Originally Posted by
braintree39
So - I'm looking to take a wheel that has an 11-speed cassette and put a 7-speed cassette on it. Can I do that or do hubs have specific speed cassettes they are compatible with?
I was thinking about just putting the wheel with the 11-speed on, but another poster said I would run into trouble with my rear derailleur...
I seriously doubt your 7-speed cassette (if it is one, see above) will fit on a hub currently running 11-speed. Aside from size issues, you also have simple compatibility issues. Even if they are the same brand (likely Shimano), the spline patterns (the ridges along the hub) will be different. I believe Shimano is pretty bad in this respect, whereas Campagnolo uses the same pattern for 9-11speed (don't know about 12), so that gives you more possibilities.
Then, with the derailleur, I don't think what you are currently using on your 7sp would play well with 11, but I don't know exactly what it is. If you do end up switching to 11, move over the derailleur you were using with the 11 originally, and get a new 11sp chain.