79FStreet

I've just joined the Mustang Forums. Many years ago, I was on the GTO Forum, so this all looks familiar. I found the tech areas to be very helpful before. Because I'm not a life-long Mustang driver, I'm still learning about the car. I hope to find answers to Mustang related questions here.
I'm driving a manual 6-speed 2015 GT Premium with Performance Pack. I've swapped out the shocks for Koni Sport adjustable shocks, replaced the front anti-roll bar with an Eibach adjustable roll bar, installed Hawk brake pads, K&N filter, and Magna Flow Cat-back Street Exhaust with X-pipe. I run on Bridgestone RE71R's with 285 X 35 X 19's on the rear and 265 X 35 X 19's up front.
My hobby is Autocross. I've been doing this for about 15 years. The 2015 GT is in the F Street class. The class index factor is pretty good for this class. I've won my class in each of this year's events. I'm registered to compete in this year's SCCA Solo (Autocross) Nationals event. I've finished near the bottom for the last two years. I hope to do better this year, but the 2018 Mustangs and Camaros fit into this class also and have a few more stock performance enhancements to work with.

Sputnik775

hey man, fellow cone-head here with a 2017 gt pp. question, how well does that 285/35/19 fit on the stock 9.5 wheel? I wanna go 285's all around, but not sure how that's gonna work out. Any advice? Thanks

79FStreet

Apparently the Ford PP 9.5 X 19 wheel bead is a little different. One installer worked for a full week trying to get the 285 X 35 X 19 Bridgestones RE71R's to seal and air-up. They ended up using a lot of grease on the bead and lit starting fluid to blow the sidewalls open and against the beads. I asked Bridgestone about this and they said some installers had issues with this rim, but installers, who worked with low profile tires and had the right equipment had no issues. The guys I use now get it down in ten minutes.

I've tried mounting the rear wheel (9.5) and tire (285 X 35) on the front and it rubbed the shock. I didn't go any further. If you're looking for a common size for all around, I'd suggest the 265 X 35 X 19 on 9.0 wide wheels all around. I'm going to stick with the staggered setup with 285 back and 265 front.

Sputnik775

Thanks, I decided to go with 275/40/19 all the way around. Gonna get them put next Sunday. Will report back on how that worked out...