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Father/Daughter Project - Part 3

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Father/Daughter Project - Part 3

Friday, November 22, 2019   |   Chris Blandford

Time to play connect the dots.

To this point, I’ve been designing my bicycles based--largely--on the published geometry charts of brands and builders that I respect. I don’t have the riding experience to have justifiable opinions about much of anything. So, I build to match models that look interesting to me, adjusting here-or-there for fit and whatnot.

Given that a kid's bike has all sorts of odd things going on (and given that nobody publishes dimensions for these little bikes) I decided that--for the Daughter Bike--I’d just go ahead and pick up a stock model to have on hand. (Sorry if that’s cheating.) On Wednesday I purchased a 16” Cleary Hedgehog from Clever Cycles here in Portland. This would’ve been the model I’d bought if I wasn’t planning to build Mathilda a bike. Yesterday I stripped the frame (see Nerdnote A) and took measurements, plugging them into BikeCAD as I went along.

This is how I usually “design” a bike. I find something to reference, and then enter those dimensions into BikeCAD. Then I iterate/adjust quickly in the computer and, once satisfied, I translate the design into a final full-scale drawing. This is probably (at least) double the necessary work, but I like idiot-checking myself on paper at this stage. And I enjoy the drafting.

Here’s where Mathilda’s bike ended up:

This design matches the Cleary, except in two ways. First, I’m allowing for a lower minimum saddle height and more standover than the Cleary. Mathilda has short little legs for her age. Second, I increased the fork length about 10mm compared to the Cleary (see Nerdnote B).

Once satisfied, I drafted up the frame and fork, full-scale. As I do this I start pulling parts, too. I tend to over-order when I buy frame bits. As such, I have a small-but-ever-growing collection of dropouts and fork crowns lying around. Helpful here. I'll likely order a few additional pieces this time around, too.

Having completed The Daughter bike drawing, I moved on to The Father bike drawing.

Little to see here, I think. When I was in college, I lusted after another student’s Gunnar Streetdog. Figured I’d take the chance to make myself one, now, with a couple slight modifications. Next, I drafted the full-scale version just as before (see Nerdnote C).

Now that these are done, I have enough info to order parts. I’ll do that tonight.

Nerdnote A:
I’m actually really impressed by the Cleary, and surprised at how much of a “real” bike it is. 68mm BB; square taper cartridge; regular 1” threadless steerer and headset; 28.6 down, top, and seat tubes; 25.4 seat post; 100mm front spacing; 110mm rear (that'll be interesting); 305 BSD (that’ll be interesting, too); little Tektro brakes; on and on. Unfortunately, though, this thing is HEAVY. Holy hell. I wish I owned a scale. I definitely don’t trust the published weight! It’s a tank. I think I can cut down on the weight significantly, both in the frame/fork and in the components. I'll give this bike away when I'm done with this project. If you'd like it, call dibs.

Nerdnote B:
I had a feeling I’d be testing the lower-limits on my Anvil jig for this project, and this indeed turned out to be the case. It was oh-so-close, though. Increasing the fork length 10mm moved the headtube bottom (the Anvil’s primary setup point) in-bounds. (I designed this bike with the jig setup dimensions displayed… shown above highlighted in orange.) That’s a slight concession, but it’s better than having to build a one-off jig for this little bike.

Nerdnote C:
Axle Line > Bottom bracket drop/rise and diameter > Seat tube angle > Effective seat tube length > Effective top tube length > Headtube angle > Fork rake > Front BSD > Front tire > Front fender > Clearance > Crown width > Lower headset stack > Headtube diameter and length > Down tube diameter > Seat tube diameter > Top tube location, angle and diameter > Rear wheel BSD > Rear tire. Chainstay length > Chain/seat stay top view (I usually do this later, though).