What's the biggest tires you've seen on GSL SE rear wheels without mods to the car?

 

225 I think...

and even those are a stretch on the stock 5.5" wheels

 

Tire shops here will mount 215's, but not 225's.. I'm told it's because too much sidewall flex (when cornering) can cause the tire to come off the bead, and cause a blowout.. so it's a liability issue for them.. and a safety issue for us.

 

I wouldn't go over 205, myself.

 

Tires that are too wide for a given rim are actually detrimental to handling. A 225 has a section width of 8.85 inches. A nearly 9 inch tire and a 5.5 inch rim are not really a good pairing.

I'm not just speaking in theory, here. At one point I had a 245 (9.6") on an 8" rim and decided to step up to a 275 (10.8") while maintaining the same overall diameter. Handling suffered. It felt 'floaty', if you will; like the rim was sloshing back and forth inside the tire a bit.

On my GSL-SE I actually stepped down to a 195 and handling is just as good, it just doesn't have quite the same stance. The only reason I went with a 195 is that it was the closest size I could find to stock whilst retaining the 'V' rating. By the time I need tires again I fear I won't be able to find a 'V' rated or better tire in remotely the correct size.

I wouldn't go with a 225 on the stock rim, but I don't think it would be dangerous to do so; it's only ~3/4" wider than the stock size.