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  1. #1
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    12-42, Seven Speed

    I filed out a chainring spider I was never going to use so that it fits onto a freehub body. SRAM just introduced an 11 speed casssette with a 42t top cog. Needless to say, it's pricey. Here's a rather inexpensive alternative for a wide range single chainring drivetrain.

    The drivetrain is 1x8, using a (3/32) bmx sprocket and some Redline Flight cranks. It's 26x12-15-18-23-28-34-42. The gaps are tolerable. I think I am going to with a 25x11, which will give roughly equal a 32x14. The 25x42 granny is about equal to a 20x34. On the kind of trails where I go on this bike, that gearing is pretty decent for 90% of what I ride.
    Attached Thumbnails Attached Thumbnails 12-42, Seven Speed-12-42-seven-speed-4.jpg  

    12-42, Seven Speed-12-42-seven-speed-1.jpg  

    12-42, Seven Speed-12-42-seven-speed-2.jpg  

    12-42, Seven Speed-12-42-seven-speed-3.jpg  


  2. #2
    All Lefty's, all the time Moderator
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    That's awesome.

    Gold star for you
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  3. #3
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    The derailleur pulley/chain/42 tooth cog don't jam together and stick? The chain doesn't get caught between cogs? I see what you did there...

  4. #4
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    Interesting. Big gaps are not a problem I guess if you're just cruising around. Do you expect the splines you filed on the 42t to hold up to all that torque?

  5. #5
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    We'll see. I hope so! The gaps are fairly reasonable for the width of the range, in only 7 gears.

  6. #6
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    Quote Originally Posted by mainlyfats View Post
    The derailleur pulley/chain/42 tooth cog don't jam together and stick? The chain doesn't get caught between cogs? I see what you did there...
    I had a 40t ring bolted to a 34t cog on there 1st. When I took it off and installed the 42t 'cog', I just had to dial out the b-tension screw a bit. The shift from the 34t cog to the 'new' 42t ring is kinda slow, but tolerable.

  7. #7
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    Quote Originally Posted by phoenixbikes View Post
    I had a 40t ring bolted to a 34t cog on there 1st. When I took it off and installed the 42t 'cog', I just had to dial out the b-tension screw a bit. The shift from the 34t cog to the 'new' 42t ring is kinda slow, but tolerable.
    This shift on to the 42 I get (-ish) - it's the shift off the 42 I really wonder about. Anyway... nice work, glad someone still tries.

  8. #8
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    The shift off the 42 works decently. It does take a bit longer than a typical cog to release the chain but it's not a problem.

    I filed another spider on which I'm using both a 38t ring, and a 42t ring. Both are ramped, so I turned them around to aid shifting under load. That one is an 8 speed setup. The cogs are
    11-14-17-21-26-32-38-42.

  9. #9
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    cool project! any pics of the cassette in profile (showing the gaps)? pics of the chain in the 42t "cog"?

  10. #10
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    How did he spacing between cogs work out?
    Zip ties? Not on my bike!

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    650B rims or wheel set. 80's vintage 32 or 36 x 135mm

  11. #11
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    Here's a pic of the 8 speed setup. The top two 'cogs' are 38t and 42t. I switched them around so that the ramps would aid shifting.

    The tabs on the chainring spider are about the same thickness as an 8 speed spacer, so it indexes just fine on the top two gears. I used 9 speed cogs on this one, with 9 speed spacers.

    There is also a spacer behind the spider so that it would work better with 8 speeds. I have run 9 speeds with a thumbie but in friction mode the shifting is a little ponderous. Between the 32t cog and the 38t ring I used two spacers to take up the gap and get the alignment right.

    The 2nd pic is of the 7 speed setup, which just needed one spacer between the spider and next cog (34t) to get it right.
    Attached Thumbnails Attached Thumbnails 12-42, Seven Speed-redline-spider-38-42-chainrings-cogs-conversion-5.jpg  

    12-42, Seven Speed-cooks-chainring-spider-42t-cog-conversion-4.jpg  


  12. #12
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    Here's a few more pics on a different bike. The 36t 'cog' has oddly shaped teeth but they seem to help shifting under load along with the chainring ramps.

    The crankset has some modifications too. The rings are 17/28/44. The granny gear is a 17t 7 speed cog. I cut an old freehub body in half. It has external threads so I used a bottom bracket lockring and a cog drilled with a 5 bolt 58mm bcd to hold the very short section of freehub body on the crank. I then mounted the cog, and cranked it down with a lockring. I've done a number of these cog-to-chainring conversions before, mostly with 18t cogs.

    The middle ring is a 28t 74mm bcd unit. Finding 29t 94mm bcd rings is hard and they can be pricey. 28t 74mm rings are common so I altered one to work with my 94mm cranks. The 28x42t combo really extends my climbing range in the middle ring.

    The 17x42 granny gear on my 29er is great. It's probably the lowest gear mechanically possible with a standard derailleur and chain drivetrain. I won't be needing the 17x42 much this winter but next summer having a super low bailout gear at high elevation will be sweet.
    Attached Thumbnails Attached Thumbnails 12-42, Seven Speed-cooks-cranks-17-28-44-shot-1.jpg  

    12-42, Seven Speed-redline-spider-36-42-chainrings-cogs-conversion-3.jpg  

    12-42, Seven Speed-redline-spider-36-42-chainrings-cogs-conversion-2.jpg  

    12-42, Seven Speed-redline-spider-36-42-chainrings-cogs-conversion-1.jpg  


  13. #13
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    Glad I saw this thread, just last night I was thinking about doing something similar to make a 10 speed cassette with a 42t big cog so I don't have to buy a new drivetrain, shifters and rear hub to work with a single chainring set-up. Now I have some ideas and photos to work from, thanks.

  14. #14
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    Here's another idea. This one works pretty well. I found a 3 bolt ring and drilled 3 holes in a 34t cog. I then attached the 40t ring with chainring bolts and washers to act as spacers.

    The stack in this picture runs 11-14-17-20-24-30-34-40
    Attached Thumbnails Attached Thumbnails 12-42, Seven Speed-34-40t-cog-attachment.jpg  

    12-42, Seven Speed-34-40t-cog-spacing.jpg  


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  16. #16
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    Don't really see the relevance.... sorry.

    The point I was trying to make here is that it is possible to go much bigger than 34 teeth, in seven or eight gears, with a little creativity.

    Also, SRAM just made a cassette with 42 teeth. This is a low priced alternative for people with some fabricating/modification skills.

  17. #17
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    Yeah, my post was pointless. I had thought those MegaRange cassettes went higher when I googled them, but posted the link anyway.

    I've been mixing and matching cogs to build my own gear ratios for ages. It seems like 40 tooth cogs would sell. As much as I like to fabricate things, I'm not inclined to spend hours filing to make my own, though. But I respect the ingenuity. Interesting thread.

  18. #18
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    12-42, Seven Speed

    Quote Originally Posted by goto11 View Post
    Yeah, my post was pointless. I had thought those MegaRange cassettes went higher when I googled them, but posted the link anyway.

    I've been mixing and matching cogs to build my own gear ratios for ages. It seems like 40 tooth cogs would sell. As much as I like to fabricate things, I'm not inclined to spend hours filing to make my own, though. But I respect the ingenuity. Interesting thread.
    There used to be 5-speed freewheels with a 36 or 38t large cog. I had one but never used it. A 14 or 15t small cog.

    Action-Tec stills offers ti cogs up to 39t
    http://www.actiontec.us/prices.htm
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  19. #19
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    Quote Originally Posted by phoenixbikes View Post

    The crankset has some modifications too. The rings are 17/28/44. The granny gear is a 17t 7 speed cog. I cut an old freehub body in half. It has external threads so I used a bottom bracket lockring and a cog drilled with a 5 bolt 58mm bcd to hold the very short section of freehub body on the crank. I then mounted the cog, and cranked it down with a lockring. I've done a number of these cog-to-chainring conversions before, mostly with 18t cogs.
    I know you like to make your own stuff (great job by the way), but just FYI they use to make a small chainring set up call "Mountain tamer quad kit" like the name emplys it was a 4th chainring that you install with a wider axle..

    I have one with a 17t but I think they make them even smaller..

  20. #20
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    12-42, Seven Speed

    Quote Originally Posted by patineto View Post
    I know you like to make your own stuff (great job by the way), but just FYI they use to make a small chainring set up call "Mountain tamer quad kit" like the name emplys it was a 4th chainring that you install with a wider axle..

    I have one with a 17t but I think they make them even smaller..
    The Mt Tamer used freewheel cogs. IIRC 16-19t (maybe 20t) Mallard cogs.
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  21. #21
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    Quote Originally Posted by phoenixbikes View Post
    I filed out a chainring spider I was never going to use so that it fits onto a freehub body.
    By hand? It looks like a pretty clean job!

  22. #22
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    Quote Originally Posted by shiggy View Post
    The Mt Tamer used freewheel cogs. IIRC 16-19t (maybe 20t) Mallard cogs.
    Sorry I forgot to mention the threaded cogs..

    Actually I remember a "updated" version (or maybe from a different company) that used cassette cogs and a cir-clip to hold them tight, or maybe I was just dreaming of how to make it better, in any case I don't remember..

  23. #23
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    12-42, Seven Speed

    Quote Originally Posted by patineto View Post
    Sorry I forgot to mention the threaded cogs..

    Actually I remember a "updated" version (or maybe from a different company) that used cassette cogs and a cir-clip to hold them tight, or maybe I was just dreaming of how to make it better, in any case I don't remember..
    There were two versions of the Mt Tamer, threaded and unthreaded.
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  24. #24
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    Quote Originally Posted by patineto View Post
    I know you like to make your own stuff (great job by the way), but just FYI they use to make a small chainring set up call "Mountain tamer quad kit" like the name emplys it was a 4th chainring that you install with a wider axle..

    I have one with a 17t but I think they make them even smaller..

    I have one on another set of cranks. I also have a couple White Industries Limbo Spider, which also uses Suntour A-type freewheel cogs. Finding a splined 17t cog is very hard, so I am in the process of turning a 17t cassette cog into a splined freewheel, with a bench grinder and some hand files.

    smilinsteve, thanks, I did do it by hand.

  25. #25
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    Quote Originally Posted by patineto View Post
    Sorry I forgot to mention the threaded cogs..

    Actually I remember a "updated" version (or maybe from a different company) that used cassette cogs and a cir-clip to hold them tight, or maybe I was just dreaming of how to make it better, in any case I don't remember..
    If you can remember the name of the company please let us know! It seems like a no-brainer for someone to come out with a small bolt-on spider like the Mtn Tamer that uses cassette cogs instead of hard to find freewheel cogs with the right spline pattern.

    The Mtn Tamer Triple and the White Industries Limbo Spider both use circlips. Never seen a threaded version of either Mtn Tamer adapter. Anyone got a picture ?

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