Determining Rim Size?

I was just reading a post about tire size on certain rim sizes.My mach doesnt have the original rims,it has blk bullits and I dunno what size they are,stock size,17x9 or what.All I know is that they have 275/40/17's on them.So how can I tell what rim width I have,and if they are stock size rims....are these size tires ok on there?

Well after looking at the tires they dont match up with the rim evenly,the tire goes just a tad past the rim.Is this bad?Will it cause drivablity issues?Im assuming they 17x8's,with that being said whats the biggest tire I just be running on these rims?My Gt had the stock size 245's but on this one I have a better ride,I know its not just the tires...the car itself has some to do with it.Im not road racing or anything like that but I want the best drivability and control.