Shorter crank arms for my [FSA SL-K Light BB30 11sp 50/34] or new crank ?
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  1. #1
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    Shorter crank arms for my [FSA SL-K Light BB30 11sp 50/34] or new crank ?

    I currently have a FSA SL-K Light 11sp 50/34 crankset (stock on my Synapse Ultegra 2014, which has a BB30) with 172.5mm crank arms and I'd like to move to shorter crank arms (as short as possible).

    Here's a picture/link to my current crank:
    FSA SL-K Light BB30 Double Chainset | Chain Reaction Cycles

    I'd like to know what are my options. Can I buy new shorter arms for this crank? If so, do I have to stay with FSA, who it seems don't make anything shorter than 165mm or is the bolt pattern standard, which would allow me to look into other companies? If it is standard, does anyone know if I can get anything under 165mm ?

    I'm trying to keep the cost as low as possible.

    Thanks!

  2. #2
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    Quote Originally Posted by ToiletSiphon View Post
    I currently have a FSA SL-K Light 11sp 50/34 crankset (stock on my Synapse Ultegra 2014, which has a BB30) with 172.5mm crank arms and I'd like to move to shorter crank arms (as short as possible).

    Here's a picture/link to my current crank:
    FSA SL-K Light BB30 Double Chainset | Chain Reaction Cycles

    I'd like to know what are my options. Can I buy new shorter arms for this crank? If so, do I have to stay with FSA, who it seems don't make anything shorter than 165mm or is the bolt pattern standard, which would allow me to look into other companies? If it is standard, does anyone know if I can get anything under 165mm ?

    I'm trying to keep the cost as low as possible.

    Thanks!
    Most cranks fall in the 165mm-175mm range, so going outside this range (especially in the shorter end) will limit your choices severely. Most affordable cranks <165mm will require square taper BBs, will come in 110 BCD (your FSA is a 130 BCD), or will not be available in 11sp (9sp and 10sp are most common). Yes, there are some benefits of going to a shorter crank, but there is such a thing as going too short. That being said, here are a couple of options:

    1) Dixna La Crank: ?????????? | ?????????????????? » ?La?Crank??????????Dixna?????????
    Use Google Translate. A 140mm option is available. It uses a Shimano Hollow-tech II BB, works with 10s (it *may* work with 11s), and you can get it without chain rings for about $150-$170. Dixna is not known in the US, but is popular in Japan.

    2) PowerCranks: https://www.powercranks.com/
    They will cost anywhere between $400 to $3500. Pretty extensive website.

    I'm running 165mm and have toyed with the idea of going shorter. I hope other members will chime in.
    Wake me up when it's alarm green.

  3. #3
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    Quote Originally Posted by Tachycardic View Post
    Most cranks fall in the 165mm-175mm range, so going outside this range (especially in the shorter end) will limit your choices severely. Most affordable cranks <165mm will require square taper BBs, will come in 110 BCD (your FSA is a 130 BCD), or will not be available in 11sp (9sp and 10sp are most common). Yes, there are some benefits of going to a shorter crank, but there is such a thing as going too short. That being said, here are a couple of options:

    1) Dixna La Crank: ?????????? | ?????????????????? » ?La?Crank??????????Dixna?????????
    Use Google Translate. A 140mm option is available. It uses a Shimano Hollow-tech II BB, works with 10s (it *may* work with 11s), and you can get it without chain rings for about $150-$170. Dixna is not known in the US, but is popular in Japan.

    2) PowerCranks: https://www.powercranks.com/
    They will cost anywhere between $400 to $3500. Pretty extensive website.

    I'm running 165mm and have toyed with the idea of going shorter. I hope other members will chime in.
    Wouldn't it be possible to change just the crank arms, so I would not be limited by my bottom bracket ?

  4. #4
    wim
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    Look into BMX cranks. They're relatively cheap, usually 110 BCD and some of them are available down to 130 mm.

    https://danscomp.com/serve-PARTS/html/BMX+Cranks.html
    Origin8 Alloy Crank Arm Set (110 BCD) | Amazon.com: Outdoor Recreation

  5. #5
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    Quote Originally Posted by wim View Post
    Look into BMX cranks. They're relatively cheap, usually 110 BCD and some of them are available down to 130 mm.

    https://danscomp.com/serve-PARTS/html/BMX+Cranks.html
    Origin8 Alloy Crank Arm Set (110 BCD) | Amazon.com: Outdoor Recreation
    Any 130 BDC available, considering my crank is a 130 BDC (btw I just learned what BCD is)

  6. #6
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    Your crankset is 110 not 130 BCD, assuming you have the compact crank (50/34). You linked to a standard crankset which is 53/39 which would be 130.

    I'm not familiar with cranks shorter than 165 so I can't help you there but keep in mind you're going to be changing your overall gearing by doing this. It will be harder to turn over your lowest gear and you might need to swap to a cassette with a lower range to match what you have now.

  7. #7
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    Quote Originally Posted by [email protected] View Post
    Your crankset is 110 not 130 BCD, assuming you have the compact crank (50/34). You linked to a standard crankset which is 53/39 which would be 130.

    I'm not familiar with cranks shorter than 165 so I can't help you there but keep in mind you're going to be changing your overall gearing by doing this. It will be harder to turn over your lowest gear and you might need to swap to a cassette with a lower range to match what you have now.
    I do have the 50/34, thank you for pointing that out.

    So any 110 BDC crank arm would fit ?

  8. #8
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    No, you'll need crankarms that are BB30 to work with your current bottom bracket. You can get bottom bracket adapters for several other bb standards that will work with BB30 though.
    CONVERSION BB | Praxis Cycles
    Wheels Manufacturing Bottom Bracket Adapters
    wiggle.com | FSA BB30 Conversion Kit | Bottom Brackets

    So to try to sum that up. To run the compact chain rings you have now you will need 110 BCD crank arms. To make it work with your current bottom bracket you will need ones that are BB30. If you find a crankset that is not BB30 you'll need to make sure there is an adapter available to make it work with BB30.

  9. #9
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    Quote Originally Posted by [email protected] View Post
    No, you'll need crankarms that are BB30 to work with your current bottom bracket. You can get bottom bracket adapters for several other bb standards that will work with BB30 though.
    CONVERSION BB | Praxis Cycles
    Wheels Manufacturing Bottom Bracket Adapters
    wiggle.com | FSA BB30 Conversion Kit | Bottom Brackets

    So to try to sum that up. To run the compact chain rings you have now you will need 110 BCD crank arms. To make it work with your current bottom bracket you will need ones that are BB30. If you find a crankset that is not BB30 you'll need to make sure there is an adapter available to make it work with BB30.
    Ok, I'm starting to get it... I don't know why but I was stuck with the idea that the BB and the crank arms were separate things. I now realize that the arms are what the BB go through, so they are indissociable.

    Aren't most adapters permanent?

  10. #10
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    Quote Originally Posted by ToiletSiphon View Post
    Aren't most adapters permanent?
    I'm not an expert on this but i don't think so... probably varies by adapter.

  11. #11
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    Quote Originally Posted by ToiletSiphon View Post
    Ok, I'm starting to get it... I don't know why but I was stuck with the idea that the BB and the crank arms were separate things. I now realize that the arms are what the BB go through, so they are indissociable.
    The bottom bracket and the crank arms are different things. The bottom bracket comprises bearings. It is probably pressed into the frame's bottom bracket shell. Your crank set comprises left and right crank arms. One of the arms has a spindle (shaft) integrated into it. The spindle presses into and through the bottom bracket bearings.

    The issue is that there are a bunch of different bottom bracket shell configurations and crank spindle diameters. You have to choose the proper combination of parts to get a functioning system of bottom bracket, crank, and frame.

    Taking a step back, why do you want the shortest crank arm you can get?

    Unless you have a specific physical issue, I would not spend a bunch of money to get the shortest ones you can. Leave the obscure Internet theories concerning short (and long) crank arms alone. They are not worth the multiple hundreds of dollars road you are going down.

    If you have convinced yourself that 165 or 170mm will make your ride better, I would ebay some cheap tiagra cranks and buy wheels manufacturing adapters (here; you can find them a couple dollars cheaper in other places). If the short cranks do in fact change your life, invest in better short cranks and/or a better bottom bracket solution.
    Last edited by crit_boy; 05-26-2015 at 08:54 AM.

  12. #12
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    Quote Originally Posted by crit_boy View Post
    The bottom bracket and the crank arms are different things. The bottom bracket comprises bearings. It is probably pressed into the frame's bottom bracket shell. Your crank set comprises left and right crank arms. One of the arms has a spindle (shaft) integrated into it. The spindle presses into and through the bottom bracket bearings.

    The issue is that there are a bunch of different bottom bracket shell configurations and crank spindle diameters. You have to choose the proper combination of parts to get a functioning system of bottom bracket, crank, and frame.

    Taking a step back, why do you want the shortest crank arm you can get?

    Unless you have a specific physical issue, I would not spend a bunch of money to get the shortest ones you can. Leave the obscure Internet theories concerning short (and long) crank arms alone. They are not worth the multiple hundreds of dollars road you are going down.

    If you have convinced yourself that 165 or 170mm will make your ride better, I would ebay some cheap tiagra cranks and buy wheels manufacturing adapters (here; you can find them a couple dollars cheaper in other places). If the short cranks do in fact change your life, invest in better short cranks and/or a better bottom bracket solution.
    I do have a specific physical problem. The conversion to a short crank arm is something my PT / fitter wants me to do. I'm on a bike break until I do it. I realize it will be expensive and a real pain in the... I currently have a 172.5 mm and preferably would like to go shorter than 165mm, which is the lowest most "big names" go.

    I did some more research, and it seems my BB is not BB30, but BB30a (Synapse 2014... thanks Cannondale!). So Wheels Manufacturing adapter is pretty much the only BB solution, as Praxis adapter is specifically incompatible with BB30a.

    I want to make sure that any adapter I put in my bike won't be there for good... if the shorter crank doesn't help me, I want to put the old FSA SL-K Light crank back and sell the bike. I've really had enough of my knee pain, PT and shelling more money on this problem.

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    Contact rotor and see if they have anything that would work for you. They make some nice cranksets and go down to 150mm on some of them. Rotor Bike Components

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    Quote Originally Posted by [email protected] View Post
    Contact rotor and see if they have anything that would work for you. They make some nice cranksets and go down to 150mm on some of them. Rotor Bike Components
    They are actually too nice... which makes them very expensive for a last-ditch experiment. I'll send them an email anyway, maybe they can work something out for me.

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    Quote Originally Posted by ToiletSiphon View Post
    Wouldn't it be possible to change just the crank arms, so I would not be limited by my bottom bracket ?
    You realize a crankset contains crank arms and chain rings, and that's it right? If you want to re-use your current chain rings you'll need a 130BCD crankset. You might as well just get a whole new crank + rings and keep this as a backup or sell it. This way you can go either 110 or 130BCD or go with the newer style cranks that are 4 arm if you want.

    FWIW I went from 170 to 165 cranks on my new bike and only notice a very small difference. You're not going to get or loose any power, spin faster, slower, or whatever other people tell you. The only real difference is that my leg doesn't come up quite as much at the top of the stroke, which can be more comfortable for some people.

    Quote Originally Posted by [email protected] View Post
    No, you'll need crankarms that are BB30 to work with your current bottom bracket.
    This statement is not correct, you just pointed out other options to "step down" his BB to work with other crank arms meant for other BB types, i.e. GXP or Shimano Hollowtech.

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    Quote Originally Posted by deviousalex View Post
    The only real difference is that my leg doesn't come up quite as much at the top of the stroke, which can be more comfortable for some people..
    That's exactly why I'm doing it. Very poor achilles flexibility (event after lots of PT), which makes my foot point down a bit too much on the top of the pedal stroke. That, in turn, raises my knees too much for what my stiff quads and hips can handle, so my knees end up receiving too much sheer force.

    I'm just afraid that going from 172.5 to 165 would end up costing me > 200$ without much results, but I'm unwilling to shell out big bucks for something shorter or make this a permanent conversion, as I'm not very positive the results will be groundbreaking anyways.

  17. #17
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    Quote Originally Posted by deviousalex View Post
    If you want to re-use your current chain rings you'll need a 130BCD crankset.
    He has a 110 BCD crankset not 130.


    Quote Originally Posted by deviousalex View Post
    This statement is not correct, you just pointed out other options to "step down" his BB to work with other crank arms meant for other BB types, i.e. GXP or Shimano Hollowtech.
    My statement is correct. Perhaps you would have preferred if i said bearings instead of bottom bracket since the only replaceable part of BB30 is the bearings?

    Needless to say if he was looking for simplicity to keep using his current bottom bracket / bearings he needs a BB30 crankset. If he switches to GXP, Hollowtech, square taper, etc he would need to purchase an adapter and if the adapter doesn't include it he'd also need the new appropriate bottom bracket, plus remove the current BB30 bearings and have the new adapter installed.

  18. #18
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    ToiletSiphon,

    Search through triathlon forums for some ideas. Shorter cranks are more popular with triathletes as the shorter cranks let them get more aero on their tri bikes. Slowtwitch.com is a pretty good resource. Slowtwitch Forums: Triathlon Forum

  19. #19
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    Quote Originally Posted by [email protected] View Post
    He has a 110 BCD crankset not 130.
    Whoops, thought he had a standard right now.

    My statement is correct. Perhaps you would have preferred if i said bearings instead of bottom bracket since the only replaceable part of BB30 is the bearings?
    Re-read your statement. You said he NEEDs BB30 crank arms on his new crank. He can use a Shimano crank for example which does not have BB30 crank arms no problem on this bike.

    Needless to say if he was looking for simplicity to keep using his current bottom bracket / bearings he needs a BB30 crankset. If he switches to GXP, Hollowtech, square taper, etc he would need to purchase an adapter and if the adapter doesn't include it he'd also need the new appropriate bottom bracket, plus remove the current BB30 bearings and have the new adapter installed.
    Again, incorrect.

    BB/PF30 Universal Adapter for 24mm Spindle Cranks (Shimano, FSA, etc.)

    Adapters such as these leave the current BB30/PF30 bearings in the frame and you just plug the adapter in. The adapters themselves do not contain any bearings, they are pieces of delrin that step down the spindle size.

  20. #20
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    This has been discussed before, really there should be no reason to go shorter than a 170mm crank arm unless you're going to be doing cross for rock / ground clearance. 165mm is a pretty significant difference from 172.5mm (it's 1.5 cm of difference from the top to the bottom of the pedal stroke, meaning for the same leg extension your leg will rise approximately 1.5cm less). The crank you have does not have a separate spider / crank arm, so you need a new crank, not new arms. The chain rings you could swap (assuming you stay with compact/110BCD) but usually it's cheaper to buy a new crank on sale rather than a new crank without rings. I'd make real sure that the fitter knows what he or she is doing before I'd try to hunt down 160mm road cranks... anytime it's something the big 3 don't make, you should be asking yourself why you're outside the 3 standard deviation boundary...
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  21. #21
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    I will probably be going with this, which is BB30:

    FSA Omega Compact Road Bike Crankset BB30 165mm 50 34T N10 Speed NEW | eBay

    It states 10 speed, but does anyone knows if it also fits 11 speed systtems?

  22. #22
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    Quote Originally Posted by ToiletSiphon View Post
    I will probably be going with this, which is BB30:

    FSA Omega Compact Road Bike Crankset BB30 165mm 50 34T N10 Speed NEW | eBay

    It states 10 speed, but does anyone knows if it also fits 11 speed systtems?
    It should work. I have a DA7900 crankset on my 6800 11 speed setup right now and shifting is fine.

  23. #23
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    165 mm is 6.49 inches
    172 mm is 6.77 inches.

    That's about 1/4 inch shorter on the downstroke, and another 1/4 inch at the top.
    So you can drop your seat 1/4 inch and you'll raise your leg 1/2 inch less high at the top of the pedal stroke. Is that enough to make a difference?

    Quote Originally Posted by ToiletSiphon View Post
    I do have a specific physical problem. The conversion to a short crank arm is something my PT / fitter wants me to do. I'm on a bike break until I do it. I realize it will be expensive and a real pain in the... I currently have a 172.5 mm and preferably would like to go shorter than 165mm, which is the lowest most "big names" go.
    .
    Does your fitter have one of those adjustable fitter trainer bikes? Some have shorter cranks to swap in.

    Crank arm shorteners are sometimes used on tandems with a smaller stoker. They screw into the pedal hole, then extend back toward the spindle with more pedal holes. They do move the pedals outward, which might cause it's own fitting problems.

    For example:
    Ride2 Crank Arm Shorteners

    Tandems East - Crankarm Shorteners


    la_02east_crankshort.jpg

    ~~~~~~~~~~~~~
    or a do-it-yourself project: drill and tap the solid aluminum arm.

    That looks kind of sketchy. He cut off the arm way too close to the drilled hole, and also says that the arm is hollowed out on the backside. So there's not as much threading as the original hole.

    Last edited by rm -rf; 05-27-2015 at 11:30 AM.

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    Quote Originally Posted by rm -rf View Post
    165 mm is 6.49 inches
    172 mm is 6.77 inches.

    That's about 1/4 inch shorter on the downstroke, and another 1/4 inch at the top.
    So you can drop your seat 1/4 inch and you'll raise your leg 1/2 inch less high. Is that enough to make a difference?
    I don't know if 1.5 cm (7.5mm x 2) will be enough . I certainly hope so.

  25. #25
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    Quote Originally Posted by ToiletSiphon View Post
    I don't know if 1.5 cm (7.5mm x 2) will be enough . I certainly hope so.
    Try raising your saddle 1.5cm temporarily. You'll have to stretch down to the bottom of the pedal stroke, but the top will match the 165mm cranks. See if it helps.

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