You have lot of experience putting tires on cars in uncommon sizes, so maybe you should figure out how much difference it really is before you take that closest in stock tire and throw it on a customer's vehicle. Pull out your calculator.
215/50R16 = 1952.185675mm circumfrence
215/55R16 = 2019.729917mm circumfrence; 103.46% of original
205/55R15 = 1985.172398mm circumfrence; 101.69%
225/55R15 = 1983.601601mm circumfrence; 101.61%
In another thread I think it was a 215/50R17 recomendation which is 2031.982128mm in circumfrence and 104.09% of the original SVT tire size.
None of the tires suggested are too far off the OEM size, but the 215R55R16 is the most, and for the worse side for handling. And some have rubbing issues with 10mm larger diameter, 21 could cause even more issues.
Wider is (very marginally) better for lateral grip when cornering regardless of which wheels are powered. See:
Reference #1 on slip angle and
Reference #2. Although there are flaws in some of his comments, the fundemental is correct.
Another tire tech thread that is informative.
So much more is to be affected by picking the appropriate tire than the size, though. An S-03 in 215/55R16 will handle better and ride stiffer than a Kumho 712 in 225/50. I have some 205/60R14 tires that are 10x better than my other car's 215/45R17 in grip, handling, feel (steering response), and comfort. But credit that to some crappy OEM 17" tires and some very good 14" tires.
Aaron
