Sanity check, built a 13x25 10sp from a 12x25 and an 18T cog

Discussion in 'Cycling Equipment' started by NomadVW, Dec 16, 2006.

  1. NomadVW

    NomadVW New Member

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    I'm doing some mountains tomorrow that I want to have the 25T for, but I don't feel like sacrificing the 18T that I spend quite a bit of time on. It ends up being the gear I use a lot for some reason at just the right spot.

    I turned my 12x25 into a 13x25 with the 18T by removing the 12T and inserting the 18T, but before I go for four hours of riding tomorrow, I wanted to sanity check that this wouldn't be a problem.

    The cassette threads on the freewheel hub with no problems, but it obviously doesn't have the "bite" to it that it would have with the 12T cog on. On the other hand, the cassette is "pulled" by the chain in the "thread tightening" direction. Are there any chances the cassette could come unthreaded without that bite?

    I don't think that it would, and tightened it nice and tight. But I wanted to check with some other folks to sanity check it.
     
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  2. alfeng

    alfeng Well-Known Member

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    WoW!

    The cogs on the freewheel body shouldn't unthread ... are those "famous last words"?

    On the older Shimano freehubs -- where only the last cog of the cassette is threaded on -- the last cog always stayed in place AND seemed to get slightly tighter with time.

    IF you hear (!) the cogs rattle, then stop and tighten that 13t cog!

    IF you feel (through imprecise shifts) the cogs loosen, then stop and tighten that 13t cog!

    OR, either put some loctite OR tub-and-tile caulk on the threads of the smallest cog if you are concerned ... the tub-and-tile caulk will deaden the vibration which might cause the last cog to loosen & provide a modest amount of adhesion.

    OR, make an ultra-thin gasket/washer out of an aluminum soda/beer can OR even 20 lbs. typing paper to snug up the last cog.

    OR, put teflon plumbers tape on the threads before threading the cogs in place ...

    FWIW. I think it is time for you to have your rear wheel relaced with a new hub ... or, am I misreading what you've written?

    Presuming you are talking about one of THOSE old Dura Ace freewheels, you will nonetheless shave between 4-and-8 ounces off the weight of your rear wheel if you go to a "new" hub which uses a freehub & cassettes ... MORE if you get something like a Hugi 240(-or-240s) hub.
     
  3. NomadVW

    NomadVW New Member

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    I think I mistyped. I have a standard NEW style freewheel hub. The 12T cog on my 12-23 has teeth along the edge which you would tighten the lockring down on and you can "feel" it biting as you tighten. The 13T however, doesn't have those, but the cassette as a whole fits properly as a 13x25.

    I did ride today with the 13x25 as I assembled it last night without problems, and even did an extra 2 hours of riding for a grand 160km on it, 1755m of climbing.

    [​IMG]
     
  4. Retro Grouch

    Retro Grouch New Member

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    How thinly can you slice the balogna?

    Back in the days when men were men and bike frames were steel we only had 5 cogs on the back and somehow managed to get by. You have 10 cogs on the back and are fretting over one tooth in an area of the cassette that has relatively small percentage differences anyway.

    First position cassette cogs are designed a little differently from their fellows. I assume there is an engineering reason for that. If it was my bike I'd sure want to test it on a casual ride close to home before I took it out on a big ride. Never change anything on your bike the night before a major event.
     
  5. alfeng

    alfeng Well-Known Member

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    The so-called "first position" cog has a lip which PREVENTS it from sliding BEYOND the end of the freehub -- it can theoretically be used without any other cogs of the cassette being in place whereas the other cogs are held in place by their neighboring cogs & spacers.

    Similarly, with the OLDER Shimano freehubs, the last cog was threaded in place ... and, the threading on the freehub was limited to the end of the freehub body.
     
  6. NomadVW

    NomadVW New Member

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    Well, 19T to 17T on the 52T chainring is a 4kph difference, where 21 to 19 is 3, and 17 to 16 is 2.5ish at around 95rpm. 4kph difference is a pretty big jump if maintaining cadence. I could also drop to the 39T and jump up to the 14T to get by, but I end up using the 18T more often than not.

    No doubt that if it wasn't there or available, I'd get by. But it is available and I can get it there, so might as well make do with the best case scenario :)

    Anyway, it was a no problem day of riding. I'm swapping back to the 12x23 tomorrow morning when I scrub down my bike from riding in the sleet/snow today and will assemble as normal.

    Thanks,
    VW
     
  7. supergrill

    supergrill New Member

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    Here is a diagram that has the part number if you want to put the proper 13T on in the fist position in the future.

    http://bike.shimano.com/media/cycli...nents/CS/EV-CS-6600_v1_m56577569830537975.pdf
     
  8. Retro Grouch

    Retro Grouch New Member

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    That's pretty much the bottom line isn't it? I'm happy to hear that you had a good ride.
     
  9. NomadVW

    NomadVW New Member

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    According to the diagram, the 13T end cog and the 13T second/third cog are different parts, so that answers the question. My guess is the 13T end cog has the ridges to tighten down against to prevent the lockring from unscrewing like my 12T and 11T cogs.

    Thanks!
     
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