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Discussion Starter · #1 ·
So I'm looking into building a 26" hardtail for my 70 lb son. I'm interested in what sort of steel tubing (wall thickness, outer diameter) would be most appropriate for such a build.

The frame I have somewhat rudimentarily come up with on bikegeocalc is going to be somewhat short in the stays. (I've just sorted out the angles, stack, reach, chainstays etc at this point). I don't know if this will have an effect on tubing choice regarding stiffness for his light weight.

I plan to draw everything up in a cad program, just having a bit of trouble getting RattleCad to load on computer at the moment, and I'm not sure I want to go all in on Bikecad.

Thoughts on this are appreciated.
 

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Certainly, 7/8" top tube, 1 1/4" down tube, 1/2" seatstays, and 5/8" chainstays would be a start.

If you want to make a GOOD bike for a kid, you'll have to learn some about fit and geometry. Almost every kids bike out there is terrible.

This is something on the topic but not final. I have a design for a kid bike that I'm working on with more seriousness.

https://www.peterverdone.com/kids-bikes/

The big thing with kids bike is to design something that is a little on the big side at first and allows for some adjustment over time that doesn't make the bike garbage
as the kid grows
 

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Discussion Starter · #5 · (Edited)
Thanks for all of this PVD. Sorry it took so long to get back to this thread, we have to drive a good clip to go ride right now, still a ton of snow up where we are! Just getting home.

I agree, geo is super important, and that's the reason I'm looking at attempting this...again. I'd asked you guys about frame stuff a few years back when he was moving to 24". I ended up finding a bike (Orbea MX 24 Team Disc) that had numbers so close to what I'd done in RattleCad, that I just went with that. This time though, with 26, I'm just not seeing anything that I like. Generally too long in the stays, too tall in the stack, and too short in the reach, among other geo issues that I don't think are optimized well enough. What I'm wanting for him is an all around XC bike that can handle most trail outside of the bike park etc. That's the way we ride.

Question regarding the tube sizes that you have recommended...what sort of wall thickness do you think is appropriate?

Am I correct to assume that a thinner wall tube is going to ride with more give? Also, as an outer diameter increases, does that balance of frame give/stiffness change, depending on the thickness of the wall?

I plan to braze this thing.

Thanks again for your advice.
 

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Question regarding the tube sizes that you have recommended...what sort of wall thickness do you think is appropriate?

Am I correct to assume that a thinner wall tube is going to ride with more give? Also, as an outer diameter increases that balance of frame give/stiffness changes, depending on the thickness of the wall?
Going from 7/4/7 to 9/6/9 is a smaller change than going up 1 tube size, at least for the tubes i've calculated. (nothing that small) I don't see any reason to use thin tubes for a kid's bike- they're easier to dent and the weight savings isn't much.

Id like to see what you make!
 

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Discussion Starter · #7 ·
Thanks for that insight Scott, that really puts tube thickness in perspective for me. And thanks for deciphering my question! I'm reading what I typed and it makes almost no sense. I think auto correct ommited a word and changed the tense on another. Or it was my fumbly fingers. (Most likely) I've fixed that now.

I'm excited to get this going. I will surely post up my progress once I do!
 

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Just use the 0.9mm wall, and if its easier to get:1" TT tube, use that.
I would design around the childs Centre of Gravity for balance between axles and rigid fork as suggested. If you design with short chainstays, you will find yourself trending towards Geo-forward currently in vogue so you can shrink down a modern frame to a degree and do tweeks to suit.

Eric
 

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Discussion Starter · #9 ·
Thanks Eric, that's pretty much what I have done geo wise. We will be running suspension, but not much by todays standards of 'too much is not enough', enduro brah. Just going to be running 80mm, but I'm designing the frame so that bumping to 90 or 100 is not going to jank up the geometry if we chose to do it.

Just a well rounded XC bike for my pretty capable son.

Thanks so much for your advice, you guys are awesome.
 

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Discussion Starter · #11 ·
Pvd, I'm new to frame building, but not new to suspension and bike tech. I worked as a mechanic for a long time back two decades ago as a young and fast whippersnapper, and still do all of my family's bikes service on everything. His suspension will work. I'm not just throwing anything on there.
 

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I too am in the process of designing my second bike for my son. The first bike was consructed from recovered tube from a couple of bikes namely a road racing bike. There were a few unexpected things i learnt on the way. 1)If you're going to order rims from halfway round the world make sure theyre the size you think they are (check the meteic sizing). 2) i ended up with an odd ball 16 inch wheel with nothing but slick tyres available. Even though the bike essentialy has slick tyres they have never ever held him back on rock roots or pavement. I just run the 1" tires between 10-15psi.
I actually am really pleased with the accidental rims i got. 3) hydraulic brakes are king. Little hand dont have much strength compensate with great brakes. I think shimano offer the most child friendly lever..
I keep coming and going on adding suspension to his 24 inch bike. I have conceptulized a few different ideas from full custom usd forks to retro fitting different lowers to 26 inch forks basically a new lower that would raise the axle up the lower to reduce the a2c height. But I am still torn on that or a rigid fork and low pressure 2"tyre.
Cheers Pete.
 

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I'm new to frame building...
Exactly. Take a minute to listen to some good advice from an experience designer. I know about bikes and I know a bit about suspension.

Do the math on how important bike weight is to a lightweight kid (factored to your scale) and you'll find that the extra weight for ZERO performance gain is a real problem. A plus tire on a rigid fork is a far better solution.

I'm going to post a bike on my blog later this week that is going to be crazy fast, super fun, and very competent. Rigid fork. Don't lose focus of the goals with the idea that some gizmo is a silver bullet. Everyone makes that mistake. Focus on first principles and good design instead.

A dropper post, on the other hand, is super important. Far more than a squish fork.

Gamechangerz | Peter Verdone Designs
 

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Discussion Starter · #16 ·
Exactly. Take a minute to listen to some good advice from an experience designer. I know about bikes and I know a bit about suspension.

Do the math on how important bike weight is to a lightweight kid (factored to your scale) and you'll find that the extra weight for ZERO performance gain is a real problem. A plus tire on a rigid fork is a far better solution.

I'm going to post a bike on my blog later this week that is going to be crazy fast, super fun, and very competent. Rigid fork. Don't lose focus of the goals with the idea that some gizmo is a silver bullet. Everyone makes that mistake. Focus on first principles and good design instead.

A dropper post, on the other hand, is super important. Far more than a squish fork.

Gamechangerz | Peter Verdone Designs
My questions were about tubing. You guys all answered those and I totally appreciate it.

If anyone has anything more about tubing choices, I'm all ears.
 

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...here...we....go...again....
Why do we need to rehash? Just design the bike around a suspension fork and it's easy enough to experiment with a rigid one. Kinda silly to do otherwise so long as you have enough stack height.

Seems like pete and eric have covered the tubing sufficiently, unless you have a specific question.

I'm a big fan of adjustable length chainstays. In this case you can use them to 'grow' the frame, and fix it if you're a little too progressive with your short rear end. Worth considering, although they add weight, complexity, and expense.
 

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Discussion Starter · #20 ·
Why do we need to rehash? Just design the bike around a suspension fork and it's easy enough to experiment with a rigid one. Kinda silly to do otherwise so long as you have enough stack height.
Is this directed towards me? I think you're talking to PVD but not sure.

Seems like pete and eric have covered the tubing sufficiently, unless you have a specific question.
Yourself as well and it's really appreciated. Right now, I don't have anything else specific, but I am positive I will.

I'm a big fan of adjustable length chainstays. In this case you can use them to 'grow' the frame, and fix it if you're a little too progressive with your short rear end. Worth considering, although they add weight, complexity, and expense.
I'm not planning on going super short, just shorter than everything that's available. A straight seattube will work fine with this length.

However, I'm not sure what to make of this. Are you pulling my leg? :)
 
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