I think Dianne was correct, you do need the spacer that is supplied with the casette to mount a 10 speed shimano casette on a wheel that accepts 8/9/10 speed casettes. I found the reason articulated well in this thread from this site http://www.bikeradar.com/road/forums...118b10e2f912b:


If I was going to be pedantic, I'd point out that a 10 speed cassette is actually wider than an 8 or 9 - it's simply that there's a recess in the back of it where it mounts to the freehub body which needs to be filled by a spacer! But of course I'm never pedantic...

Anyway, since this seems to be a bit of a FAQ, I'll have a go at a definitive and comprehensive answer:

With Shimano factory wheels, you never need a spacer to fit an 8-speed or 9-speed cassette. You'll need a thin spacer to fit a 7-speed cassette on any modern 8/9/10 speed hub, since the whole cassette is narrower. For most Shimano wheels you need a thin spacer to fit a 10-speed cassette (which should come with the cassette if bought separately) due to the recess. However the older DA 10-speed wheels and the Ultegra wheels are 10-speed only - they won't take anything other than a 10-speed cassette, and you won't need a spacer for this.

With Mavic wheels you need a Mavic spacer for any Shimano cassette (this is assuming an M10 freehub body, as the cassette won't fit at all on an ED10 Campag body). Additional spacers as above - ie none for 8/9, an extra spacer for 7, a different extra spacer for 10.

Any other wheel with a Shimano compatible freehub, including handbuilts (apart from handbuilts with DA 7800 hubs) as Shimano 8/9/10 wheels - ie no spacer for 8/9, a spacer for 7, a different spacer for 10. DA 7800 hubs are the same as older DA and Ultegra wheels - ie 10 speed only, and no spacer needed.