I am putting a disc brakes on my new bike wich in turn has freed up a wheelset for my old bike. The wheel set is a deore hubset laced to mavic x139 rims. I want to put this wheelset on my old bike but it has a 7 speed drivetrain which is a mixture of stx and alivio. obviously I will have to buy a 7 speed cassette becuase the bike currently has a freewheel. I noticed on nashbar that they sold a spacer that was supposed to allow you to run a 7 speed cassette on a 8 speed hub. do they make 8 speed spoecific hubs or do they really mean 8/9 speed hubs. will a 7 speed cassette work on my hubset?