Originally Posted by
The_Joe
I'd say 90% sure. According to Velobase the Cyclone MK-II maxes out at 26. According to the Disraeli Gears site I think it said 28 was possible if you use a longer bracket. Since I'm on forges dropouts and I've never measured the distance, I was always erring of the side of caution. Although having a 28 would be beneficial with all the hills around me.
If you have the derailleur, go by what you have, not by what it says on a website.
You don't need a lot of clearance when you get to the largest sprocket, you just don't want the derailleur jockey wheels to be bumping on the sprocket.
B-Screw adjustment?
Anyway, by looking at the derailleur on the bike, you might be able to estimate what it would look like with a sprocket 2 teeth larger. Also look at your chain wrap (big/big vs small/small gear combos).
Did you say you were heading to the co-op? Perhaps they could loan you a 6 or 7 speed cassette to try out (or allow an exchange).