There were/are a couple reasons: One was at the time I didn't want to put 275's on a 9" wheel, thought there might be too much sidewall flex. Also, my car currently has the stock motor pushing out an earth-shaking 185 rwhp, so I didn't think wider tires were really necessary at that point. Also, I'm going to be participating in NASA TT, and I get assessed points for tire sizes over my base class, so I probably won't be going any larger than 255, and maybe drop down to 245 with R-comps. I'm going to be working over the engine, so we'll see if I need more traction, but even then I'm going to be keeping it to like 260 rwhp or so. And I've got MM coil-overs in the garage for the front/rear and a panhard bar - I expect to be able to use more of my traction in the rear. If I was going all out with regard to power, then I would put the biggest tires on there that would fit. And I still may go to 275, it just depends on how the points fall out and if I can afford those points.