So my tires are toast on my 09 CTS-V Sedan. The rears are 285/35zr19s. I'm replacing them with 305/35zr19s, so the tire diameter is going up by half an inch - 26.9" to 27.4". The fronts will remain stock size of 255/40zr19. I was going to use the gear/tire wizard, but it has my current diameter as 26.06, which is incorrect, so the scaling to 27.4 is off. It won't let me change the current diameter to be correct without scaling things, either.
What's the proper way to set all the params to ensure that my shifts stay optimal and speedo/etc is correct? Is there a calculation I can use for VSS Tire Revs per based on the tire height? I've been searching around on Google but haven't found anything conclusive. I'm using Bluecat to set the shift points, so I figure on the shift points I can just put the new tire height into Bluecat and be good to go, correct? Any idea why tire revs per dist and tire revs per dist - trans are different in the speedo calibration?
Thanks in advance!