My memory says that the hubs are different in a couple of ways. 7 speed used a 126mm spacing while 8 and 9 speed used a 130mm rear axle spacing. It also seems like the Shimano 7-speed cassettes used the smallest cog as the lockring. 8 and 9 speed cassettes used a lockring for the lockring--imagine that! If it is a freewheel, then you might be able to use an 8 speed freewheel, but I still think that the rear axle/dropout spacing is different.

So, you can go through the trouble of buying a new axle and freehub body and replacing your old ones with the new, but I'd only do that if you just really like the hub and wheel that you want to upgrade. 8 speed cassette bodies are compatible with 9 speed cassettes, so an older model wheelset from the 8 speed shimano cassette era will work with 9 speed.

The derailler will also need to be changed as you mentioned. I don't think that the 7-speed derillers had enough 'throw' to work on 8 speed. I tried an 8 speed dura ace derailler with a 9 speed STI lever and cassette, but that didn't seem to work very well. Bar end or down tube shifters would probably work, epecially if you used friction mode.

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Brandon Marsh - Website | @BrandonMarshTX | RokaSports | 1stEndurance | ATC Bikeshop |

The rear spacing is 126mm on a 7 sp and 130 mm on a 8/9 sp. If you have a steel frame this is easily cold flaired by your LBS. If aluminium then you're out of luck. You may not have to change derailleurs, depending on the model. You'll have to change shifters. The 7 sp is a one piece freewheel instead of a 9 sp cassette. You'll definitely need a new hub/cassette as well as shifters.

Do a goggle search about this along with "Sheldon Brown". I believe he's written a number of articles on this.

There's a very good chance that this will be more of a pain in the ass than it's worth, and end up costing you a good chunk of change to boot. Unless your frame is steel, you won't be able to open up the rear end enough to get the spacing in. If your frame is steel, you can take it to a top-shelf bike store and have them "cold set" it for you (you DO NOT want to watch them do this!). Unless your frame is a nice one, this is likely not worth what it'll cost you. Then you'll need to replace the hub & freewheel body, shifters, and possibly the derailleurs. Might need to re-dish the wheel, too.

I'd be inclined to leave it as it is, and save up for a new ride. Keep this one around as a beater, 'cross bike, or turn it into a fixie.

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[reply]If your frame is steel, you can take it to a top-shelf bike store and have them "cold set" it for you

I have a 7spd steel frame which I simply pry apart the rear drops to accomodate the 130mm spacing of a newer wheel that I bought. I am probably risking fatigue failure over time, but I don't take the rear wheel on and off that often.

As far as the cassette is concerned, a 7spd is still compatible with the newer wheel as well, but you have to add a spacer to make up the the missing gear (very cheap). So, in summary, I think all you need is the 8spd rear derailleur, rear wheel and cassette to upgrade from 7 to 8. If I remember right, the 9spd would also require a more narrow chain. Again, assuming a steel frame.

dave judice

the derailleurs are fine, it's the hub and wheel that will be a problem.. If your 7speed is a freehub, with a cassette, upgrading is as simple as replacing the 7spd with an 8/9spd freehub body, and redishing the wheel. If it's a freewheel, then you'll need to rebuild with an 8/9 speed freehub instead, or replace the wheel. And as observed earlier, if this is anything but a steel frame, it can't be done, because of the spacing issues.
See http://www.sheldonbrown.com/k7.html for a full explanation of hubs etc..