I'm no expert on this by any means, but I've seen this topic come up again and again on 250cc boards. Usually some kid who really wants to be riding an R1 but who's stuck with a GPX250 complains that the bike looks wimpy because of its rear tyre.
The consensus seems to be that the skinny tyres that 250s come with as standard are one of the reasons they can corner so well. I don't know how to describe the physics involved, but the decreased curvature (in cross section) of the fatter tyres doesn't do a lot to help their ability to lean into corners.
The bigger tyres on the bigger bikes are there to put their much greater power down on the bitumen. If you don't have that greater power, there's not a lot of benefit in having the big tyres. The RS250 probably does something like 55 or 60hp at the rear wheel, whereas your ZX2R is probably more like 35-40hp?
How this would work out with a larger tyre but the same profile (ie something with bigger overall diameter) I don't know, but I reckon you're then starting to run into probs with clearance.
I've seen sites that tell you the largest tyres that can squeeze onto a GPX250 or ZZR250, but can't help you with the ZX2C sorry
