A motorcycle shop put a Pilot power 2CT up front and a regular Pilot Power 50 on the rear of my bike.
I had been riding the k3s for the last couple of years and the ones i had were in bad condition so of course I immediately noticed the bike was handling differently, but I wrote it off as just having new tires. It seemed that it wouldn't hold the same lines that it would before and the traction control flickered a couple of times where I thought there was no reason for it to do so.
I was wiping the bike down after a spirited ride and noticed the markings on the tires and it all made sense, but honestly, there were too many variables (brand, compound, size, pressure) to blame my issues on just the size of the rear tire alone. If you do a search, you'll see some guys don't have any issues, others have the traction control lights flash and such...what I do know is this-if tire size wasn't an important factor to the calculations that the ECU makes, then it wouldn't be an adjustable variable on the HP Race calibration kit. As such, I would rather stick to the recommended sizes, even though there still are differences in diameter/circumference between brands with the exact same ratios.
*another thought* Maybe the ECU/TC can ascertain the tire sizes during the calibration process it goes through when you first pull off