Thursday, February 20, 2014

new bike, part 4: Eric Estlund revises geometry

The next step after playing with BikeCad was to send the link to the project to Eric Estlund. Why Eric Estlund? For one, because there's an excellent local shop dealing in randonneuring bikes, Box Dog Bicycles, and they have a stock frame they sell called the Pelican. Jan Heine reviewed it a few years ago and liked it. But since then manufacturing of the Pelican has been transferred to Eric, who is Winter Cycles. I looked at his web site and really liked some of the work I saw. There was no doubt his work was superb. So I sent him an email. And he seemed enthusiastic, supporting my ideas while not afraid to disagree on occasion. That's what I wanted. After all, I don't know anything about these bikes, other than what I read or what I get from talking to others. So I wanted someone who'd drive toward a design without ignoring my preferences.

And here's what he ended up with. All in all, I think I did a fairly good job on the initial design, because this came back fairly close:

dimensionWinterBikeCADBIKECAD vs Winter
HTA:73 deg73 degsame
STA:73 deg75 deg2 deg steeper
TTA:-2 deg0 degflat vs 2 deg slope
TTL:55.0 cm54.0 cm1 cm shorter
effective TTL:55.6 cm54.0 cm16 mm shorter
STL:52.5 cm53.5 cm c-c10 mm longer
effective STL:54.4 cm53.5 cm c-c9 mm shorter
Q-factor:149.8 mm150 mmsame
Chainstays:440 mm425 mm15 mm shorter
front-center:598 mm604 mm4 mm longer
HTL(top of headset to bottom of headset):150 mm151 mmsame
bottom bracket drop:75 mm75 mmsame
handlebar drop (top to top):80 mm83 mm3 mm more
top of saddle to center of BB:735 mm735 mmsame
stem:110 mm90 mm20 mm shorter
seatpost diameter:25.4 mm25.4 mmsame
handlebar width:40 cm c-c38 cm c-c20 mm narrower
bar diameter:26.0 mm26.0 mmsame
handlebar reach100 mm (to hoods)120 mm (to hoods)20 mm more
tires:30x622 nominal
32x622 actual
32x622same
fork rake:65 mm60 mm5 mm less
trail:39 mm @ 30 mm
39.6 mm @ 32 mm
40 mm @ 32 mmsame
Handlebar-x (BB to center)476 mm464 mm12 mm closer
Handlebar-y (BB to center)605 mm618 mm13 mm higher
Hoods-x576 mm584 mm8 mm further
spokes front28324 more
spokes rear28324 more

To be fair, he never sent me this list, at least not initially. This was part of the deal, I felt. What I sent him was that initial design and a series of fairly standard body measurements. He used the body measurements, along with the requirements of bike design, to come up with the revised dimensions.

For example, my chainstays were 425 mm. That wasn't going to work for the sort of clearances I was after: 34 mm tires and a fender. So he increased the chainstays to 440 mm.

I specified 75 degree seat tube. I did so because I like my saddle relatively far forward: around 3 cm of set-back. He decided I could get a good enough position with a classic 73 degree seat tube. Slacker seat tube meant longer top tube to put the head tube in the same position.

Initially I was after a 650B frame, having read enough Jan Heine to think that was the way to go. 650B allows 42 mm tires with a reasonable rolling diameter sufficient to provide clearances for fenders. But he talked me into 700C, or 26-inch if I wanted to go fattie. The reason was availability of replacement parts on the road, since I said I wanted to use it for lightly loaded but self-supported tours. If you break a wheel you want to be able to find a replacement. 700C also affords compatibility with my Powertap wheel, should I decide I want to do power testing on the bike. This was an early decision, before dimensions were determined, so I'd already switched by the time I did that BikeCAD design.

He sloped my top tube. That's mostly an aesthetic thing. He felt the sloped top tube looked less retro, I think. That's fine with me.

Many of the other dimensions came out very close. You can see that in the table.

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