MTB gear range is easy to misread. Two mountain bikes can both have 12 gears and still feel very different on a steep climb. The number of sprockets tells you how many ratios you can select. It does not tell you how low the easiest gear is, how fast the hardest gear goes, or how big the jumps between gears will feel.
That matters on an eMTB too. Assistance helps you turn the cranks, but choosing a suitable gear still makes it easier to keep pedalling smoothly when a climb gets steep or technical. Here is how to read the numbers on a specification sheet before spending money on a different cassette or chainring.
What does 500% gear range actually mean?
On a bike with one front chainring, cassette range is the largest sprocket divided by the smallest, multiplied by 100. A 10–50-tooth cassette therefore has a 500% range: 50 ÷ 10 × 100. The hardest ratio is five times the easiest ratio.
For real examples, SRAM’s XG-1275 Eagle 10–52 cassette has a 520% range. Shimano’s XT CS-M8200 10–51 cassette has a 510% range. Neither percentage tells you the size of the front chainring, so neither describes the complete bike’s lowest gear on its own.
The easiest gear depends on both ends of the chain
Divide the chainring tooth count by the rear sprocket tooth count to calculate a gear ratio. A smaller number means an easier gear, assuming the same rear wheel and tyre. With a 32-tooth chainring and a 50-tooth sprocket, the ratio is 0.64. That means the rear wheel turns 0.64 times for each complete turn of the cranks.
Swap to a 34-tooth chainring while keeping the same cassette and the lowest ratio becomes 0.68. The cassette still has exactly the same range, but every gear is 6.25% higher. At a given cadence the bike travels 6.25% farther per crank revolution, and you need more crank torque to produce the same driving force at the tyre.
This is why a bike with a headline-grabbing wide-range cassette can still have a harder climbing gear than another bike with a narrower range. Compare the chainring and largest sprocket together.
A smaller chainring moves the whole range down
Going from a 34-tooth to a 32-tooth chainring lowers every ratio by about 5.9%. It makes climbing gears easier, but also lowers the speed you can reach at a given cadence in the hardest gear. It does not change the cassette’s percentage range or add more gears.
Moving from a 50-tooth to a 52-tooth largest sprocket, with the same chainring, lowers the easiest ratio by about 3.8%. That can be useful, but it is a smaller change than those two extra teeth might suggest. A different smallest sprocket can also widen the advertised range without making the easiest gear any lower.
More speeds can mean smaller jumps, not a lower bottom gear
Adding another sprocket can help spread the available ratios more closely. It does not automatically extend the range. When two cassettes share the same smallest and largest sprockets, they offer the same overall range regardless of how many sprockets sit between them.
Look at the sequence as well as the endpoints. SRAM’s 10–52 XG-1275 cassette ends with 36-, 42- and 52-tooth sprockets. The change from 42 to 52 is noticeably larger than a closely spaced road-style shift. A wide spread is useful on varied terrain, but a bigger step can make it harder to find your preferred cadence on a steady climb.
Wheel size changes the result at the ground
The same gear ratio rolls farther per crank revolution on a larger rear wheel. Tyre size changes the actual rolling circumference too. This is worth remembering when comparing a full 29er with a mixed-wheel bike: matching chainring and cassette numbers do not necessarily mean identical climbing gearing.
For a straightforward comparison between your own bikes, use the actual rear wheel and tyre circumference multiplied by the gear ratio. The result is distance travelled per crank revolution. Less distance means a lower gear.
What should eMTB riders change first?
Start by identifying the problem. If you repeatedly run out of lower gears on steep climbs, a lower bottom ratio may help. If you keep switching between two gears because neither cadence feels right, closer spacing may be more useful. If the chain skips or shifts poorly, changing the range will not repair the underlying fault.
Check the bike and drivetrain manufacturers’ compatibility information before buying parts. A larger cassette may exceed the rear derailleur’s supported sprocket size. A chainring change can affect chain length, chainline and frame or motor clearance. Our MTB freehub compatibility guide explains why the cassette must also fit the rear hub, while our chain compatibility guide covers the different drivetrain families.
For your next bike, compare three things before counting speeds: the lowest ratio, the highest ratio and the gaps between them. Those numbers tell you far more about how the gearing will suit your riding than “12-speed” on its own.
MTB gear range: common questions
Does a 520% cassette always climb better than a 500% cassette? No. Compare the largest sprocket and front chainring together, then account for rear wheel size. The range percentage alone does not tell you the lowest ratio.
Will a smaller chainring give me more range? It lowers all the gears, including the hardest one, but leaves the percentage range unchanged. Check the permitted chainring sizes and drivetrain compatibility for your bike before changing it.