Old 01-10-12, 03:01 PM
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Monster Pete
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Bikes: 2000-something 3 speed commuter, 1990-something Raleigh Scorpion

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Originally Posted by Thulsadoom View Post
It seems to me that if you are in a gear in which you're in a 39 front chainring and a 20 rear cog, then it should be essentially the same gear as being in a 42 front chainring and a 23 rear cog, is that not correct?
It's not correct. You divide the chainring by the sprocket to get a gear ratio. For example, a 38t chainring coupled to a 19t sprocket gives you a 2:1 ratio, the same as 42/21. Higher ratios give you more speed, but less torque.

Originally Posted by Thulsadoom View Post
If you look at an old singlespeed bike, or a fixie, the front ring is always significantly larger than the rear cog. When you consider chain wrap and how chains and sprockets/gears wear out when they are put under stresses associated with not having many teeth engaged when under power, doesn't it seem like it would make more sense to have the same sized sprockets on front and back to more evenly space out the load?
This combination gives you a fairly high gear ratio, which is what you want if you only have one gear. This allows you to pedal at speed without having to pedal like crazy. The same sized gears would give you a 1:1 ratio, which might be good for rock-crawling but little else.

Originally Posted by Thulsadoom View Post
Motorcycles are opposite and typically have a smaller front drive sprocket and a larger rear wheel pulley, so I can't figure that out either.
Motorcycle engines are capable of high revs but low torque, the exact opposite of a human cranking pedals. The low gear ratios of a motorcycle convert a high speed, low torque output to a low speed, high torque one.
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