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  1. #1
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    Installing my 20 T chain ring

    On a normal 64mm bolt circle diameter 22 T is normally the smallest ring you can use. But on my 29er, there isn't a good option for a cassette with a 36 tooth cog, so to get the extra range, I installed a 20T ring on the front instead (this is a lighter weight than going to a 12-36 cassette also).

    I got the ring off Ebay for about $30, but now I see you can get the same thing for $15?
    CHAIN RING SPROCKET MOUNTAIN 20T TOOTH 64 BCD STAINLESS | eBay

    This shows the size of the 20 T compared to the normal 22T.
    Attached Thumbnails Attached Thumbnails Installing my 20 T chain ring-p1020730.jpg  


  2. #2
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    If you install the ring without modifying the crank, it almost looks like it fits, but it doesn't. The chain is resting on the crank post where the bolt inserts. The posts have to be filed down a bit to give the chain clearance. In this picture the chain looks like it's seated ok, but it will not hold and skip if you try to ride it like this.
    Note that the chainring tooth is not sticking up above the chain at the bolt location like the teeth are on both sides of the bolt. The chain is not seated down far enough because its resting on the crank post behind the ring.
    Attached Thumbnails Attached Thumbnails Installing my 20 T chain ring-p1020733.jpg  

    Last edited by smilinsteve; 10-22-2011 at 03:32 PM.

  3. #3
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    Once I filed down the post, the chain seemed to rest on the bolt head. This is not good either, so I had to file down the bolt heads as well. To file the bolt heads, I tightened them down and then colored the section that needed filing with a Sharpee. Then I held them this way, which was better than trying to hold the threads with pliers.
    Attached Thumbnails Attached Thumbnails Installing my 20 T chain ring-p1020742.jpg  


  4. #4
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    This is what the posts look like after filing.
    Attached Thumbnails Attached Thumbnails Installing my 20 T chain ring-p1020744.jpg  


  5. #5
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    After filing you can see there is clearance between the chain and bolt head. Note how the bolt head is no longer round.

    It seems to work fine now, but need a real uphill challenge to test it out. Shifting from small to big ring is slower than it used to be, but I think I just need to adjust the front derailleur a bit more.
    Attached Thumbnails Attached Thumbnails Installing my 20 T chain ring-p1020741.jpg  


  6. #6
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    Yup-- brings back memories when I had to do all that to fit an action tec 20t on my XT crank a few years ago. Good pictorial!

  7. #7
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    Quote Originally Posted by padrefan1982 View Post
    Yup-- brings back memories when I had to do all that to fit an action tec 20t on my XT crank a few years ago. Good pictorial!
    How did the 20T work out for you? Were you able to get good front shifting?

  8. #8
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    Quote Originally Posted by smilinsteve View Post
    How did the 20T work out for you? Were you able to get good front shifting?
    Similar to your experience. It was a tiny bit slower going from the 20 to the 32 middle (I was running 20-32-42), but nothing that was horrid.
    I have since taken it off, however, because when I tried a 2x9 set up, with 24-36 chainrings, I found out for my fitness, in my part of the world, and my bike, I was faster up everything with the 24 granny, and no change in in rear cassette.

    I have kept that 20t ring though, just in case I ever move to a area where climbs require it, or a different bike needs it. I like having some options.

  9. #9
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    Curious why you aren't able to do the 36t cassette?
    Florence Nightingale's Stormtrooper

  10. #10
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    Quote Originally Posted by scrublover View Post
    Curious why you aren't able to do the 36t cassette?
    For 9 speed, as far as I know, the only option is the Shimano HG 61 which is really heavy, or exotic (very high priced) Ti cassettes like Actiontec or Lucky Nino.
    It seems both Shimano and SRAM decided you don't deserve a nice lightweight cassette with 36T big cog unless you switch to 10 speed.

    So, my first attempt at lower gearing was to buy a 36 T cog from MTBTools on Ebay. You slide the 36T on your free hub, add a spacer, then use 8 of the 9 cogs of your normal cassette (remove the 11T). Well, adding the 36T steel cog made my set up weigh about the same as buying the HG 61, and it didn't shift that well, and I bent it.

    So, I figured I could just keep my light 11-34 (SRAM PG 990 305 g), and lower the gearing up front instead. This option is lighter as follows:

    PG 990 = 305
    PG 990 + 36T from MTB Tools= 440g
    Shimano HG 61 = 420g

    There's not much weight difference switching from a 22 to a 20 up front, but still, overall using the 20 up front with my 11-34 in the back saves me a quarter pound over those other two options.

    Did a serious ride today for my fist test of the new set up, with over 4000 ft climbing. It worked great. No skipping, no chain suck. I rarely used the low low combo, but it was nice to have.

  11. #11
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    Hey smilinsteve, this is a great post you made. I know this is a little late, but thanks. Question: your thoughts on aluminum vs steel freehub bodies for the large cog when you used it?

  12. #12
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    Quote Originally Posted by skim500 View Post
    Hey smilinsteve, this is a great post you made. I know this is a little late, but thanks. Question: your thoughts on aluminum vs steel freehub bodies for the large cog when you used it?
    My hubs are Bontrager race light and I don't even know if they are steel or Al.
    I never had a problem with freehub body damage from using the 36 T cog, but I didn't use it for very long.

    But I could see the concern. All the torque on the cog is applied to the small area of contact between the one cog and the FH body. It's not distributed as if it were attached to the other cogs or a carrier. So with an AL body, it might dig into it. There's probably someone on this forum who has tried it.

  13. #13
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    Thank you!

  14. #14
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    Well done. Just like how I did it, except I had access to a metal lathe to reduce the diameter of the bolt heads small enough to clear the chain. I'm now running an ebay 20T granny and Anderson 30T and 40T rings. Now my 29er has about the same gearing as my old 26" did. (And my old legs need this gearing to ride in the santa monica mtns.)

  15. #15
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    Quote Originally Posted by roadrider1 View Post
    Well done. Just like how I did it, except I had access to a metal lathe to reduce the diameter of the bolt heads small enough to clear the chain. I'm now running an ebay 20T granny and Anderson 30T and 40T rings. Now my 29er has about the same gearing as my old 26" did. (And my old legs need this gearing to ride in the santa monica mtns.)
    I imagine you have to go through the same filing process to make the 30T middle work?

  16. #16
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    Quote Originally Posted by smilinsteve View Post
    I imagine you have to go through the same filing process to make the 30T middle work?
    Thats right. The Anderson Machine web site shows just filing a bevel on the mounting tabs, but that isn't enough. You need to file in a parallel groove similar to the above pix to allow adaquate clearance for the chain. But once you do, it works great.

    Product Info « Andersen Machine's Blog

  17. #17
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    Hey Smilinsteve,

    Got a question for you. I got my Action Tec 20t (which took forever), and filed the crank posts, it went great. I looked at the bolts and they "looked" okay (XT cranks). Should I file them anyway, and how do you know what part to file when they're not screwed down?

    Thanks. skim

  18. #18
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    I took the bolt heads down the same amount as I took off the crank posts:


    - DSCF1256

    That was about 1mm off each. Since I had access to a lathe, I just turned the heads of the bolts from ~12mm to ~10mm, but I imagine you could mark on the bolt where it lines up when tightened then remove it and grind of file a flat on the outer edge.

    I may have taken off a bit more than minimally required judging by the chain link clearance:


    But I find that chain lube (I use a dray wax lube) does tend to build up in those areas after a bit of riding, so a little extra room helps.

  19. #19
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    Thanks for this detailed info. Great pictures too!

  20. #20
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    Quote Originally Posted by skim500 View Post
    Hey Smilinsteve,

    Got a question for you. I got my Action Tec 20t (which took forever), and filed the crank posts, it went great. I looked at the bolts and they "looked" okay (XT cranks). Should I file them anyway,
    You can try using them without filing. You will know it right away if there is interference.

    and how do you know what part to file when they're not screwed down?

    Thanks. skim
    I screwed them all the way down, and used a sharpy to color the top part that needed to be removed. Then I took the bolt out and filed away the part I colored with the sharpy.

  21. #21
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    On a side note you can shape round parts very easy by inserting the part on a drill and then use a grinder/file/dremmel


    Ps: thanks for the great write up..

  22. #22
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    Great tip. Great thread.

  23. #23
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    Good pics of the modification. I tell everybody about this solution to get better gearing for steep hills, but I find most people here are afraid to work on their own bikes. I am a native Californian too, so it must be something else!
    The guy who makes those sprockets on Ebay is right here in Simi Valley. Nice guy, and makes a good product.

  24. #24
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    Interesting thread! I thought I was going to have this problem when I was planning the build of my 29er. I checked out the gearing,
    ratios, saw the 24t granny and thought to myelf:

    "The wheels are bigger, the granny ring has 2 more teeth, therefore I'm gonna have to get custom chainrings to achieve lower gears".

    In practice I've found that I get on just fine with the XT 42-32-24 setup. So much so that my beautiful Turner Flux sits in the garage whilst I ride my Salsa El-Mariachi all the time. I'd say if you are just about to swap from 26" 9-speed to 29" 10-speed don't panic. Give the standard setup a try, get used to the different pedalling cadence, and you may find (like me) that you prefer it.

  25. #25
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    Quote Originally Posted by Tea@Dimbola View Post
    Interesting thread! I thought I was going to have this problem when I was planning the build of my 29er. I checked out the gearing,
    ratios, saw the 24t granny and thought to myelf:

    "The wheels are bigger, the granny ring has 2 more teeth, therefore I'm gonna have to get custom chainrings to achieve lower gears".

    In practice I've found that I get on just fine with the XT 42-32-24 setup. So much so that my beautiful Turner Flux sits in the garage whilst I ride my Salsa El-Mariachi all the time. I'd say if you are just about to swap from 26" 9-speed to 29" 10-speed don't panic. Give the standard setup a try, get used to the different pedalling cadence, and you may find (like me) that you prefer it.
    It depends on the terrain you ride of course, but going from 26 to 29 and adding 2 teeth to your small chain ring would not be something I could just adapt to.

  26. #26
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    Well that's just it Steve: I felt exactly that way until I actually tried it and found I could get up the hills just as easily with 29" wheels and a 24t granny as with 26" wheels and 22t granny.

  27. #27
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    Quote Originally Posted by Tea@Dimbola View Post
    Well that's just it Steve: I felt exactly that way until I actually tried it and found I could get up the hills just as easily with 29" wheels and a 24t granny as with 26" wheels and 22t granny.
    Thats great for you, but regardless of how you think you feel, it is not just as easy. Come to Colorado and I'll show you some hills that will change your mind

  28. #28
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    I'm getting my 20T chainring tomorrow so I prep the cranks for it.


    But I did it in a little different way, making a "triangle" in the hopes of leaving more structure to the bolt to hold on.


    On the 20T the tooth are located exactly on axis with the bolt holes, so you can have the "point" and the chain will clear it, actually I was trying to make the shape convex but I fail.


    I tell you how it works tomorrow after I install the chainring..

  29. #29
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    The chainring is install with the chainring bolts ground down for clearance..
    Installing my 20 T chain ring-img_4210-m.jpg

  30. #30
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    Thanks, great pics and a reminder of how to. I did this before but need to do it on the new bike.

  31. #31
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    Good luck.

  32. #32
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    Here is why I was looking. I just got a new specialized enduro 29, but even the 22 T is too high a ring for me, so I wonder if there a 20 tooth granny gear that will fit the Custom SRAM S-1250, 10-speed AM double, PF30 spindle w/ shift guard, 175mm that comes on this bike? I know most people don't want a granny that they can walk faster than, (but with that logic, everyone would walk in LA at rush hour, and nobody walks in LA). But I even have a 20x34 on my 26". It took some filing of the crankset, but no chain suck and I love it as I grind up hills always firmly in last place. But like you said with more energy for the downhills which is the fun part for me. Does this look like the right one?
    CHAIN RING SPROCKET MOUNTAIN 20T TOOTH 64 BCD STAINLESS ACTION TEC MOUNTAIN GOAT?

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    One small update, I "square Shave" the chainring bolts (reduce diameter of the head) so they clear the chain, but the other day I drop the chain next to the small chainring and got totally wedge in between the E-type plate and "square" shoulder of the chainring bolts, hell I need to take two of chainring bolts to liberate the chain, what a pain, so the minute I got home I made a new set of chainring bolts but this time as "Conical" as possible (low profile) in hopes of avoid the same problem..

  34. #34
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    You didn't post a link but that should work. You can check ebay for a cheaper version though. The link in post 1 will still get you there. Action tech makes a pricey titanium version and I can't imagine the weight savings would be more than a couple of grams.

    I'm pretty sure your crank has 64-104 bolt spacing. If it has a 22 on it now, it can't be any bigger than a 64 and I don't think they're using anything smaller than a 64 these days either (I've got an old 5 bolt crank that has 58 mm spacing, but I digress).

    I'm sure you'll like the mod. The lower the gearing, the more you stay on your bike, and the less you walk. That's a good thing.

  35. #35
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    Quote Originally Posted by K2D2 View Post
    CHAIN RING SPROCKET MOUNTAIN 20T TOOTH 64 BCD STAINLESS ACTION TEC MOUNTAIN GOAT?
    I got the 64 four bolt BCD in Titanium from action tech, because I got it cheap, if I was buying new I go for the stainless version..

  36. #36
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    Thanks Patineto and Smilinsteve,
    that's exactly the info I needed. Here's the link and you're right it's from the one you list and where I got one for my 26" Stumpy but with Shimano cranks. Although it feels weird to start filing on a brand new bike, I love the idea of very low gearing and getting it by shaving weight and going smaller rather than getting a bigger cassette. Now I'll have to figure out the new Crankset/bottom bracket since my old bike still has and old school BB cartridge style.
    Chain Ring Sprocket Mountain 20T Tooth 64 BCD Stainless Action Tec Mountain Goat | eBay
    Last edited by K2D2; 05-01-2013 at 06:57 AM. Reason: correction

  37. #37
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    Quote Originally Posted by K2D2 View Post
    Thanks Patineto and Smilinsteve,
    that's exactly the info I needed. Here's the link and you're right it's from the one you list and where I got one for my 26" Stumpy but with Shimano cranks. Although it feels weird to start filing on a brand new bike, I love the idea of very low gearing and getting it by shaving weight and going smaller rather than getting a bigger cassette. Now I'll have to figure out the new Crankset/bottom bracket since my old bike still has and old school BB cartridge style.
    Chain Ring Sprocket Mountain 20T Tooth 64 BCD Stainless Action Tec Mountain Goat | eBay
    If is 64 BCD it will fit, I'm also running a ISIS bottom bracket as you can see from the pictures..

  38. #38
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    Thanks,, I have to do the same on my cranks and bolts, the chainring start to "jump"

    Thanks,, I have to do the same on my cranks and bolts, the chainring start to "jump" on the chainring, so I do the Cranks Jobs. now is good to go. You can see the pics of the before and after, did the Job with a Dremel,,, In the before Pic you can see how the chain seat on the crankInstalling my 20 T chain ring-20150917_101735.jpgInstalling my 20 T chain ring-20150917_111008.jpgInstalling my 20 T chain ring-20150917_111047.jpgInstalling my 20 T chain ring-20150917_105431.jpg

  39. #39
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    You realize this thread is two years old - but it still has some good information - good luck!

  40. #40
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    Quote Originally Posted by matuchi View Post
    You realize this thread is two years old - but it still has some good information - good luck!
    This thread is actually turning 4 years old next month, but thanks!

    I still have that bike as a second bike and it still has the 20t. It was a good option for 9 speed back when 34 was the max size cog on the cassette. Still an option. Why not?

  41. #41
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    Quote Originally Posted by smilinsteve View Post
    This thread is actually turning 4 years old next month, but thanks!

    I still have that bike as a second bike and it still has the 20t. It was a good option for 9 speed back when 34 was the max size cog on the cassette. Still an option. Why not?
    I know it's 4 years old and can still offer solutions to going to a 20 tooth chainring - I myself have contemplated it - I just wanted to let the poster know this thread hasn't been active in years - and as so - may not get an immediate response.

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    Still usefull info

    Yes!! 4 years but still useful information.

    Quote Originally Posted by smilinsteve View Post
    This thread is actually turning 4 years old next month, but thanks!

    I still have that bike as a second bike and it still has the 20t. It was a good option for 9 speed back when 34 was the max size cog on the cassette. Still an option. Why not?

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