SS cassette spacer question- Mtbr.com
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  1. #1
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    SS cassette spacer question

    Okay, so sorry for another conversion question as I'm sure you guys get bombarded with them.

    I've got a Surly spacer kit and will be running two rings in the back, one with an 8mm base and a standard Surly cog.

    I've measured everything and think I have my chainline numbers figured out, so now I'm getting in mind how my spacer stack will have to be.

    No matter how I orient my spacers, I'm going to have to cut one of them down to get proper fit on my freehub body, which is fine. My question is, Surly specifies their spacer stack with cog as measuring 35.45mm or something. How precise does that have to be?

    And also, how close does chainline need to be? Is within 1 or 2mm close enough? I eyeballed my last SS and it never killed me, but I'd like to be as close as possible on this bike. But between spacer arrangement and my measuring skills, I'm not positive I'll be spot on.

    Thanks!

  2. #2
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  3. #3
    Downcountry AF
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    do you have any old spacers from a used cassette? they could be used in addition to your Surly kit to fine tune chainline. or if necessary, buy a few extra small spacers at LBS or ebay for a couple bucks. thats easier than trying to cut up spacers IMO.

    if your using two cogs in the rear your chainline won't be perfect. split the difference but get it as close as possible. I would throw your cogs on the freehub and play with different combinations of spacers till you get it right.
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  4. #4
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    I always considered it a trial by error thing. You'll get close with the math you've done, but after that, just shift the spacers as you see fit. Sometimes, you have to use bad chainline for tire clearance. Every scenario is different.

    And definately don't try to cut/sand/shim the spacers. Just get used ones from a junk 8-speed cassette. There is no load on them, so the material choice boils down to getting as light as possible.
    "a hundred travel books isn't worth one real trip"

  5. #5
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    Cool thanks guys. So basically it just has to be close to that 35 mm number to tighten down properly?

  6. #6
    more skier than biker
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    Quote Originally Posted by watts888 View Post
    There is no load on them, so the material choice boils down to getting as light as possible.
    Is it true that there is no load on them? I've been having an issue lately with dropping my chain on my SS and it always seems to have been dropping off the rear cog, not the chainring. I thought it was a chainline issue, but even when I thought I had the chainline correct, the chain would still drop in very high torque situations (i.e. smashing fast up a steep climb, or really torquing down to clear the last few bits of a hard hill)...it would just kind of pop off the rear cog in those situations.

    So the other day, I was taking everything apart and I noticed that the small spacer that sits right up against the inside of the cog was cracked clean through. I replaced it and my chain drop issues went away. My theory now is that with the cracked spacer in there, in those high-torque situations I described above, the cog would kind of 'squash' the cracked spacer a bit thus briefly changing the chainline for an instant which could result in dropping the chain off the rear cog. Which if true, would imply load on that spacer....no? yes?

    I've been a singlespeed racer and rider for many many years....first time I have ever cracked a spacer like that so this was a new one to me.
    Last edited by Tyrone Shoelaces; 07-07-2016 at 03:04 PM.

  7. #7
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    That's why I made this, nothing moves, spacers are aluminum and stainless.




  8. #8
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    Lot of things that could have caused it, but normally, there isn't any rotational or side load on the spacer. Could have come from the factory with a crack and wasn't noticed. If the cassette retainer ring is over tightened, it could crack the spacer. If the retainer ring isn't tightened down and the drive cog has a lot of force exerted on it, it could shift and create enough twisting force to crack the spacer. It could have been installed on a cold day and left in a car on a hot day where the plastic expanded and cracked the spacer.

    Basically, there's a lot of "coulds" and "maybes" in there. Normally, those spacers don't break. Exact same material used in 8, 9, and 10 speed cassettes in between the cogs. I've never seen one of those break, but I'm sure they do. I've seen cogs break though.
    "a hundred travel books isn't worth one real trip"

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