Originally Posted by
wphamilton
In fact, a "9-speed wheel", having a 9-speed cassette just might be an 11-speed wheel, with a spacer behind the cassette. Mine is like that. One of those details to research, that you don't even know is a detail without the research.
But if you’re talking about an OE wheelset on a 7/8/9-sp era bike, like the OP we’re responding to, it’s more than likely NOT a 11-sp wheel.
I’d find it highly unlikely that a mid-range Y2K Cannondale would have been fitted with a 11-sp wheelset, because it wasn’t a thing yet.
Probably why the OP was told by his shop, that a 11-sp cassette wouldn’t fit on his bike, without making a lot of other changes.