DXMachina (dxmachina) wrote,

Look, Ma! No Hands!

Hot... Hazy... Humid... I spent most of the weekend inside with the a/c. I did venture out for a couple of rides, though. Yesterday's ride was miserable. I had no energy, and it showed in my time. It was my worst average mph since early June. Dunno why I felt so burnt. I hadn't ridden since Wednesday. Shrug.

Today it was even hotter. I rode the three-speed today. The odd thing was that I felt much stronger. My speed was almost what it was yesterday, despite riding the slower bike.

I used to be able to ride no-handed when I was younger, even to the point of being able to steer the bike just by shifting my weight. I don't remember when I stopped being able to do it, but in the last couple of decades, whenever I tried it I never felt comfortable doing it for more than a few seconds at a time. It was downright scary how unstable the bike felt, if you want to know the truth. Very frustrating, because I remembered it as being easy. I sort of chalked it up to weighing a lot more than I did back in the day, which would move the center of mass of the bike-DX system somewhat higher from the ground, destabilizing the whole thing. Either that, or I had forgotten how to ride a bike. Well, no-handed, anyway.

Then I got the three-speed, the same bike upon which I used to ride sans hands all the time. So one day last year, I was toodling along on it, and I figured, what the hell, let's give it a try for old times sake. And it was fine. I was pedaling along with my arms at my side, and it was perfectly stable. Huh.

I bring it up because this weekend the path was pretty empty, presumably because of the heat, so I was able to ride no-handed for stretches, there being no risk of running into someone. Yesterday I was on the Fuji, and it felt just as unstable as always, so I only tried it a couple of times. But today, on the three-speed, I was doing it for minutes at a time, even uphill. I was even negotiating gentle curves. Double Huh.

So, why is it so much easier to do on the three-speed than on the Fuji (or the Univega, for that matter)? If only there was a scientist around. Oh... Wait...

Bicycles run on angular momentum. They are basically two gyroscopes in tandem, aligned sideways to the ground. The faster the gyros (i.e., the wheels) turn, the greater angular momentum becomes, and the more stable the bike will be. So let's compare the two bikes. The angular momentum (L) of a ring or a disk, which is a good approximation of a bicycle wheel, is calculated by the following:

L = mr²ω

where m is the mass of the wheel, r is the radius of the wheel, and ω is the angular velocity. Increase any of these, and the angular momentum goes up, stabilizing the bike.

The wheels on the three-speed are steel, and heavier than the snazzy, high tech aluminum wheels on the Fuji. The tires and tubes are slightly heavier, too, so the mass of both wheels is higher for the three-speed. On the other hand, the wheels are bigger on the Fuji, 27" vs. 26". The radius of the three-speed is a bit more than a centimeter smaller, not a lot, but remember that the radius is squared in the equation. Advantage Fuji. However, since it has smaller wheels, the three-speed has to run at a higher angular velocity to achieve the same linear speed as the Fuji, i.e., it takes more turns of the wheel to go the same distance, so that eats up some of the Fuji's advantage in radius. So the angular momentum on the three-speed is probably higher, although I can't tell how much without taking the bikes apart to weigh the wheels. Maybe over the winter.

The other thing is that favors the three-speed is that its frame is half again (or more) heavier than the Fuji, which lowers the center of mass a bit. It also has fatter, softer tires, so more of the rubber meets the road, which also helps stabilize things, I suspect. All sorts of variables to test someday. It's like a physics lab on wheels!
Tags: biking, science, weather

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