Percentage numbers are the new gear inches - but are they misleading?

Some manufacturers are starting to quote percentage numbers when talking about wide-range cassettes: for example SRAM’s new Eagle 12-speed cassette has a gear range of 500% and the E13 TRS+ 11-speed cassette has a range of 489%.

What do these numbers mean and why are they important?

The percentage figures refer to the gear range of the cassette, or the difference between the highest and lowest available gears.

To work out the range of a cassette, you simply divide the largest sprocket by the smallest and then multiply this by one hundred (50 ÷ 10 = 5 x 100 = 500%). Since the two cassettes mentioned are dedicated 1x, the figure also represents the drivetrain as a whole.

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SRAM’s new 12-speed Eagle cassette offers a huge 500% range

SRAM’s new 12-speed Eagle cassette offers a huge 500% range

What about double-ring drivetrains?

You can also calculate gear range for a 2x drivetrain, but you do this by dividing the biggest chainring by the smallest and multiplying that by the cassette calculation.

For example, an 11-36t cassette combined with a 36/24t chainset has a gear range of 491% (36 ÷ 24) 1.5 x (36 ÷ 11) 3.27 x 100 = 491%.

Why should I bother?

Joel Peters at E13 says: “it’s just a simple figure that’s easy to get your head around and gives you an idea whether or not 1x is the right choice for you. If you’re struggling in the granny gear in this scenario, then 1x likely won’t be the right choice. If you don’t often drop to the granny, 1x could be the perfect solution.”

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Our handy Range Explainer

The smallest sprocket is your starting point for working out your gear range, at 100% (basically maths speak for one). The biggest sprocket on SRAM’s Eagle cassette is exactly five times the size of that smallest one, giving it a 500% range.

Screen Shot 2016-08-04 at 09.55.41

Anything else I should know?

Range doesn’t tell the whole story. To give a clearer understanding of gearing, and whether you have the correct gears for the terrain you’re riding on, we need to talk about gear inches of development. This is the distance one revolution of the crank propels the wheel, measured on a straight line along the ground.

The problem is, gear development is dependent on the tooth count of each cassette sprocket, the chainring size and overall circumference of the tyre. These are things you can change, but the cassette ratios are fixed, which is why companies like E13 and SRAM are keeping it simple and quoting gear range instead.