Ok, I haven't even started #1 but know what it's going to be (simple, single speed, probably somewhat askew) but then i'm thinking #2 will be for my younger son who is 6 and about 50 lbs.

I've spent the past 3 hours surfing the forums and archives reading tons of interesting stuff but haven't really found a thread that correlates height/weight to tube diameter/wall thickness (and then at the extremes). I'm guessing there's a sort of range for Rider X who weighs 180lbs, 6" tall, hard charging road racer (lots of watts). I'm guessing there's a set of tubes 'he could get away with' and then a 'preferred' set and then a 'whoa, that's a stout frame' set. The pros here probably have all of this in their heads and just know what will or won't work well (knowledge born from doing it a lot and getting feedback and doing it some more).
It seems most current kids bikes - even the nicer ones - are built with fairly heavy aluminum frames and forks and I'm wondering if it might be a good challenge to try to build something lighter with steel with smaller tubes. His bike is used mainly to get 4-5 blocks to school in the morning and then some easy dirt trail riding 5-10 times per year for 20 - 30 minutes per outing. We have one of these( 2014 Conquest 24 | Redline Bicycles ) from my older son still in the garage ready to go but thought it might be fun to build something.

Would it be ill advised to build a 24in wheel cx bike with (for example)
  • 7/8th .028 wall thickness DT,
  • 3/4 .028 TT
  • 3/8 .028 ST
  • 1/2in .028 or .035 CS
  • HT and BB shell would be standard items


I need to do the math to see if it would actually be any lighter - the tubes aren't butted. Are there things that could be tweaked (eg thicker CS) to make the above make sense or is it just a bad idea all 'round. I suppose the lightness is how I'm rationalizing doing it so, if it wasn't actually lighter, I wouldn't be that bothered. It would still be fun and he'd love helping with the sanding and finishing and assembly of the bike.

I'm just thinking of early 'mini' BMX bikes which typically had pretty small tubes.

Thanks for any advice. Just be warned that if this is a silly idea and you discourage me, I will just spend tomorrow dreaming up another plan that will likely be just as silly.