Finally, to finish off the last question about wheel radii, the equation to compute it is:
radius = zz/2 + xxx/25.4 * yy/100
where Pxxx/yyRzz are the tire sizes. Multiply the radius by two to get the diameter. By the way, these are for the overall wheel outer diameter (or radius).
For example, on the StingRay front, using the specification sheet given above for P245/40ZR18 we have:
18/2 + 245/25.4 * 40/100 = 12.85827 inches radius = 25.71654 inches outer diameter
For the SingRay rears with P285/35ZR19 we have:
19/2 + 285/25.4 * 35/100 = 13.427 inches radius = 26.854 inches outer diameter.
For the StingRay Z51 fronts with P245/35ZR19 we have:
19/2 + 245/25.4 * 35/100 = 12.87598 inches radius = 25.75196 inches outer diameter (note how close this is to the Base StingRay's fronts!)
For the StingRay Z51 rears with P285/30ZR20 we have:
20/2 + 285/25.4 * 30/100 = 13.366 inches radius = 26.732 inches outer diameter (again, note how close this is to the Base StingRay's rears!)
By the way, this is why Glen E. and others were telling someone last night in another thread that you can put the Z51 rims + tires on a Base StingRay with no problems: the outer diameter for Base versus Z51 is SO CLOSE!