Sunday, May 7th, 2006
9:37 am - On Your Marks...  
Yesterday was another lovely day, sunny and mild, except for the bit right in the middle of the afternoon when the sky turned to deep, dark gray. Of course, that is exactly the time I chose to go for a ride. It was such a great day, it never occurred to me that it might cloud up. Actually, it was the clouds that convinced me to head down to the path a little earlier than I normally might. First, though, I wanted to try and figure out what was going on with the bike computer for the Univega.

A bike computer is just a speedometer with delusions of grandeur. Besides telling you how fast you're going, it also times you, and keeps track of stuff like total mileage, maximum speed, and what time it is. The one I have is a Vetta C-10 that I bought in 1993. The much newer, snazzier Bell computer I have for the widow-maker will also calculate your average speed for you. The way they work is you attach a small magnet to the spokes of your front wheel, and then attach a sensor to the fork opposite the magnet. As the wheel turns, the magnet will pass the sensor on each rotation, inducing a teeny electric current in the sensor, which then travels up a wire to an interface shoe clamped to the handlebar. The computer slides into the interface until a pair of contacts on the back touch their respective contacts on the interface. When you first set it up, you enter the circumference of the wheel (in mm) in the computer, and then everytime the wheel rotates, the computer can calculate how far you've gone. The problem I was having was that the timer functions were working fine, but it wasn't reading anything from the sensor unit. Sometimes the magnet and sensor can get a little out of alignment, but that hadn't happened here.

My last thought on this was that the wire from the sensor up to the interface must have been nicked or cut somehow. The wire is really thin, and is usually way longer than necessary, which means it winds up being wrapped around and around various tubes and bars along the way so as to use up the excess slack. This affords plenty of opportunity for accidental snags or pinches. Unfortunately, the Vetta is thirteen years old, and they don't make spare parts for it anymore.

Now, I do have a spare sensor unit for the Bell computer, obtained when I bought a replacement Bell for the widow-maker. When I had my accident, the casing of the original Bell was crushed. Remarkably, it still works, despite a good chunk of the casing being missing. The sensor escaped damage, so I don't need the sensor assembly that came with the new unit. The interface shoe on the sensor unit for the Bell is very similar to that of the Vetta, and the Vetta fits into it. (It's not an exact fit. You can't do it the other way round. The Bell doesn't fit into the Vetta interface. The Bell's rails are too thick.) Maybe I could use the Vetta with the Bell sensor.

I wanted to see if that would actually work before I actually removed the old sensor, so I hauled the widow-maker up out of the basement, slid the Vetta into the interface shoe, and spun the wheel. Nothing. I took a closer look at the interface. The contacts on the Vetta and the interface were lined up properly, but they weren't actually in contact. It was that rail thickness thing I mentioned. Although the Vetta fits in the shoe, the rails are two thin to push it down to make contact. Sigh.

So, if the sensor is frelled, I'm frelled until I find some sort of viable replacement (either a replacement sensor, or a new computer). But I still didn't know for sure if that was really the problem. Is there anything that could be wrong with the computer itself? There's only one replaceable part in the computer itself, the battery. Just for grins, I swapped batteries between the Bell and the Vetta. I didn't really expect anything, because the Vetta was still keeping good time, but to my surprise, the Vetta started working again. Huh. I guess measuring the sensor input takes more juice than the timer functions do, and a battery that's only mostly daed can't provide it. At least the sensor assembly is okay.

(All this is reminded me of the speedometers some of my friends had on their bikes when I was a kid. They were nothing more than a cheap red plastic box with a little blade inside that moved from one side of an open window to the other as the wind from the bike's motion passed through the box. There were numbers under the window to show you how fast you were going. It was that it was "calibrated" up to 60 mph, which was very cool to a ten year-old boy, even if it's pretty clear that, in retrospect, our legs were being pulled.)

Anyway, as long as I had both bikes out, I decided to ride the widow-maker for the first time in almost two years. The clouds were getting ominous, but it wasn't very windy, and a quick check of weather.com gave me only a 20% chance of precipitation, so I decided to chance it. The widow-maker rides exactly as I remembered it. If it were adjusted to fit me properly, it would be a joy to ride. As it is, the seat post is about an inch too short, so I can't really really extend my legs fully on the down stroke. I could almost live with that. The real problem is that the handlebar stem is about four inches too short, which means I have to ride in a position that feels like at the starting block at a swim meet. This causes my lower back to hurt, and the extra craning I have to do to see what's in front of me makes my neck hurt. I also wind up having to put way more weight on my hands and wrists than is comfortable. Now, on the Univega, both the seat post and the handlebar stem are adjustable (as they are on most older bikes. On the widow-maker, only the seat post is adjustable, and it's already even a little past the line that says "don't raise this thing any higher." Nowadays, the only bikes with adjustable stems are cruisers and "comfort" bikes, it seems. So, Monday it's off to Caster's with it to see if I can't get a longer stem and post. While I'm there, I also need to get a mirror for it, and perhaps see if they have a saddle worth trying. (Although I think that unlikely. I have a whole rant about saddles coming.)

The moral of the story is that I probably would have avoided all this if I'd actually taken the bike on a test ride, rather than buying it on impulse on a day when it was pouring rain out.

While I was riding, I ran into Michelle, Shane, and Alka coming the other way, and we chatted for a bit. Hadn't seen any of them in a couple of months, so that was good. After that, I went up the path a little further, but then it started sprinkling, so I figured I'd better get back before the really heavy stuff started coming down. It was still a decent ride, 7 miles or so. (The rain never really came, and a hour later the sun was shining again. Bozhe moi.
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