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Old 08-21-12, 04:21 PM   #1
lungimsam
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How do I figure gearing comparisons between a compact and a triple?

I have a new bike with a compact crankset, and I was wondering which gear combos are the equivalents to what I was doing on the triple.

Is there a chart or something for this somewhere online?
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Old 08-21-12, 05:22 PM   #2
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Try this...http://www.usacycling.org/forms/mechanics/GearChart.pdf
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Old 08-21-12, 05:29 PM   #3
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To compare one chainring at a time, try Mike Sherman's Gear Calculator. All the charts and graphs update on the fly as you make changes, so it's easy to make comparisons.

Scroll down to see the Speed over RPM Range chart, with each chainring in a different color. And farther down, see the Speed at X RPM table.

For instance, you can compare a 30 chainring from a triple to a 34 compact chainring: Here's a 12-27 cog set, with 30, 34, and 50 chainrings: Link to that setup
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Old 08-21-12, 05:32 PM   #4
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Or just calculate the ratio between the front and rear gears. For example 53/19 = 2.79. This is approximately equivalent to 50/18 = 2.78.
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Old 08-21-12, 06:07 PM   #5
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Chainring teeth divided by rear cog teeth times wheel diameter in inches.

Using a pocket calculator I can calculate an entire drivetrain about as quickly as I can look them up on a table and I can usually find a calculator faster than I can look up a table.

It's kind of an interesting process. Whenever I've checked out a number of alternative drive trains that I was considering, one has always jumped out as right for me.

One thing that I think gets frequently overlooked is the flat road gear. It's nice to have your favorite flat road gear fall in the middle of the cassette. That way you have a couple of trim gears in each direction without having to shift front chainrings.
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Old 08-21-12, 06:22 PM   #6
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I personally like this one for it's easy to use/understand interface:

http://www.gear-calculator.com/#
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Old 08-21-12, 10:39 PM   #7
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I like the Sheldon Brown gear calculator http://www.sheldonbrown.com/gears/index.html

As a real rough rule of thumb: if you have the same cassette in back, you will have more than one, probably closer to two less low gears if that makes sense.
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Old 08-21-12, 11:12 PM   #8
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Quote:
Originally Posted by mkeller234 View Post
I personally like this one for it's easy to use/understand interface:

http://www.gear-calculator.com/#
That's the one. You can set it up to compare drives.
Like so:
http://www.gear-calculator.com/#KB=2...5&UF=2205&SL=2
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Old 08-22-12, 08:26 AM   #9
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Originally Posted by Retro Grouch View Post
One thing that I think gets frequently overlooked is the flat road gear. It's nice to have your favorite flat road gear fall in the middle of the cassette. That way you have a couple of trim gears in each direction without having to shift front chainrings.
+1. On paper (or the Internet tool of your choice), the range offered by different schemes might look great, but the cross-chaining and front-shifting needed to work around your cruising gear might be really heinous in practice. (I'm thinking of the compact double here. )
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Old 08-24-12, 10:05 PM   #10
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So, a gear ratio of 1.5 would be harder to pedal than a combo that is 1.25?
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Old 08-26-12, 11:47 AM   #11
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So, a gear ratio of 1.5 would be harder to pedal than a combo that is 1.25?
Yes. "Harder" but the wheel moves more for each crank revolution.
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Old 08-26-12, 02:34 PM   #12
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Originally Posted by Camilo View Post
I like the Sheldon Brown gear calculator http://www.sheldonbrown.com/gears/index.html

As a real rough rule of thumb: if you have the same cassette in back, you will have more than one, probably closer to two less low gears if that makes sense.
I like Sheldon's 'gain ratio' concept too which you can select on his calculator http://sheldonbrown.com/gain.html
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