that issue is concerned. If that stopped it you just need to input the right tire size into your computer to fix that little issue, or get different size tires to match things up front/back. Just my .02 cents

The tire height between the front and rears should not exceed 1" in difference or you will have transmission shifting issues most likely. What tires do you have on the front and rear?

I dropped to 275/30R19 front and 295/30R19 rears on APEX ARC-8 19" wheels so a bit over 1" less overall front and rear tire height and have absolutely no shifting issues or otherwise.

I have to give that a try i guess, didnt so it last time i tried them on.

My front is the stock wheel and stock tires, rear is 18x10.5 wheels and 305/45/18 tires

Your front tire height stock for a 285/30R20 tire is 26.7".

The rear tire height for a 305/45R18 tire is 28.8".

You are absolutely having issues because the difference in height between the front and rear is too substantial (need to be < 1" difference and you dont want rear shorter than the fronts). Your rear is currently 2.1" taller than the front.

FIX: You need a different rear tire or a taller front tire, if it will fit. The tire height for the rear (assuming you use a stock front tire size) should be between 26.7" and 27.5" to be safe and to resolve your issue.

Optional sizes that will work with your OEM fronts without issues for transmission shifting if you can find a tire available in them that you want. Be sure to verify that the tire you pick will fit on the specific wheel you have in the rear based on its width and the wheel's acceptable tire width range. Also if you go to 315/325's etc, be sure that the tire wont interfere with the rear suspension etc:

- 275/40R18
- 285/40R18
- 295/40R18
- 305/40R18 (27.6" tall, i would not suggest going this big, leave a buffer)
- 315/35R18
- 325/35R18

Note, as you increase tire diameter, you effectively change the gearing of the car. You will have less torque multiplication delivered to the rear by the taller tires (although more traction based on tire type potentially and softer sidewalls). Shorter tire heights amplify torque multiplication as if you changed gear ratios, while also lowering top speed.

Typically folks will use a 17" rear (fits with OEM brakes) with a 17x10 or 17x10.5 rear drag radial if you are dragging the car.

Use this website: https://tiresize.com/height-calculator/ to do a quick check on tire height per tire, or check the specific tire for the most accuracy on Tire Rack in the tire specs.

Oh, i tried the comparison and yeah the difference was 1.3” could that be the problem? And do you have an idea if i need to tune the transmission or not to change the rear wheels? I am talking if i fixed the 1.3” difference issue.

It's been said here that tuning the T93 can lower your 1/4 by ~.30

Have I missed something, when did tuning the T93 become possible? Or did you mean a T87A swap (in which case pre-2019 TCM tune gains would apply, I presume)?

What exactly would the difference in feel be for an A10 tune?

Honestly, I have no idea, because I don't have an exhaustive list of differences between the T87A and the T93. Without that everything is just conjecture :noidea:

HHP now sells the editable T87A. They will tune it or your tuner can, which means all those wonderful edits discussed here are in play (you will need HPTuner's credits)

It’s going to come with a base calibration same as all the other unlocked T87A’s for 10 speeds that HP Tuners does.

It's not a T93. It's a T87a unlocked and modified to work on 2020+ cars.

I just had my 2017 SS tuned for E85 and I asked the tuner if it was worth it to get the 8-speed auto tuned. Basically, the answer is no. It requires the same number of HPT credits as tuning the engine. And the factory tuning was quite good already. I would suspect the same would be true for the 10-speed.