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  1. #1
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    Need Advise on custom Mtb for my 5 year old

    So, My 5 year old (5 1/2) has outgrown his 16" bike and is still a little too small for all the 20" bikes we've tried. He wants to go trail riding with me and he needs at a minimum a 6 or 7 speed to be able to climb, I'd also like to a front shock for him. Main issue with everything we've seen is that he has to bend forward to reach the handlebars b/c of his height, and the crank is too long as well as the BB is being too high off the ground (i think).

    I know how to weld and I've worked on roll cages/fabrication and for a while so I figured why not just build one and have decided to proceed. Plan is to either pick up used (in 20") and build the frame and reuse the components, this is the easiest way i think.

    Harder option is to build him one from adult parts, I'd really like to make it a full suspension bike. I was thinking about getting air shock/fork (and setting air pressure accordingly for his weight) and i'd be nice to make it disc brake as well. I was thinking of using a front fork from a 26" bike with 20" wheels...anyone done this before?

    So here are my questions:
    1) Any guide/resource/best practices on geometry design?
    2) What size tube and thickness to use? I'm thinking about going with 1" SS304 tubes but need help deciding on the wall thickness.
    3) Are there any 20" wheels with provisions for disc brakes? Maybe i'm better off not going disc brakes b/c of his light weight?


    Appreciate any feedback/advise/help.

  2. #2
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    Great project!

    My advice would be to focus on light weight above everything else. Rigid fork on a light weight bike will be much more fun for the little guy vs. a heavier bike with suspension. You can get some really light stuff for 20 inch if you look at high end bmx stuff.

    Hope you guys have fun; please share photos when you get it going.
    Mark Farnsworth
    http://febikes.wordpress.com, Raleigh, NC

  3. #3
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    Time to start reading!

    You need to start by reading the FAQ, including the links, but especially Jay's first frame (the WWTP stuff). Based on what you've written you have a long way to go in terms of bike-specific knowledge, regardless of how much fabrication experience you've got. Building a frame that makes your son love to ride, rather than scaring and/or frustrating him will take a lot more than the ability to stick pipes together.

    Random thoughts that may or may not be helpful:
    -4130 is the material of choice. Use .035" throughout if you've got some thin wall experience, otherwise .049". If you use all 1" or 1 1/8" tubes you're probably fine.
    -Forget FS your first time out, you aren't ready (I mean no offense, but you're not) and your kid doesn't need it at this stage.
    -Build yourself a town bike or something first to figure some stuff out. Your first frame usually (though plenty of jerks here like to show me up and do really nice ones, cough *trailmaker* cough) will suck in at least some ways and maybe suck in general - there's no shame in that but you should inflict the suckiness on yourself, not your son.
    -I'll say it again: start reading. If you want to succeed you should devote some time to reading a LOT of threads here as well as the phred.org archives. Even conversations that don't seem obviously relevant to your situation often contain incredibly useful nuggets of information. Many famous and not-so-famous-but-awesome builders have freely posted their favorite tricks and techniques, go read them.

    -Walt



    Quote Originally Posted by sonu View Post
    So, My 5 year old (5 1/2) has outgrown his 16" bike and is still a little too small for all the 20" bikes we've tried. He wants to go trail riding with me and he needs at a minimum a 6 or 7 speed to be able to climb, I'd also like to a front shock for him. Main issue with everything we've seen is that he has to bend forward to reach the handlebars b/c of his height, and the crank is too long as well as the BB is being too high off the ground (i think).

    I know how to weld and I've worked on roll cages/fabrication and for a while so I figured why not just build one and have decided to proceed. Plan is to either pick up used (in 20") and build the frame and reuse the components, this is the easiest way i think.

    Harder option is to build him one from adult parts, I'd really like to make it a full suspension bike. I was thinking about getting air shock/fork (and setting air pressure accordingly for his weight) and i'd be nice to make it disc brake as well. I was thinking of using a front fork from a 26" bike with 20" wheels...anyone done this before?

    So here are my questions:
    1) Any guide/resource/best practices on geometry design?
    2) What size tube and thickness to use? I'm thinking about going with 1" SS304 tubes but need help deciding on the wall thickness.
    3) Are there any 20" wheels with provisions for disc brakes? Maybe i'm better off not going disc brakes b/c of his light weight?


    Appreciate any feedback/advise/help.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  4. #4
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    I built two of these for last spring for my 5 and 6 year old. I had a bunch of regular mtb parts laying around. With the lack of 20" air forks, I decided to use a 26" Manitou Skareb and Manitou Mars and they work great. I laced the wheels using cheap disc hubs and 20" Sun CR18 rims. Geometry: HA: 72 deg, SA: 73deg, Chainstay 13.5", TT: 17.5", BB height 9". For cranks I used regular cranks and cut 50 mm from the arms. Epoxied them back together an reinforced them with carbon fiber. In hindsight, I should've gone with a much slacker head angle. The steering is a little twitchy.





  5. #5
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    Those are some psyched kids. Awesome.

    It's worth noting that if you have access to some machine tools, you can just drill/tap the pedal threads anywhere you want on cheap solid forged cranks, then cut off the excess. Saves the work of bonding them back together.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  6. #6
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    Quote Originally Posted by kosayno View Post
    I built two of these for last spring for my 5 and 6 year old. I had a bunch of regular mtb parts laying around. With the lack of 20" air forks, I decided to use a 26" Manitou Skareb and Manitou Mars and they work great. I laced the wheels using cheap disc hubs and 20" Sun CR18 rims. Geometry: HA: 72 deg, SA: 73deg, Chainstay 13.5", TT: 17.5", BB height 9". For cranks I used regular cranks and cut 50 mm from the arms. Epoxied them back together an reinforced them with carbon fiber. In hindsight, I should've gone with a much slacker head angle. The steering is a little twitchy.
    Thanks for the info...they look great. This is kind of what I have in mind. I now know what to do about the wheels! I've got some spare parts sitting around and can put them to good use on my son's bike.

    As for the forks...are they plush enough even with the kids weight? I want to make sure that they are soft enough that they actually dampen at his weight (~50lbs). Any other forks (looking to buy used ~$100) that may be better suited?

  7. #7
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    Quote Originally Posted by Walt View Post
    Those are some psyched kids. Awesome.

    It's worth noting that if you have access to some machine tools, you can just drill/tap the pedal threads anywhere you want on cheap solid forged cranks, then cut off the excess. Saves the work of bonding them back together.

    -Walt
    That would've saved me at least 2 hrs per crankset but I have no access to a tap. Only machinery I have is a Dremel, angle grinder, hand held drill, hand held belt sander and a vacuum pump. All cheap stuff from Harbor Freight except the Dremel.

    Quote Originally Posted by sonu View Post
    Thanks for the info...they look great. This is kind of what I have in mind. I now know what to do about the wheels! I've got some spare parts sitting around and can put them to good use on my son's bike.

    As for the forks...are they plush enough even with the kids weight? I want to make sure that they are soft enough that they actually dampen at his weight (~50lbs). Any other forks (looking to buy used ~$100) that may be better suited?
    For reference my daughter was less than 48" in the picture. Both my kids were about 45 lbs when I build the bikes. They're just a hair over 50 lbs now. I set them at about 15-20 psi per fork. I put zip ties on the stanctions to measure travel and also just watch them do some bumps and curb drops. They get full travel and from my observation the forks seems to behave the same way as if they were regular riders. I picked up these forks for less than $150 total on ebay. My experience with Manitou has always been positive that's why I chose these for their bikes. Lots of cheap used air forks out there if you look around.

    As for the wheels, make sure you lace them no more than 2x. This was my first experience building wheels and I laced them 3x. The spokes are too short for 3x and you can see the bend in the spokes.

    BTW, total weights for the bikes were 22 lbs. Yes heavy for small bikes, but they are using regular mtb parts.

  8. #8
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    Get a monster long stem, install backwards. Reach problem solved!!! Did this for my daughters hotrock

  9. #9
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    Quote Originally Posted by Walt View Post
    You need to start by reading the FAQ, including the links, but especially Jay's first frame (the WWTP stuff). Based on what you've written you have a long way to go in terms of bike-specific knowledge, regardless of how much fabrication experience you've got. Building a frame that makes your son love to ride, rather than scaring and/or frustrating him will take a lot more than the ability to stick pipes together.

    Random thoughts that may or may not be helpful:
    -4130 is the material of choice. Use .035" throughout if you've got some thin wall experience, otherwise .049". If you use all 1" or 1 1/8" tubes you're probably fine.
    -Forget FS your first time out, you aren't ready (I mean no offense, but you're not) and your kid doesn't need it at this stage.
    -Build yourself a town bike or something first to figure some stuff out. Your first frame usually (though plenty of jerks here like to show me up and do really nice ones, cough *trailmaker* cough) will suck in at least some ways and maybe suck in general - there's no shame in that but you should inflict the suckiness on yourself, not your son.
    -I'll say it again: start reading. If you want to succeed you should devote some time to reading a LOT of threads here as well as the phred.org archives. Even conversations that don't seem obviously relevant to your situation often contain incredibly useful nuggets of information. Many famous and not-so-famous-but-awesome builders have freely posted their favorite tricks and techniques, go read them.

    -Walt
    Thanks for the warning and understand where your coming from but I think i'm going to give it a shot!

    I've been playing around with bikecad and just reading up on geometry design and such. I've got some idea, but wanted to hear from people who've built these bikes for kids and to get feedback on how it worked out.

    I've got some .058 DOM and .065 SS304 sitting in the garage so thats why I was thinking about going with the ss304. I figured I could just brush it and leave it raw. But I'll look into getting some 4130 tubing, It'll end up being lighter, I'll just have to see how much lighter.

  10. #10
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    Quote Originally Posted by kosayno View Post
    That would've saved me at least 2 hrs per crankset but I have no access to a tap. Only machinery I have is a Dremel, angle grinder, hand held drill, hand held belt sander and a vacuum pump. All cheap stuff from Harbor Freight except the Dremel.



    For reference my daughter was less than 48" in the picture. Both my kids were about 45 lbs when I build the bikes. They're just a hair over 50 lbs now. I set them at about 15-20 psi per fork. I put zip ties on the stanctions to measure travel and also just watch them do some bumps and curb drops. They get full travel and from my observation the forks seems to behave the same way as if they were regular riders. I picked up these forks for less than $150 total on ebay. My experience with Manitou has always been positive that's why I chose these for their bikes. Lots of cheap used air forks out there if you look around.

    As for the wheels, make sure you lace them no more than 2x. This was my first experience building wheels and I laced them 3x. The spokes are too short for 3x and you can see the bend in the spokes.

    BTW, total weights for the bikes were 22 lbs. Yes heavy for small bikes, but they are using regular mtb parts.
    Good to know! I'll look into finding one of these forks.

  11. #11
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    Not a warning!

    I wasn't trying to "warn" you - I am just saying you should do some more reading. .065" tubes are INSANE overkill for someone who weighs 50 pounds. You'll end up with a 5-6 pound frame using that stuff. If that's what you want just put some nicer parts on a department store frame.

    Here's what I'd get:

    From Nova or Henry James:
    -1 piece (200mm or so) of the thinnest 1 1/8 head tube stock you can get. If you decide to do rigid 1" might be even better.
    -Cheap single-bend chainstays. You'll cut off a ton of the dropout end, that's fine in most cases but try to find the smallest diameter you can. If you have equipment for bending small tubes you could get some 5/8" 4130 instead.
    -Cable stops/guides as needed.

    From Wicks or Aircraft Spruce:
    -A bunch (10' or so) of .035" x 1.125" 4130. This is your down/seat/top tube stock. Seat tube will take a 26.8 post. If you want 27.2 get single butted .9/.6 seat tubes.
    -1' of .058" x 1.25" 4130 to sleeve the seat tube.
    -6' of 1/2" x .028" 4130 - seatstays. If you can't bend them yourself, get .035" and cut/weld back together to make your bends.

    Paragon Machine Works:
    -Bottom bracket shells. English 68mm, you could even get sneaky if you have access to a lathe and some old BBs and machine down narrower.
    -Disc dropouts. Pick your favorite from the wide selection.

    You'll be out a couple hundred bucks by the time all is said and done but nobody said this was a cheap hobby...

    -Walt


    Quote Originally Posted by sonu View Post
    Thanks for the warning and understand where your coming from but I think i'm going to give it a shot!

    I've been playing around with bikecad and just reading up on geometry design and such. I've got some idea, but wanted to hear from people who've built these bikes for kids and to get feedback on how it worked out.

    I've got some .058 DOM and .065 SS304 sitting in the garage so thats why I was thinking about going with the ss304. I figured I could just brush it and leave it raw. But I'll look into getting some 4130 tubing, It'll end up being lighter, I'll just have to see how much lighter.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  12. #12
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    Nice!!!

    Quote Originally Posted by kosayno View Post
    I built two of these for last spring for my 5 and 6 year old. I had a bunch of regular mtb parts laying around. With the lack of 20" air forks, I decided to use a 26" Manitou Skareb and Manitou Mars and they work great. I laced the wheels using cheap disc hubs and 20" Sun CR18 rims. Geometry: HA: 72 deg, SA: 73deg, Chainstay 13.5", TT: 17.5", BB height 9". For cranks I used regular cranks and cut 50 mm from the arms. Epoxied them back together an reinforced them with carbon fiber. In hindsight, I should've gone with a much slacker head angle. The steering is a little twitchy.





    Those are some lucky kids!!
    PAYASO 36er.....Live the Circus

  13. #13
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    I've built a bunch of kids bikes, the smallest for my youngest when he was not quite 5. I would recommend a rigid fork. The little guys can run super low pressure in their tires. Suspension fork in overkill IMO, though my older boy's 20" bike did have a suspension fork - it was also a tank.

    Make the bike as light as you can. Even so, you will be approaching 50% of the riders weight. 1" od 035 is as heavy as you need. Use a 9/6 seat tube from Nova though to save yourself some aggravation.

    Shorten the cranks. This is one of the most important things for the little guys. Cranks they can spin instead of running hurdles is #1 important in my experience. The Sram 300's - maybe that's the model - are cheap and perfect for shortening. It is super easy to do on a drill press or mill. If you can't figure a way to do it, PM me and I'll hook you up.

    I would have loved to use disk brakes on the blue bike, but just couldn't source the spokes and such. I went with v-style brakes.

    Skip the FD. You can run a double up front if you want, but the little guy will be in the granny ring on the trail the whole time. The bigger ring is fine for bikepath - you can change it by hand when needed. Use the smallest front ring you can find. Use a thumb shifter. You would think that the twister would be better for little hands, but that doesn't seem to be the case. Use a short cage rear derailleur, because a long cage will just about hit the ground.

    Do not put cables on the top of the TT. Use full housing. Make sure the housing guides are somewhere such that the cut cable tie cannot cut their leg.

    Again, use the lightest stuff you can. Scour your part bins for old Ti ars and posts and whatever.

    If you need dimension help, let me know. I hand draw all of my plans, so I can't really email the pic to you, but I can send you the dims.

    A thread that allows me to show off my kids and bikes! Excellent:
    Attached Thumbnails Attached Thumbnails Need Advise on custom Mtb for my 5 year old-p3110233.jpg  

    Need Advise on custom Mtb for my 5 year old-p3120258.jpg  

    Need Advise on custom Mtb for my 5 year old-pc221042.jpg  

    Need Advise on custom Mtb for my 5 year old-pc221039.jpg  

    Attached Images Attached Images  
    I am Belltown Bikes LLC. Steel bicycles hand made in East Hampton, CT

  14. #14
    Belltown Brazer
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    Couple of more pics

    Don't know why last post only showed 3 of the 5 I attached. Here's some more. Can't help myself, nothing better than building for and riding with your kids!...B
    Attached Thumbnails Attached Thumbnails Need Advise on custom Mtb for my 5 year old-p3110233.jpg  

    Need Advise on custom Mtb for my 5 year old-p9150752.jpg  

    Need Advise on custom Mtb for my 5 year old-pc221053.jpg  

    Need Advise on custom Mtb for my 5 year old-pc241081.jpg  

    Attached Images Attached Images  
    I am Belltown Bikes LLC. Steel bicycles hand made in East Hampton, CT

  15. #15
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    Thanks Walt. I blusheth... a little.

    Sonu - Your tangential fabrication experience will likely stand you well. You'll likely find the fab part is "easy," as I have. Although I have learned a whole bunch of new processes, all on a far different scale than racing safety system work, the basics are not so different than lots of other stuff I've done. It is the bike specific-part and tooling that burns the brain cells.

    I have a different perspective, I guess. If you are someone who builds bikes, then building another bike is not a big deal, and this is a great excuse to build another. If not, you might not finish it in time! Anything you build they will outgrow by the end of next week. As such, I would look to economize. Kiddy bikes are everywhere; to the curb up and down the street on trash day, at the Thrift stores, even Walmart, all for nothing-to-super cheap. I've had/have a bunch of them kicking around here for ever, all free. I'd be looking at grabbing something to rape for parts. Even to the extent of hacking off HTs, BB housings, and the like. It's very likely you could just selectively section and re-weld an existing bike to work quite nicely, and learn a lot of the rudiments in the process.

    Light is nice, but above all, keep it simple! Kids that age have an attention span of "I was on to something else 2 minutes ago." Single speed, rigid, coaster brake, etc. K.I.S.S. will work for you too, getting your feet wet. Nothing saying you can't at the same time be working out things like suspension forks, gears, and other such in your head, concurrently.

    Just my thoughts. Whatever you do, have fun, and post up on your progress.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  16. #16
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    Thanks for sharing and cool pics! Seeing pics is motivating to build this thing. Also thanks for the info guys.

    I'm currently looking for a adult 26" to pillage for parts (something with disc brakes and such). I've considered just chopping the the tubes off on an adult bike and salvaging it for the parts (including BB and Head tube), but its a lot easier to just buy new ones. What is the lightest/smallest size aluminum (6061) tubing I can get away with (to keep weight down even more)?

  17. #17
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    +1 for MDEnvEngr's thoughts on kids bikes.

    I'll throw one more thing in there, don't bother getting fancy unless you really want to. These kids grow so fast you'll be needing a 24" rig before you know it. Start basic, get him riding it, figure out where you may have messed up, and then concentrate on your next masterpiece (so to speak.)

  18. #18
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    Troll the weight weenies forum for info on inexpensive light weight parts.

    This is one time you can run the uber inexpensive super light weight china carbon seat post and bars without worrying.

  19. #19
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    6061 eh?

    For a kids bike, you might get away with a non-re-heat-treated creation. Might.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  20. #20
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    Quote Originally Posted by TrailMaker View Post
    6061 eh?

    For a kids bike, you might get away with a non-re-heat-treated creation. Might.
    I coached some kids this summer who had been riding on a non-heat treated 6061 bike that their dad built, the HT-DT cracked. Those guys were pretty hard shredders though for being 8 and 10.

  21. #21
    The dirty knacker
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    Here's a pic of a crazy mini mtb made by BMW:
    Rosko Cycles Inc.
    New York City, NY, USA
    www.rosko.cc
    My flickr gallery of projects etc.

  22. #22
    pvd
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    Here's a bike I did for a 6 year old. My be the print will help. Try not to copy what is out there for the juvinile market. Those are designed for use in a driveway. You want to get close to the body position most of us use for best results.
    PVD Micro-DH – PodRacerOne | Peter Verdone Designs


  23. #23
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    The Brooklyn's kid bike is awesome. That front suspension setup is really interesting. Are they old marzocchi bomber Z1s? The ones with the allen bolted crown?

    I really like the use of 24" wheel for bikes like this. PVD, what fork did you use on yours? Is it a 26" fork? Btw, it looks absolutely superb. I would have been seriously pumped to get a bike as good as that when I was 6!

  24. #24
    pvd
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    It's an old Fox Float lowered to 80mm. The biggest issue with building a quality kids bike is getting the handlebars low enough for proper positioning. Note the flat bars and negative stem. I would have loved a lower 24" fork for this build, but there are pretty much none out there worth building with.

    Also, with smaller wheels, you need a longer front center to keep the kids from getting snagged and flipped over the bars. Small wheels are like magnets for holes and roots.

  25. #25
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    If you guys on flickr want to show these fancy kid bikes off, I created a new group for custom kid bikes: Flickr: Custom Bikes for Kids

    I have to start a new one for my six year old, and this thread is getting me fired up to see what guys are building for kids these days.

    Hijack over.

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