Friday, January 23, 2009

Tringle-speed Bicycle

Back in November, Jill up in Alaska wrote:

I was able to get in plenty of bursts of hard effort today after I snapped the rear shifter cable on my mountain bike. I feel bad for my Karate Monkey; only seven months old, and she's already been through the war. But after riding most of the morning with three speeds (and really only using the middle ring), I have to say, I still don't understand the single-speed thing. It's not a matter of being able to push a high gear up steep hills - that I can do if I have to. But I prefer to have my rotations per minute stay the same no matter how fast I'm going. Single-speeders must have their legs spinning all sorts of different crazy speeds. And once your RPMs drop down to two or three, don't you start questioning the efficiency of your one gear?
As somebody whose put a fair number of single-speed miles under his wheels, I guess I'd respond to Jill by saying that crazy spinning is kind of the point. If you only train to turn one range of RPMs, you're only good at that range of RPMs. Kind of like if you only rode when it's 70 degrees and sunny, then you'd only be good at riding when it's 70 degrees and sunny. But what would you if it was below freezing and dark? But then again, who'd want to ride when it's below freezing and dark? Why would anybody do that? Would that be at all interesting? I don't know maybe some people like things to be a little tough.

Me, I like single-speed bikes. While I certainly enjoy fixed gear bikes and I've logged a lot of fixed gear miles, I do like coasting now and then and I like the dynamic of a single-speed, cranking it up a climb, tucking and coasting on a descent, spinning it as fast as I can go on the flats. But still, Jill does have a point. There are times when a bit more versatility would be good. Not necessarily a full-bore derailleur system or the precise clockworks of an internal hub. It's more that it would be handy to have one single-speed that's geared kind of high for pavement riding. And one bike that's geared somewhat lower for general mountain biking. And maybe a third bike that's geared really low, for when I'm hauling camping loads up steep grades or when the snow is deep. Yeah, not a bike that you shift exactly but three single-speeds. Three single-speeds in one bike.

Sheldon Brown pointed me to the answer and I read about it here:

Sheldon states:
Bruce Ingle, a fellow member of the Charles River Wheelmen, has gone me one better, and made a triple-fixed mountain bike. He used a Shimano cassette hub, which he immobilized by brazing the ratchet mechanism together. I am a bit nervous as to the long-term prospects for this hub, in particular the connection between the freehub body and the hub shell, but I think I will have to copy his setup. He's got:





I loved the idea of this but I figured I'd skip the brazing part and keep the ratcheting mechanism. As an homage to Mr. Ingle, I figured the logical name for such a machine would be a Tringle-speed. I wrote to Bruce asking for his advice on setting up such a machine. He wrote me back with good advice on selecting components and getting a good chainline. About the name he said simply, "I love it!"

Once again, the near infinite supply of parts that is Bike Works yielded all the components for this project. The design is simple: three chainrings up front, three cogs in the back. The cogs fit on a Shimano freehub body (in my case an old 7-speed freehub) with spacers filling in the empty spots. The cogs are positioned in such a way that the outermost cog is in a straight line to the outer chainring, the middle cog lines up with the middle chainring and the inner cog aligns with the inner chainring. And while the front-to-back ratio is different in each combinaton, the total number of front and back teeth remains the same,. Thus the chain length is the same for each combination and you have three basically perfect chainlines. Changing from one combination to another is not something you do while pedaling, but it only takes a minute to stop and change gears when the pavement ends or at the top of a mountain pass. All I need to do is loosen the quick-release, slide the wheel a bit forward in the dropouts, move the chain to the desired combo, slide the wheel back into position and tighten the quick-release.

This chart shows the gear combinations I have on my tringle-speed.

ChainringCogGear Inches

The 69.3 inch gear is for civilized conditions, while the 45.5 inch gear is for off-road and hilly stuff. The 31.2 inch gear should let me climb walls like Spiderman.

Now yeah, a derailleur set-up might be easier. So would a Harley-Davidson. That's not the point now, is it? Sometimes you want things to be a little tough. And fun. Really, really fun.

Stay tuned for some ride reports.

Keep 'em rolling,

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