Help matching wheel & tire sizes

[Touch of Fast]

Loooking at 18x9.5's and 20x10.5's on a 2004 ZO6. What tires sizes works best? Any concerns i should have with going to these sizes? Thanks.........

[Luke@tirerack]

275/35-18 and 305/25-20

[Touch of Fast]

Thanks Luke, on ocassion we we be at 140+ any concerns in going with this plus size set-up. I checked your web site last night and I thought it suggested 265x35 and 285x30. What is the diff between your suggestion and these sizes? It also looked like Mich Pilots were the only option for those sizes.
Thanks for your help.