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Old 09-08-11, 11:31 PM   #1
SlimRider
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Gears, Sprockets, Casettes, Freewheels, and Stuff...

Hey guys!

For those of you with a little time on your hands...Could you please explain the difference between gears, sprockets, cassettes, and freewheels to me.

I'm pretty good when it comes to changing derailleurs, brakes, handlebars, stems, wheels, tires, etc.

Known:
I can even replace a cassette. I know that your gears or sprockets are lined up and attached together to form a cassette. I know that each gear or sprocket will change your mechanical advantage, in making the wheel turn as you pedal.

I think that's right so far...Right?

Now, what I really, really, really, don't know is...

How do you know which gears to change in order to match up with other gears?

What do the gear ratios have to do with matching front gears with rear gears?

Can you change the sprocket sizes on a cassette in order to change the mechanical advantage?

Weew!

Thanks in advance guys...

- Slim

Last edited by SlimRider; 09-09-11 at 09:15 AM.
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Old 09-08-11, 11:33 PM   #2
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http://www.sheldonbrown.com/

Read the whole site. It will answer all your questions, I promise.
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Old 09-09-11, 07:44 AM   #3
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The most common way Americans express bicycle gear ratios is "gear-inches" which goes back to the old high-wheel bikes of the 1800's. A gear-inch value gives the same distance per crank rotation as a wheel of that diameter would. For example, a 54 gear-inch ratio gives the same travel distance per revolution as a wheel 54" in diameter.

Gear inches are calculated by multiplying the number of teeth of the chainring by the wheel diameter and dividing that value by the number of teeth in the rear cog. For simplicity both 27' and 700c wheels are assumed to be 27" in diameter and MTB wheels are 26". So if you are in a 42T chainring and a 17T cog on a 700c wheel roadbike your gear inches would be 27*42/17 = 66.7

Smaller gear-inch values are easier to pedal but you go slower at the same cadence. Larger gear-inch numbers are harder to pedal but you go faster. So you climb in small gears and use larger ones on the flats or downhills.

You can do the calculation for all of your chainring and cog combination and build up a table to see how they compare and where the overlap and duplicates are and to see the effect of changing to other size rings and cogs. The Sheldon Brown web site referred to above has a gear-inch calculator that makes this easy.
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Old 09-09-11, 09:19 AM   #4
SlimRider
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Originally Posted by HillRider View Post
The most common way Americans express bicycle gear ratios is "gear-inches" which goes back to the old high-wheel bikes of the 1800's. A gear-inch value gives the same distance per crank rotation as a wheel of that diameter would. For example, a 54 gear-inch ratio gives the same travel distance per revolution as a wheel 54" in diameter.

Gear inches are calculated by multiplying the number of teeth of the chainring by the wheel diameter and dividing that value by the number of teeth in the rear cog. For simplicity both 27' and 700c wheels are assumed to be 27" in diameter and MTB wheels are 26". So if you are in a 42T chainring and a 17T cog on a 700c wheel roadbike your gear inches would be 27*42/17 = 66.7

Smaller gear-inch values are easier to pedal but you go slower at the same cadence. Larger gear-inch numbers are harder to pedal but you go faster. So you climb in small gears and use larger ones on the flats or downhills.

You can do the calculation for all of your chainring and cog combination and build up a table to see how they compare and where the overlap and duplicates are and to see the effect of changing to other size rings and cogs. The Sheldon Brown web site referred to above has a gear-inch calculator that makes this easy.
Now this, was exactly what I needed!

Thank you so much, Hillrider

- Slim
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Old 09-09-11, 09:20 AM   #5
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Originally Posted by FastJake View Post
http://www.sheldonbrown.com/

Read the whole site. It will answer all your questions, I promise.
Thanks for the Link, FastJake!
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