Hi Tom A 27.5 should do , but I don't actually know. It's only a half an inch. I have disc brakes which may have a barring on thinks. My dropout is 13.5cm and I require a cassette wheel. 9 gears preferably.
Hi. 9 speed cassette is fine and the dropout width of 13.5cm is also fine. As it is a disc brake you should be OK, with a wheel that is 0.5" smaller in diameter. Though it will obviously slightly alter the angles of the bike, compared to the 28" wheel it is designed for. Thanks.
