Cassette ratios explained for better gear choices
A bicycle cassette can look like a simple stack of sprockets, yet its tooth counts have a major effect on climbing, speed, cadence, and shifting feel. The difference between an 11–28T cassette and an 11–34T cassette is not just one extra climbing gear. It changes the range available to your drivetrain and the size of each step between gears.
Understanding cassette ratios becomes much easier when you connect three measurements: sprocket teeth, chainring teeth, and wheel diameter. Together, they tell you how far the bike travels with each crank revolution. This measurement is called gear inches, and it offers a useful way to compare gearing across different bicycles and wheel sizes.
The goal is not automatically to install the widest cassette available. A suitable setup gives you a low enough gear for the steepest terrain you ride while preserving smooth, useful steps between gears. The right choice depends on your fitness, terrain, riding style, derailleur capacity, and preferred cadence.
What cassette ratios mean
The cassette is the group of sprockets mounted on the rear wheel. The smallest sprocket has the highest tooth count ratio relative to the chainring and produces the hardest gear. The largest sprocket produces the easiest gear. A cassette described as 11–32T therefore has an 11-tooth smallest sprocket and a 32-tooth largest sprocket.
The basic gear ratio is calculated by dividing the number of teeth on the front chainring by the number of teeth on the selected rear sprocket. With a 50T chainring and an 11T sprocket, the ratio is 50 ÷ 11, or 4.55. With the same chainring and a 32T sprocket, it is 50 ÷ 32, or 1.56. A lower ratio requires less force at the pedals but reduces speed at the same cadence.
Cassette ratios are therefore relative rather than absolute. A 34T sprocket may feel easy with a 34T chainring, but substantially harder with a 50T chainring. This is why comparing cassette size without considering the crankset can lead to misleading conclusions.
Gear inches in practical terms
Gear inches combine the gear ratio with the effective wheel diameter. The common formula is:
Gear inches = wheel diameter in inches × front chainring teeth ÷ rear sprocket teeth
For example, a bike with a 27-inch wheel, a 34T chainring, and a 34T sprocket has approximately 27 gear inches. At the other end, a 50T chainring paired with an 11T sprocket on the same wheel gives about 123 gear inches.
A higher gear-inch value means the bike travels farther for every complete turn of the cranks. It is useful for fast roads, descents, and strong tailwinds, but it demands more pedal force. A lower value makes steep climbs and loaded riding easier because the rear wheel turns less for each crank revolution.
Gear inches are not a measurement of speed by themselves. Speed also depends on cadence. If you pedal at 90 revolutions per minute in a 50-inch gear, you will travel faster than at 60 rpm in the same gear. Still, gear inches provide a consistent way to compare two gearing options and estimate whether a climbing gear is genuinely easier.
Range and the size of each step
Cassette range is the difference between the smallest and largest sprockets, usually expressed as a percentage. The formula is:
Range percentage = largest sprocket ÷ smallest sprocket × 100
An 11–34T cassette has a range of 309 percent, while an 11–28T cassette has a range of 255 percent. The wider cassette offers a considerably lower climbing gear when paired with the same chainring. A 10–36T cassette reaches 360 percent, giving an even broader spread.
Range does not tell the whole story. Two cassettes can have similar overall range but different sprocket progression. A cassette with tightly spaced middle sprockets may offer smooth cadence changes on rolling roads. Another may use larger jumps near the climbing end to provide a very low gear without adding many sprockets.
Large jumps between sprockets can be noticeable when shifting under load. For example, moving from a 28T to a 34T sprocket changes the ratio more dramatically than moving from a 28T to a 30T. Wide-range mountain bike cassettes accept these larger changes because climbing capability is usually more important than perfectly even cadence steps.
Comparing common cassette choices
The following examples assume a 27-inch wheel and a 50/34T compact crankset. The values are approximate, but they show how the largest sprocket changes the low and high ends of the drivetrain.
| Cassette | Range | Lowest gear with 34T chainring | Highest gear with 50T chainring | Typical emphasis |
|---|---|---|---|---|
| 11–25T | 227% | 36.7 gear inches | 122.7 gear inches | Flat roads and close shifts |
| 11–28T | 255% | 32.8 gear inches | 122.7 gear inches | Fast road riding with moderate climbs |
| 11–32T | 291% | 28.7 gear inches | 122.7 gear inches | Mixed terrain and longer climbs |
| 11–34T | 309% | 27.0 gear inches | 122.7 gear inches | Steep roads and loaded riding |
| 11–36T | 327% | 25.5 gear inches | 122.7 gear inches | Very steep terrain or touring |
The table also illustrates an important point: changing the largest sprocket affects the low end, while leaving the highest gear unchanged. If you want more speed at the top end, you generally need a larger chainring or a smaller smallest sprocket, provided the drivetrain and riding conditions justify it.
A compact crankset with a wide-range cassette can cover demanding terrain without using an extremely large front chainring. A double crankset also gives more overlapping gears, so some combinations may feel nearly identical. That overlap is normal; riders usually shift between chainrings when a larger change in gearing is needed and use the cassette for smaller adjustments.
Matching a cassette to your riding
For flat roads and group rides, a cassette with closely spaced sprockets can help maintain a steady cadence. An 11–25T or 11–28T option may suit riders who spend most of their time on smooth roads and rarely face long, steep climbs. The smaller jumps can make it easier to settle into an efficient rhythm.
For rolling terrain, an 11–30T or 11–32T cassette is often a balanced choice. It provides a useful climbing gear without creating extreme gaps across the middle of the cassette. Riders who regularly encounter short hills may benefit more from consistent progression than from an exceptionally low bailout gear.
Touring, bikepacking, and hilly gravel routes often justify an 11–34T, 11–36T, or larger cassette. Extra low gearing becomes valuable when carrying bags, riding loose surfaces, or managing a long climb late in the day. A lower gear also lets you maintain a comfortable cadence instead of forcing the pedals slowly under excessive pressure.
Your preferred cadence matters as much as terrain. Riders who naturally pedal at a high cadence may appreciate a lower gear for climbs, while powerful riders who prefer slower revolutions may be comfortable with a smaller largest sprocket. Use the gear you can turn smoothly, rather than choosing a cassette based only on the hardest climb you have completed.
Compatibility and shifting performance
A cassette must match the rear derailleur’s maximum sprocket capacity and total chain-wrap capacity. The derailleur specification will usually state the largest supported sprocket, such as 28T, 32T, or 36T. Exceeding that limit can cause poor shifting, insufficient clearance, or damage if the upper pulley contacts the largest sprocket.
Total capacity accounts for both the cassette range and the difference between the chainrings. It can be estimated as:
Total capacity = largest cassette sprocket − smallest cassette sprocket + largest chainring − smallest chainring
For a 50/34T crankset and an 11–34T cassette, the calculation is 23 + 16, giving 39 teeth. The derailleur must be able to absorb that amount of chain slack while still reaching the largest rear sprocket.
Freehub standards and cassette speed also matter. A replacement cassette must fit the wheel’s freehub body and use the same number of speeds as the shifter and derailleur system, unless the manufacturer explicitly supports a different arrangement. Before buying, check the drivetrain specifications and the advice in this guide to drivetrain shifters, since indexing and cable-pull compatibility affect whether the gear changes will work correctly.
A larger cassette may require a longer chain, a derailleur adjustment, or a different rear derailleur. The B-tension screw controls the distance between the upper pulley and the largest sprocket, but it cannot make an incompatible derailleur genuinely compatible. If the chain is too short, shifting into larger sprockets can place dangerous tension on the drivetrain.
Choosing your next cassette
Use these practical checks before changing sprocket sizes:
- Identify the smallest and largest sprockets on your current cassette and write down the front chainring sizes.
- Calculate your current low gear in gear inches, then compare it with the low gear offered by the replacement.
- Check the derailleur’s maximum sprocket and total chain-wrap capacity before ordering.
- Decide whether you need a lower climbing gear, closer cadence steps, or a higher top gear.
- Inspect chain wear and cassette condition together, since a worn chain can quickly damage new sprockets.
A useful test is to note which gears you actually use on familiar routes. If you regularly run out of low gears and grind up climbs, a larger cassette or smaller chainring is likely worthwhile. If you rarely use the largest sprocket and dislike cadence gaps, a closer-ratio cassette may be a better match.
Changing the cassette is only part of the adjustment. After installation, check chain length, derailleur alignment, indexing, and upper-pulley clearance. Shift through every sprocket under light pedal pressure, then test the bike on a quiet road before relying on the new setup for a long ride.
Once the numbers make sense, cassette selection becomes a straightforward fit between rider and terrain. Compare your current gear inches with the options available, confirm compatibility, and choose the range that lets you pedal smoothly across the routes you actually ride. Then install and tune the cassette carefully so your drivetrain can deliver that range cleanly.