Shimano cassette spacer, why?

cojones Posts: 131
edited August 2013 in Workshop
So this may seem like a naïve question and I’m sure there’s a sensible answer…why do shimano cassettes need spacers on some hubs and not others?

I’ve got an ultegra cassette that I swapped from a DT Swiss wheel (which required a spacer) to a Fulcrum wheel.  I didn’t put the spacer on as the cassette was tight and the indexing was better without it.  10 miles into my next ride it started rattling and sure enough the sprockets were loose and moving laterally on the hub. 

The cassette was fixed on tight and had no play when I put it on but seems to have worked itself loose during the ride.




  • rolf_f
    rolf_f Posts: 16,015
    Person buys thing. Thing instructions say fit spacer. Person ignores instructions and doesn't fit spacer. Thing doesn't work. There's a moral in this story somewhere but I'm damned if I can find it! ;)

    But yes, I think some wheels need spacers and some don't for Shimano - Fulcrum being an example.
    Faster than a tent.......
  • cojones
    cojones Posts: 131
    Reply above not required. Please waste someone else's time.

    For your information, instructions say it may or may not be required.
  • chrisaonabike
    chrisaonabike Posts: 1,914
    Question is of interest to me too. Switched an Ultegra 12-28 (or it might have been 11-28) for an Ultegra 12-30 on my OH's Mavic wheel. The wheel came with a spacer which was needed to get the new cassette on tight. A thinner spacer that came with the cassette was surplus.

    Does more muck get in the gap if you have a hub needing a thicker spacer?
    Is the gorilla tired yet?
  • drlodge
    drlodge Posts: 4,826
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • Because stupidity ;). Bicycles are great because a lot of the components are standardised so you can chop and change bits. Drawback, there are far too many different 'standards' that it's a full time job to get your head around it.
  • rolf_f
    rolf_f Posts: 16,015
    cojones wrote:
    Reply above not required. Please waste someone else's time.

    For your information, instructions say it may or may not be required.

    Because your time is so important isn't it.....

    Anyway, don't be such a prissy humourless drudge. It was just a bit of a joke and, if you'd bothered to read the whole post, I did say that Fulcrum need the spacer. And as drlodge points out, the information is here if you can be bothered to use the search function or are you too busy for that as well?! But do carry on rattling.....
    Faster than a tent.......
  • satanas
    satanas Posts: 1,303
    drlodge wrote:
    This is mostly correct, except for the comments on Mavic wheels. A bit of history is required.

    When Mavic first made complete wheels, Campag 10 speed had just come out and this needed a wider freehub body than Shimano 8/9. Presumably because Mavic didn't want to make two freehub bodies, their body had Shimano pattern splines, but with the Campag width. If you wanted to use Campag 10 you had to use Mavic cogs and spacers; the Campag cogs won't fit on the Shimano splines. If you wanted to use Shimano 8/9 cogs, these fitted straight on, but because the body was wider an extra spacer was needed behind the cassette.

    Later on Mavic started making freehub bodies with the Campag spline pattern, but kept the Shimano bodies wide so swapping freehub bodies didn't require modification of the axle spacing or redishing the wheel. This wider cassette body is the reason why Shimano/SRAM 11 speed cassettes will fit onto older Mavic hubs, so nobody should complain about it!

    As aracer said, early DA 7800 freehub bodies (and those found on some DA and Ultegra wheels) were alu to save weight, and these used a taller spine, and thus were not backwards compatible with 8/9 speed cassettes. Shimano chose to recess the back of the 7800 cassettes, presumably for some sensible mechanical reason to do with the freehub body. Because of this recess, fitting a DA 10 cassette to other 8/9/10 speed Shimano hubs means that a 1mm spacer is needed. When fitted to a Mavic hub, another thin spacer (1.8mm IIRC) is needed to make up the difference between Shimano and Campag freehub body width.

    And since Shimano decided that nobody was going to use their Ultegra junior cassettes on DA 7800 hubs, these had the standard 8/9 speed spline depth and won't fit on some DA and Ultegra hubs/wheels. The problem freehub bodies are easy to spot as they have alu bodies and taller splines. If the body is steel or Ti, then 8/9/10 will work, but a 1mm spacer is required with (most) road 10 speed cassettes...

    Simple innit? :mrgreen: