40T-Rex cog on XTR 9 speed cassette- Mtbr.com
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  1. #1
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    40T-Rex cog on XTR 9 speed cassette

    I've been waiting for the Absolute Black 9 speed 40T cog, but they have now decided not to make a cog for 9 speed. It doesn't look like anyone else is going to do one either. I ride alot of really tight up & down trails with big logs - almost trials stuff, so I'm a holdout for low normal rear derailleurs as these work great in this type of terrain.(you can't get low normal der in 10 or 11 speed ) I've contacted several of the 10 speed 40 & 42 cog makers to see if theirs would work on 9 speed and they all said it wouldn't work due to shift ramps and/or spacing.
    I bought my son the T-Rex for his 10 speed 11/36 cassette, but I couldn't resist mounting it up to my 11/34 9 sp XTR cassette just see how bad the shifting really was.
    I noticed the shift ramps lined up to 34 cog like the rest of the cassette and the spacing also looked correct. Surprise! it shifts great. I didn't mount the longer B-Tension screw - just turned my current one in 2 1/2 turns and adjusted the "L" limit screw 1/4 turn. I would mount the longer B screw though for more clearance. There is one issue though that prevents this from working in its current state. There is approx. 2mm to much materail where the 40 cog meets the 34 cog which is not letting the chain fully engage the teeth on the 34 (orange pen pointer ). Even still its shifting great from the 40 to the 34. And from the 11 to the 15 ( I removed the 13T). Back pedaling in the 40T does not drop the chain.
    If no one comes out with a 40T 9sp cog in the near future, I have a friend with a CNC machine that could easily machine 2mm off the 40T - and there would be plenty of material left to support the 40 against the 34.
    I'm wondering if the reason this shifts so good is because of the low normal deraileur,( XTR 970 Med cage) which uses the spring tension to move the chain from the 34 to 40T which is opposite of all other derailleurs.
    Attached Thumbnails Attached Thumbnails 40T-Rex cog on XTR 9 speed cassette-img_7000_1.jpg  

    40T-Rex cog on XTR 9 speed cassette-img_6999_1.jpg  


  2. #2
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    Any more update to this? Did you keep using it? I found this thread googling!

  3. #3
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    Subscribed for a friend looking to do the same hack...

  4. #4
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    40T-Rex cog on XTR 9 speed cassette

    I am looking at a guy on eBay right now as well. That sells quite a few very high quality custom machined parts. I am really thinking I might just get my 1x9 done sooner than I thought.

  5. #5
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    subscribed, looking for a status update.

  6. #6
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    I never did anything else with this because I've been waiting for my Absolute Black 30T, NW chain ring for my S-Works cranks since spring. They were supposed to be done in the summer - still nothing.
    My son ran the T-Rex 40T ring all season on his 10 speed XTR cassette and it performed very well.
    Would love to get a wide range 1 x 9 with a low normal der. worked out.

  7. #7
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    Just seems like a nice easy way to go 1X9 and keep some wider ratio gearing. Looked at the HG61 12-36 option, but didn't like the final ratios it offered.
    1X9 with a 40t and a PG990 34 tooth, removing the 11 tooth sprocket, using a Shimano extra tall lock ring, and a 30 tooth front chainring seems like a nice option, but I am concerned about the shifting/spacing with the 40 tooth, and was hoping someone had already gone down that path.
    Oh, 2014 Salsa Mukluk, X7 long cage rear der, X5 double 22-32 front crankset, want some more clearance on the chainline without sacrificing too much gear range.

  8. #8
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    Quick question: when you removed the 13T cog did the 11T play nicely with the 15T cog? I mean , does the built in spacer of the 11T fits well and gives the proper space to the 15T?

    As cheaper expander alternatives appear I'm thinking of buying a 14T Shimano cog separately and the Superstar Components 40T XPR and turn a HG-80 11-34 9 speed cassete into a 11-40 by ditching the 13 and 15 and replacing those with the 14T and 40T.

    Any thoughts?

  9. #9
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    There was a thread in All mountain awhile back where a guy was running a 9spd cassette and a giant cog of some sort.


    I'm actually considering putting a 42 on with my HG-61 and messing with some other cassette parts I have here to get a good spread out of it. I'll have to ditch the pins or drill them to get off the cogs I want.
    I like to fart when I'm in front of you on a climb:skep:

  10. #10
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    Thats on way to do it, break apart all the cogs and re-assemble them, but It doesnt seem a good idea to run it on an alloy freehub.
    I was just curious if the original poster of this thread had to do any mods on the 11T cog as the 13T he removed has a groove to insert the 11T spacer pins.
    A 42 to 34 gap could prove too much, also as noted by the original poster of this thread the expander cogs have some "fins" to prevent the chain dropping in the middle and at least on 42T I've seen those would be just below where chain runs on a 36T cog:


  11. #11
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    Hey guys! I have been running an e-thirteen 40t cog with my Shimano xt 9 speed cassette for roughly 6 months now with no issues what so ever! Slid the e-thirteen 40t cog on the freehub first followed by the xt cassette minus the two smallest cogs (11t and 13t), And in their place added a 12t cog! Bam done! Shifts perfect, chain stays put on any cog while back pedaling! Oh i had to turn the B screw like two turns in also.

  12. #12
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    I tried the TRex 40t with a 11-34 XTR 9 speed cassette and it did not work due to the ramp on the TRex interfering with the chain on the 34 cog. (as pictured above) This caused the chain to skip severely while in 34t. Looks like a different brand may work, like E-13. I might revisit this.

  13. #13
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    Quote Originally Posted by megaguy View Post
    Hey guys! I have been running an e-thirteen 40t cog with my Shimano xt 9 speed cassette for roughly 6 months now with no issues what so ever! Slid the e-thirteen 40t cog on the freehub first followed by the xt cassette minus the two smallest cogs (11t and 13t), And in their place added a 12t cog! Bam done! Shifts perfect, chain stays put on any cog while back pedaling! Oh i had to turn the B screw like two turns in also.
    so what you are saying is the 12T cog fits OK to the 15T cog of the XT cassette?? i thought only a 13T could fit on the 15T of a 9-speed XT cassette. thanks!

  14. #14
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    40T Rex on 9 speed

    Quote Originally Posted by megaguy View Post
    Hey guys! I have been running an e-thirteen 40t cog with my Shimano xt 9 speed cassette for roughly 6 months now with no issues what so ever! Slid the e-thirteen 40t cog on the freehub first followed by the xt cassette minus the two smallest cogs (11t and 13t), And in their place added a 12t cog! Bam done! Shifts perfect, chain stays put on any cog while back pedaling! Oh i had to turn the B screw like two turns in also.
    I am checking if anyone has tried this on SLX 9 speed 11-34T cassette?

  15. #15
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    Another loyal 9 speeder here. Not going to 10 or 11 speed anytime soon.

    Any newer solutions to a bigger cassette ring for 9 speed?

  16. #16
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    wondering if anyone has ever used one of these for a 9 speed upgrade:

    MTB Tools 38 Tooth Cog for Mountain Bike Cassette, 38t Sprocket

    seems a little heavy at 175g, but it's stainless steel. i'm looking at going from 3x to 2x, maybe even 1x, so the weight would be negated anyways in my case.
    >>>RAD

  17. #17
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    Quote Originally Posted by bbender785 View Post
    wondering if anyone has ever used one of these for a 9 speed upgrade:

    MTB Tools 38 Tooth Cog for Mountain Bike Cassette, 38t Sprocket

    seems a little heavy at 175g, but it's stainless steel. i'm looking at going from 3x to 2x, maybe even 1x, so the weight would be negated anyways in my case.

    well then. more searching revealed this:

    http://forums.mtbr.com/drivetrain-sh...de-838687.html
    >>>RAD

  18. #18
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    Quote Originally Posted by megaguy View Post
    Hey guys! I have been running an e-thirteen 40t cog with my Shimano xt 9 speed cassette for roughly 6 months now with no issues what so ever! Slid the e-thirteen 40t cog on the freehub first followed by the xt cassette minus the two smallest cogs (11t and 13t), And in their place added a 12t cog! Bam done! Shifts perfect, chain stays put on any cog while back pedaling! Oh i had to turn the B screw like two turns in also.
    Greetings - Am interested in trying this set up on my wife's shimano xtr 9 speed (currently 3 x 32 - 11). Is your XT setup still working? Any additional tips to offer? Her rear derailleur cage measures about 3 1/8 inches center to center on pulleys.

    Thanks!

  19. #19
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    So by the sounds of it you can buy a 40t gear. Then buy a 12-36 and a 11-34 cassette, remove the 11 and 13 from the 11-34 and add the 12 and the 40 and you get a 12-40 wide range 9 speed.

    Might need a goat link from wolf tooth as well.

    Thinking of doing this to my sora group, i see wolf tooth has a road goat link.
    Fatbike, XC bike, Gravel Bike....

  20. #20
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    Fatbike, XC bike, Gravel Bike....

  21. #21
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    Last season I ran a sram 990 11-40t cassette with an e13 cog. I had to remove the tabs that FMCurto pointed out above. I removed the 13t and 15t cogs and replaced them with a 14t from my parts bin. It shifted great with a gs cage slx derailleur and saint shifter

  22. #22
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    Quote Originally Posted by bengxe View Post
    Last season I ran a sram 990 11-40t cassette with an e13 cog. I had to remove the tabs that FMCurto pointed out above. I removed the 13t and 15t cogs and replaced them with a 14t from my parts bin. It shifted great with a gs cage slx derailleur and saint shifter
    This guy got it to work with a shimano cassette but i'm gonna try it with the 990 that you suggested and a e*thirteen 42...

    FAQLoad - Wide ratio 9 speed cassette

    will check in after i get it to work (or not) My set up is a total mutt 1x9 set up with a sram X0 9s shifter and a new xt der with the clutch. just found a used red 990 and gonna buy a new 40 or 42 (thinking the 40 might be more realistic.

  23. #23
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    Also what i have found is sunrace makes a 11-36 9 speed. M99.
    Fatbike, XC bike, Gravel Bike....

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