This backspacing doesn't sound right!!!

Take your tire/wheel assembly to any tire store. They'll have a tool to measure the wheel width without removing the tire.

If you were closer, I'd lend you mine...

I'm going to pop the wheel off tonight and run it over to tire discounters. I just want to get these street tires on so I can go out in my car without worrying about getting stuck with slicks in the rain.