Source for tires to see what fits?
 

So when you guys are trying to figure out what fits, where do you get a tire from to mount to, say, a Wheel Fit tool? I can't imagine Tire Rack, for example, would send out a bunch of tires for you to try only to send back what won't work for a full refund.

A neighbor has the tool, but no one close that I know of has spare tires laying around in the sizes I am leaning toward.

On a more serious note, you have to know approximately what you are looking for. Craigslist, the local autocrossers, and tire shops are all loaded with used tires. I have stacks of used tires here, you are more than welcome to take as many as you want.

If it's a toss up between 275 or 285, put the 275 on there and see where you end up, it's just a bit of math once you know what room you have.