[LA_LT1]

Originally Posted by Msquared

This is a bad idea. 275s on a 8.5" rim width will not give you more grip or traction than a 245, because they won't properly supported by the narrow wheel. They will also have to run at higher slip angles to generate any given level of lateral grip. Therefore, if you run 275/35/20 (to keep the proper diameter) in back with proper 245/40s up front (i.e. a "staggered" setup), you'll have a car that feels loose on corner entry. It's just a bad idea.

If you want wider tires, you should install them on wider wheels. You can probably buy OE SS wheels and tires and run 275/35/20 in back for not a lot of money. There are also even wider sets of wheels for sale in the Classifieds section here all the time. Any sizes up to SS 1LE should fit fine, as long as you get the offsets correct (spacers with longer studs are fine, where needed). Here's one example of a great deal available now. If you paired those with 285/35/19 tires, you'd be golden, and you could still rotate them since they would be a square fitment.

My question was if I need to change the aspect ratio to run 255s on the stock Lt1 wheel. 255s aren't a massive difference from the stock 245s