Hendo252 

Greetings.

I'm installing a new Ultegra CS-6700 12-30t cassette onto a Shimano R-500 wheel.

The cassette is packaged with a 1mm inner spacer that fits between the cassette and the freehub.

The CS-6700 installation instructions have a somewhat cryptic note that "If using a special freewheel, a spacer is not required" but it doesn't give any information about what a "special" freewheel means in this context. <and yes, they use the term "Freewheel" not "Freehub">

Here's a link to the installation instructions; see the gray box on the LH side of the page:
https://tinyurl.com/9qa7j2x

The previous cassette was a Shimano 5600 12-25t, and it had the spacer installed but since I bought this bike used I have no idea about its prior history.

So I originally installed it with the spacer since there was one installed behind the old cassette, and since there didn't seem to be anything "special" about the freehub. It all seems to fit, but clearance between the chainstay and chain on the 12t inner cog is none too large and I thought it would be prudent to see what y'all think.

The bike is a new-to-me 2009 Specialized Roubaix (stealth gloat) and the drive train is Ultegra 6700/6703 triple, if that makes a difference.

Thanks in advance for your help!

-Tom in SoCal

FBinNY 

Don't try to remember whether each particular combination needs an extra spacer behind the cassette or not.

Instead remember why you'd need a spacer and you'll know whether or not to use on for any combination.

The lockring is supposed to compress the cassette and lock it place. For that to happen the cassette must overhang the front of the freehub body by 1mm or so. Otherwise the lockring will bottom out on the freehub body instead of the cassette. It's the same logic as why the stem and spacers must stack up above the top of the steerer for the top cap to adjust the headset.

Hendo252 

Thanks FB -- that makes all kinds of sense.

Thanks for this advice, and all your contributions to the board.

-Tom in SoCal