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  1. #1
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    Choices for kid-sized Crank Sets

    I just scored a nice little Craigslist find for my 11 year old daughter - a 2006 Stumpjumper Women's, size 13.5" .

    Overall it fits her very well (I switched out and flipped the stem, replaced the front tire, and will swap the saddle soon). However, the cranks are 170mm. I know there are a few sources for shortened cranksets, as that info is scattered among multiple threads, but I am wondering if you knowledgable folks would mind consolidating them into this one thread. Thanks!

    As pic'd, 24.3 pounds.

    Last edited by antonio; 04-30-2015 at 02:59 PM.

  2. #2
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    Trailcraft has 152 mm cranks for $80. I got them for my sons bikes, they seem fine so far.

  3. #3
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    Is there enough material on the current cranks to have them drilled and tapped to the length you want?

    There are places you can send your cranks to do this. Others have bought the bits and had local machine shops do them. And there is the DIY option.

  4. #4
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    Quote Originally Posted by wpgbike View Post
    Trailcraft has 152 mm cranks for $80. I got them for my sons bikes, they seem fine so far.
    Thanks. Those seem to be a popular choice which I'm strongly considering. Glad to hear they're working out for your boys.

  5. #5
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    Quote Originally Posted by CJH View Post
    Is there enough material on the current cranks to have them drilled and tapped to the length you want?

    There are places you can send your cranks to do this. Others have bought the bits and had local machine shops do them. And there is the DIY option.
    I never even knew this was an option, Thanks! Seems like I have a little bit of research to do.

  6. #6
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    I bought the Trail Craft crankset for my daughter's bike. They are a very nice 2X crank. I also bought a 152 mm crankset off ebay (Spectra branded) for another bike. It was surprisingly nice. I set it up for a 1 x 9 on my other daughter's bike. I think that was $28 with $14 shipping.

  7. #7
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    If you need to go shorter than the Trailcraft cranks and it's a square taper BB, some options include:

    -SINZ makes BMX cranks down to 115 mm. Only available in a 5-arm 110 BCD spider though. You can find them on BMX websites.

    -Spawn sells 127 mm cranks with a standard 104 BCD spider
    Alloy Cranks ? 127MM - Born to Ride | The World's Best Kids Bikes!

    -I found this website in Holland that sells a bunch of short steel cranks (85, 102, 115, 127 and 152 mm options) with fixed chainrings.
    https://en.hollandbikeshop.com/bicyc...en-s-crankset/

    edit: The Holland Bike Shop cranks turned out to be steel, not aluminum as I was told. Thankfully they fully refunded me (including shipping).
    Last edited by RMCDan; 05-07-2015 at 09:57 AM.

  8. #8
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    Pair Thorn triple Solo Alloy crankset 110/74 pcd - £69.99

    Thorn do 140 145 and 152 (iirc) not sure if they are available outside uk.

  9. #9
    CJH
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    Quote Originally Posted by antonio View Post
    I never even knew this was an option, Thanks! Seems like I have a little bit of research to do.
    There is an online article out there somewhere that not only discusses this but also lists cranks that are good candidates. If I find it I'll post it back here.

  10. #10
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    Lil shredder is getting into the market too. Not sure if available to the public yet. They had some on their FB page a few months back.

    You can checkout Bike Smith Design for shorting cranks:
    Short Bicycle Cranks

  11. #11
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    Recent thread with my DIY crank shortening pictures and description at:
    http://forums.mtbr.com/families-ridi...ld-961774.html

    Minimum amount that a crank can be shortened is around 20mm, probably best to find a set of ubiquitous used 175mm MTB cranks if you want to shorten, save the 170mm set a couple of years for her to grow into. (it will not take long!)

    I you cannot borrow a set of R&L 9/16" thread taps (or a LBS shop that will tap the new holes for cheap and or you are not planning to have a dozen kids), then it probably makes more sense just to buy the pinecraft cranks rather than DIY or trying to pay someone do shorten them for you.

  12. #12
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    Quote Originally Posted by SAAZ View Post
    I also bought a 152 mm crankset off ebay (Spectra branded) for another bike. It was surprisingly nice. I set it up for a 1 x 9 on my other daughter's bike. I think that was $28 with $14 shipping.
    what was the bcd on those? they look like a decent, affordable option, hoping they take 104mm chainrings

  13. #13
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    Yep, they do take 104mm chainrings. I'm actually really pleased with how nice they are.

  14. #14
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    I will likely give the Spectra a try.

    SAAZ, what bb did you use? What was the spindle length? Thanks.

  15. #15
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    I used a Shimano UN55 square taper, 68 x 113. Fit perfectly. Not the lightest thing in the world.

  16. #16
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    I've got a list of short cranks that I've been maintaining over the years here. I've also shortened a number of sets of cranks and its a good way to go to get the exact size you need.
    Last edited by TigWorld; 05-02-2015 at 05:00 AM.

  17. #17
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    Quote Originally Posted by SAAZ View Post
    I also bought a 152 mm crankset off ebay (Spectra branded) for another bike. It was surprisingly nice. I set it up for a 1 x 9 on my other daughter's bike. I think that was $28 with $14 shipping.
    Is the chainring on that riveted or screwed on. Can it be replaced with different chainrings or a bash guard? I'm looking at it for my sons bike.

  18. #18
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    Well I just ordered this crank. I saw 2 sold in the hour before and just decided to give it a try. Which one of you ordered 2 of them?

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    Quote Originally Posted by Fargo1 View Post
    Is the chainring on that riveted or screwed on. Can it be replaced with different chainrings or a bash guard? I'm looking at it for my sons bike.
    It is bolted on...a standard 104 bcd pattern so there are quite a few chainrings available as well as bashguards. I have a 32 tooth ring on there now. I'm thinking about trying a race face 30 tooth.

  21. #21
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    I have two of the Spectra cranks, the first one I've installed a 30T Raceface narrow-wide, and it also has the smaller BCD if you wanted to go with a sub-30T chain ring. I used the chain ring bolts that were holding on the original Spectra chain rings. The second one I plan to use soon, and was going to go with 32 on that one. Both going on Hotrock 24" bikes. The first one was an incomplete bike I got at my LBS, and I put Ace 20 rims on XT disk hubs, and I'm lazy so I only put half the spokes on. It's 9-speed 11-34. My youngest daughter loves the bike. The other one will be 10 speed 11-36 with the rear wheel being an Ace-20 laced to a Circus Monkey purple anodized to match the bike. No plans to re-build the front wheel.

    I didn't know what size BB to get, and with the 113mm Shimano square taper it looks like I could use a spacer to improve the chain line. No hurry though, she doesn't shift out of low gear.

    The 30T and 32T might be too low for them in a few years, but those would be good things to have in the parts bin.

    I have a little postal scale somewhere, I'll weigh the Spectra arms I haven't used yet if somebody else doesn't get to it first.

    I was trying to figure out what the Spectra brand is, and all I can tell is it may have been part of the Bianchi group. Not my area of expertise.

  22. #22
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    Thanks for the info guys. Glad to get confirmation the rings are bolt on. That is what I thought they were from the pictures.

    I'm getting excited about these cranks. Everything you guys say is sounding great. ETChipotle I'd love to hear what they weigh out at for you. The info on the ebay page says "531g + 219g (750g)" I was a bit confused what the 2 weights were for. I assumed crank at 531 and steel chainrings at 219. So I've been toying with going to a aluminum 30t 1x8 setup. I figured that could really same some weight.

  23. #23
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    Weights are probably right side crank arm (with rings etc) and left side crank arm.

  24. #24
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    Quote Originally Posted by TigWorld View Post
    I've got a list of short cranks that I've been maintaining over the years here. I've also shortened a number of sets of cranks and its a good way to go to get the exact size you need.
    That's the article I've been looking for.

    Do you have an opinion on crank length for kids? My son's Superfly 20 has 145 mm cranks and his inseam is only 20.5". He has a long torso and short legs, evidently, so the bike fits him fine but it's clear the cranks are too long.

    Want to swap them out before his first triathlon next month.

    I'm torn between the Spawn 102mm and 127mm cranks.

  25. #25
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    My son's inseam is 18.5 inches and he is riding 127mm cranks comfortably.

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    My son's inseam is 22"ish and he seems good with his 140mm cranks.

    He had been using 125mm cranks until a few weeks ago with no issues

  27. #27
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    Quote Originally Posted by CJH View Post
    I'm torn between the Spawn 102mm and 127mm cranks.
    127's for sure. 102 is probably too short, and the biggest chainring you can put on that 64 BCD spider is 30t.

  28. #28
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    My 8 year old rides with 130 mm Sinz cranks and is very happy with them. The cranks are 5 arm 110 mm BCD. I have a 34 tooth chainring and a Race Face bash guard on them. He is 1m25 tall (49 inch and a bit).





    Kind regards,

    Clemens

  29. #29
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    Ok, I have a 28-29" inseam. Last year I shorten my cranks. Wished I had known this thirty years ago...could have won more races....Now I'm riding 125mm on the road bike and 135mm on the CX and MTB bikes. So, so much better....Breathe better, spin faster, or push a harder gear...
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-dscn3367.jpg  

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    Choices for kid-sized Crank Sets-dscn3349.jpg  


  30. #30
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    Have a look at this thread I created a while back http://forums.mtbr.com/families-ridi...l#post11110874

  31. #31
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    Quote Originally Posted by ladljon View Post
    Ok, I have a 28-29" inseam. Last year I shorten my cranks. Wished I had known this thirty years ago...could have won more races....Now I'm riding 125mm on the road bike and 135mm on the CX and MTB bikes. So, so much better....Breathe better, spin faster, or push a harder gear...
    Show us more of that BTC-equipped mtb. Looks like it has a custom anodized Rohloff.

  32. #32
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    MTB and CX with Rohloff...
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-rscn2187.jpg  

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  33. #33
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    Quote Originally Posted by ETChipotle View Post
    I have a little postal scale somewhere, I'll weigh the Spectra arms I haven't used yet if somebody else doesn't get to it first.
    ETC or anyone else have an actual weight on the Spectra Crankset?
    It looks interesting - half the price of trailcraft or lasco and probably very similar weightwise when accounting for steel vs alloy rings.

    If possible would love to know actual crank weights plus separate ring weights.

    If the 750g is somewhat accurate I'm assuming I'd be down to 650-670 just by pulling the outer ring and with 104 BCD could possibly go 1x drivetrain with a 30 or 32 middle ring and be at around 580g for crankset plus additional saving from no shifter and derailleur.

  34. #34
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    I got my cranks a couple weeks ago and haven't put them on yet. I'll try to weigh them before I do. I did notice on one of the crank arms that it says Prowheel on it. That is the same company that made the OEM cranks on my kids Raleigh Mt Scout. Its a very different crank though, but it gives some insight into the company who makes them for Spectra.

  35. #35
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    I put the Specter cranks on my kids bike tonight. Using my wifes cooking scale the left arm weighed 218g and the right arm with the rings weighed 531g. Together both arms weighed 750g. Which was 100g lighter than the factory cranks. However, the factory arm was actually lighter than the Spector arm, so all the wight savings came from the rings. The big ring on the Spector is actually aluminum and the 2 smaller rings are steel.

    I did notice that the rings are offset quite different on the Spector though. My chain line is now way off. So I'm not sure what to do. I might just grind off the outside ring and make it a chain guard and make it a 2x. Since its aluminum (I checked with a magnet) it should grind down pretty quickly and not rust. If I knew what I was doing there is probably a way to adjust the bottom bracket too. I never touched the BB. Both bikes had the same square taper crank so I just took the factory off and put on the Specter.

  36. #36
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    Not trying to dig up overly-old threads, but found these when trying to find some lighter weight components for my daughter's bike: Trailcraft Cycles

    Edit.. NM, missed the reference to these cranks in the first post. ^ Here's the link to them though...

    2x in the front at under 650g. About the best I've seen and the price is good. They also offer a 24" titanium fork at 660g but it's way on the high price end, at $400. Kid better be an active racer to even remotely justify that cost IMO.

    I ended up going the Spectra route before I found these cranks. Running the spectra's in a 2x up front, with a 36 tooth equivalent race face light bash guard in place of the large ring. Comes in at under 700g and cost about $60 total. Still trying to find a cheap Ti or other lighter BB but this is still a vast improvement over every OEM crank I've found on youth bikes.

  37. #37
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    Can anyone direct me towards square taper 94 BCD five arm short cranks?
    Only boring people get bored.

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    I have a 20" bike for my son and it has 114mm cranks with a fixed 32t ring (very light setup, just not ideal gearing). I would like to find either a 114mm or 127m crank that will take a 28t chain ring. Given how small the 20" wheel is, I'm getting pretty close to the ground with the rear derailleur as I increase the size of the cassette. I'm currently at 32t and at most think I can put a 34t on, so I really need to get a smaller front chain ring on. Any sources for 114-127mm cranks that will take a 28t?

  39. #39
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    Quote Originally Posted by jh_on_the_cape View Post
    Can anyone direct me towards square taper 94 BCD five arm short cranks?
    I have never seen any commercially for sale. I did make a set of short cranks from some old LX cranks with 94BCD.


  40. #40
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    Are you sure you need such a small front ring? A 32 ring to 32 rear on a 20" wheel sounds like a pretty low gear for a young kid. unless you are doing really big climbs... My son ran a 35 ring to 34 rear for years and it worked well for us. Albeit we didn't do huge climbs or anything, but he was only 4-6 years old.

    But I guess if your son is older and looking to do longer climbs, then I can get my head around wanting a 28 up front.

  41. #41
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    Quote Originally Posted by jh_on_the_cape View Post
    Can anyone direct me towards square taper 94 BCD five arm short cranks?
    Turn3 racing has some. Not cheap though.

    Product Spotlight: Turn3 Racing cranks for the Micro Riders | bmxultra.com

    https://www.facebook.com/turn3racing

  42. #42
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    Still struggling here. Definitely need 28t for the climbs we do. I have 24t front 42t rear, and use it a lot ;-)

    Bottom line is that virtually all of the short cranks I find are 110BCD and so cannot go small on the chain ring.

    I found this triplelizer thingy that adds a 74 BCD ring to any 110BCD double. Possible I could use that on a set of 110BCD cranks as a "doublelizer" but I really only want one ring. Anyone seen a 110BCD rockring that includes mounting for 74 or 64 BCD chain ring? That or just an outright reducer from 110BCD to 74/64BCD? I have be sending this problem to a local machine shop...

  43. #43
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    Maybe you should check the roll out that the options you are looking at gives. Dont forget that a 24:42 on a 26" is about a third less roll out on a 20" wheel. This means a easy gear ratio on an adult bike is a super, super easy gear on a small wheeled childs bike. They are also hauling way less weight up hill. Kids have less strength and less leverage due to crank length but be careful assuming they need as low or lower gearing than adults as you also need to consider that their bikes have lower roll out lengths.

    eg: bmx example - on my 24" bmx I ride a 39:17 gear with 175 mm cranks
    my six year old on 20" wheels rides 36:15 with 125mm cranks. Just on gear numbers he is on a harder gear than me but take into account the wheel size and he is on a easier gear (not by heaps though and he spins this gear like crazy).

  44. #44
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    I've used Sheldon Brown's online calculator, using "Gain Ratio" which he suggests is the only measure that takes into account crank length. I was surprised too, my off the cuff thinking when I bought the bike was that 32/32 would be fine. I put a 38t rear on and even 32t front/ 38t rear isnt enough granny for the steeps. I definitely need something smaller than 32t on the front. I am increasingly coming to realize i will likely have to use one of the 3x options and just keep it on the granny. Who knows, I may fit a front derailleur on later...


    Quote Originally Posted by silvascape View Post
    Maybe you should check the roll out that the options you are looking at gives. Dont forget that a 24:42 on a 26" is about a third less roll out on a 20" wheel. This means a easy gear ratio on an adult bike is a super, super easy gear on a small wheeled childs bike. They are also hauling way less weight up hill. Kids have less strength and less leverage due to crank length but be careful assuming they need as low or lower gearing than adults as you also need to consider that their bikes have lower roll out lengths.

    eg: bmx example - on my 24" bmx I ride a 39:17 gear with 175 mm cranks
    my six year old on 20" wheels rides 36:15 with 125mm cranks. Just on gear numbers he is on a harder gear than me but take into account the wheel size and he is on a easier gear (not by heaps though and he spins this gear like crazy).

  45. #45
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    Quote Originally Posted by backinmysaddle View Post
    Still struggling here. Definitely need 28t for the climbs we do. I have 24t front 42t rear, and use it a lot ;-)
    ... I have be sending this problem to a local machine shop...
    If you are willing to get some machine work done, the Spawn 127mm cranks, while intended for 104mm chainrings, have undrilled bosses where a 64mm chainring would bolt on to.

    If you don't mind spending the money on Turn 3 cranks, I believe they have a 64mm spider available. If not, PM me. I have a spare spider that fits their cranks.

  46. #46
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    Here's the weight breakdown on the spectras in case anyone wants them. This is with everything disassembled.

    Drive arm: 298g
    Other arm: 218g
    Outer ring (Al): 80g
    Middle (steel): 84g
    Inner (steel): 38g
    Outer bolts and retaining nuts: 18g
    Inner bolts: 16g

    ~750g total. Can easily get this under 700g for 1x running a light bash guard and removing the inner ring, or if you went to Al middle and inner rings it would still come out under 700g.

  47. #47
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    I found that Islabikes actually have a 28t chain ring on 140mm cranks for their Creig hardtail model
    I couldnt get their US distributor to answer any questions about this crank and if it is available for order, so I contacted the UK office and hopefully they can hook me up with one. 28t front and 38t rear should be pretty close to what we need.

  48. #48
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    One other direction to consider.... What about getting a OneUp or Wolftooth 42 cog instead? Then you could keep your current cranks with the 32 ring, and still get a pretty darn low gear. Seems like it could be more cost effective, and potentially reusable on future builds, rather than hunting a unicorn crank?

    Just a thought.

  49. #49
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    I'd thought about that, but the rear derailleur pulley will be way too close to the ground with a 20" wheel. 38t is about the max you can safely go with a 20" wheel. This is doable with a 24" wheel for sure though.

    Quote Originally Posted by Surfpoodi View Post
    One other direction to consider.... What about getting a OneUp or Wolftooth 42 cog instead? Then you could keep your current cranks with the 32 ring, and still get a pretty darn low gear. Seems like it could be more cost effective, and potentially reusable on future builds, rather than hunting a unicorn crank?

    Just a thought.

  50. #50
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    Quote Originally Posted by backinmysaddle View Post
    I'd thought about that, but the rear derailleur pulley will be way too close to the ground with a 20" wheel. 38t is about the max you can safely go with a 20" wheel. This is doable with a 24" wheel for sure though.
    What about a Shimano mid-cage derailleur with a longer b-tension screw and 42 tooth cog with 30 tooth narrow-wide ring?

  51. #51
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    Wow, what a PITA this has been. I was also working on my daughter's 24" bike as well (also came stock 32x32 as granny).

    For both, it was a snap to add a 38t rear cog, but moving to 42t was out of the question on the 20" (regardless of derailleur I tried, it dropped the pulley wheel to the ground). And for the 24" bike, I had clearance, but it was going to require too many parts changes to make sense. The 38t slides on and works with the existing 8 speed derailleur/shifters/casettes. The 42t wasn't working well, I think it requires moving to 9 or 10 speed stuff to really work well. So I scratched that.

    So for my daughter I decided to get the Origin8 145mm crankarms, it's a 130/74 BCD triple set up ($48), then add an Origin8 26t chain ring for the 74 BCD mount ($20) and a 42t 130 bash guard to give it a finished look ($25). With the 38t rear and 26t front, she should be fine. And as she progresses I figure I can add a second chain ring and front derailler if she ever needs that.

    Now to figure out the equivalent solution for the 20" bike, which is even hard given how few cranks there are in the 114mm-125mm range that I would like. I'm convinced there are no single chain ring options and it will be another triple crank/ bash ring type solution. Again, hoping to keep it under $100.

  52. #52
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    My son loves his Lasco 152mm cranks from Utah Trikes. They're square taper triple cranks, we run them as a 2x with great results. Utah Trikes - Lasco 44/32/22 Triple Crankset 152mm w/Chainring Guard

  53. #53
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    Quote Originally Posted by backinmysaddle View Post
    Wow, what a PITA this has been. I was also working on my daughter's 24" bike as well (also came stock 32x32 as granny).

    For both, it was a snap to add a 38t rear cog, but moving to 42t was out of the question on the 20" (regardless of derailleur I tried, it dropped the pulley wheel to the ground). And for the 24" bike, I had clearance, but it was going to require too many parts changes to make sense. The 38t slides on and works with the existing 8 speed derailleur/shifters/casettes. The 42t wasn't working well, I think it requires moving to 9 or 10 speed stuff to really work well. So I scratched that.

    So for my daughter I decided to get the Origin8 145mm crankarms, it's a 130/74 BCD triple set up ($48), then add an Origin8 26t chain ring for the 74 BCD mount ($20) and a 42t 130 bash guard to give it a finished look ($25). With the 38t rear and 26t front, she should be fine. And as she progresses I figure I can add a second chain ring and front derailler if she ever needs that.

    Now to figure out the equivalent solution for the 20" bike, which is even hard given how few cranks there are in the 114mm-125mm range that I would like. I'm convinced there are no single chain ring options and it will be another triple crank/ bash ring type solution. Again, hoping to keep it under $100.
    127mm cranks, a good length for 20" bikes, are easy to find on the Spawn site.

    Alloy Cranks ? 127MM - Born to Ride | The World's Best Kids Bikes!

    $60CAN ended up about $60USD including shipping with the currently US-favorable conversion rate.

  54. #54
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    But those Spawn ones come with 32t ring which is what we already have, and it is 104BCD so only goes down to 30t right? I looked at these and passed 'em up for that reason.

    Quote Originally Posted by Feldybikes View Post
    127mm cranks, a good length for 20" bikes, are easy to find on the Spawn site.

    Alloy Cranks ? 127MM - Born to Ride | The World's Best Kids Bikes!

    $60CAN ended up about $60USD including shipping with the currently US-favorable conversion rate.

  55. #55
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    Yeah. Guess I was focused on only your last paragraph where you were talking about a 20" bike and didn't see the connection to the rest of the post.I think a 30T ring is pretty damn small on a 20" wheel, but YMMV. A 30T on a 20" wheel results in a smaller gear than a 26T on a 24" wheel.

  56. #56
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    I'm really liking the idea of the Spectra eBay cranks (152mm triple; I would swap the big ring for a bash guard), but does anyone have any idea if there's a square taper BB that would fit into BB92? The frame I'm looking at is a BB92 - the next best thing I can find is a set of 165mm FSA cranks.

  57. #57
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    Here's the spectra with the light aluminum bash guard and a 32T SNW chaining on it. Pretty respectable weight considering the cost and that most kids cranks come in somewhere around 2 - 4 lbs.

    Even running 2x, something like 24T/ 36T / Bash, this would probably come out well under 700g.



    Bash guard is very well made but pretty light aluminum and was only $12 so we'll see how long it lasts. Got it from BBG - MOUNTAIN | bbgbashguard

  58. #58
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    Thanks for all the info everyone, I pulled the trigger on the Spectra's today. Hope they show up before Christmas

  59. #59
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    Need kids cranks? Easy...

    Trailcraft Cycles

    Call Trail Craft and speak with Ginger. Super to deal with and carry great kids bikes and components, including cranks.

  60. #60
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    Quote Originally Posted by ETChipotle View Post
    I didn't know what size BB to get, and with the 113mm Shimano square taper it looks like I could use a spacer to improve the chain line. No hurry though, she doesn't shift out of low gear.
    I'm getting ready to pick up a bottom bracket to use with my son's spectra's. Are you saying that a longer spindle would have improved your chainline(i.e. the chainrings are too far inboard)? How far off does it look?

    Thanks
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  61. #61
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    I don't think the GT Speed AL cranks have been posted in this thread yet. I just got some for my daughters Ripcord build and I'm really happy with them. I set out looking for a relatively affordable 2 piece, external BB, 104bcd crank with short arm length options. Seems like everything is either square taper (heavy) or 5 bolt (not small enough rings) so when I stumbled on these and given that the price was decent and they ticked all the boxes I ordered them hoping that the weight was okay. $150 and there are web coupons out there for this store to knock them down 15%. There were a couple other online shops that list them but they either didn't have sizes listed or the sites weren't quite as legit looking. J&R lists 135-165 in 5mm increments, I went with the 135s.

    GT Speed AL Cranks at J&R Bicycles

    Box included the crankset and the anodized blue external BB (looks like it's a Shimano Deore by the markings/seals) and ano blue chainring bolts. Cranks/chainring bolts are 558 grams and the external BB is 105 grams. Add a 30t N/W ring and it should be right at 693 grams for the setup. Dropped 409 grams from the stock square taper setup.

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  62. #62
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    Good option if we need to go smaller front than a 34 with a 34 rear on the 20" bike. Time will tell.

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  63. #63
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    Quote Originally Posted by Dreamerof1 View Post
    I'm getting ready to pick up a bottom bracket to use with my son's spectra's. Are you saying that a longer spindle would have improved your chainline(i.e. the chainrings are too far inboard)? How far off does it look?

    Thanks
    I went with a 106mm on a Giant 24. Puts the chain right in the middle of the rear cassette.

  64. #64
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    BTW, for our 2016 20" Hotrock Girls build, I went with 140mm Origin 8 cranks, the BB length specified by Origin 8 and an Origin 8 chainring. Cost was reasonable. These are square tapers, and the BB is pretty light. Sealed bearings and spins silly good. Doubting my granddaughter will flex the BB spindle at 40 pounds.
    Reps! We don't need no stickin' reps!

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    Thanks, these are really nice and I particularly like the BB upgrade. A couple of questions:
    (1) how is the 30t working out on steeps, what is the large rear cog size?
    (2) what is the threading on the BB? I have no idea if the threading on my son's bike (currently has threaded square taper BB) would accept this BB.
    (3) what is the width of the BB shell, the bike my son has is really narrow (which is good for his small body) but I am not sure these would work as a result.


    Quote Originally Posted by catch22 View Post
    I don't think the GT Speed AL cranks have been posted in this thread yet. I just got some for my daughters Ripcord build and I'm really happy with them. I set out looking for a relatively affordable 2 piece, external BB, 104bcd crank with short arm length options. Seems like everything is either square taper (heavy) or 5 bolt (not small enough rings) so when I stumbled on these and given that the price was decent and they ticked all the boxes I ordered them hoping that the weight was okay. $150 and there are web coupons out there for this store to knock them down 15%. There were a couple other online shops that list them but they either didn't have sizes listed or the sites weren't quite as legit looking. J&R lists 135-165 in 5mm increments, I went with the 135s.

    GT Speed AL Cranks at J&R Bicycles

    Box included the crankset and the anodized blue external BB (looks like it's a Shimano Deore by the markings/seals) and ano blue chainring bolts. Cranks/chainring bolts are 558 grams and the external BB is 105 grams. Add a 30t N/W ring and it should be right at 693 grams for the setup. Dropped 409 grams from the stock square taper setup.

  66. #66
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    Quote Originally Posted by backinmysaddle View Post
    Thanks, these are really nice and I particularly like the BB upgrade. A couple of questions:
    (1) how is the 30t working out on steeps, what is the large rear cog size?
    (2) what is the threading on the BB? I have no idea if the threading on my son's bike (currently has threaded square taper BB) would accept this BB.
    (3) what is the width of the BB shell, the bike my son has is really narrow (which is good for his small body) but I am not sure these would work as a result.
    Well, the plan is to run the 30t up front paired with a 11-36 rear to start but I may throw a spare 42t cog I've got on there to see how it shifts. With the shorter stays of the 24" I'm thinking the chainline of the 42t might be a bit too much. This is going on a bike for her 7th birthday in January so I won't be able to review much for a bit. I'm probably a good 2-3 weeks from having the wheelset built that is going on the frame so I won't be testing much in terms of gearing, chainline, etc. til then. These are standard english/BSA threaded cups so they should swap right in for the square tapered setup you are working with. I didn't put a caliper on the BB but I'd be shocked if it wasn't setup for a standard 73mm mountain BB shell (and would be pretty surprised if that wasn't what you had). Hope that helps, I'll try to get some updates once I've got it all together (hoping for mid-Dec.).
    Sipping the Knolly Whisquillappa

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    Quote Originally Posted by catch22 View Post
    ... I'm thinking the chainline of the 42t might be a bit too much...
    On my daughter's XS 26er with a 40t rear cog, the chainline was touch and go with a 30t front chainring aligned with the middle of the cluster. It gets worse if you have a longer caged derailleur as in the big ring the chain is tightest as the lower jockey wheel can extend a long way forward (effectively shortening the space the chain has to do its "diagonal" thing). You can see what I mean in this pic:



    The derailleur at the time was a short cage XTR, but I subsequently replaced that with a 9 speed clutched XTR mash-up that I put together.



    It has been an excellent setup but I did have to space the 30t cog slightly inboard (3mm) to get it to work properly (and that's with a relatively short RADr cage).

  68. #68
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    Has anyone tried a set of Redline microline 2-piece cranks? They seem to come in a range of sizes, and have an external bottom bracket.

    I'm looking at a pair for my daughters new road bike (she has the Utah trikes 152mm on her MTB), and want 155mm cranks with a 110BCD. But I don't want a square taper bb, and there is hardly any choice for external bearings. I spotted the Redlines and they look good. It doesn't say if you can run a double chainring set-up though.

  69. #69
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    This was great to learn, turns out the threads are the same size so I put in a spare external style Deore BB and it fits well. The shell on my BB is actually slightly narrower than standard size (one of the selling points of the IslaBike is the narrower space between pedals for small kids). I did put some spacers in and got an extra pair of HollowTechII cranks to work just fine, they are way too long for a kid of course, but found they are not suitable for shortening (at least that is what the crank shortener guys site says).

    So now I love the idea of the lighter external BB, and can't bear to put a square taper back on, just really would like to find something in 150mm range that will allow 28t front ring. I have tried 28t Front and 38t Rear and it is perfect, so really want to find a 28t compatible 2 pc crankset.

    The BMX 2 pc cranksets are either 110BCD (min 32t) or 104BCD (at least can squeeze a 30t on there), anyone know of a 2 piece (non square taper) 2x crankset that comes in sub 160mm crank arm length? At least with a 2x I can put a sub-30t ring on as the smaller ring.


    Quote Originally Posted by catch22 View Post
    Well, the plan is to run the 30t up front paired with a 11-36 rear to start but I may throw a spare 42t cog I've got on there to see how it shifts. With the shorter stays of the 24" I'm thinking the chainline of the 42t might be a bit too much. This is going on a bike for her 7th birthday in January so I won't be able to review much for a bit. I'm probably a good 2-3 weeks from having the wheelset built that is going on the frame so I won't be testing much in terms of gearing, chainline, etc. til then. These are standard english/BSA threaded cups so they should swap right in for the square tapered setup you are working with. I didn't put a caliper on the BB but I'd be shocked if it wasn't setup for a standard 73mm mountain BB shell (and would be pretty surprised if that wasn't what you had). Hope that helps, I'll try to get some updates once I've got it all together (hoping for mid-Dec.).

  70. #70
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    Great minds think alike?

    Pic didn't upload...I have same setup

    Quote Originally Posted by jestep View Post
    Here's the spectra with the light aluminum bash guard and a 32T SNW chaining on it. Pretty respectable weight considering the cost and that most kids cranks come in somewhere around 2 - 4 lbs.

    Even running 2x, something like 24T/ 36T / Bash, this would probably come out well under 700g.



    Bash guard is very well made but pretty light aluminum and was only $12 so we'll see how long it lasts. Got it from BBG - MOUNTAIN | bbgbashguard
    Last edited by Rue; 12-10-2015 at 11:35 AM. Reason: Pic

  71. #71
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    I'm in a quandary with crank length, and looking for some guidance.

    In the coming months, I'm going to be building up an XS 26er for my 11-year old son. I measured him up last week, and came up with a 25.5" inseam (true inseam). Gearing will likely be 1x9 or 1x10, with a 26- or 28- chain ring and a cassette that tops out at 36 teeth.

    His current 24" bike has a 14-28 cassette and the smaller two rings are 32/22.

    Using Sheldon's gain ratio:
    Current 24" bike 152mm cranks, 22T crank gear, 28T rear = gain ratio of 1.6
    New 26" bike 160mm cranks, 28T crank gear, 36T rear = gain ratio of 1.5
    New 26" bike 170mm cranks, 28T crank gear, 36T rear = gain ratio of 1.4

    My goal is obviously to get something that's comfortable, but also get him some more gear to tackle hills with. Also, hitting the 170mm bogey opens up a lot of choices, 165mm less-so, and 160 and below I'm pretty limited.

    What are your thoughts?

  72. #72
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    Turn3Racing....I have a 29" inseam, running 125mm and 135mm. Wished I had short crank thirty yrs ago....

  73. #73
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    I'm not seeing those Spectra cranks on Ebay anymore, but now Trailcraft is here

  74. #74
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    Not as useful for really little kids, but new SRAM NX cranks go down as low as 155mm:

    SRAM releases a full 1x11 group for $310. This is good news for all.

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    That is good news. Pity they are not direct mount like other SRAM cranks, but I suppose we can't have everything.

  76. #76
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    I went through all of this for my older kids.**For the younger kids I just made the solution.**I know this is a bit spammy but I desperately want this to work so that 1. my wife doesn't kill me over what I have sunk into it.**2.**I want to make carbon kids bikes, for about what the big guys sell these 26lb turds.***Next thing in the shop is thru axle disc forks in 20/24/26 then frames.**Forge the joints, bond tubes.**I have rim aluminum extrusion done for disc 20/24/26 in china tubeless compatible but I am still searching for 20" tires.**And a 38t cassette around 200g.**Those are on the Facebook.
    So save a life and lighten the kids/wife's or even your bike up by supporting this indiegogo https://igg.me/at/forgedcarbon
    Any shares/likes/tweets/shouts are greatly appreciated.
    cheers

  77. #77
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    I just bought some 135mm cranks from these guys- https://www.facebook.com/turn3racing and with a 28tooth 94bcd wolftooth chainring they weigh ~400grams.

  78. #78
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    Quote Originally Posted by catch22 View Post
    Well, the plan is to run the 30t up front paired with a 11-36 rear to start but I may throw a spare 42t cog I've got on there to see how it shifts. With the shorter stays of the 24" I'm thinking the chainline of the 42t might be a bit too much. This is going on a bike for her 7th birthday in January so I won't be able to review much for a bit. I'm probably a good 2-3 weeks from having the wheelset built that is going on the frame so I won't be testing much in terms of gearing, chainline, etc. til then. These are standard english/BSA threaded cups so they should swap right in for the square tapered setup you are working with. I didn't put a caliper on the BB but I'd be shocked if it wasn't setup for a standard 73mm mountain BB shell (and would be pretty surprised if that wasn't what you had). Hope that helps, I'll try to get some updates once I've got it all together (hoping for mid-Dec.).
    Were you able to confirm these work on a 73mm BB width? I've looked everywhere and can't determine if they will work on 73, or if a bmx BB width is typically 68. DOing a build and it doesn't look like the SRAM NX cranks are out yet, so was looking at these as another option.

  79. #79
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    i have a used 140 mm square taper AC MiniLE crankset if anyone is interested. Can include 34t ring. PM me if interested.

  80. #80
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    Just confirmed the GT Speed Al cranks do not fit a 73mm frame.

    The crank shortening option on bike smith design is down as well, not sure if this is temporary, but if so leaves the SRAM NX basically the only option for short external cup cranks on a 73mm frame.

  81. #81
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    Quote Originally Posted by jestep View Post
    Just confirmed the GT Speed Al cranks do not fit a 73mm frame.
    Spindle length only enough for 68mm BB shells?

  82. #82
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    Quote Originally Posted by gtrguy2 View Post
    Spindle length only enough for 68mm BB shells?
    I guess that's why, they were a bit vague in their response. It's possible that it would work but the included BB is made for 68mm so I guess it might cause issues if the plastic tube can't properly sit in the BB cups. 5mm does sound like enough of a gap that the arm could end up getting smashed against the outside of of the cup when tightening.

    Anyway, I don't really feel like taking a $120 risk on it, so if anyone has successfully used one, with or without the included BB, I'd definitely still like to know.

  83. #83
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    After looking at all the possibilities, I ended up getting the Bombshell Spinnergy Mini cranks. For about $275 I got lightweight cranks in the size I want (140), with a 30T narrow wide ring along with a ceramic BB. Hopefully it all comes together.

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  85. #85
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    Quote Originally Posted by murrdogg11 View Post
    Those look killer with the direct mount ring. They don't post the weight but probably decent.
    WTB: Med Bontrager Ti Lite, PM Me...

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    Quote Originally Posted by murrdogg11 View Post
    Dang, wish I had seen these before. They must have just added them, as I'm sure I checked Spawn to see if they had any alternatives. Will definitely keep these in mind for the next bike though.

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    Quote Originally Posted by BullSCit View Post
    Dang, wish I had seen these before. They must have just added them, as I'm sure I checked Spawn to see if they had any alternatives. Will definitely keep these in mind for the next bike though.
    they seem to only be on their canadian site.

  88. #88
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    I had this issue a couple years ago with my son's 20" bike. Ended up getting a set of Sinz cranks (110 BCD) and pairing them with an IRD tripleizer chainring I already had so I could add a smaller inner ring. It made for a nice 2 ring setup and the chainline was fine with the stock bb.

  89. #89
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    Quote Originally Posted by jestep View Post
    Anyway, I don't really feel like taking a $120 risk on it, so if anyone has successfully used one, with or without the included BB, I'd definitely still like to know.
    Decided to give a set of these a try for my son's bike. I should have them in a week or so and will let you know what the deal is as far as the compatibility with a standard threaded BB.

  90. #90
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    Quote Originally Posted by jestep View Post
    Anyway, I don't really feel like taking a $120 risk on it, so if anyone has successfully used one, with or without the included BB, I'd definitely still like to know.
    Just to follow up- got the GT cranks and fitted them to my son's Stinky. No problems whatsoever. I didn't bother to change the bottom bracket and just left the Shimano in there and everything went together fine.

  91. #91
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    Thanks to this thread I just ordered a set of the GT cranks in 150mm for the bike I am building my son. They had a $5 coupon code for signing up for their email list, with that they came out to $100 shipped.

  92. #92
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    Quote Originally Posted by jestep View Post
    I guess that's why, they were a bit vague in their response. It's possible that it would work but the included BB is made for 68mm so I guess it might cause issues if the plastic tube can't properly sit in the BB cups. 5mm does sound like enough of a gap that the arm could end up getting smashed against the outside of of the cup when tightening.

    Anyway, I don't really feel like taking a $120 risk on it, so if anyone has successfully used one, with or without the included BB, I'd definitely still like to know.
    Quote Originally Posted by gtrguy2 View Post
    Just to follow up- got the GT cranks and fitted them to my son's Stinky. No problems whatsoever. I didn't bother to change the bottom bracket and just left the Shimano in there and everything went together fine.
    What's the BB shell width on the Stinky though? I think what Jestep is concerned with is if the cranks spindle can accommodate the extra 5mm of width with a 73mm shell and still have enough clamping area for the left arm. Not to mention that the bearing surfaces on the spindle will be off set and not fully (if at all) supporting the bearing on the non drive side...

  93. #93
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    Valid points. The Stinky is a 68mm shell but since I'm using a Hollowtech II BB, it's spaced to 73mm. I was happy with the fit as far as the amount of spindle clamping area for the non-drive side arm and where the spindle was sitting in the non-drive bearing. In my case I have the option of dropping the spacers the decrease the overall width but didn't feel it was necessary. YMMV.

  94. #94
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    I think you can take the spacers out. If you have spacers on both sides to even out the cups, then the bearings are only riding on 1/2 the spindles bearing surfaces on each side. The sealed spacer that runs between the cups is designed to work with both 68 and 73 by way of an o-ring fit on the non-drive side I'm pretty sure.

    Edit...there's a good chance that I am wrong on that with the Shimano BB. I just pulled out my XTR BB that has sat in the box since I got my cranks and it is dedicated at 73 with no way to adjust the width due to the seal/spacer.

  95. #95
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    The Shimano BB I'm using is good for 68mm or 73mm- I didn't realize they even made dedicated 73mm versions, I've never seen one. Are you sure about that?

    I just couldn't be bothered to pull the spacers. If the spindle length had been much shorter I would have.

    A couple of other notes about the crankset- JR list it as having an aluminum spindle but it's not. Also, the crank arm attachment interface is a bit odd- the spindle has large-ish splines like an ISIS BB but uses a bearing preload adjuster and pinch bolts like a Hollowtech II.


    Also, it doesn't matter how many spacers you use, the drive side of the spindle bearing surface will still sit 100% in the right place. That's not true of the non-drive side though, the amount of spacers will affect that.

  96. #96
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    Yeah I'm sure, just measured it. Choice is 73, and 73 . The spacer has hard steps on each end and doesn't allow adjustment.

    Ditto on the spindle material. Pissed me off a bit, but hey, they were only 95 bucks. Let me guess, you got them from J&R? I just got the last pair of 135's. Weren't even on the site, but I called to ask about the others, thinking I'd just cut them down, and he said they were out in the race trailer! Woohoo! Last ones! LOL!

    Those cranks really disappeared quickly. I put this stuff on the back burner for snowboard season, and when I checked again, stuff was already done gone..

    Edit...duh, you said that you got them from J&R...I'm doing A LOT of edits today. Reading comprehension and all that.

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    The GT Speed cranks come and go from the J&R site, I've been watching them for a long time.

    Regarding the BB- for a 68mm shell, the extra space is normally taken up by the spacers. The overall width once the cups are installed in a 68mm or 73mm shell is the same.

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    Not sure they'll be coming back this time, although that would be good for everyone else if they did. Talking with GT, they aren't making them anymore...

    It's SM-BB90A Came with my M980 Trail cranks.

  99. #99
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    Quote Originally Posted by jochribs View Post

    Ditto on the spindle material. Pissed me off a bit, but hey, they were only 95 bucks.

    Those cranks really disappeared quickly.
    Trailcraft Cycles has aluminum spindle direct mount cranks in 140mm and 152mm lengths now with 26, 28, and 30t chainrings in stock. Same cranks as what are on the PRO builds.

    Another option if the GT cranks are really discontinued.

    Trailcraft Cycles
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-crop_file_002-5.jpg  

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  100. #100
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    Does anyone know if the direct mount is inter-changable with SRAM direct mount?
    (looks like it should be so if you wanted larger than 30T you could use any SRAM direct mount?)

  101. #101
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    Is there a difference between direct mounts, or is it a standard interface between anything that is referred to as direct mount?

    The Trailcraft direct mounts look like a good option. Are the arms hollow?

  102. #102
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    There are a couple of different direct mount styles- Raceface DM and SRAM DM are not the same thing and are not interchangeable. If I recall correctly, the Trailcraft cranks use the SRAM style.

  103. #103
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    Just for reference: https://www.wolftoothcomponents.com/...tions/mountain

    They make rings for most DM and spidered setups. There's quite a few DM options, definitely not anything close to universal.
    WTB: Med Bontrager Ti Lite, PM Me...

  104. #104
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    Quote Originally Posted by 2melow View Post
    Trailcraft Cycles has aluminum spindle direct mount cranks in 140mm and 152mm lengths now with 26, 28, and 30t chainrings in stock. Same cranks as what are on the PRO builds.

    Another option if the GT cranks are really discontinued.

    Trailcraft Cycles
    These are sweet, finally somebody built the right crank for kids!

  105. #105
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    this looks like a good, cheap option. why would they not be compatible with a 113mm bb? would they work with any other size?
    https://www.universalcycles.com/shop...s.php?id=76620
    104bcd so should be an easy 1x set-up.

    opinions?

  106. #106
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    I'd say it would most likely be because running it as a 3 ring, with a 113 bb, you might run into interference issues with the rings on the frame in some applications, and then again, sometimes not. Or it could be that the taper section of the crank might bottom out on the cup before it is on tight enough, due to the spindle being shorter.

    Best way to find out would be to give Suntour a call or an email and ask them. For what you want to do with it, it may be fine, but you never know.

  107. #107
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    Quote Originally Posted by 2melow View Post
    Trailcraft Cycles has aluminum spindle direct mount cranks in 140mm and 152mm lengths now with 26, 28, and 30t chainrings in stock. Same cranks as what are on the PRO builds.

    Another option if the GT cranks are really discontinued.

    Trailcraft Cycles
    Trailcraft has good stuff for kids and they are good to work with.

    Are those rings narrow/wide?

  108. #108
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    Yeah, trailcraft has their own branded NW rings.

  109. #109
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    Imo, if you're going for the 152mm crank, I'd rather go with the Sram NX in 155mm for the wider selection of rings. I'd also rather replace a ring than a spider or have to throw in more money for a wolf spider and ring combo.

  110. #110
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    Quote Originally Posted by thesmokingman View Post
    Imo, if you're going for the 152mm crank, I'd rather go with the Sram NX in 155mm for the wider selection of rings. I'd also rather replace a ring than a spider or have to throw in more money for a wolf spider and ring combo.
    pretty sure both of these cranksets have a 104bcd...how would the sram have a better selection of rings?

  111. #111
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    Quote Originally Posted by murrdogg11 View Post
    pretty sure both of these cranksets have a 104bcd...how would the sram have a better selection of rings?
    The hollow trailcraft cranks are direct mount and use a spider. The trailcraft cranks that use rings are not hollowtech. Also the NX is 94mm BCD and ring choices run the gamut.

  112. #112
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    Quote Originally Posted by thesmokingman View Post
    The hollow trailcraft cranks are direct mount and use a spider. The trailcraft cranks that use rings are not hollowtech. Also the NX is 94mm BCD and ring choices run the gamut.
    oh sorry i thought you were talking about the sun tour cranks i posted above...ive been looking at them and others and having a hard time getting past the $30 price point..... cheap bb and readily available nw rings with 104bcd. i guess the only real draw back could be weight, but how much could it be?

  113. #113
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    Quote Originally Posted by murrdogg11 View Post
    oh sorry i thought you were talking about the sun tour cranks i posted above...ive been looking at them and others and having a hard time getting past the $30 price point..... cheap bb and readily available nw rings with 104bcd. i guess the only real draw back could be weight, but how much could it be?
    Those suntour cranks iirc are in the 920+ grams range w/o a BB. Add in a 300 gram BB and well it's real heavy!

    Another thing to think about is that at 152mm and up we're getting close to adult sizing, meaning the kids are about to hit their teens and sprout. That's why I'd go for the NX crank for its flexibility, and besides that I 'd want to stick to an external BB, so moving it to a bigger frame as they grow to a 26in. It's easier to do this and more worthwhile to keep and reuse with the NX or Trailcraft. Btw, those trailcraft prices are steep, replacement spiders are 45 bucks!

  114. #114
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    Quote Originally Posted by thesmokingman View Post
    Those suntour cranks iirc are in the 920+ grams range w/o a BB. Add in a 300 gram BB and well it's real heavy!

    Another thing to think about is that at 152mm and up we're getting close to adult sizing, meaning the kids are about to hit their teens and sprout. That's why I'd go for the NX crank for its flexibility, and besides that I 'd want to stick to an external BB, so moving it to a bigger frame as they grow to a 26in. It's easier to do this and more worthwhile to keep and reuse with the NX or Trailcraft. Btw, those trailcraft prices are steep, replacement spiders are 45 bucks!
    ya thats a good point.....a good chunk of weight. i think you would lose a couple hundred grams taking off those steel chainrings though.

  115. #115
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    Smokingman, the direct mounts, get a chainring mounted 'directly'...there is no spider.

    And 45 bucks for a direct mounting narrow wide chainring seems like a good deal to me, considering that a much lesser machined 'ring' for 104 bolt pattern will set you back in the range of 50-70 bucks. (Race Face, Wolf, One Up etc.)

    Not to mention, for 159 you're getting cranks, BB, and direct mount chainring. Shyte, if my son needed 140's or longer I'd have just gotten them. It's a no brainer. Solid, future proof, good looking crank...(that's what she said!)

    Sorry, I've been watching Office re-runs...

  116. #116
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    Doh, I wrote spider but meant sprocket. Or is that too bmx? lol And yea, 160 is decent for crankset with bb. I prefer a spider setup for flexibility, use of shims, slap on a bashguard, quick ring change, etc etc. As for rings on the NX, why go aftermarket when you can buy Sram X-sync for 20 bucks? But as I wrote before it's preference.

  117. #117
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    Quote Originally Posted by murrdogg11 View Post
    ya thats a good point.....a good chunk of weight. i think you would lose a couple hundred grams taking off those steel chainrings though.
    You won't lose the 300g bottom bracket though .. except you might have to anyway as the 3x will likely not have the correct chainline if fitted with a decent quality crankset....

    Then you need to buy the new ring(s) anyway.... and you are still stuck with a boat anchor BB/cranks and they are 152mm ANYWAY.....


    If your going to do it I'd do it properly.... you can buy brand new SRAM S600's in square taper for not much more.then cut to the right length.. and change the BB while at it to the UN55....

    I paid GBP£15 ($20?) for some used Alivio's which cut down to 140mm... (I'd say as short as they can be cut) the SRAM's can go even shorter... and both take a standard 104 BCD

    When he needs 152 ... I'll get some NX 155's... on his race bike but if it wasn't a race bike I'd just go for another set of cut down cranks at 150mm once 140 is really too small.

    Meanwhile I'm considering the Trailcraft but would need to know they are SRAM direct mount .... as annoyingly I'd need to have a few front chainrings as well... and he pushes 34 on the "kids XC" which is really more like cyclo-cross and has a lot of paved and non technical...

    I can honestly say I'd never use the Suntours that were supplied.... they are terrible in almost every way.... from chainline to weight to Q-factor to the actual fit onto a BB....

  118. #118
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    Quote Originally Posted by Steve-XtC View Post
    You won't lose the 300g bottom bracket though .. except you might have to anyway as the 3x will likely not have the correct chainline if fitted with a decent quality crankset....

    Then you need to buy the new ring(s) anyway.... and you are still stuck with a boat anchor BB/cranks and they are 152mm ANYWAY.....


    If your going to do it I'd do it properly.... you can buy brand new SRAM S600's in square taper for not much more.then cut to the right length.. and change the BB while at it to the UN55....

    I paid GBP£15 ($20?) for some used Alivio's which cut down to 140mm... (I'd say as short as they can be cut) the SRAM's can go even shorter... and both take a standard 104 BCD

    When he needs 152 ... I'll get some NX 155's... on his race bike but if it wasn't a race bike I'd just go for another set of cut down cranks at 150mm once 140 is really too small.

    Meanwhile I'm considering the Trailcraft but would need to know they are SRAM direct mount .... as annoyingly I'd need to have a few front chainrings as well... and he pushes 34 on the "kids XC" which is really more like cyclo-cross and has a lot of paved and non technical...

    I can honestly say I'd never use the Suntours that were supplied.... they are terrible in almost every way.... from chainline to weight to Q-factor to the actual fit onto a BB....
    roger all of that...thanks.

  119. #119
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    If anyone is interested, I have the 152 arms from the Orbea MX24. They weigh 563 stripped down.

  120. #120
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    Quote Originally Posted by murrdogg11 View Post
    roger all of that...thanks.

    Yep sorry a bit long winded way to put it...

    The price difference on the SRAM S600's is minor .... (Amazon UK its £10 difference)
    The difference in quality feels huge though...

    Even Shimano UN55 BB's are cheap.... (well even their XT/XTR level HT II BB's are cheap compared to most bike stuff)

    so between them you get a pretty good improvement for very little $$$ and since you are upgrading anyway it seems like one of those things to try and do properly..

    Once you invest in the pedal taps (I found mid range work perfectly as its soft alloy not steel) then you can make a new set up as and when needed for very little outlay... (this is how i got the Alivio's as they were just on ebay for not much more than postage costs)


    Probably also fair to warn you though... this can get quite addictive....
    I started off donating spares from my bike to the kids bike.... a year or a bit more later it's reversed

  121. #121
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    I bit the bullet and ordered the spawn 155mm cranks with direct mount... Should be here next week. I'll post some weights.

  122. #122
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    https://spawncycles.com/brood-eldorado-syx-140

    If anyone is curious the 155mm crank arms/spindle weighed in at 600g
    Bb is 110g without the spacers

  123. #123
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    Quote Originally Posted by jochribs View Post
    If anyone is interested, I have the 152 arms from the Orbea MX24. They weigh 563 stripped down.
    So that’s cranks minus bash guard and chainring, right? Any idea how much that square taper bottom bracket weighs?

  124. #124
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    Quote Originally Posted by martinizer View Post
    So that’s cranks minus bash guard and chainring, right? Any idea how much that square taper bottom bracket weighs?
    Not exactly as we didn’t write it down but it’s lighter than a UN55.

    It was a bit of rush as a friend came over with his kid and a MX24 he’d picked up (cheapest possible no discs etc.) and we did a rebuild from our spares bins.

    I had a spare set of S600 cranks I’d shortened to 140 and UN55 but when we pulled the B.B. and weighed it was less and good condition so we put it back in.

  125. #125
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    ST BB's are usually around 300 grams and up, not exactly light. The UN26 Shimano for instance is 355 grams. With a 560gram crank, that's 1k grams roughly, then there's the bolts too.

  126. #126
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    FS Orbea MX 24 Trail Cranks

    I have an unused set of the Orbea 152 mm cranks with 32T chainring and square taper bottom bracket. $50, shipped. PM me for pics, questions and/or purchase

  127. #127
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    Quote Originally Posted by thesmokingman View Post
    ST BB's are usually around 300 grams and up, not exactly light. The UN26 Shimano for instance is 355 grams. With a 560gram crank, that's 1k grams roughly, then there's the bolts too.
    The UN55's are quite a bit lighter and still only a few $$
    The overall weight difference between Shimano external BB with Zee cranks cut to 140 vs the SRAM S600's at the same length and UN55 was 12g (from memory).

    I just checked an old photo and the SRAM's + 118mm UN55 + 30T chainring and all bolts weigh 876g.

    Trailcraft 140mm with 30T are quoted as 558g. I'm not sure if this includes BB but that's 113g (and I'm guessing not or they wouldn't list separately)... so if its without then that's 671g vs 876g and $160 vs 200g weight saving. (Which is quite a bit less than say 2 inner tubes or less than the difference in saddle weight between the stock one came with my kids bike vs the $15 one I replaced it with)

    All that said the price of the Trailcraft direct mount is good (compare with any half decent adult one) but its not good for us (because I'd need to buy extra direct mount chainrings when I have a stock of 104BCD and as a minimum he'd need a 34T as well. Or I'd need to go to more expense of fitting a SRAM XD driver and a 10T cassette.)

    We ability of fitting a smaller chainring than a 30T has no utility for us but if for some reason you need a smaller chainring then that would be different.

    At the end IMHO the benefits of having the correct sized cranks are huge compared to 200g of weight...
    However the benefit of almost anything half decent over the Suntour kids cranks is also huge... the are just really poorly made. The difference in quality over the cheap SRAM's is like night and day... not just the chainrings but the way they fit (or don't really fit*) onto the BB...

    *The suntour cranks we had didn't fit onto the BB as such.. they sorta got rammed on by the bolts until the poor tolerance square taper got deformed enough to fit on... it's probably a mis-representation to call them square taper even... (as the manufacturing tolerance hardly approximated a square... granted it had 4 sides but all slightly different lengths)

  128. #128
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    The SR Suntour XCT Jr. Crankset that Steve-XTC references uses a JIS square taper standard, so was likely mated with an ISO square taper bottom bracket, hence the fit issue. They can be forced to fit but mating is poor and it generally ends up loosening.

  129. #129
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    Give [email protected] a shout....they will take care of all your problems. Update; 5' with 27" inseam...been riding 135mm on mtb and cx, 125mm on road bike for a few yrs. Wished I had known this twenty yrs ago. Find Turn3 racing on FB.

  130. #130
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    SRAM Rival with removable spider is easy to shorten, and mount whatever size direct mount chainring you want!Choices for kid-sized Crank Sets-crankset-drill1.jpg

  131. #131
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    Oh this is great. I found this looking for cranks to go on a hardtail 13" 27.5 frame I'll be building up for my daughter.

    So the turn 3 cranks look super light but use a square taper BB thats fairly heavy. They list 125mm cranks at 373g, so guessing 155mm at 420g ish? Then a BB at around 180g for $90 and ring and bolts at 60g for 50 bucks. So total weight at 660g for $296

    Then trailcraft DM is at 582g for 30t 152mm and 113 for BB, so 695g for $160

    Sram nx 155mm is claimed at 680g with 32t. Add 118g for bb for $30 and its 798g for about $135


    Thinking I'm going Trailcraft for now. I'm hoping to see other options become available as well!

  132. #132
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    I went with the NX because it will take a 28T. That coupled with an 11-42T (Sunrace) cassette, makes for a considerably better low than a 30T and works with a 10 Spd med cage rear derailleur

  133. #133
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    Quote Originally Posted by xprmntl View Post
    I went with the NX because it will take a 28T. That coupled with an 11-42T (Sunrace) cassette, makes for a considerably better low than a 30T and works with a 10 Spd med cage rear derailleur
    Trailcraft Direct Mount's can go down to a 26 tooth, and use an aluminum spindle to save weight over steel spindle.

    For reference, just replaced a NX crankset off a Transition Ripcord (30 tooth, 155mm length) and replaced it with a Trailcraft 152mm and 26 tooth for a better mountian climbing gear.

    SRAM NX 155mm with 30t and bb = 810g

    Trailcraft 152mm with 26t and BB = 665g

    145g savings over stock NX setup, so not a ton but taking 145g off the bike in 4-5 places is well over a pound.
    Front Range Forum Moderator

  134. #134
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    That Trailcraft direct mount option is cool. It wasn't available this past winter while I was swapping out a few parts on my daughter's 24" Orbea MX Trail.

    It's all trade-offs, though, right? At the time, I wanted a reasonable way to get that bike to ~16 gear inches. That was accomplished with the 28T x 42T combo with 24" wheels and 155 mm crank arms

    More numbers for those considering similar (using numbers off google searches)...

    Trailcraft 152mm with 26t: 570g + Trailcraft BB 113 g (total 683g) $160

    SRAM NX 155 mm with 32t - 680 g $92
    GXP Team bottom bracket: ~115 g (varies) $25
    Aftermarket narrow-wide 28T $30 (sell SRAM 32T for $35) -$5, -10g
    Total: 785g; $117

    In choosing a chainring size, a 26T seems like a good idea for a kid, but that 2T difference from 28T doesn't keep from having to use a newer high range cassette to get a good low gear. I consider a "good low gear" as one equivalent in gear inches to a 22T x 36T on a 26" bike with 175mm which is ~15.9 gear inches (according to the Sheldon Brown calculator).
    For a 24" bike and 152/155 cranks:
    26T x 36T = 17.3 gear in
    26T x 40T = 15.6

    28T x 42T = 16.085g

    Shimano XT 11x36T 9spd $50, ~300g
    Shimano XT 11x36T 10spd $50, ~340g
    Sunrace MX3 11x40T 10spd $45, ~ 380g
    Sunrace MX3 11x42T 10spd $45, ~390g (~430g for Shimano M8000)

  135. #135
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    In choosing a chainring size, a 26T seems like a good idea for a kid, but that 2T difference from 28T doesn't keep from having to use a newer high range cassette to get a good low gear. I consider a "good low gear" as one equivalent in gear inches to a 22T x 36T on a 26" bike
    I consider a good low gear as one that i can ride up the steepest and longest hills I ride.
    If I had stuck with gear ratio's I'd never have gone 1x....

    Having gone 1x I quickly found I didn't actually need most of the low gears I had been using... probably more surprisingly I found it was actually easier overall without them.

    Whatever the gear ratio was on my 2x it got used and I got stuck in it. Stick it in 1st 200' into a 3000' climb for a steeper bit and getting out of it gets harder... every root and rock becomes a static challenge more than a rolling challenge because I don't have the momentum.

    Looking back the whole 3x and 2x was with exceptions like carrying tents just part of the bigger and wider is better.
    We were given gears that made it harder and convinced ourselves to an extent they were needed based on once we used them. Even with my current set-up I've done a ride not realising I hadn't got my mech adjusted and didn't have 1st gear and not missed it.

    With the kid I found this even more so... when he 1st had a 40T expander he was using it all the time... and once in it on a climb getting out of it was difficult. I took it off one day and didn't say anything and he did fine... he didn't even notice the missing gear he'd been using ..

  136. #136
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    Quote Originally Posted by Steve-XtC View Post

    With the kid I found this even more so... when he 1st had a 40T expander he was using it all the time... and once in it on a climb getting out of it was difficult. I took it off one day and didn't say anything and he did fine... he didn't even notice the missing gear he'd been using ..
    Totally agree with ya Steve. I went ahead and threw a Sunrace 11-42 10spd cassette on my sons hardtail. Grabbed an 11 spd XT rear derailleur to handle the larger cog. He isn't completely enthralled with the steps between the lower gears and on the hardest/techiest climbs he just isn't using the 42. He'd been running an 11-36 previously. 30t front.

    I myself ride a 36t front to an 11-34 rear. I don't think I'm super human. I don't have any problems. Like father like son, I guess.

  137. #137
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    Quote Originally Posted by Steve-XtC View Post

    Having gone 1x I quickly found I didn't actually need most of the low gears I had been using... probably more surprisingly I found it was actually easier overall without them.


    Yes! Dropping the 3x, front shifter, all the housing and complications was the best move we ever made by going 1x. Do it!

  138. #138
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    Quote Originally Posted by jochribs View Post
    I myself ride a 36t front to an 11-34 rear. I don't think I'm super human. I don't have any problems. Like father like son, I guess.
    You're a harder man than I.

    #humblebrag #saystheguywholivesinjersey

    j/k
    Last edited by RMCDan; 07-06-2018 at 08:59 AM.

  139. #139
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    Quote Originally Posted by RMCDan View Post
    You're a harder man than I.
    Jochribs, 32in waist, 34in quads. Can only bike in early 90's MC Hammer pants.

  140. #140
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    Lol!!

    Make that 31 inch waist.

    Don't be jealous. Just turn your cranks

  141. #141
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    Svinyard, just recently started riding. Is now the authority on all things bro bra. Son will lay the coals to him in maybe year. (That's his son. My son probably already can)


  142. #142
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    I worry about crank length for my kid, too, especially after reading this forum. But then there are kids like this, riding bike that do not fit at all, long cranks, heavy 30+ pound bikes, improper leg extension...yet nonetheless developing ridiculous skills and connection to their bike.

    It's amazing what kids can do when motivated, and nothing motivates them more than their peers.




    I have to remind myself when I get on these shopping missions that if my kid isn't keeping up, there may be other things more important than crank length.

  143. #143
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    You sure those are crap bikes? I mean weight in a BMX/DJ hybrid bike isn't the same situation as with little kids trying to climb distance and throw a bike around at high speeds over chunk on single-track. It's a high stakes game for little groms, maybe THE most high stakes game you'll see a kid play. I love the rigid bikes there. Wish people would buy those instead of the crappy Riprock style stuff.

  144. #144
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    Not sure some kids 'walking the bike' is an argument for cranks that are too long.

    As Svinyard brings up, there's a massive difference between that and putting in repetitive cadence and pyshing out watts on a bike meant for covering distance, and tech riding.

    Plus bmx bikes generally have longer cranks as you are standing the majority of the time. That kids have fresh synovial flyid in their joints is not withstanding in just figuring they should push longer cranks than is mechanically sound for those said joints. A 150 crank for a 4'6" kid is like us pushing a 200+mm crank.

    Would you like to push 200mm cranks? If you do, let us know how that goes. I'm not thinking too well.

  145. #145
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    Quote Originally Posted by MidnightFattie View Post
    It's like an SE sponsored wheelie inspirational video!

  146. #146
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    Quote Originally Posted by thesmokingman View Post
    It's like an SE sponsored wheelie inspirational video!
    No kidding.

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    Quote Originally Posted by jochribs View Post
    No kidding.
    Yea hehe. Oh and apparently Speccy will not be out done!


  148. #148
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    While doing a build for my 12yo I came across these Suntour Zeron cranks, $70 for a direct mount 1x crank (includes Hollowtech-type external BB and 30t chainring) available in sizes from 152mm. With 11-40t 9sp cassettes available, a 1x9 setup is affordable and simple.

    Not in the same league as the Trailcraft cranks but less than half the price.

  149. #149
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    Quote Originally Posted by murrdogg11 View Post
    https://spawncycles.com/brood-eldorado-syx-140

    If anyone is curious the 155mm crank arms/spindle weighed in at 600g
    Bb is 110g without the spacers
    That is without a chainring? So the Trailcraft are about 100g lighter?

  150. #150
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    Quote Originally Posted by david.p View Post
    While doing a build for my 12yo I came across these Suntour Zeron cranks, $70 for a direct mount 1x crank (includes Hollowtech-type external BB and 30t chainring) available in sizes from 152mm. With 11-40t 9sp cassettes available, a 1x9 setup is affordable and simple.

    Not in the same league as the Trailcraft cranks but less than half the price.
    Really sucks that the spectra 152mm is no longer available. It was like $35, under 600g for 1x, and fit on the typical square taper BB's that most kids bikes still come with without any modification.
    WTB: Med Bontrager Ti Lite, PM Me...

  151. #151
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    Quote Originally Posted by jestep View Post
    Really sucks that the spectra 152mm is no longer available. It was like $35, under 600g for 1x, and fit on the typical square taper BB's that most kids bikes still come with without any modification.
    Spectra same as Thorn cranks possibly? (not $35 but if local not a bad deal)

    https://www.sjscycles.co.uk/cranks/1...black/?geoc=US

  152. #152
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    Quote Originally Posted by GSJ1973 View Post
    Spectra same as Thorn cranks possibly? (not $35 but if local not a bad deal)

    https://www.sjscycles.co.uk/cranks/1...black/?geoc=US
    Slightly different but that looks like a great option.
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    Totally agree with crankset length on kids bikes. Now daughters moving up in size and problem starts all over. 170mm cranks for a 147 cm (4'10") on the 27.5 xs...wouldn't think so. Looking for 160mm cranks hollowtech II, fruitless. Anybody knows? Except for Lightning in carbon - I don't even dare to ask price on those.

    I do disagree with small chainring with wide range cassette. My youngest boys ride 20" mtbs with 125mm cranks, 11-42t cassette and 38t up front. They rarely use the lowest gear, only on technical uphills in the woods. On paved road the highest gear is not enough - they spin out, at around 45 kph.

  154. #154
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    Quote Originally Posted by guaruska View Post
    Totally agree with crankset length on kids bikes. Now daughters moving up in size and problem starts all over. 170mm cranks for a 147 cm (4'10") on the 27.5 xs...wouldn't think so. Looking for 160mm cranks hollowtech II, fruitless. Anybody knows? Except for Lightning in carbon - I don't even dare to ask price on those.

    I do disagree with small chainring with wide range cassette. My youngest boys ride 20" mtbs with 125mm cranks, 11-42t cassette and 38t up front. They rarely use the lowest gear, only on technical uphills in the woods. On paved road the highest gear is not enough - they spin out, at around 45 kph.
    Check out the sram nx which comes in 155mm.

  155. #155
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    Quote Originally Posted by thesmokingman View Post
    Check out the sram nx which comes in 155mm.
    Definitely.. at 155 the problem is easier solved.
    Don’t worry about 5mm shorter than ‘ideal’ as opposed to 5mm too long.

    If anyone is feeling flush, has just received a bonus, inhertitance or such it seems Hope now are selling their kids cranks they made for their own lease only fleet.
    Designed specifically for children's bikes and their wee legs. Choose either 135mm or 150mm lengths. These cranks don't include a spider or chainring.
    Around $200 + spider + chainring

  156. #156
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    Thanx for advice. I've read about the sram nx 155 in this thread. I would need a different bb for that (not sure?). And then the 2x chainrings. So I might as well ask about price for the Lightning crankset for the size I (my daughters) would be fit for.
    Found the Bor xm557 165mm at roughly 600 usd. Kill to birds in one stone: lighter bike and lighter wallet! It's just annoying to sit on a thick wallet while commuting to work. It makes my hip crooked.

    I also found Federleicht 160mm, but they only make them in 1x. Only 500 usd. Rider max weight 50kg. Hey...just like my wallet, in grams.

  157. #157
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    Are you absolutely set on 2x?
    Unless you have long sections of road to link up I find it hard to find a need nowadays.
    There are a few fire trails I spin out on 27.5 (depending on chain-ring) but not often enough or for long enough or I'd be going much faster .. to make me want to go back to 2x and I'm nowhere near maximum range possible today on any of my 27.5 bikes.

    (Neither is jar but he's on 24" wheels)

  158. #158
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    I tried to convince them to go for 1x front but both wanted 2x. With four kids I've noticed their cadence is different from adults, and if they didn't make use of all the gearing it wouldn't be up to them to decide, but they make use of it.

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    Huh? You're gonna spend 600 bucks on a 2x crank for your kid????

    Your kids asked for 2x??? What the?

  160. #160
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    Uhm. No, not gonna spend 600 bux on a crankset. I was being ironic.
    No, they didn't ask for 2x. Bike has 2x and I asked them if they'd prefer 1x. They tried it on brothers bike and didn't like it.
    And besides, even if the answer was the opposite, it would be my choice and not anybody elses problem. They do have killer bikes, but I build them with great deals I find on ebay or elsewhere.

  161. #161
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    Quote Originally Posted by guaruska View Post
    Uhm. No, not gonna spend 600 bux on a crankset. I was being ironic.
    No, they didn't ask for 2x. Bike has 2x and I asked them if they'd prefer 1x. They tried it on brothers bike and didn't like it.
    And besides, even if the answer was the opposite, it would be my choice and not anybody elses problem. They do have killer bikes, but I build them with great deals I find on ebay or elsewhere.
    Hehe, gotcha.

    And on them preferring 2x, that is really surprising. Sequential shifting is logistically the easiest, granted if its the same total range. However using 2x or more, is not all that efficient because you lose some range in the process. Its also a pain in that when you hit that multi (change front ring) you get put out in a wrong gear and have to knowingly compensate. Thus its kind of surprising that the kids would prefer 2x.

  162. #162
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    Maybe surprising. Imho they use the 2x as intended: large chainring by default, granny when required on technical uphills. The young girl (12 y o, 138 cm 30 kg) has a road/mtb setup for the 2x, 40t and 34t with 11-36t cassette, on her 24er. It took her a little practice to get the point, but once the point made it through the use of it is easy as pi. The older (on the 27.5 with 170mm cranks) has 36t and 22t in front, 11-36t rear. She understands it perfectly without an explanation. But cranks are not ideal. She's 13 y o, 148 cm with 43 kg of muscles. Stronger than most boys in her class and with more stamina by far. A short ride round the neighborhood for us is at least 20-30km.
    She was the only child in her class to make the gymclass challenge: hang from the 3 m platform (height from the water) with hands only, and climb back up. First girl in school history to make it. On her first day. (Can u tell I'm proud?)

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    Quote Originally Posted by murrdogg11 View Post
    https://spawncycles.com/brood-eldorado-syx-140 If anyone is curious the 155mm crank arms...
    Don't you mean 140mm? Both the URL and the actual webpage say 140mm. I cannot find any mention of 155m at spawncycles.com

  164. #164
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    Quote Originally Posted by MXIV424 View Post
    Sram nx 155mm is claimed at 680g with 32t. Add 118g for bb for $30 and its 798g
    Real weight for ours is
    475g right arm + GXP spindle, w/32T + 4x CR bolts
    229g left arm
    2g pedal washers
    706g out-the-door

  165. #165
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    Quote Originally Posted by david.p View Post
    I came across these Suntour Zeron cranks, $70 for a direct mount 1x crank (includes Hollowtech-type external BB and 30t chainring
    THANK-YOU! I've been searching far and wide for a 160mm two-piece crankset to up-size my (now 5'3") daughter's SRAM NX-155's.

    I'd prefer something better quality than SR-Suntour; but this is only the second offering I've found.

    If I were Steve-XtC in the UK, I'd be trying to buy the German VPACE 160mm at http://www.vpace.de/produkt/max-kind..._laenge=160+mm for €129. But I cannot find any way to buy them in the USA.

  166. #166
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    Quote Originally Posted by guaruska View Post
    (on the 27.5 with 170mm cranks) ... She's 13 y o, 148 cm with 43 kg of muscles
    Good grief!! A 4'10", 95'lb person on *170mm* cranks?!? I ride 171cm at 172cm tall.

    Even 165mm are too long IMHO, but at least those should be SO EASY to source for use with your existing BB + chain rings there's no reason not to at least give her those.


    First girl in school history to make it. ... (Can u tell I'm proud?)

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    Quote Originally Posted by Acrophylos View Post
    SRAM Rival with removable spider is easy to shorten
    What did you shorten them to? Do you have pics of the finished product [from the back side]?

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    Quote Originally Posted by guaruska View Post
    I also found Federleicht 160mm
    Uggg, http://www.federleicht-bike.at/index...tur-160-detail for 388€ ?? [US$448 before shipping, etc...] More than Double my budget for this.

  169. #169
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    ?? Why do you think a 5'3 rider needs another 5mm?

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    Quote Originally Posted by Dr_UNIX View Post

    If I were Steve-XtC in the UK, I'd be trying to buy the German VPACE 160mm at MAX Kinderkurbel - VPACE Bikes for €129. But I cannot find any way to buy them in the USA.
    They ship them worldwide. Contact them for info on this. I know their website is in german only, but I did figure that part out. They answer in English, I've contacted them before. You'd probably be slaughtered with customs but if u can't get anything else...in that price range. U have the lightning cranks at a respectable cost of 740 usd, in Califas.

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    The difference is huge on shorter persons. My daughter on the 24" went from cruising speed of 15 kph to almost 25 when shortening cranks to ideal length (from 152mm to 140mm).

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    Quote Originally Posted by thesmokingman View Post
    ?? Why do you think a 5'3 rider needs another 5mm?
    A fair question. Based on how short she was when using 155mm/152mm cranks, the "look" of her pedaling, her typical cadence and gear she says she can push - I think 155mm is too short. Looking at 4-5 on-line guides, I also compute 160mm as the right crank size.

    Also, anything shorter and that would seem to call into question the 170mm I use for road/CX/XC at 5' 7.5".

    Determining Crank Length for Children
    10% height: 160cm * 10% => 160mm

    https://highpath.co.uk/crank-shortening/
    effective leg length = 749mm => 749mm * 22% for child = 165mm
    effective leg length = 749mm => 749mm * 20% for adult = 150mm

    measured inside leg length = 75.9cm
    Bicycle cranks: Check your Cranks!
    inside leg length 66 to 70cm : 155mm
    inside leg length 72 to 75cm : 160mm
    inside leg length 75 to 78cm : 162.5mm

    Bicycle Crank Length
    2.16 * 75.9cm = 163.9mm
    Last edited by Dr_UNIX; 09-09-2018 at 08:04 PM.

  173. #173
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    Short cranks

    5' 28" inseam...went from 170/165mm to 125/135mm never go back...wished I did this 20yrs ago.
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-dscn3367.jpg  

    Tread killer....

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    If I were Steve-XtC in the UK, I'd be trying to buy ....
    When we needed the them it was just quicker and easier to make them from existing cranks.
    Having done it once .. it's much easier than I'd expected.

  175. #175
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    Quote Originally Posted by Dr_UNIX View Post
    A fair question. Based on how short she was when using 155mm/152mm cranks, the "look" of her pedaling, her typical cadence and gear she says she can push - I think 155mm is too short. Looking at 4-5 on-line guides, I also compute 160mm as the right crank size.

    Also, anything shorter and that would seem to call into question the 170mm I use for road/CX/XC at 5' 7.5".

    Determining Crank Length for Children
    10% height: 160cm * 10% => 160mm

    https://highpath.co.uk/crank-shortening/
    effective leg length = 749mm => 749mm * 22% for child = 165mm
    effective leg length = 749mm => 749mm * 20% for adult = 150mm

    measured inside leg length = 75.9cm
    Bicycle cranks: Check your Cranks!
    inside leg length 66 to 70cm : 155mm
    inside leg length 72 to 75cm : 160mm
    inside leg length 75 to 78cm : 162.5mm

    Bicycle Crank Length
    2.16 * 75.9cm = 163.9mm
    Most of those links are all based on assumptions. There's no science in their science. Studies have shown that the formulas are wrong, all wrong. There is actually no appreciable difference in power output from 130mm to 190mm crank lengths.

    Did you read your first link? And yet you are planing to upsize cranks by 5mm? Moving up 5mm is just throwing money away imo. How I judge crank length is not longer is better or even longer as the goal. Instead its how the hips of the rider vs their knee's top dead center. If the rider has to rock or drop their hip to complete a pedal rotation, then that needs to be looked at. That said, if I were you would not be wasting money on cranks.

    OTOH a lot of testing and real world examples show that you can go considerably shorter than this length with no loss of power. This is because your knees are straighter so you can push harder on the pedals. And because your muscles are in the length range where they can apply peak tension through more of the circle (I list a few examples below.)
    So, as a child grows to a height where they COULD ride longer cranks, they aren't giving up anything by riding the cranks that were fine for them a year or two ago. On the other hand a child riding cranks sized for the height he or she will be in a couple of years will not only be slower but also risks knee injury. About 15% of my customers have damaged their knees riding cranks that were too long.
    Moving on...

    One of my customers, 5'-7" (170cm) tall professional triathlete Courtney Ogden, won the big money 2011 Western Australia Ironman on 145s. The next day, despite being wasted, he ordered a set of 130s. He's done extensive work with the people at PowerCranks where they are becoming big advocates of shorter cranks.
    A better introductory to crank length is Cervelo's take on the study...

    But for each of these pros, the change to a shorter crank solved a range of motion issue at the hip that allowed them to comfortably make other changes to reduce aero drag without decreasing power.
    https://www.cervelo.com/en/engineeri...n-crank-length

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    Awesome post Smoking. The mindset of Dr. Unix (no offense meant personally), is why we have such limited options for varying crank lengths. Companies have little reason to produce shorter options because end users and bike companies (that should straight up know better) will buy the longest ones they can anyway.

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    Good info smoke. Helps alot!

  178. #178
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    Quote Originally Posted by Dr_UNIX View Post
    Real weight for ours is
    475g right arm + GXP spindle, w/32T + 4x CR bolts
    229g left arm
    2g pedal washers
    706g out-the-door
    Then a bb around 100-120 grams puts it at the 800 mark, correct?

    Quote Originally Posted by thesmokingman View Post


    A better introductory to crank length is Cervelo's take on the study...



    https://www.cervelo.com/en/engineeri...n-crank-length
    Good read, thanks.

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    I think best is to 0.21 to 0.216 x inseam, have to find source for this though (here it is as 20-22% https://highpath.co.uk/crank-shortening/). This will give about 102-105mm cranks for my 6yo daughter (current 127mm is insane) and completely out of luck finding proper cranks. There is prowheel 102mm in author bicycles but it's not available as oem. I'm thinking about converting some road crank as they tend to have lower q-factor, any suggestions?

  180. #180
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    There are cheap 105mm on ebay. Steel cranks with 30t chainring. I also think hollandbike has some of that size. Here: https://www.ebay.co.uk/itm/CHILDS-BI...byXT:rk:1:pf:0

    And some really expensive to pick your own chainring: https://www.ebay.co.uk/itm/Von-Sothe...4B40:rk:3:pf:0

  181. #181
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    Quote Originally Posted by Eneen View Post
    I think best is to 0.21 to 0.216 x inseam, have to find source for this though (here it is as 20-22% https://highpath.co.uk/crank-shortening/). This will give about 102-105mm cranks for my 6yo daughter (current 127mm is insane) and completely out of luck finding proper cranks. There is prowheel 102mm in author bicycles but it's not available as oem. I'm thinking about converting some road crank as they tend to have lower q-factor, any suggestions?
    And here: https://www.ridewill.it/c3/en/cyclin...nksets-mtb/37/

  182. #182
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    Spawn sells 102mm cranks for $50. They even go down to 89mm if you'd want that:

    https://spawncycles.com/spawn-cycles-alloy-cranks-102mm

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    Quote Originally Posted by guaruska View Post
    And some really expensive to pick your own chainring: https://www.ebay.co.uk/itm/Von-Sothe...4B40:rk:3:pf:0
    Wow, 230 grams.

    I'll second the Spawn recommendation, assuming were talking square taper. If 2-piece thru-axle are needed, then get the 115s Flow sells (not on their website, I've been told you can email them and they'll sell you a set).

  184. #184
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    Quote Originally Posted by Eneen View Post
    I'm thinking about converting some road crank as they tend to have lower q-factor, any suggestions?
    See my post from June (same thread). Shortening SRAM Rival with removable spider is very easy to shorten if you have a drill press and the pair of thread taps. Considering that we're talking about kids, presumably under 110lbs / 50kgs strength really isn't a concern.

    My son has been riding the shortened 115mm Rival cranks on his Flow Kids Bike for ~5 months and I'm very happy with the result.

    Feel free to PM me if you have questions.

  185. #185
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    Quote Originally Posted by RMCDan View Post
    If 2-piece thru-axle are needed, then get the 115s Flow sells (not on their website, I've been told you can email them and they'll sell you a set).
    The Flow cranks are cut down MTB cranks with 175mm Q factor. I have a set that I would be happy to sell, PM me if interested.

    IMHO cutting down SRAM Rival is a better solution, yielding 150mm Q factor but it takes a bit of work as the backside of the crank needs to be tapered to clear chainstays (and won't work on some bikes).

  186. #186
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    Thank you guys!
    Spawn are really nice, though seem not to be available in EU, need to ask them if they can send directly.
    My daughter owns spec riprock 20 and original cranks have Q=172 and L=127. There's about 8mm of free space to chainstays each side so I can assume that Q=162 is save option here. BB is 68, and axis length 118 and I've got spare 107mm UN72. Chainline is awfully moved to smaller cogs, need to think about this but indeed road cranks may be option here. However take a look at these:
    https://www.bike-project.pl/pl/p/Kor...CS720-42T/1124
    They are using cranks from sunrace except they are 104:
    https://http2.mlstatic.com/pedivela-...6_052017-F.jpg
    This is nice as I can buy two and make 4 holes every 20mm and swap. And it uses BCD104 so oval NW is way to go.
    Need to ask dealer what's depth of recession, will let you know.

    BTW, spec cranks are about 520g
    Last edited by Eneen; 11-19-2018 at 02:22 AM.

  187. #187
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    Shortened SRAM Rival Cranks

    @Dr_UNIX [What did you shorten them to? Do you have pics of the finished product [from the back side]?]

    Sorry I didn't see your post sooner...here's a closeup pic of the left and right crank arm ends. Note that I tapered the backside to clear the chainstay.

    I used a drill press to punch the hole, tapped the threads by hand, then cut the arms. Using a belt sander I shaped the ends, and finally finished with a rasp to fine-tune things.
    Attached Images Attached Images  

  188. #188
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    What is the q factor on
    Trailcraft direct mount cranks?
    Vpace makes goog short direct mount cranks, but with a 167mm q factor. That's too much.

    A 20 inch Woombike has a 130 q factor on 110mm cranks (square taper with the shortest spindle shimano makes) and for the next bike i'm searching for 130-140mm cranks with a 130-140 (150 at most) q factor

  189. #189
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    152mm Suntour Zeron 30t $59.46 shipped from Suntour with 15% coupon and free shipping.

    Steel chainring definitely doesn’t help the weight. For the price it’s okay but chainring mounting is proprietary. The smallest replacement is a 30t and the aluminum rings cost almost as much as this entire crankset.
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-6bd97e27-a2d5-4f00-a5f1-6142a36ff14c.jpg  

    The Good Times are Killing me

  190. #190
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    I think TrailCraft is now selling 127mm, 140mm, 152mm & 165mm direct mount crankset with BB and your choice of chainring down to 26t for 160$. Pretty awesome

    https://www.trailcraftcycles.com/pro...-mount-cranks/

    Pretty awesome weight savings for the money!
    Lengths Available: 127mm, 140mm, 152mm 24mm 7050 ALLOY Spindle 51mm Chainline, 168mm Q-Factor

    140mm with 30t - 558g including BB
    152mm with 30t - 582g including BB

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    Quote Originally Posted by svinyard View Post
    I think TrailCraft is now selling 127mm, 140mm, 152mm & 165mm direct mount crankset with BB and your choice of chainring down to 26t for 160$. Pretty awesome

    https://www.trailcraftcycles.com/pro...-mount-cranks/

    Pretty awesome weight savings for the money!
    Lengths Available: 127mm, 140mm, 152mm 24mm 7050 ALLOY Spindle 51mm Chainline, 168mm Q-Factor

    140mm with 30t - 558g including BB
    152mm with 30t - 582g including BB
    There are Babyracing cranksets, from Italy. Square taper 110 bcd. In alu. Lightweight. They have in sizes 125, 140, 155 and 165 on ebay. They used to have more sizes, such as 130 and 135 also, maybe they're not made anymore. Quite cheap too, comparing to others. Some 27 euros for the set w/o bb. Shipping will cost though. There are some italian stores online that sells them too. I think they're 2x.

    There's also Sugino square taper 110 bcd, 152mm. They come in 1x, 2x or even 3x. Little more expensive than baby racing, but come in black (except the 3x) or natural.

  192. #192
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    Quote Originally Posted by guaruska View Post
    There are Babyracing cranksets, from Italy. Square taper 110 bcd. In alu. Lightweight. They have in sizes 125, 140, 155 and 165 on ebay. They used to have more sizes, such as 130 and 135 also, maybe they're not made anymore. Quite cheap too, comparing to others. Some 27 euros for the set w/o bb. Shipping will cost though. There are some italian stores online that sells them too. I think they're 2x.

    There's also Sugino square taper 110 bcd, 152mm. They come in 1x, 2x or even 3x. Little more expensive than baby racing, but come in black (except the 3x) or natural.
    I think you're referring to their previous 1x crank. These DM ones use a 24mm spindle.
    WTB: Med Bontrager Ti Lite, PM Me...

  193. #193
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    Quote Originally Posted by igormskru View Post
    What is the q factor on
    Trailcraft direct mount cranks?
    Vpace makes goog short direct mount cranks, but with a 167mm q factor. That's too much.

    A 20 inch Woombike has a 130 q factor on 110mm cranks (square taper with the shortest spindle shimano makes) and for the next bike i'm searching for 130-140mm cranks with a 130-140 (150 at most) q factor
    Just emailed Trailcraft and they responded a few minutes later that the q factor is 168mm for the 152mm direct mount cranks.

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    I just replaced the OEM Trailcraft square-taper 152mm (on a Pineridge I recently picked up used) with the Flow external-cup 135mm . Here's what I learned...

    The Flow stuff is all made by Lasco...arms and BB. Crankset weighs 635g complete (30t RaceFace NW & bolts, preload bolt), BB 120g (with all spacers) = 755g. Typical mtb Q-factor (170mm +/-).

    The Trailcraft frame uses a 68mm shell (unfaced/unchased at original assembly but corrected before new BB went in...come on guys! Brake bosses also unfaced). Arms are also Lasco, BB by Neco. Crankset weighs 540g (same ring/bolts), BB 275g = 815g. Typical mtb Q-factor (and very little room to shorten spindle). All into the cabinet for him to grow into...
    Last edited by dookie; 12-14-2018 at 11:46 AM.

  195. #195
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    Working on 3D printed crankset. Q-factor 150 or less (depends on frame), BCD 104, 110mm, about 400g without chainring. Up to 30kg. Let you know if prototype survives my 65kg
    Attached Thumbnails Attached Thumbnails Choices for kid-sized Crank Sets-korba_urszuli_fem01.jpg  


  196. #196
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    Quote Originally Posted by Eneen View Post
    Working on 3D printed crankset. Q-factor 150 or less (depends on frame), BCD 104, 110mm, about 400g without chainring. Up to 30kg. Let you know if prototype survives my 65kg
    Cool project - square taper cranks? Fairly heavy, but they look cool, almost like DXRs or Saints.

  197. #197
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    Thx!
    Yep, square, due to compatability. They are empty inside, so I can make thinner wall, no problem, but problem is with pedal thread, there's weak spot there. Feeling like I will need aluminium plate and additional M16 thread to fix this, but will see...

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    What is the material, aluminum? Can you just make the end solid and then tap in the pedal threads or use a helacoil?

  199. #199
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    Quote Originally Posted by Eneen View Post
    Working on 3D printed crankset. Q-factor 150 or less (depends on frame), BCD 104, 110mm, about 400g without chainring. Up to 30kg. Let you know if prototype survives my 65kg
    Looks like an interesting experiment -- would there be much point / weight savings in integrating the chain ring as part of the design?

    Was looking at this YouTube channel with a guy who plays around with 3d printing bmx parts (including a sprocket) and it made me wonder:
    https://www.youtube.com/watch?v=iY0OEg9XM4I

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    I've designed them to be PLA, they need to be cheap. Yeah, helacoil is what I'm thinking about, but need to get pair first. However will test without and will see how that works. Helacoil has external M16 thread and will surely reinforce pedal mount due to larger diameter.

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