Kid's Bike - Tubing Considerations

[cblandford]

Hi all -

Currently building a 16" bike for my 4-year-old daughter. Two questions:

1. I have a pair of 16mm s-bend seatstays that, shape-wise, would work perfect as chainstays on this thing. Any hesitation?

2. How about nudging some .8 oval chainstays and using them as forkblades?

Given a <40 lb. rider, any other thoughts on my plan? I wouldn't normally ask this type of question--and would just overbuild whatever I was working on--but I want this bike to be as lightweight and enjoyable as possible, for obvious reasons. So, thanks in advance.

-Chris

[jon_norstog]

I've built several small (16" wheel) BMX bikes for kids that young - 3-4 YO. I used 5/8" and 3/4" x .028" chrome moly for seat and chainstays, a 1 1/8" butted seat tube and 1 1/*' and 1 1/4" x .7=.4-.7 top and down tubes. The frames are [plenty stout and came in under 3 pounds. Forks I used 1"x .049" for legs and 1"x .058" for the steer tube,

A decent 16" BMX wheel is VERY hard to find. By decent I mean sealed bearings, stainless spokes and a good alloy, double-wall rim.

Your proposed build looks OK to me although the .035" downtube is overkill. You could use 5/8" x .028" for the twin top tubes, same weight and a lot stiffer.

Good luck!

jnnonis_bike_1.jpg

[cblandford]

... a 1 1/8" butted seat tube...

Jon - Thanks for the reply! That's super helpful.

One quick question: On that little seat tube... I was planning on 1 1/8" .049, to fit a 26.0 post. I had thought about a regular single-butted seat tube with a sleeve (like yours, shown), but I thought the butt taper might get in the way of the post. Is that a 27.2 post just cut extra short? Or did you shim and run a smaller post?

-Chris

[jon_norstog]

Jon - Thanks for the reply! That's super helpful.

One quick question: On that little seat tube... I was planning on 1 1/8" .049, to fit a 26.0 post. I had thought about a regular single-butted seat tube with a sleeve (like yours, shown), but I thought the butt taper might get in the way of the post. Is that a 27.2 post just cut extra short? Or did you shim and run a smaller post?

-Chris

Chris, I used a 28.6 x .9-.6 seat tube. I cut it so I had some of the transition to braze to the bottom bracket, then used a regular 27.2mm seatpost, cut short. I like the looks of the Origin8 'posts that J&B sells and use them as a poor man's Thomson. Kid wont break it and it micro-adjusts. Kids that age range, it's their bodies that are growing and their legs kind of stay the same, so they won't need a taller 'post for a couple years and by then their bodis will be too long to fit in that front cabin. Time for a 20" bike.

jn

[cblandford]

Jon -

Sweet - thanks! That all makes sense... I appreciate the help. And yes, I'm anticipating undertaking this project a few times in the next decade! Ha. This version only needs to fit a couple years.

-Chris