2005 Mustang GT 4.6L Roush Convertable - looking to replace Wheels &Tires

Just go look at any of the major parts retailers that sell wheel/tire sets, they generally have the widest tires you can run front/rear without causing issues.

I have 18 inch wheels on my car (also an 05 Roush), and I run 295’s in the rear without issue. Widest I’ve run was a 305, and even that didn’t have an issue. However, my car is a street car and isn’t making “spin the earth off it’s axis” power, not to mention cost, so I stepped down to a smaller tire.

The speedo - if you bump from a 17 to an 18 inch wheel, the speedo will be off a bit, but not by a significant amount. So, it’s not like the speedo will say 60 mph, and you are actually doing 70, for example. That, and you can buy a handheld tuner (SCT is a good brand) and use it to recalibrate your speedo if it means that much to you.

Roush makes very nice wheels, but as you’ll soon learn (if you haven’t already) anything you want with the name Roush on it comes with a price.