Single-Speed Gear Ratio Guide: Choose the Right Chainring and Cog
Start near 2:1 for a 26-inch off-road bike, then adjust for wheel size, hills, cadence, load, and terrain. Lower ratios climb more easily.
Table of Contents
A useful single-speed starting point is 2:1 on a 26-inch off-road bike, such as a 32-tooth chainring with a 16-tooth rear cog. That is not a universal answer. Larger wheels, steeper hills, heavier loads, loose terrain, and a preferred high cadence all call for an easier ratio.
Change one or two teeth at the rear cog before making a large chainring change. A larger rear cog makes pedaling easier; a smaller rear cog makes it harder.
How to calculate a single-speed gear ratio
Divide the number of chainring teeth by the number of rear-cog teeth:
gear ratio = front chainring teeth ÷ rear cog teeth
Examples:
| Chainring | Rear cog | Ratio | Relative feel on the same bike |
|---|---|---|---|
| 32T | 18T | 1.78:1 | Easier |
| 32T | 16T | 2.00:1 | Middle starting point |
| 34T | 16T | 2.13:1 | Harder |
| 42T | 18T | 2.33:1 | Harder still |
Surly’s Single Speed Gearing 101 uses the same calculation and explains that one crank revolution at 2:1 turns the rear wheel twice. It also cautions that the familiar 2:1 starting point came from 26-inch off-road bikes.
What lower and higher ratios do
A lower numerical ratio is easier to turn. It helps with hills, loose surfaces, starts, and technical riding, but the rider spins faster at cruising speed.
A higher numerical ratio travels farther for each crank revolution. It can feel efficient on flat, fast roads, but starting and climbing require more force.
Compare ratios only on the same wheel and tire size. A 2:1 ratio on a 29-inch mountain bike produces more development per pedal revolution than 2:1 on a 26-inch bike.
Practical starting points
These ranges are testing directions, not prescriptions:
| Riding use | Reasonable first test |
|---|---|
| 26-inch trail bike | Around 2:1 |
| 27.5- or 29-inch trail bike | Slightly lower than the equivalent 26-inch setup |
| Flat urban riding | A higher ratio than trail use may suit |
| Hilly commuting or loaded riding | Lower than a flat-road setup |
| BMX or track use | Follow the bicycle’s discipline, fit, and manufacturer guidance |
Do not copy another rider’s ratio without accounting for wheel size, tire size, terrain, fitness, cadence, crank length, and carried load.
Use gear inches when wheel sizes differ
Gear ratio alone compares sprockets. Gear inches adds the approximate wheel diameter:
gear inches = wheel diameter × chainring teeth ÷ rear cog teeth
A 29-inch wheel with 32/16 gearing is about 58 gear inches. A 26-inch wheel with the same sprockets is about 52 gear inches. The larger wheel travels farther per crank revolution and therefore feels harder, all else equal.
Actual tire diameter varies. Treat gear inches as a comparison tool rather than an exact prediction of speed.
How one rear-cog tooth changes the ratio
Rear-cog changes are an efficient way to tune a single speed:
| Setup with 32T chainring | Ratio | Change from 16T cog |
|---|---|---|
| 14T cog | 2.29:1 | Much harder |
| 15T cog | 2.13:1 | Harder |
| 16T cog | 2.00:1 | Baseline |
| 17T cog | 1.88:1 | Easier |
| 18T cog | 1.78:1 | Easier again |
| 20T cog | 1.60:1 | Substantially easier |
Frame adjustment range and chain length may limit a cog change. Horizontal dropouts, sliding dropouts, an eccentric bottom bracket, or an approved chain tensioner all manage chain tension differently.
Our single-speed conversion kit guide explains the larger compatibility questions before you buy cogs and spacers.
How to test a ratio without guessing
Choose a repeatable route that includes the steepest normal climb, a common start, and a flat cruising section.
- Warm up before judging the ratio.
- Ride the climb seated and standing.
- Note whether cadence stalls or wheel traction breaks.
- Check whether flat-road cadence becomes uncomfortably high.
- Change one variable, then repeat the same route.
Do not solve knee pain by forcing a harder gear. Pain, numbness, or loss of control is a reason to stop and address fit, technique, or medical concerns.
Chainline and tension matter as much as ratio
The chainring and rear cog should run in the same plane. A visibly angled chainline increases noise, wear, and derailment risk. Chain tension must be tight enough to retain the chain without binding the drivetrain.
Spin the crank through a full revolution because chain tension can vary with chainring or cog runout. Stop riding if the chain climbs teeth, repeatedly drops, develops tight links, or the rear axle will not remain secure.
The single-speed conversion kit guide compares spacer-and-cog systems with a chain-tensioner option.
Ratio is not a speed guarantee
Speed depends on cadence, wheel rollout, terrain, wind, tire pressure, load, and rider power. A larger ratio does not make a rider faster if it reduces cadence below a sustainable range or makes starts and climbs inefficient.
Use gearing to match the route and rider. Do not select a road ratio only from a desired speed.
Bottom line
Begin with a moderate ratio, account for wheel size, and tune at the rear cog in small steps. Move to a larger cog if climbs or starts are too hard. Move to a smaller cog only when you can comfortably handle the route and are spinning out on the flats. Correct chainline, chain tension, and axle retention are non-negotiable.
Ratio choice cannot compensate for a worn chain. Measure it with the process in our bike chain wear guide before replacing sprockets or changing gearing.
