Choices for kid-sized Crank Sets - Page 2- Mtbr.com
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  1. #201
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    Quote Originally Posted by TimTucker View Post
    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
    Not sure now, I drew them yesterday, so it's really fresh
    Draft is currently printing, after everything fits I will print full sample and test it.

    WOW this sprocket is really great, if this is possible I will surely integrate oval one.
    Last edited by Eneen; 02-18-2019 at 02:40 AM.

  2. #202
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    Quote Originally Posted by Eneen View Post
    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...
    If you want to go really deep down the rabbit hole of custom designs, you could try an approach to pedal design like this (bearings for the pedal embedded in the crank itself):
    https://www.bikeradar.com/us/gear/ca...dals-09-34550/
    https://forums.mtbr.com/downhill-fre...l#post11495303

  3. #203
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    Damn square taper, diameter is so small... I need metal adapter from taper to something bigger due to plastic plasticity... Even 24mm shimano spindle seems too small...

    EDIT: Ok, decided to do 24mm spindle mount. It will take a while to redesign this, but first need to do pedal mount stress testing.
    Last edited by Eneen; 02-14-2019 at 01:33 PM.

  4. #204
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  5. #205
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    Quote Originally Posted by Eneen View Post
    110BCD is the main downside I see to those, since that limits you to 33T chainrings at minimum.

    If you're feeling really adventurous, I suppose there may be enough material there to drill & tap for 74BCD.

    If you're OK with 110 chainrings, the Sinz Expert cranks are pretty similarly priced and go down to at least 120mm:
    https://www.ebay.com/sch/i.html?_fro...LH_TitleDesc=0

  6. #206
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    Dm is really where itís at. The ability to throw a 26 or 28t ring on there makes it perfect for a kids bike.

  7. #207
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    Quote Originally Posted by MXIV424 View Post
    Dm is really where itís at. The ability to throw a 26 or 28t ring on there makes it perfect for a kids bike.
    If you've got 64BCD you can still go down to 22T or 24T narrow-wide pretty cheap (at 74BCD, i.e., old triple chainrings, you can go down to 24T or 26T):
    https://usamade.myshopify.com/collec...-pro-64mm-74mm

    As a point of reference, I have the Trailcraft 152mm DM cranks on my MTB and a set of Suntour Jr 152mm cranks run as 1x7 w/ a 24T 64BCD chainring on an old Trek I use for pavement rides / pulling a bike trailer.

    Both work well -- the Trailcraft is certainly lighter, but the Suntour + narrow-wide ring was a great cheap way to test to see if I'd like shorter cranks.

  8. #208
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    Choices for kid-sized Crank Sets-a02c0241-4901-4754-9d33-ca2bb8eaff66.jpgChoices for kid-sized Crank Sets-c9df6ddf-17b4-409c-b55b-5b24aed8403b.jpg
    shortened xtr cranks 175mm down to 152mm

  9. #209
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    Found these pretty affordable Miranda branded alloy/steel 127mm 32T cranks. Supposedly they would be at least somewhat lighter than the all-steel 36T Prowheel cranks (900g) we have now but can't find any weight data. Does anyone recognize these being sold or used under any other brand? https://fahrradtopshop.de/epages/72f...2&Locale=de_DE

    Granted they would not be a huge investment even if they weren't that light but the pretty steep delivery costs would make it an extra bummer.

  10. #210
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    It looks like the shorter suntours are out of stock now and when i price out thr 152 NX vs 152 Trailcraft, there isnt a ton of price difference as the Trailcraft comes w the BB and chainring size of my choice whereas NX has no BB and Iíd want to move to a 30t ring.

  11. #211
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    In the meantime:
    https://www.aliexpress.com/item/Prow...951019209.html
    Must haven ended recently but maybe possible to ask seller.

  12. #212
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    Suntour 152mm back in stock, grabbed a pair for my daughterís new xs 29er hardtail i built up. Firstorder code takes 15% off.

  13. #213
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    Quote Originally Posted by backinmysaddle View Post
    Suntour 152mm back in stock, grabbed a pair for my daughterís new xs 29er hardtail i built up. Firstorder code takes 15% off.
    The chainline blows on these things. I had several longer 1x cranksets on and had no problem w backpedal issues. These are a solid 10mm off in chainline from other cranks. Drops to 3rd gear when back pedaling.

  14. #214
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    Quote Originally Posted by backinmysaddle View Post
    The chainline blows on these things. I had several longer 1x cranksets on and had no problem w backpedal issues. These are a solid 10mm off in chainline from other cranks. Drops to 3rd gear when back pedaling.
    Just went out and measured the one I have on my around town bike: looked pretty close to 48mm chainline on the small ring. I'm running it as a 1x7 with a 64bcd narrow wide ring, so it actually works out really well.

  15. #215
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    Quote Originally Posted by backinmysaddle View Post
    The chainline blows on these things. I had several longer 1x cranksets on and had no problem w backpedal issues. These are a solid 10mm off in chainline from other cranks. Drops to 3rd gear when back pedaling.
    Are you referring to the square taper triple cranks that are $30 on ebay or the zeron 2 piece cranks?
    https://www.srsuntour.us/collections...nt=45338041742

  16. #216
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    Quote Originally Posted by 53sled View Post
    Are you referring to the square taper triple cranks that are $30 on ebay or the zeron 2 piece cranks?
    https://www.srsuntour.us/collections...nt=45338041742
    In my case, the $30 square taper triple cranks.

    47.5mm to the middle ring is pretty standard for square taper, so if you were expecting to run as 1x using the middle ring, I could see how it might cause problems.

    If you're planning to run 1x using the 64BCD small position, it works out OK.

  17. #217
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    So here's a different thought on crank length-- I know that (is it Sheldon? is it BikeSmith?) whomever started the conversation on this is talking about seated pedaling.
    I watch 6yr old Rowan {edit: he is 4'6"} riding standing (on 160mm), and I can see he is swaying his hips/ body all the way down one way, and then swinging to the other side. So I feel a shorter crank would be useful.

    Then I think about how much faster he'd have to spin his legs-- and I wonder, will a shorter crank be detrimental to riding standing? Or does it just mean that I can continue to stay away from the dinner-plates on the back wheel?
    Last edited by rabitoblanco; 04-23-2019 at 07:33 AM.

  18. #218
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    Quote Originally Posted by rabitoblanco View Post
    So here's a different thought on crank length-- I know that (is it Sheldon? is it BikeSmith?) whomever started the conversation on this is talking about seated pedaling.
    I watch 6yr old Rowan riding standing (on 160mm), and I can see he is swaying his hips/ body all the way down one way, and then swinging to the other side. So I feel a shorter crank would be useful.

    Then I think about how much faster he'd have to spin his legs-- and I wonder, will a shorter crank be detrimental to riding standing? Or does it just mean that I can continue to stay away from the dinner-plates on the back wheel?
    Just shift to a harder gear and spin slower....I'm on 135mm
    Tread killer....

  19. #219
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    Quote Originally Posted by rabitoblanco View Post
    So here's a different thought on crank length-- I know that (is it Sheldon? is it BikeSmith?) whomever started the conversation on this is talking about seated pedaling.
    I watch 6yr old Rowan riding standing (on 160mm), and I can see he is swaying his hips/ body all the way down one way, and then swinging to the other side. So I feel a shorter crank would be useful.

    Then I think about how much faster he'd have to spin his legs-- and I wonder, will a shorter crank be detrimental to riding standing? Or does it just mean that I can continue to stay away from the dinner-plates on the back wheel?
    In my experience on bikes and putting in lots of miles for a number of years, you shouldn't worry about increased cadence due to the tighter circle. And actually, the cadence won't really be increased for the same given gear.

    Think about it. A clock hand or a windmill blade is moving faster at its tips than it is moving the further down the hand/blade you go for a given revolution speed.

    You have seen it for yourself, the cranks are grossly too long, and it's throwing off his physical mechanics. There is virtually no good reason to push long cranks. We actually make power better on shorter ones. At 6, I'm going to throw out a guess that 125-130 would be better for him, without actually seeing his size. The circles he will be pedaling will be functionally better for his leg length, his joints will not be getting strained, the saddle height will be able to come up for better leg extenxion since he won't need to reach nearly as low for the bottom of the stroke.

  20. #220
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    Quote Originally Posted by rabitoblanco View Post
    So here's a different thought on crank length-- I know that (is it Sheldon? is it BikeSmith?) whomever started the conversation on this is talking about seated pedaling.
    I watch 6yr old Rowan riding standing (on 160mm), and I can see he is swaying his hips/ body all the way down one way, and then swinging to the other side. So I feel a shorter crank would be useful.

    Then I think about how much faster he'd have to spin his legs-- and I wonder, will a shorter crank be detrimental to riding standing? Or does it just mean that I can continue to stay away from the dinner-plates on the back wheel?
    I think chrisjobs already covered this but he is still making the same revolutions on every gear his feet just donít travel the same distance.
    If he was pedalling efficiently which by your description he isnít then for 130 cranks he would have a tiny amount of less leverage (130/160) delivered on the downstroke ... but he isnít pedalling efficiently and he is basically reducing the part where he can put power down to a very small arc by moving his weight over the pedal.

    At the same time heís more or less missing being able to put power down in the larger part of the downstroke ... and moving his whole body over to do this.

  21. #221
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    Even if the efficiency were the same, gaining over 1" greater ground clearance on a kid's bike with an already low BB is nothing to scoff at.

    Here's a perspective from one BMX company on why shorter cranks may be just as useful for standing:
    https://www.profileracing.com/tech-tip-2-crank-it-down/
    1. Shorter cranks allow you to bunny hop higher. As a simple experiment, try jumping with your feet spread apart, then try with your feet closer together (as if being in a position for pedaling). You can always jump higher with your feet closer together.
    2. Ambidextrous spinning: Itís much easier to 180 (360, 540 etcÖ) both ways with your feet closer together.
    3. Lighter weight: The shorter the crank, the less steel used in its tubular construction.
    4. More rigid/less flex: Shorter cranks should, in theory, last longer over time because thereís less leverage put upon them.
    From the various BMX forums where I've looked into this, the general consensus seems to be that techniques like manuals are also easier on shorter cranks -- which could translate into quicker skills development for kids.

  22. #222
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    BMX racers are very serious with their crank lengths. My boys race, and there is a good crank length formula/ calculator that I use for them at https://heliumbikes.com/tech-articles

    The formula is just inseam/0.173. Make sure to measure the inseam with their shoes on and use the method on the site. Of course there is still a bit of trial and error, but it gives you a good place to start with.

  23. #223
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    Quote Originally Posted by Gangly1 View Post
    BMX racers are very serious with their crank lengths. My boys race, and there is a good crank length formula/ calculator that I use for them at https://heliumbikes.com/tech-articles

    The formula is just inseam/0.173. Make sure to measure the inseam with their shoes on and use the method on the site. Of course there is still a bit of trial and error, but it gives you a good place to start with.
    THAT looks good!

    When my little guy got his Yoji 16"...his inseam was like 15.5. The 102mm cranks (I think) were EASILY too long and I swapped them for 95mm. Instantly better.

    When I run that against your calculator iits pretty close.

    My 51" 7yro has a 22in inseam. That works out to 124mm cranks. He is on 127mm on his Spawn Yama Jama 20". Those crank have worked well for him over the last couple of seasons. I'm working on getting him on a 24" bike with 140mm cranks. (most stock crank are 152 or 155 tho...). It all seems long.

    I don't understand the differences between MTB and BMX Racing but I'm guessing its not drastic. Interesting.

  24. #224
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    Thanks for a bunch of great responses. So shorter cranks it is--upgrade wheels later. Also a point about clearance I hadn't thought about. I was riding behind him yesterday and saw a spark as he hit something getting out of a turn--fun to see, but obviously undesirable, haha

    @jochribs your guess is right on-- at 4'6", given the calculator above I come up with exactly that range for him.

    This is what's on the Specialized FSR 24 now:
    Crankset: Truvativ ISO Flow, alloy 160mm with replaceable chainrings and capless bo, Truvativ 42t 7075alloy, heat treated Cr-Mo 32t and 22t teeth
    Bottom Bracket: TruVativ LE, 113mm spindle
    BB Shell Width: 68mm English

    Will the Spawn 127 fit directly over the existing square-tapered BB? Or is there a chainline issue I need to solve?

    https://spawncycles.com/spawn-cycles-alloy-cranks-127
    For $60 this would be a lovely move forward--but is there something about chainlines I need to watch out for?

  25. #225
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    Quote Originally Posted by rabitoblanco View Post
    Thanks for a bunch of great responses. So shorter cranks it is--upgrade wheels later. Also a point about clearance I hadn't thought about. I was riding behind him yesterday and saw a spark as he hit something getting out of a turn--fun to see, but obviously undesirable, haha

    @jochribs your guess is right on-- at 4'6", given the calculator above I come up with exactly that range for him.

    This is what's on the Specialized FSR 24 now:
    Crankset: Truvativ ISO Flow, alloy 160mm with replaceable chainrings and capless bo, Truvativ 42t 7075alloy, heat treated Cr-Mo 32t and 22t teeth
    Bottom Bracket: TruVativ LE, 113mm spindle
    BB Shell Width: 68mm English

    Will the Spawn 127 fit directly over the existing square-tapered BB? Or is there a chainline issue I need to solve?

    https://spawncycles.com/spawn-cycles-alloy-cranks-127
    For $60 this would be a lovely move forward--but is there something about chainlines I need to watch out for?
    Make sure the taper style is the same. It will effect how far the cranks need to pull onto the BB in order to tighten. There's JIS and I forget the other one (I should know this, I was a wrench for years) Anyway, it probably is fine. I'll look it up.

  26. #226
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    Quote Originally Posted by rabitoblanco View Post
    Thanks for a bunch of great responses. So shorter cranks it is--upgrade wheels later. Also a point about clearance I hadn't thought about. I was riding behind him yesterday and saw a spark as he hit something getting out of a turn--fun to see, but obviously undesirable, haha
    If the shorter cranks aren't enough to solve pedal strikes on turns, you could also look into narrower pedals (depending on how wide his feet are). So far we've tried Tioga Dazz Lites (nice, relatively cheap nylon option) and some Kactus pedals from aliexpress (super light metal, but needs different pins to be usable).

  27. #227
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    So Spawn doesn't say anything about the taper style other than use them with "standard square taper" which is pretty much JIS, of which the Truvativ BB you have is as well, so I'd say giddy up.

  28. #228
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    If I switched to something like the Answer cranks that use an ISO taper would I need to use a longer/shorter spindle than what's in a JIS taper bottom bracket? Not sure if the length difference is built into cranks or if I'd need to account for it in the new bottom bracket. And being the spindle sets the Q factor I'd assume the crank arms should clear the chainstay as long as i keep the crank arm length the same or shorter?

  29. #229
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    Looking at the 16" commencal ramones, it has 114mm steel cranks, seems like it would be possible to drill a second set of holes for ~95mm, then tap with 1/2-20. Any reason not to do this?

  30. #230
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    https://www.sheldonbrown.com/bbtaper.html


    This does a pretty good job of describing the difference and when and how you can mix them. With and ISO crank, you will need a shorter JIS BB to have the right chainline. At that point, if you are needing a different BB, just get an ISO (Answer) BB. My thought anyway.

  31. #231
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    Quote Originally Posted by carlhulit View Post
    Looking at the 16" commencal ramones, it has 114mm steel cranks, seems like it would be possible to drill a second set of holes for ~95mm, then tap with 1/2-20. Any reason not to do this?
    Opinions might vary, but my view is that I wouldn't. It would probably be fine though. I'd sooner get my hands on some aluminum take-offs from another bike and hack them down.

    I actually have a set from my sons Raleigh RX24 if you want them.

  32. #232
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    Quote Originally Posted by jochribs View Post
    So Spawn doesn't say anything about the taper style other than use them with "standard square taper" which is pretty much JIS, of which the Truvativ BB you have is as well, so I'd say giddy up.
    Talk about analysis paralysis--just as I was about to get those, I came across the from Flow :
    Is the weight reduction from the threaded BB (vs. existing UN-55) worth exchanging for a 7mm longer crank(127mm Spawn vs 135)?

    https:///product-page/flow-crankset
    "2 piece system with 68mm threaded bottom bracket
    135mm arm length."



    Sent from my Pixel using Tapatalk

  33. #233
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    Quote Originally Posted by rabitoblanco View Post
    Talk about analysis paralysis--just as I was about to get those, I came across the from Flow :
    Is the weight reduction from the threaded BB (vs. existing UN-55) worth exchanging for a 7mm longer crank(127mm Spawn vs 135)?

    https:///product-page/flow-crankset
    "2 piece system with 68mm threaded bottom bracket
    135mm arm length."



    Sent from my Pixel using Tapatalk
    I think it's better to get the best length, probably the 127's. You can always get a lighter BB.

  34. #234
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    My 4í 8.5Ē 9yr old is on 142mm cranks.
    Get the right length

  35. #235
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    Thanks x2!

    Sent from my Pixel using Tapatalk

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    The other thing worth mentioning is square taper has loads of disadvantages but other than weight they donít really apply to kids. Itís not like they will be complaining the BB isnít stiff enough when they lay down 500W

    It also has advantages... you can easily change the chain line and new BBS are cheap.
    You can get a Shimano UN55 <<$20

    Weight wise I cut down some Shimano Zee (not the lightest) and some SRAM S600ís ($40?) to the same length and stuck everything on the scale and the Zee + External bb were 12g lighter than the SRAM and UN55.

    Like 12g thatís a tire valve or bit of mud... obviously wonít be exactly the same for you but the point is itís not a huge weight saving vs getting the right length, chainline etc.

  37. #237
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    Quote Originally Posted by Gangly1 View Post
    BMX racers are very serious with their crank lengths. My boys race, and there is a good crank length formula/ calculator that I use for them at https://heliumbikes.com/tech-articles

    The formula is just inseam/0.173. Make sure to measure the inseam with their shoes on and use the method on the site. Of course there is still a bit of trial and error, but it gives you a good place to start with.
    One thing to remember though is BMX is a sprint for a very short time and they never sit. Its been mentioned they typically go a bit longer for this reason.

    Sitting to pedal over longer distances might be exact opposite of this formula, but I am no expert. High knees is typically the dead givaway when pedaling.

  38. #238
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    Quote Originally Posted by GSJ1973 View Post
    One thing to remember though is BMX is a sprint for a very short time and they never sit. Its been mentioned they typically go a bit longer for this reason.

    Sitting to pedal over longer distances might be exact opposite of this formula, but I am no expert. High knees is typically the dead givaway when pedaling.
    We don't BMX race so I can't speak to that BUT this particular calculator is dumping out values that close to what mtb are using for kids or a fair bit below. So too long is def not an issue with this calculator at least.

    This is really interesting too because kid cranks are a pain in the ass. Not only are our kids growing so we put them a bit early on a bike so they get more than one season on it... And the cranks are always a bit long. Secondly even the short-ish cranks are still really close to the ground for pedal strikes due to their tiny bikes and wheels.

    So with this calculator pointing to us using even smaller cranks, it might be the best of both worlds and solve the sizing/high knees BS and make the bike a bit safer from pedal strikes (which happens in some chunky stuff).

    My questions: how widely accepted is this site within the BMX world? Is there any downside to having cranks slightly too small?

    My 51" 7yro is moving to a 24" bike and this calculator indicates he should be on cranks around 125mm rather than the stock 155 or Trailcraft style 140mm. That's a big drop. I'm happy to accept that but curious as to what others would think.

  39. #239
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    My 6yo has inseam of about 52cm and 114mm cranks. She says they are just perfect, much better then stock 127mm. Now she spins much faster. As I've written before, 0.2 x inseam seems to be sweet spot. I'm currently using 165mm having 82cm inseam and they are ok for me, much better then 175 or even 170. I've tried 152mm shortened xt cranks that my wife uses and they are fine too, I don't feel that they are too short or something. In general shorter cranks are better for geared bikes. They save knees and force you to use bit higher cadence.

  40. #240
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    I've come across thaf bmx formula in the past too. Having looked at most of the studies with adults on crank length, there's really almost no downside to shorter cranks.

    Thr one caveat for kids bikes is that moving to shorter cranks usually requires the saddle slightly higher for pedaling while seated, which could pose an issue for standover for a kid just starting out.

    The flipside of that is that once kids are comfortable with a bike where the saddle is higher than their inseam it could help give a little more height for running a dropper.

    I'm 5'10" and running 152mm cranks now.

  41. #241
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    Quote Originally Posted by svinyard View Post

    My 51" 7yro is moving to a 24" bike and this calculator indicates he should be on cranks around 125mm rather than the stock 155 or Trailcraft style 140mm. That's a big drop. I'm happy to accept that but curious as to what others would think.
    I had my guy on 120's on his 20". Cut down from the 160's that came on it. Insane how long they were.


    I need to check out this calculator and see what it says about his crank length. I've just been doing a comparative percentage to my legs on 175's vs. his legs length and it's given me 135. However, who's to say that 175 is actually right for me?

  42. #242
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    What's your inseam?

  43. #243
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    Quote Originally Posted by jochribs View Post
    I had my guy on 120's on his 20". Cut down from the 160's that came on it. Insane how long they were.


    I need to check out this calculator and see what it says about his crank length. I've just been doing a comparative percentage to my legs on 175's vs. his legs length and it's given me 135. However, who's to say that 175 is actually right for me?
    I have a 34"/86.3cm inseam and am also on 175. I rode 170's the other day on that Ripmo and it was fine. Maybe 165 would be too?

    Regardless, at this point I might be able to take my 7yro 127mm cranks on his 20" Yama Jama and just put them on the kids next 24" bike and be good to go.

    OR if the next bike comes with SRAM 155mm...I just cut them down to 130mm? I've never done that but there is a good machine shop here in town. I'd like to not have to drop a bunch of cash on new cranks/BB for a new bike.

  44. #244
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    Exactly, I have some decent cranks that were take offs on my bikes (switching from Sram to Shimano) that I can use too.

  45. #245
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    Quote Originally Posted by svinyard View Post
    I have a 34"/86.3cm inseam and am also on 175. I rode 170's the other day on that Ripmo and it was fine. Maybe 165 would be too?

    Regardless, at this point I might be able to take my 7yro 127mm cranks on his 20" Yama Jama and just put them on the kids next 24" bike and be good to go.

    OR if the next bike comes with SRAM 155mm...I just cut them down to 130mm? I've never done that but there is a good machine shop here in town. I'd like to not have to drop a bunch of cash on new cranks/BB for a new bike.
    If his next bike comes with 155s, just keep him on the 127s and try the 155s on your bike.

  46. #246
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    Quote Originally Posted by TimTucker View Post
    If his next bike comes with 155s, just keep him on the 127s and try the 155s on your bike.
    I think BB is a SRAM Dub one on the new bikes I'm looking at. Maybe I can yank the one out of our Yama Jama? I don't have all the details if it'll work. Unsure of the shell size on the Yama Jama.

  47. #247
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    Quote Originally Posted by svinyard View Post
    I have a 34"/86.3cm inseam and am also on 175. I rode 170's the other day on that Ripmo and it was fine. Maybe 165 would be too?

    Regardless, at this point I might be able to take my 7yro 127mm cranks on his 20" Yama Jama and just put them on the kids next 24" bike and be good to go.

    OR if the next bike comes with SRAM 155mm...I just cut them down to 130mm? I've never done that but there is a good machine shop here in town. I'd like to not have to drop a bunch of cash on new cranks/BB for a new bike.
    Donít forget the pedal hole is 13mm (5/16ths) so you need to factor that in to minimum lengths and still have some material at the end.

  48. #248
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    Quote Originally Posted by Steve-XtC View Post
    Donít forget the pedal hole is 13mm (5/16ths) so you need to factor that in to minimum lengths and still have some material at the end.
    So if I wanted to chop some 155's down to 135...would that work? I'm guessing that may not be enough material and I'd have to drop down to 130mm.

    Have you done this before? Is it challenging? I'm concerned about getting the hole drilled out right/straight/centered/etc and then having to purchase pedal taps too. Wondering if its worth it vs spending some money on cranks like TC or something.

  49. #249
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    Quote Originally Posted by svinyard View Post
    So if I wanted to chop some 155's down to 135...would that work? I'm guessing that may not be enough material and I'd have to drop down to 130mm.

    Have you done this before? Is it challenging? I'm concerned about getting the hole drilled out right/straight/centered/etc and then having to purchase pedal taps too. Wondering if its worth it vs spending some money on cranks like TC or something.
    Done it lots ... 25mm is a good guide. If you go much less then the end of the existing hole will be really close.

    As to buy vs make ? I certainly got value from the pedal taps and 13mm drill bit. Note 13mm is slightly under the recommended hole for 5/16ths tap but then thatís in steel. I prefer leaving a few thou extra for the thread.

    The tapping part is simple but I tend to add grease and do 3forwards - 2 back to clear the swarf...

    The drilling is scary first time...

    first time I made a jig but itís actually not so hard to get straight. Dot punch then I pilot something like 5, 10 then 13. I use oak behind the crank to drill into or it can really torque up ... like broken wrist torque if it doesnít break through clean.

    Decent bits go though like its cheese so the important bit is control the speed or youíll practically melt it with a fast drill .. just keep it so you get a good clean swarf not breaking off.

    An old pedal is useful in the existing hole as a guide but I just use my hand rechargeable.




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  50. #250
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    Steve and Svinyard, to avoid the torque from grab, use some sort of cutting fluid while your drilling through. Something viscous will work fine, like 3 in 1 or even motor oil. WD-40 will work in a pinch.

    Funny story about drill torque. I had a co-worker that had long hair and it got wrapped up in the drill as he was drilling through something. It wound up super fast and when it got tight to his head, the drill swung up and clocked him with the battery. Nearly knocked him off the ladder he was on. He then had to reverse it to unwind his hair.

  51. #251
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    Quote Originally Posted by jochribs View Post
    Steve and Svinyard, to avoid the torque from grab, use some sort of cutting fluid while your drilling through. Something viscous will work fine, like 3 in 1 or even motor oil. WD-40 will work in a pinch.

    Funny story about drill torque. I had a co-worker that had long hair and it got wrapped up in the drill as he was drilling through something. It wound up super fast and when it got tight to his head, the drill swung up and clocked him with the battery. Nearly knocked him off the ladder he was on. He then had to reverse it to unwind his hair.
    Oh man that sounds like an awful comedy!

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  52. #252
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    Thought you guys would get a kick out of this-- while I'm here trying to figure out the difference of millimeters for his 24" bike, I turned around yesterday to find Rowan riding my (adult, Small frame, 26") bike...
    https://www.instagram.com/p/BxD4QtgA...id=flc825sse9r


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    Last edited by rabitoblanco; 05-04-2019 at 09:26 PM.

  53. #253
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    Still at the point of crank paralysis for my 51" with I think 20" inseam 8.5 yr old daughter. Struggling with 140mm vs the 152 that are stock on her Liv Enchant 24. She has the seat slammed because that's where she's comfortable. She's already not getting full leg extension with this on the 152mm. Going 140 seems like even worse extension. Once I get that nailed down I can decide between the trailcraft 104bcd or DM cranks.

  54. #254
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    My daughter is 6, has 52cm inseam and uses 114mm cranks. 152mm and 140 are both too long for sure and will hurt her knees. IMO 127mm would most probably be optimal. 152mm uses my wife with about 76cm inseam.

  55. #255
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    Quote Originally Posted by Cerpss View Post
    Still at the point of crank paralysis for my 51" with I think 20" inseam 8.5 yr old daughter. Struggling with 140mm vs the 152 that are stock on her Liv Enchant 24. She has the seat slammed because that's where she's comfortable. She's already not getting full leg extension with this on the 152mm. Going 140 seems like even worse extension. Once I get that nailed down I can decide between the trailcraft 104bcd or DM cranks.
    Too long cranks lead to a lower saddle so they can pedal
    lower saddle means the saddle is further forwards (due to seatpost angle)
    saddle further forwards leads to stand over moving forwards which usually due to top tube angle means less standover but either way they are pushed forwards leading to loss of confidence... leading to slammed saddle.

  56. #256
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    Quote Originally Posted by Eneen View Post
    My daughter is 6, has 52cm inseam and uses 114mm cranks. 152mm and 140 are both too long for sure and will hurt her knees. IMO 127mm would most probably be optimal. 152mm uses my wife with about 76cm inseam.
    My 9yr old rides an adult XS with 142mm cranks.
    Couldnít guarantee his height but he says itís 143cm

    Choices for kid-sized Crank Sets-75d8236f-fcb0-4359-a460-99f983b4dd81.jpgChoices for kid-sized Crank Sets-dd67dd0a-9fb9-4599-8c51-37d5be8b8232.jpg

  57. #257
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    Quote Originally Posted by Cerpss View Post
    Still at the point of crank paralysis for my 51" with I think 20" inseam 8.5 yr old daughter. Struggling with 140mm vs the 152 that are stock on her Liv Enchant 24. She has the seat slammed because that's where she's comfortable. She's already not getting full leg extension with this on the 152mm. Going 140 seems like even worse extension. Once I get that nailed down I can decide between the trailcraft 104bcd or DM cranks.
    My son is also 51" --We just installed 127 mm Spawn cranks on his 24" and the difference in how level his hips stay is enormous.
    (Much thanks to several of you here--Steve, Chris et al...)
    Not a particularly good photo below, but this is with his seat at "street height" and gives you some idea of hip angle and leg extension.
    On the trails, we tend to ride with the lower seat, usually standing, and I'm waiting to see what that will look like. Will report back!


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  58. #258
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    Ahhh yeah that what I was hoping to see. We have those cranks on our 20". I just need to swap for the shimano BB on the 24" and put those cranks on. His knee height/angle there looks ideal from the info I've seen on Dynamic Bicycles site etc. I ran most of the various Crank calculators the other day. Most had my 51" son riding around 125mm cranks. Some less, some more. I think the highest was 140mm tho that Calc was somewhat simplistic. It's kids so it's hard to tell but that Pic shows that it looks fairly decent to my less than expert eyes.

    Fwiw I put my kid on 155mm cranks a couple months ago on a 24" bike and his knees came up really high. Like 90 degree angle. Apparently it's supposed to be closer to 70d.

  59. #259
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    Quote Originally Posted by rabitoblanco View Post
    My son is also 51" --We just installed 127 mm Spawn cranks on his 24" and the difference in how level his hips stay is enormous.
    I think this is a bit of leap-of-faith.
    Itís hard to imagine just how much crank length changes so many things.
    This is possibly doubly so since adult bikes have traditionally ignored crank length.
    Iíd never thought of this for myself until I encountered it with Jnr.

    Once you do the change the difference is (in my experience) usually more dramatic than expected

  60. #260
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    Does anyone know if it's possible to buy the Sunrace FCM80T 160mm 30t that I see speced on a few kids bikes?

  61. #261
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    Iíve been shopping for lightweight 165mm cranks for my oldestís next bike and...theyíre not cheap https://bythehive.com/products/trs-r...on-cranks-gen4

    Maybe if I beg theyíll make the xcx in a 160???

  62. #262
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    Just got the Brood Bike Co (aka Spawn) Styx Crankset in 130mm. This comes with an integrated BB and SRAM direct mount ring compatible.

    Here are my weights (sans chainring):

    Drive Side: 364g
    Non-drive arm: 204g
    BB, spacers, HW: 158g

    Thats 726g plus maybe 40-150g for a ring depending on material.

    Seems heavier than what I was hoping for. I will weigh the stuff coming off my Orbea MX20 Team Disc next. I hope its a net savings or that will be a disappointment, but of course this still allows me to use a smaller ring than what is possible with the stock Orbea, so its still a benefit.

  63. #263
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    Update. The Orbea Mx20 Team Disc stock crankset (with 34T ring) and BB came in at 792g. Thats lighter than the new brood styx setup I just put on by about 66g!

    Granted, I put a steel 28T ring on the new setup that weighs 132g itself, but all things considered Id call it a negligible weight savings for the Brood Styx crank. Disappointed for a $115 crank/BB (not including ring), and yet also amazed that the Orbea, as a $500 bike, did so well.

  64. #264
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    One pretty cheap weight saving is to swap the heavy Brood BB with a Shimano XT at 82g.

    See my nerdy spread cheat in OP here https://forums.mtbr.com/families-rid...t-1098353.html

  65. #265
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    A status update on the Spawn 127mm crankset:
    the attached chainring is 32t, and that's too high for a six year old to 1x with --on hilly trails.
    And because it's 104bcd, it's hard to go smaller chainring.
    (Assuming run of the mill rear cogs, not Sram Eagle!)

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  66. #266
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    Quote Originally Posted by rabitoblanco View Post
    A status update on the Spawn 127mm crankset:
    the attached chainring is 32t, and that's too high for a six year old to 1x with --on hilly trails.
    And because it's 104bcd, it's hard to go smaller chainring.
    You can do 30t with standard rings.

    Not sure how well these work, but as far as I know these rings with integrated guards are the only option out there to go to 26t or 28t on 104bcd;
    https://usamadeco.com/collections/sh...tegrated-guard

  67. #267
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    Was going to second the 30T suggestion. Also excellent call on those integrated bash rings. Not having seen them in person (but having a 127mm spawn crank), Iíd wager theyíd fit. FWIW, Iíve used a usamade ring on my bike and itís worked just fine. Maybe not the most durable (seems to be wearing faster than other rings) but I would think it would take several kids to wear one out. The potential added benefit of a 30T (or the integrated bash Iíd guess) is that itís slightly offset to the inside which improves chainline to the bottom of the cassette which is a big deal if your kid has a bike with short stays.

    Eagle was mentioned. Interestingly, a 32x36 with a 20Ē wheel is actually a slightly smaller gear ratio at 17.8Ē than a 32x50 with 18.6Ē. So, plenty small. If Sheldon Brownís ghost (RIP) joins in this argument and brings up ďgain ratioĒ (i.e. taking into account crank length), Iíd concede that is a good point. However, how slow is one expecting a 5-8 year old to be able to ride before they fall over?

    Choices for kid-sized Crank Sets-2038e479-98f7-4e38-b4c7-fe8b3f192b81.jpg
    I make bikes. www.feldybikes.com

  68. #268
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    FWIW we got Prevelo Heir 140mm cranks (86$ Shipped!!) and XT BB (19$) for my sons Clash 24". They are the same as Trailcraft etc. The chain ring is a 30t and with a 10-42 cassette, it's been excellent on the climbs and def using the 10t cog at times too. I want sure how it'd work but it really has been seemingly ideal. I wouldn't go down to a 28t with the smalls wheels and cranks.

    Also the prevelo chain ring isnt offset 3mm to towards the bike. Since the kids bike is Boost, I think it's actually an improvement as the ring is about dead center to the cassette. I'm not expert tho, is that a good thing or do you want it closer to the 42t?

    So far so good tho.

  69. #269
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    I'm saying this with the best intent; imho I think the parent should watch closely to why the kid doesn't get up the hill with ex 30t front and 11-36t rear (just an example). Dont confuse not being able to hold balance at such slow speed with needing lower gearing.
    My 6 yo had 38t front with 11-42t gears, 125mm cranks on 20" wheel and barely ever used lower than 3rd gear, even on really really steep and long hills. I was about to change to 40t front when his technique improved to such a degree that he was able to hold balance on lowest gear and technical terrain. But those situations were rare.

  70. #270
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    I got the Trailcraft 140mm cranks with 28T ring. I'll be pairing it with a 11-42 Deore 10 speed group on a 26" bike for my son. I should have time to build it up in the next week.

  71. #271
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    Quote Originally Posted by slowride454 View Post
    I got the Trailcraft 140mm cranks with 28T ring. I'll be pairing it with a 11-42 Deore 10 speed group on a 26" bike for my son. I should have time to build it up in the next week.
    I put together basically the same drivetrain for my son's bike, except it's a 27.5 and the cranks are 152 length. He loves it.
    2013 Salsa Horsethief 2 (ironically, bike was stolen)
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  72. #272
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    Edit for clarification, I have a 9 speed DH (Zee) derailleur on old school 7 speed wheels here. That's why not all the sprockets are accessible, so he's actually got a 5 speed!
    As it happens, I realized the error in my adjustment and now he's got the five easiest speeds with the 32 teeth front cog, and is doing great for all kinds of terrain. We don't do a lot of long uphills, but instead have punchy climbs and technical descents more often.

    Quote Originally Posted by guaruska View Post
    I'm saying this with the best intent; imho I think the parent should watch closely to why the kid doesn't get up the hill with ex 30t front and 11-36t rear (just an example). Dont confuse not being able to hold balance at such slow speed with needing lower gearing.
    My 6 yo had 38t front with 11-42t gears, 125mm cranks on 20" wheel and barely ever used lower than 3rd gear, even on really really steep and long hills. I was about to change to 40t front when his technique improved to such a degree that he was able to hold balance on lowest gear and technical terrain. But those situations were rare.
    This is good advice regardless of my specific situation.
    Thanks for the advice above regarding options-- those integrated ones I hadn't seen before!

    My kid's problem is the biggest ring was actually not accessible, so my 6-year-old was on a 32T front, and 14-24 in the back on 24" wheels. His balance is somewhere between really good and great, but that's some hard gears to push on blue and black climbs.

    Meanwhile, his frame just broke so more modern wheels are going to change the game.

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    Last edited by rabitoblanco; 2 Weeks Ago at 08:43 AM.

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  74. #274
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    Quote Originally Posted by svinyard View Post
    FWIW we got Prevelo Heir 140mm cranks (86$ Shipped!!) and XT BB (19$) for my sons Clash 24". They are the same as Trailcraft etc. The chain ring is a 30t and with a 10-42 cassette, it's been excellent on the climbs and def using the 10t cog at times too. I want sure how it'd work but it really has been seemingly ideal. I wouldn't go down to a 28t with the smalls wheels and cranks.

    Also the prevelo chain ring isnt offset 3mm to towards the bike. Since the kids bike is Boost, I think it's actually an improvement as the ring is about dead center to the cassette. I'm not expert tho, is that a good thing or do you want it closer to the 42t?

    So far so good tho.
    How did you get ahold of those cranks? They aren't available on their website.

  75. #275
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    Quote Originally Posted by heet View Post
    How did you get ahold of those cranks? They aren't available on their website.
    https://forums.mtbr.com/families-rid...d-1105847.html
    2013 Salsa Horsethief 2 (ironically, bike was stolen)
    2015 Salsa Beargrease 2
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  76. #276
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    Moved my 7 yr old down to a 142 mm. I have a 155 mm NX crankset with 28T chainring and a matching 68 mm threaded cartridge bottom bracket. Used for maybe 10 miles of road riding This is a special OEM set off of an Early Rider. $100 shipped.

  77. #277
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    I have a 135mm truvativ crank that fits a square drive BB. Works great on 20"&24" wheeled bikes. It's new and never installed. I also have a bash guard and two different pull front derailleurs to go with it all. $100 hit me up!

    Choices for kid-sized Crank Sets-82585589_10221522213393438_2648801052651945984_n.jpg
    It's the perfect time of year, Somewhere far away from here.

  78. #278
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    Moved my 7 yr old down to a 142 mm. I have a 155 mm NX crankset with 28T chainring and a matching 68/73 mm threaded cartridge bottom bracket. Used for maybe 10 miles of road riding This is a special OEM set off of an Early Rider 24T. $100 shipped.

    No longer available.
    Last edited by xprmntl; 2 Days Ago at 11:33 AM. Reason: Gone

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