March 09, 2005

Up for the downshift

My radio alarm is set to my local public radio station. This morning, I woke up to hear the following:

... and then rotate it clockwise, as I'm looking at it ...

It turns out this was the second part of a two-part story on two wounded Marines, and Marine 1st Sgt. Brad Kasal was talking about a contraption on his wounded leg; as NPR's Joseph Shapiro explains: "Twist one of the screws, and Kasal's bone is literally pulled apart, just a tiny bit. That stimulates the bone to grow; the muscles, nerves, blood vessels, and skin too. Eventually, Kasal will turn these screws himself, a little every day." Kasal goes on: "Right now the doctors are still doing it, and it's relatively simple. It's a little bit uncomfortable ... well, quite a bit uncomfortable ..."

Now I have no idea what this contraption (called a "ring external fixater") looks like or how the screws are oriented, but I think it's safe to assume that the distinction between turning them clockwise and turning them counterclockwise is pretty important. This reminded me of the (comparatively far more trivial) discussion a few months ago about shuttle-loop directions and related matters (see here, here, here, here , here, here, here, and even over there).

Actually, I've just been searching for an excuse to come back to this issue, because I spent quite a bit of time thinking about it in relation to bicycles -- specifically, the gear shifters on mountain bikes. (If you're really interested in the technicalities of this topic, I suggest looking here and/or here. I need to get into a few technicalities here, but I'm putting aside the more complicated and interesting ones in the interests of my own time.)

In case you didn't know, gear shifters are the things on your handlebars that allow you to change gears. The shifter on the left-hand side of the handlebar (as you're mounted on the bike -- the shifter you would control with your left hand while riding normally) controls the front derailleur and the one on the right-hand side controls the rear derailleur. As explained here:

The derailleur is the device that changes gears by moving the chain from one sprocket to another. There are two derailleurs: one on the rear and one on the front. The highest ratio (when the bike can go fastest) is produced when the chain is on the biggest sprocket in the front and the smallest in back. The lowest ratio (the bike is easiest to pedal up hills, but very slow) is produced when the chain is on the smallest sprocket in front and the biggest in back.

In the front, the biggest sprocket is on the outside and the smallest is on the inside; in the back, the smallest is on the outside and the biggest is on the inside. Thus, when you're in the lowest gear, the chain is more or less parallel and flush with the bike frame; when you're in the highest gear, the chain is parallel but furthest away from the frame.

A lot of this information is second nature to many biking enthusiasts, but the average bike-riding person doesn't care about anything other than the following distinction: shifting one way makes it easier to go uphill, shifting the opposite way makes you go faster otherwise. Reflecting this need of the average Joe, many (standard) gear shifters have numbers to indicate the difficulty of the gear. For example, a 21-gear bike (3 sprockets in the front, 7 in the back) has numbers 1-3 (easiest-hardest) indicated on the left-hand shifter and 1-7 (also easiest-hardest) on the right-hand shifter.

Over the past 15 years or so I've ridden mountain bikes with three types of shifters, which I believe entered the market more or less in the following order. (There are probably other, newer, cooler, better, more expensive ones now; I limit my attention to these three.)

  1. "lever shifters", with which you shift gears by moving a lever back and forth with your thumb and/or forefinger -- or maybe left and right or up and down, depending on the lever's orientation on the handlebars. Moving the lever one way shifts to a higher gear, moving it the other way shifts to a lower gear.
  2. "click shifters", which which you shift gears by clicking one of two buttons, usually oriented one on top of the other within easy access of the thumb and/or forefinger. Clicking one button shifts to a higher gear, clicking the other shifts to a lower gear.
  3. "grip shifters", with which you shift gears by turning a knob embedded in the handlebar grips themselves, such that you simply have to rotate your wrist one way or the other (toward you or away from you). Rotating your wrist one way ... well, you get the idea.

Here in San Diego I own a bike with click shifters, but while I was in Vancouver last term I bought a used bike with grip shifters. While riding the Vancouver bike I noticed something interesting (and relevant to the shuttle-loop business): with the right-hand shifter, I had to rotate my wrist away from me to shift to a higher gear (which is sort of intuitive -- it feels more or less like "up", and "up" = "higher"), but with the left-hand shifter I had to rotate my wrist toward me to shift to a higher gear (which is sort of counterintuitive, mutatis mutandis).

If you're having trouble picturing this, here's another way to look at it. Suppose I'm on my bike and you're standing beside it, facing it from the right-hand side (like this). To shift to a higher gear, I would rotate my right wrist in such a way that it would turn clockwise from your point of view. If you changed your point of view by standing on the other side of my bike, my left wrist would also turn clockwise when I shift to a higher gear.

But as the person riding the bike, I only have one possible point of view -- and from that point of view, my wrists rotate in opposite directions to achieve what is essentially the same goal. Why did the bike (part) manufacturers do this? My brother, an avid cyclist, suggests that maybe it's because the real goal is not higher vs. lower gear, but smaller vs. larger chain sprocket. (Recall that the effect of shifting to the larger chain sprocket in the front is the same as shifting to the smaller one in the back and vice-versa.) He may be right, but this seems about as un-user-friendly as you can get in terms of design.

Another possibility I'm entertaining (at least until someone else suggests something else, or better yet settles the matter) is that someone at least as convincing as Geoff Pullum was somehow involved in the early design phase of the original grip shifters. This hypothetical person persuaded the engineers that the way to look at the shifters was from each side of the bike, and that the distinction between "clockwise" and "counterclockwise" should be perfectly understandable to anyone. The engineers, not wanting to seem like idiots, agreed.

[ Comments? ]

Posted by Eric Bakovic at March 9, 2005 09:14 PM