Will 15x8 5.5 backspace fit???

[allgo]

will these fit my 2008 gt 500 rear?

 

[stkjock]

as far as the details you supply - yes.

However you need to have the proper offset as well

 

[Markstre302]

However you need to have the proper offset as well

Backspacing and offset are just 2 ways of measuring the same thing. The centerline of the wheel compared to where the mounting face is. With an 8" wide wheel and backspacing of 5.5" that means the mounting face is 1.5" towards the outside of the wheel. In offset speak, that's going to be about -38mm.