Hello everyone! Aspiring frame builder here. I’ve spent the past few months learning how to machine / weld and am finally feeling confident enough to take a crack at a real bike. I’m thinking of making a 16" kids bike to get my feet wet and to give my 5yr old a bike good for his size
As I start to design this my question is about sourcing parts, specifically:
- Seat / chain stays
- Head tube
- crank set
I’ve been unable to find any forks or stays in the 16" size. Whats a good BB to use? Would I find a head tube off the shelf or will I have to make one? I’m thinking of this like a conventional bike and maybe thats the problem. How do you all approach something like this?
Not sure on forks but for chainstay I would use 5/8" * 035 4130 tube and seat stays 1/2" or 3/8" * 035. I usually get it from aircraft spruce, you can buy it by the foot. Bike fab supply has head tube stock you can cut to length for headtubes. BB I would probably use a 68mm BSA from bike fab supply and find a short square taper crankset to suit.
I think for a 16" bike I would be looking at doing a monotube instead of downtube/toptube to make it easy for standover.
I recently built a 14” bike for my kids. Most of my build kit came from AliExpress.
I would have liked to build with nicer parts but big brands don’t make the weird things I required.
Hubs- knock off NovaTek 24 hole disk.
Rims- K-Funn 14 inch folding bike
Spokes- custom cut from porkchopBMX.com
I wanted a disk rear brake so I had to use a multi speed hub. This was good because I could dial in chain line because it was off between freewheel rear hub to -6mm chainring offset used on 142mm hub spacing.
Cranks were the hard part. I wanted 89mm crank-length with as narrow Q factor as possible. Kids bike square taper cranks are really bad so I got these but it doesn’t look like the 89mm length is available anymore.
I would also build a fork. If you buy one, look into 16” folding bike forks. Your requirements are going to be more specific than factory options have. I got some old Uni crown fork blades and QR dropouts that were “outdated” by modern adult bike design for cheap. The fork fixture was posted elsewhere here and can be built for around $70.
I also highly recommend Tektro HD-J285 brakes. They have a smaller lever for kids. My 3 year old can operate them with ease. She struggles with coaster brake bikes but rips on the hydro disk.
I built a 16" disk bike a few years ago, I used a 16" BMX fork off eBay, and had the wheels built by albes BMX . they were very helpful
The cheapest option for a 16" disk wheel is probably lace them yourself. I learned to build wheels a year ago. Wish I would’ve learned sooner. It really opens up options imo
So custom everything and use a standard BB/head tube? I guess I’ll have to find tapered 1-1/8 forks that fit.
Bmx forks is all I can find. Is Bmx hub spacing different? I can lace the wheels myself if I can get hubs and cut spokes what did you do for the chain/seat stays and the BB?
I just used 5/8 035 chromo for stays, and a BSA 68 bb shell.
I used a 3/8*100 disk hub for the front and a 135qr disk hub in the rear
BMX front hub spacing is 100mm.
Rear is 110mm.
I used Von Sothen Racing cranks on my kids 20 incher. You can get them on eBay in lengths down to 100mm. I used a 107mm titanium BB also from eBay. Week 8 was the brand IIRC. Tried a 103mm but the cranks hit the BB cups when fully seated. The VSR cranks have a very narrow Q factor anyway. In fact, the VSR cranks had a significantly narrower Q factor on a 107mm BB than the Sinz BMX cranks had on the 103mm BB. All these were for 68mm BB shells.
I did 1/2” chainstays and 3/8” seat stays. I would caution you against doing rim brakes on stays that small. They are not rigid enough in those diameters and the brakes will howl. If you want to do rim brakes, do 5/8 chainstays and mount them there.
Also, a 26.8mm seatpost fits nicely in 1 1/8 x .035 tubing and still gives you some decent seatpost choices.
I used disc brake road bike hubs because they were light and had lower spoke counts.
Ashima 140mm rotors are lighter than any of the 120mm rotors I found.
I made my own head tube. Most of the bike tubing suppliers sell 1 1/8 headtube stock. Brazed some small reinforcing rings on the ends. Not so much for strength, but for surface area to keep the head tube from punching through the alloy headset cup.
Thanks everybody, this is great info as I find myself looking to build up one for my daughter!
They’re way over the top for kids bike, but I do make cranks in 100mm crank length if anybody needs them. Email me and I can get you setup with a framebuilder discount.
The really bring this build home!
I’d go with 20” wheels, lots more tire and rim options. I used lighter road fork legs and built my own fork with 100x12 spacing. Also used 5/8” chainstays and 1/2” seatstays in 4130 .035”. I used a BSA 68mm BB shell.