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I removed a Shimano HG 10 speed cassette from my Bontrager rim and it has a indexed spacer below the 10 speed cassette. I want to install a Shimano HG 9 speed cassette on that hub. I have a 1 mm non-indexed spacer that I had bought in anticipation of doing this. The indexed spacer that is on the Hub is definitely thicker than 1 mm. I am wondering should I leave the indexed spacer in place and also install the 1 mm spacer that I have before I install the 9-speed cassette and tighten it down or should I install the 9-speed cassette on top of the original indexed spacer and not use a 1 mm spacer?

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The term "indexed spacer" isn't a standard one.

Some (many) 10-speed Shimano cassettes come with a 1mm spacer that's always used except with a very few hubs.

What's in question here is whether your wheel has an 8/9/10 HG freehub body, or 11-speed road. (If it's a road wheel from around the last decade, it's probably 11-speed-compatible).

If it's 11-speed road (36.85mm long from the end of the freehub body to the shoulder that the cassette/spacer rests against), and it's any kind of normal road or mountain 9-speed cassette, you'll use a 1.85mm spacer under it.

If it's 8/9/10 (35mm long), you don't use any spacer.

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    Thank you for the great advice, what I meant by a indexed spacer is that it has the shape of the Hub stamped into it so that it slides on the Hub as the cassette does. I believe that spacer is 1.85 mm. I guess I'm not sure if I should leave that spacer in place and not use the 1 mm spacer that I had bought in anticipation of changing the cassette from a 10 to a nine. I will have to try to make some of the measurements that you mentioned. Thanks again for the great advice I really appreciate it
    – Michael
    Mar 1 at 22:37
  • If it had it before, yes use it. It's an 11spd conversion spacer. The 1mm spacer is here nor there for nine-speed. Mar 2 at 5:12
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I have found at least two combinations of cassette and freehub that do or do not need spacers, when the expectation was opposite.

I prefer to fit the cassette and do up the lockring, and then see if it needs more spacer. The cassette should not have lateral play and still have sufficient thread engagement on the lockring to tighten it all down.

Note: spacers go between freehub and cassette. You should not put a spacer between cassette and lockring/locknut.

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    Okay that is pretty much what my Biking friend told me to do. So I guess I will just leave the original spacer in place which seems to be a 1.85 mm and install my 9-speed cassette on top of that. So I guess I should be looking to tighten the lock ring down enough to where it's in place very tightly but still has room to be tightened down just a bit more
    – Michael
    Mar 1 at 22:40
  • @Michael I'm concerned about your last sentence. The lock ring should be tightened to 40 Newton-meters, which is quite tight, leaving no room for "a little more" when one is using standard length tools (which I define as having an 8-10 inch handle portion as found on, say, a common adjustable (Crescent) wrench, a 3/8" or even 1/2" drive ratchets used with a socket). Using a torque wrench and a 1" socket (usual size of the hex flats on a lock ring tool) if & when 40N•m is reached, that's it: a torque wrench will click and a normal man using a tool mentioned above won't coax it in a bit.
    – Jeff
    Mar 3 at 9:56
  • Thanks much Jeff, I guess what I meant by " a little more" is that there would still be some thread left on the Hub after reaching tightness of 40 newton meters. I realize you would not be able to know if there is thread left unless you tried to tighten Beyond 40 Newton meters which would probably destroy your Hub threads at some point. I will get out my trusty old torque wrench and use that rather than guessing that it's tight enough.
    – Michael
    Mar 3 at 13:19

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