There are many threads on here about tyre size. Yes a 280 will fit, just, but it's too wide for the rim. You're simply wasting rubber, as not all the tread will actually contact the tarmac, and it won't/can't corner as well. Depending on the make either a 250 or 260 is the widest usable tyre for these bikes. Sure put a larger size on, your bike and your money, but it's not gonna do anything except look a little fatter.