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Step 1When you enter
your bike's data into the calculator, the first things to enter are your
chainring sizes. The chainrings are the 3 large rings in between your
pedals. The 2000 Rocket uses a 62/52/39 tooth combination. This means
that your Large Chainring is a 62, the Middle Chainring is a 52, and the
Small Chainring is a 39. |
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Step 2The next
thing to enter is your cassette. The cassette is the cluster of gears at
the rear of the bike. The calculator automatically calculates every
possible gear between your largest and smallest cog so you only need to
enter your largest and smallest cassette cogs. Our Rocket has a
11-28T cassette. The 28 is the number of teeth on the largest cog, and
11 is the number of teeth on the smallest cog. |
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Step 3
The next item to enter is the diameter of your rear wheel. It's important
to physically measure the diameter of the outside of your tire (the rubber
part - not the metal rim) - just like the diagram shows. For example, the
rear wheel on a Rocket is referred to as a "20 inch" - but the actual
outside diameter (with a stock Primo Comet tire) is approximately 18.5
inches. So you would enter "18.5" into the rear tire diameter. |
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Step 4
The last section is an option for those who use a 3 speed rear hub in
addition to their regular cassette. This option will triple the gear
ranges available for each cassette cog. Since we're using a standard
Rocket, we'll leave
this box unchecked. |
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Click on the "Calculate" button to see your gear ratios. |
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After your ratios are calculated, you will be shown a page that breaks
down your gear ranges by chainring. Print the results for easiest
analysis. In our example with the Rocket, the first chainring table shown
is the 62 Tooth (the biggest one). The first column of the table (Rear
Cog) is showing your cassette starting with the smallest cog and counting
up to the largest in increments of one tooth. Obviously, you don't have
18 cogs in your cassette. For a really detailed analysis, you'll need to
count the number of teeth on each cog in YOUR cassette. For example, a
common Shimano 8 speed cog setup is 11, 12, 14, 16, 18, 21, 24 and 28.
You'd then use the numbers in the table that correspond to each cog in
your cassette. |
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The second column in each table shows you the Gear Inches. "Gear Inches"
is a term that dates back to the old-fashioned high-wheeler bikes - Gear
Inches would be the actual diameter of the big wheel on the high wheeler -
back then, the larger your wheel was, the faster you could go. This number
isn't quite as useful as the rest of the columns. Basically, all you need
to know is that a 120 inch gear is huge, and a 20 inch gear will let you
climb trees.
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The next six columns in each table show you the speed you will be
traveling in a certain cog and chainring combination at a certain cadence.
Your cadence is the rotations per minute (RPM) of your cranks. Here's an
example: In the first table of our example (62 Tooth Chainring), you can
see that when you're in your 11 tooth cog (first row) you're pushing a
104.3 inch gear. This means that when you're turning the pedals at 110
RPMs (Cadence 110 rpm) you'll be traveling at 34.1 miles per hour. When
your legs get really tired and you start slogging through the same gear at
60 RPMs (last column) - you're moving at 18.6 mph. Basically what this
chart is telling you is that your bike can go 34.1 miles per hour in it's
biggest gear when you're pedalling REALLY fast. |
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Now, if you skip down to the last table (39 Tooth Chainring) - you will
see the same cassette range being used to calculate gear inches using the
smallest chainring in the front. If you look at the last row in our
example (28 tooth cog) and move all the way over to the furthest right
column (Cadence 60 rpm) you can see that this table is telling
you that you will be moving forward at a whopping 4.6mph in your EASIEST
gear when you are pedalling slowly. |
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So, at it's most basic level, this chart has told you that your bike has a
104-26 inch gear range. Or that your bike is capable of speeds between
34 and 4 mph (approximately). |
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