Subject of changing the speedo for a different tire, I had tried it when my TCM was still locked (pertinent to the 2020+ auto owners). Car was 2017 SS A8 with MT 305/45-17 DRs on the back. I had found that these were taller than stock, and the car was able to get 116mph in 4th gear at 6500rpm with the stock tune. With these tires on, traction was better, but the shifting with the locked tcm was worse than with the stock tires. I did try changing the speedo cal for them, but shifting remained roughly the same as with the stock speedo calibration. Illustration below, the 109mph is with stock speedo calibration and the 114mph is with speedo calibration adjusted closer to the MT's actual size. The cursor is at top of 4th gear.
