Eight Tubes, Part 3: Getting Jiggy With It

Ironically, it is a bike race – the Tour de France – that is impeding progress on this little cycling-related project. This happens every July; I come home from work, eat dinner, flip on the TV, and immediately get lost in rooting for whatever hopeless break has gone up the road or holding my breath as the group descends some alpine col. (In the interest of full disclosure, I am a Thomas Voeckler fan…)

Anyway, watching the Tour does allow a lot of time to ponder some of the unresolved decisions that I have about this particular build, especially things like how to braze up the fork so it is vaguely straight, what geometry and sizing will I target, and just what sort of an asshole would throw tacks on the road at the start of a high-speed mountain descent (I am watching Stage 14 of the Tour as I am writing this, Cadel Evans and about a third of the peloton has just flatted, chaos abounds, and the normally unflappable broadcast team of Phil Liggett and Paul Sherwin are sounding like they have The Fear).


I have come up with a plan: build the fork first so I will have it in hand when I build the frame. When I put together Old Number One, it became manifestly clear that I really needed the fork that I was going to use in hand before I could finish the frame itself.  


With Old Number One I basically designed the frame around a couple of key measurements:

1. Top tube length,
2. Seat tube length,
3. Head tube and seat tube angle.

The remainder of the front triangle – the length of the head tube and the down tube – pretty much riffs off of those measurements.

Oh…..I didn’t tell you…I don’t have a set of plans or blueprints for my bike. I do know what size and geometry work for me, so it all sort of works out when I start cutting metal. Sure, this method sounds a little Rube Goldberg and I don’t think that Dario Pegoretti or Richard Sachs will be copying my proprietary sizing technique an time soon, but it worked just fine on Old Number One. I ended up with a 55cm frame (seat and top tube) that has a 160mm head tube. Granted, a 160mm head tube is tall, but it makes for a comfortable bike. (This time around I am shooting for a 140mm head tube).

The problem that I had with Old Number One was that, having no plans, I had to figure out length and angle of the chainstays.  Tough to do with no plans. 

The way that I figured out how to do it was a little bit of common sense.  Recognizing that the top tube of Old Number One would be parallel with the road when it was finished and the wheels attached, that meant that if you knew how high the front end of the bike was going to be hiked up off of the ground with the fork attached, then one could figure out where the rear wheel (and the chainstays and drop outs) should go. 



It actually turned out pretty simple.  On Old Number One, I took the completed front triangle, popped on the headset and fork, put the uncompleted frame in my bike stand, leveled it up so that the top tube was parallal with the garage floor,  and then measured the distance from the fork end to the ground.  I then popped the chainstay in the bottom bracket and adusted it until the distance from the floor to the dropout matched the measurement at the front.   

If you are bored or confused by all of this, just look at the picture of the pretty girl. That’s why she’s there.

So….before I build the frame, I need to have the fork.  Never having built a fork before, I have been running around the shop measuring all the road bike forks that I have laying around. The key measurement that I am interested in (for now) is the distance from dropout to crown, i.e. will a wheel and decent sized tire fit in the fork. Based on this ad hoc survey, somewhere around 365mm seems to be what I am shooting for. That will allow for a 700 x 25c tire, and is also compatible with the brake calipers that I probably will be using.

I haven’t been a total slug this week, however. We did cut some metal. I came up with a simple jig that should hold the various parts of the fork in situ while I braze them in place. Behold It’s crude elegance. Total cost: about $10 worth of angle iron and bolts as well as the noble sacrifice of an axle from an old front hub.



Next: Strong Language, And The Blue Sharpie Is Your Friend


4 Responses to “Eight Tubes, Part 3: Getting Jiggy With It”

  1. 1 Nick Belletti
    December 3, 2012 at 10:01 pm

    She looks “fully equipped”

  2. January 1, 2013 at 8:01 am

    Hi friends, nice paragraph and fastidious arguments commented at this place, I am truly enjoying by these.

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