Friday, August 5, 2011

Bike gear ratios

I'd been idly wondering for awhile now about two things:

1) How far my bike commute to and from work really is.
2) How the different gear combinations on my bike compare to each other.

So a week or so ago I worked it out:

Number of teeth on each of my front three gears: 22, 32, 42
Number of teeth on my back 8 gears: 11, 13, 15, 18, 21, 24, 28, 32
Gear ratios, in descending order:
3/8 3.8181818182
3/7 3.2307692308
2/8 2.9090909091
3/6 2.8
2/7 2.4615384615
3/5 2.3333333333
2/6 2.1333333333
3/4 2
1/8 2
2/5 1.7777777778
3/3 1.75
1/7 1.6923076923
2/4 1.5238095238
3/2 1.5
1/6 1.4666666667
2/3 1.3333333333
3/1 1.3125
1/5 1.2222222222
2/2 1.1428571429
1/4 1.0476190476
2/1 1
1/3 0.9166666667
1/2 0.7857142857
1/1 0.6875

So for all intents and purposes, shifting the front gear changes the effective ratio by about 2 "notches": 1 and 8 is about the same as 2 and 6 is about the same as 3 and 4.

Having worked that out, I measured the outer diameter of my bike tire - 82.5 inches - and worked out that if I leave it in 3/6 (which is around where I generally ride) and never backpedal, it takes about 69 turns of the crank to go a quarter mile:

5280 ft/mile * 12 in/ft / 82.5 inches/wheel = 768.0 wheels/mile
768.0 wheels/mile / 2.8 wheels/pedal = 274.3 pedals/mile
274.3 / 4 = 68.6 pedals in a quarter mile.

Then I rode home by my usual route, without changing gears and without backpedalling (which is surprisingly hard) and it comes out very close to three and a quarter miles. Which is pretty darn close to what Google Maps comes up with, even though it doesn't let me trace my actual route, which winds in and out of some back alleys and such.

I can't really imagine why I'd want to know this again later, but I haven't really got anywhere else to put it at the moment...

Friday, January 7, 2011

Of Balloons and Bridges

The religious zealot who denies science - and yes, I'm looking at you, Creationists - sees science as just another belief system. Since their religion is based on belief, not fact, questioning any part of it is to question the whole. To disprove any part of it would be to bring the entire edifice of faith tumbling down. Its not supported from the outside, like a bridge; it supports itself, like a balloon. Even a small hole is bad for a balloon.

These people expect science to behave the same way. So when they find a gap which the current scientific theory fails to explain, or prove one of its predictions wrong, or read about some scientist caught fudging their data, they clap their hands and say "Ha! Told you so!" as if the entire discussion were now over, and they'd been proven right. Scientists and skeptics then go into conniptions about the religious folk being disingenuous because proving one thing wrong doesn't necessarily prove anything else in particular to be right, but I think many of the zealots are genuinely confused by such arguments. Obviously, they've already proved your belief system to be false; why is the discussion still going on? They've poked a hole in your balloon - have the decency to fall. Meanwhile the true scientist looks at the gap, or the error, or the fraud, and simply nods and says "Yep; thats how science works." And then gets to work making the next revision better.

Noone really seriously bothers to expose gaps, or contradictions, or frauds in religion, except possibly as a form of entertainment. There wouldn't be anything left.