This Space for Rent

Fun with bicycle geometry!

Compare the Soma Speedster/Stanyan (58cm version, numbers converted to imperial units for easy comparison):

seat tube 22.6"
top tube 22.6"
head tube 5.4"
s/t angle 73°
h/t angle 73.5°

The Surly Big Dummy (16" version, because the mountain biking world doesn’t seem to like the metric system):

seat tube 16"
top tube 22.6"
head tube 5.2"
s/t angle 73°
h/t angle 72°

And my 1989 Trek 1000:

seat tube 22.3"
top tube 21.7"
head tube ~5"
s/t angle 73.5°
h/t angle 73.5°

Now, in the fantasy world where I could afford to spend $750 on a frame (actually about $670 for a frame, from which I’d rip off and discard, with extreme prejudice, the unicrown fork that Surly supplies with the Big Dummy frameset, and about $80 for a cyclocross-style lugged fork) the teeniest possible Big Dummy frame would make a good replacement for the woefully too small Trek. The one benefit of the Xtracycle coming out of the mountain/utility biking world is that they assume that everyone riding an xtracycle will have some sort of upright bars that swoop waythedevilback from the headset and that the rider will be perched bolt upright on their approximately bench-shaped seat, with a loooooong virtual top tube to get room between them and their handlebars. This means that someone like me, who has a long torso and short stubby legs, but who strongly prefers drop bars (though the mustache bars on the Murray Baja Experience! are nice and comfortable, even in the current too-short-for-me-seatpost configuration,) could theoretically set up a teeny baby Big Dummy, and (modulo losing a couple of mm to the head tube angle) get much the same fit as I have right now on the MLCM.

There would be some trail differences; losing 1.5° of head tube angle pushes the trail up by 9mm (64mm vs. 53mm, assuming a 44mm fork rake, 700c wheels, and 26mm tires in both cases) which might push the bicycle over the edge into being hilariously twitchy. Or maybe not, given that the recommended tire width for Xtracycles is something in the ballpark of 2 inches, and you don’t hear very much about industry standard 26x2"ed Xtracycles twitching all over the road and being abandoned by their drivers.

I’ll have to think about this for a while. The xtracycle is okay for riding short distances (up to 30 miles, I think) so the porteur rack (brazing flux is ordered and on the way; a trip to the hardware store will get me a brazing torch, and then a bit of work filing the rails square will get me ready to braze up the rack deck) for the MLCM may be what I need for my 50-60 mile donut pickup runs. But I would like to be able to shoe-leather cargo out into the countryside for camping trips, and there’s no way I’m going to realistically carry a reasonable subset of our camping supplies out to Estacada or a campground in the Columbia gorge via any sort of porteur rack on the MLCM.