What is a good size of 15 inch wheels and backspacing for a 99 GT. Also what size slick or drag radial. If anyone is running Welds or Prostar 15 inch wheels I would like to know what you all are running too.
I've got ProStars on my '03 GT. I'm running 15X10's out back, with 6.5" of backspacing. Up front I've got 15X5's, which only come in one backspacing. You'll need a 7/16" spacer (Mr. Gasket makes them) for the front wheels. Many folks recommend changing out the front studs to long ones for safety sake, but, knock on wood, I've never had a problem. For tires, I run 205/70/15's on the front, and 295/50/15's on the rear.
You can run 15X8's out back also, with 5.5" backspacing. Some folks like the 15X3's up front, but I'm not a fan of running these on the street when you have to do freeway-speed driving. Also, if the diameter of the front and rear tires is way, way off, it can trigger the ABS light if you have it.