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  1. #1
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    Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?

    I'm considering buying a stages powermeter, just the left side/non-drive crank arm, either X9 or XT.

    I'd like to use it on both road and mtb and switch it back and forth. The x9 will bolt up to the sram force crankset on my roadbike and clear the fraem of course.

    Anyone else try this? any downsides? I guess q-factor is a bit different, but does that matter so much?

    I guess i'm surprised more mtb'ers aren't trying this. Or maybe it doesnt work? What am I missing?

  2. #2
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    Also: i asked this here instead of in Drivetrain forum, since I figure this crowd is more apt to play with powermeters and understand my motivation for doing this.

  3. #3
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    Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?

    The q factors are way out if you were to try mixing and matching road and MTB cranks without any modifications. Un-modified the asymmetry is going to be horrible and likely to cause body issues (hip, knee, back), unless you're crooked on the bike to begin with.

    In theory you could use a pedal extender on one side, in order to even out the q factor of the mis-matched cranks. Ideally you'd have the pedal extender made to exactly half the q factor difference (eg: SRAM would need a 13mm pedal extender) so that the q factor of each crank is equal again.

    Pedal Extenders
    http://www.kneesaver.net/ecommerce/


    Crank q factors

    SRAM Force double BB30 145mm q factor
    http://cdn.sram.com/cdn/farfuture/Dg...4165_rev_b.pdf

    SRAM X9 double BB30 170.9mm q factor
    http://cdn.sram.com/cdn/farfuture/Z6...76_-_rev_b.pdf

    Dura Ace 9000 147mm q factor (Shimano 105 might be a little wider)
    http://fairwheelbikes.com/c/forums/t...nk-review-5-2/

    Shimano Deore XT 176mm q factor
    http://faqload.com/faqs/bicycle-comp...ious-cranksets

  4. #4
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    The kneesavers are intriguing.... so I could make it match up and be symmetrical. But it appears I need a kneesaver closer to 10-15mm rather than the listed sizes starting at 20

  5. #5
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    Another idea: if i have sram cranks with removable spiders, could i put larger q factor crank on the road bike and just put on the spider with road gearing.

  6. #6
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    Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?

    Assuming that you're happy to run Speedplay pedals on your road bike then a neater option would be to use an optional Speedplay longer spindle on the right hand pedal.

    "OK, I got the answer from my LBS. Speedplay makes spindles in 1/8, 1/4, and 1/2 inch longer than stock, which you can buy as a kit (spindles only) for $80, or as an option on the pedal set for an additional $20. This is a nice inexpensive option that it seems few people are aware of, but it might be of help to some of you with wider hips. " mpearson76

    http://www.bikeforums.net/showthread...length-options

    http://www.speedplay.com/index.cfm?f....thumbs&cgid=6

    That 1/2" (12.7mm) longer right hand pedal spindle gets you very close to the q factor difference whilst keeping a nice clean appearance for your bike too. If needed a small additional tweak could be made up by a pedal washer between the crank arm and pedal, plus adjusting the cleat on your shoe if needed.

    That's a much better solution than pedal extenders which should work without any issues.

  7. #7
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    Excellent suggestion!

    Hmmm. If I could find longer spindles for shimano mtb pedals, that would be awesome.

  8. #8
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    Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?

    You can get aftermarket Shimano MTB spindles but they're just the titanium ones, rather than specific widths.

    Shimano pedal spindles have quite a few different shapes involved (bearing surfaces, threads etc) so it would probably be too much hassle for a machine shop to make you a single one off custom length pedal spindle. If they did it would be quite expensive too I'd have thought.

  9. #9
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    I wonder if different shimano pedal versions (xtr vs 540, etc) have diff lengths... I could run he longer pedal on driveside...

  10. #10
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    There's only going to be a few mm difference in spindle length at most between different models of Shimano SPD pedal, nowhere near the amount you need to even the q factor width difference from mismatched cranks. Using different pedals on each side also has the effect of changing the stack height of each pedal, so then your saddle height will be slightly out between legs too.

    The aim has to be to try and avoid introducing any new problems. There's no point injuring yourself for the sake of saving a few hundred dollars. It's a false economy.

  11. #11
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    Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?

    I just remembered. If you're going to be swapping left hand cranks between road and mountain bikes you should use either SRAM GXP or Shimano Hollowtech cranks, rather than SRAM BB30.

    The reason for avoiding SRAM BB30 is that with SRAM GXP and Shimano Hollowtech crankarms the bottom bracket axle is integrated into the right hand crank arm, requiring no disassembly to swap left hand cranks. SRAM BB30 in contrast has the bottom bracket axle integrated into the left hand crank arm, so you'd be swapping both the left hand crank arm but also the bottom bracket axle between bikes. That introduces a lot more hassle and problems.

    Using GXP or Hollowtech it would only be a quick 5 minute job to complete the task.

  12. #12
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    Cool. I'm all GXP on my bikes.

    Quote Originally Posted by WR304 View Post
    I just remembered. If you're going to be swapping left hand cranks between road and mountain bikes you should use either SRAM GXP or Shimano Hollowtech cranks, rather than SRAM BB30.

    The reason for avoiding SRAM BB30 is that with SRAM GXP and Shimano Hollowtech crankarms the bottom bracket axle is integrated into the right hand crank arm, requiring no disassembly to swap left and cranks. SRAM BB30 in contrast has the bottom bracket axle integrated into the left hand crank arm, so you'd be swapping both the left hand crank arm but also the bottom bracket axle between bikes. That introduces a lot more hassle and problems.

    Using GXP or Hollowtech it would only be a quick 5 minute job to complete the task.

  13. #13
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    If you've already got both SRAM Force and SRAM X9 chainsets then it's straightforward to determine exactly what additional width you need to add onto the right hand crank.

    Measure from the inside edge by the axle to the outer edge of the pedal hole on both left hand cranks. Subtract the SRAM Force crank width from the SRAM X9 crank width and that's the width of the pedal extender or pedal axle that you'll need to add onto the right hand side for an even q factor.



    It's also worth making sure that you have the same length cranks on both bikes. For this to work you'll need to have matched crank lengths. You don't want to end up with the situation where you have a 170mm length crank on one side and a 175mm length crank on the other side. That isn't a combination that you should use, as uneven crank lengths can lead to backache, saddle sores from rocking on the saddle etc.

  14. #14
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    Quote Originally Posted by WR304 View Post
    Using GXP or Hollowtech it would only be a quick 5 minute job to complete the task.

    It's also worth making sure that you have the same length cranks on both bikes. For this to work you'll need to have matched crank lengths.
    Bummer. It sounded like a great idea - until I realized my MTB has XT 175mm and my CX/Road bike has Ultegra 172mm....

    Mtb = Shimano FC M772 175mm
    CX = Shimano FC6601/6604/6650 172.5mm

    I guess I could get 175mm crankset for CX bike and then figure what the q factor issues are

    On the other hand, 2.5mm is less than a 1/10th of an inch (0.0984252")

  15. #15
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    Rfxc, did you pull the trigger on this? I am considering doing this for the same reason.

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    I am in the 'process of' with shimano bikes (XT MTB and Ultegra CX bike).

    I bought a take off 175 compact ultegra crank for CX bike and in the process of obtaining XT stages power crank.

    Q factor on MTB crank is wider, I will offset drive side with 2.5mm spacer on CX bike and maybe add a pedal shim. Q will then be even within a couple mm's if I remember right.

  17. #17
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    I haven't done this. My chiropractor/racing buddy says I don't want the medical bills after pedaling thousands of miles with mismatched q factor cranks. Still, it's tempting to get "close enough"with the pedal extenders mentioned above. Low On, the q factor difference between xt & ultegra cranks is probably much higher than 2.5mm. Don't confuse crank length with q factor.

    Sent from my Nexus 7 using Tapatalk

  18. #18
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    Quote Originally Posted by rfxc View Post
    I haven't done this. My chiropractor/racing buddy says I don't want the medical bills after pedaling thousands of miles with mismatched q factor cranks. Still, it's tempting to get "close enough"with the pedal extenders mentioned above. Low On, the q factor difference between xt & ultegra cranks is probably much higher than 2.5mm. Don't confuse crank length with q factor.

    Sent from my Nexus 7 using Tapatalk
    Just so we have the same understanding of Q factor
    Sheldon Brown's Bicycle Glossary Q
    I realize my Q will not be 'centered'. All MTB's generally have wider Q's than road bikes to clear chain stays. What I am discussing is Q being offset - I think that is what you mean also when you refer to "pedaling thousands of miles with mismatched q factor cranks."

    I can see your chriopractors point - but it is not like every 'body' is symetrical to begin with - ask your chiroractor - equal leg lengths to begin with for example, it is probably one of the first things he checks on patients

    Let alone bikes come with Q centered on bike, for example from a poster:
    "I just went downstairs and measured a couple of older bikes with square taper BB's. The Trek 330 double was 2 mm farther on the drive side; the Cignal Tandem triple was 7 mm farther on the drive side. Neither I nor anyone else who has ridden either has ever commented that it felt odd -The human body is pretty adaptable, and is also not exactly symmetric. I would vote for trying it and seeing how it feels before jumping through a lot of hoops to get something symmetric which is probably not so on many bikes ."
    or
    "You can put a 2.5mm spacer behind the DS bearing cup (which come with many MTB BBs to allow installation in 68mm BBs instead of 73mm), and you should still have plenty of axle sticking out of the NDS to attach the HTII crank to. I've done this to tweak the chainline on one of my bikes (105, 5600 crankarms on both sides), and have had no problems after 4000+ kms."

    You are right, the Q on my XT bike is MUCH higher than 2.5mm compared to Ultegra bike - approx. 26mm wider! Good stuff!

    But, keep in mind I am only using one XT crank arm that pushes L/S crank out 12mm roughly further than R/S. Adding 2.5mm spacer to R/S brings offset down to 7mm - add 2mm pedal spacer and that comes down to 5mm or 1/8" (all rough measurements)

    Thanks for heads up - I won't confuse crank length with Q factor

  19. #19
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    Another option to keep the q factor consistent without worrying (medical or shimming)we would have to use the identical crankset on both bikes. If so, would probably be best to use an MTB crankset. I don't think that I would trust a road crankset on my mtb bike.

    I have two identical mtb cranks but its 104bcd. I think that the largest chainring for that bcd is 44t. Not sure if that will be enough for road.

  20. #20
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    A road crankset likely won't clear the chainstays on your mtb. (I tried this)

    A mountain crankset will have a chainline thats too far towards the driveside on a mtb for a typical road front der to work. (Haven't tried it, but I doubt it would work. Chainlines are different.)

  21. #21
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    I would just run the power on the road bike and be done with it. It's difficult to do power based workouts on the Mtb, so it's mostly used for analysis anyway. Or look for a used powertap wheel for the road bike to keep costs down, it might not be that much more than the workarounds.

    Sent from my HTC One using Tapatalk
    "Great things are not accomplished by those who yield to trends and fads and popular opinion."-Jack Kerouac

  22. #22
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    I know this isn't necessarily germaine to this thread but

    my n=1

    fwiw, this year I ran a x9 (2x10) mtb crank on my "A" cx bike so I could use my stages arm. "generally" cx rigs are designed around road drivetrains.

    I've no idea how to measure/quantify my driveline (in)efficiencies from odd chainlines but I have had absolutely no problems with using the big/big combination (frequently). I don't typically downshift up front while racing but (knock on wood) have yet to experience a chaindrop.

    ***Drivetrain is 7800 dura-ace front and rear (small cage), x9 42/28 chainrings, sram 1070 chain and 1070 11/28 cassette

  23. #23
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    Quote Originally Posted by DLd View Post
    I would just run the power on the road bike and be done with it. It's difficult to do power based workouts on the Mtb, so it's mostly used for analysis anyway. Or look for a used powertap wheel for the road bike to keep costs down, it might not be that much more than the workarounds.

    Sent from my HTC One using Tapatalk
    1. Thread is titled "Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?" Not "do you think I should run a Stages power crank or a used power tap wheel"

    2. No mention in post of "what do you think of doing power based workouts on MTB"

  24. #24
    DLd
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    Quote Originally Posted by scottz123 View Post
    1. Thread is titled "Anyone run an X9 or XT left side crank on their Sram Force or 105 road crank & bike?" Not "do you think I should run a Stages power crank or a used power tap wheel"

    2. No mention in post of "what do you think of doing power based workouts on MTB"
    Sorry, didn't mean to offend. I just thought it was more trouble than it was worth. Sometimes something seems like a good idea or a good way to save money but ends up costing you more in time and money in the long run. Like running offset Q-factor (mismatched) cranks and then dealing with knee or back issues years down the road. It's good once in a while to question whether something is a good idea in the first place.
    "Great things are not accomplished by those who yield to trends and fads and popular opinion."-Jack Kerouac

  25. #25
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    Quote Originally Posted by DLd View Post
    Sorry, didn't mean to offend. I just thought it was more trouble than it was worth. Sometimes something seems like a good idea or a good way to save money but ends up costing you more in time and money in the long run. Like running offset Q-factor (mismatched) cranks and then dealing with knee or back issues years down the road. It's good once in a while to question whether something is a good idea in the first place.
    I see your point.

    To me, it is not that big of a deal to add washer to help center Q. My Trek Superfly AL Elite came from the factory with a spacer (2.5mm) to center Q. (XT). When I measure 'Q center' I have a hard time telling if it is off a couple of mm's without fancy tools on any of my bikes

    I put spacers on my 1x10 setup chainring to help center chainline for example - it's no big deal

    How many people actually measure there bikes to see if there Q is centered to begin with. Let alone ride with leg/foot length discrepencies, cleats not being in perfect alignment L to R, etc. and ride for years and not notice

    You need to (should?) put a 2.5mm spacer behind the DS bearing cup which come with many MTB BBs to allow installation in 68mm BBs instead of 73mm for example

    Peace

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