That is a good question. Almost all large Shimano freehubs will hold eight, nine and ten speed cassettes. MTB, road and hybrid Shimano freehubs are pretty much the same. The only freehub that won't take a eight speed cassette is the smaller seven speed freehub. You may have to spread your frame a little to accomodate the larger, 130mm axle for the larger freehub (if your frame is 126mm). But that's usually no big deal UNLESS your frame is one of those older aluminum tubes bonded to steel. I've been told some of them failed when stressed to 130mm.