I have a 2000 Blazer LT. I have 15x8 rims with 4" backpacking and I want to go a few sizes bigger. I want to put 15x12" rims with 5" backscaping on it but don't understand the whole backspacing stuff. Will they fit ?

 

Why do you want such a wide rim? Do you have any other mods like a lift? Factory BS is 6" so the closer to that you stay the better you will be but I'm not even sure a 12" wide rim will clear without running spacers.