A buddy of mine has an old Hed deep dish rear wheel with a 7 sprocket cassette. He was asking me today about moving up to a 9. Is this possible? Would he most likely have to buy a new wheel or are there other alternatives?
Is it a 7 sp freewheel? AFAIK, it is not interchangeable with a 9 sp cassette.
I think most 7 speed wheels are freewheel, meaning the ratchet mechanism is within the gear cluster itself, rather than part of the wheel hub. If this is the case, the best you can do is get an 8 speed freewheel (look on ebay), and get a spacer to widen the wheel to the wider 8/9/10 speed width. Hed can provide these for their disks, I did just this about a year ago. You will probably have to run your shifter on “friction” mode unless you want to replace it with an 8 gear shifter. Of course you can just stick with the 7 speed freewheel if you want also, but you still need the spacer. It’s not optimum for shifting but that won’t make you any slower, esp. on a flat course where you don’t need 9 gears anyway.
I had an olde Hed wheel and yes, it was Shimano 7spd Cassette. To upgrade to 9spd you’ll need at a minimum a new 9spd freehub (the splined body that the cassette mounts upon). Probably also a longer axle since most 7spd wheels were made for 126mm dropout spacing, and most 9/10 road bikes have 130mm spacing. You’ll also need some axle spacers, and you’ll need to recenter the wheel on the wider spacing. Any competent LBS should be able to do this (in fact, if they can’t, they’re not competent!)
See http://www.sheldonbrown.com/k7.html#up7 for details