Road Cycling - How do the cassette ratios work?

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View Full Version : How do the cassette ratios work?

Bioluminescence
05-07-11, 08:00 AM
I'm a bit confused when people end up posting numbers with hyphens.

11-28, 12-27, etc.

Is there a simple way to tell all these things apart?

Also, do some ratios deliver more torque or speed than others?

StanSeven
05-07-11, 08:13 AM
Take a look at this chart/tool. You can also change it to your exact gears.

http://www.bikecalc.com/gear_inches

What it shows is how far the bike moves each time the the crank turns. So a lower number means less distance but not as much effort going in. A higher number means you go further (faster) but you put out more work.

So what this means is an 11 cassette as opposed to a 27 means you go fast and it's hard work - an all out speed effort on the flats or downhill; a 27 means you go slow and easy - what you need for climbing a steep hill.

dstrong
05-07-11, 08:45 AM
These are references to the cassette a person is using on the rear wheel.

http://farm4.static.flickr.com/3364/3652908968_63ccd6a199.jpg

The first number refers to the number of teeth on the smallest cog, the second number is the number of teeth on the largest cog. So the two numbers together represent the high-to-low range of the entire cogset. There are other cogs in between, typically spaced 1-2 teeth apart from the one on either side of it.

You'll also see people reference a gear combination like 53/11 or 34/28. These represent a selection from the chainring (the front two or three chainwheels) and one of the cogs in the back. So...53/11 means you've got the chain on the large chainring on the front and the smallest cog on the rear...the 34/28 means you've got your chain on the small chainring up front and the largest cog on the rear.

Playing with the gear ratio tables is interesting but I tend to think of the combinations in terms of how fast I'd be traveling if I pedal 80 rpm. Below are two tables...down the left are the cogs in my 12-27 9-speed cassette...on the top are my two different chanrings...my standard double (53/39) and my compact double (50/34). Each cell represents the approximate speed I would expect to travel in that combination on flat terrain if I were turning the pedals at 80 rpm.

200873

mvnsnd
05-07-11, 08:47 AM
The numbers referenced are the low-high number of teeth on the cogs of the cassette. 11-28 means that the smallest cog has 11 teeth and the largest has 28.
See here for standard configurations: http://www.sheldonbrown.com/k10.shtml

rufvelo
05-07-11, 10:33 AM
...http://farm4.static.flickr.com/3364/3652908968_63ccd6a199.jpg..

Pics of clean cassettes on bikes are the best!

urbanknight
05-07-11, 12:19 PM
In general, a hyphen designates the range of the cassette, so a 12-27 would have a 12 as the smallest and a 27 as the largest, without specifying the cogs in the middle. A slash should be used to designate a specific gear ratio (i.e. 53/12 meaning the 53 up front and 12 in the back).

big chainring
05-07-11, 12:28 PM
Take a look at this chart/tool. You can also change it to your exact gears.

http://www.bikecalc.com/gear_inches

What it shows is how far the bike moves each time the the crank turns. So a lower number means less distance but not as much effort going in. A higher number means you go further (faster) but you put out more work.

So what this means is an 11 cassette as opposed to a 27 means you go fast and it's hard work - an all out speed effort on the flats or downhill; a 27 means you go slow and easy - what you need for climbing a steep hill.

Gear inches refers to the size wheel equivalent. For instance a 70 inch gear would be equivalent to a 70 inch wheel diameter on a high wheel bike, when your cranks were attached to the hub of the wheel and you were turning the wheel directly.

rm -rf
05-07-11, 01:25 PM
Most rear cogs have their number of teeth stamped on them, or you can just count them.

As you are riding, just click up to an easier rear cog if you are pushing hard, or down to a faster cog if you are spinning the cranks too fast. You don't need to know pedal rpms or which combination of gears to use at each speed.