Bike Gear Ratio / Gain Ratio

How Gear Ratio, Gain Ratio, and Development Are Calculated

Gain ratio is a bicycle drivetrain figure that accounts for wheel size and crank length, making it directly comparable across completely different bikes. Enter your chainring, cog, wheel diameter, and crank length to find it, alongside the simpler gear ratio and the more intuitive development figure.

Key Factors to Consider

• A higher gain ratio means a “taller” gear — more distance per pedal stroke, but more effort per stroke too. A lower gain ratio is easier to pedal (useful for climbing) but covers less ground per revolution; a higher gain ratio covers more ground but requires more force to turn over, especially from a stop or on a climb.
• Multi-speed drivetrains have a range of gain ratios, not just one. A bike with multiple chainrings and cogs has a different gain ratio for every combination — calculate the lowest (easiest, for climbing) and highest (hardest, for descending or sprinting) combinations to understand your bike’s full usable range.
• Crank length affects gain ratio just as much as wheel size or gearing. A longer crank gives more mechanical leverage for the same gearing, which is exactly why gain ratio (unlike plain gear ratio) includes crank length in its calculation — two bikes with identical gearing but different crank lengths will have different gain ratios.
• Development is a more intuitive figure for comparing to real-world speed. Since development is expressed directly as a distance (how far the bike travels per pedal revolution), it’s often easier to reason about in practical terms than an abstract gain-ratio number, especially when planning gearing for a specific route or terrain.

Interpreting Your Results

Gain ratio numbers are only meaningful relative to a rough band of what feels easy, moderate, or hard to pedal:

• Below about 3 — a very easy, “spinning” gear built for steep climbs or a heavily loaded touring bike, where turning the pedals takes little force but each pedal stroke only advances the bike a short distance.
• Roughly 4 to 6 — the range most everyday road, hybrid, and gravel gearing sits in for cruising on flat-to-rolling terrain — enough distance per stroke to hold a reasonable pace without excessive effort.
• Above about 7 — a “tall” gear for flat, fast riding or sprinting, where each pedal stroke covers a lot of ground but takes real force to turn over, especially from a stop.

These bands are a rough guide, not hard cutoffs — rider strength, cadence preference, and terrain all shift where a given number actually feels comfortable.

Common Mistakes

• Comparing plain gear ratios across different bikes. A given gear ratio (chainring teeth divided by cog teeth) feels completely different on a bike with large road wheels than on a small-wheeled folding bike, because gear ratio alone ignores wheel size and crank length — always compare gain ratio or development, not plain gear ratio, when the bikes themselves are different.
• Assuming a tire size label gives the exact rolling diameter. Tire width and tread height change a wheel’s real rolling diameter even when the rim size stays the same — a wider, higher-volume tire rolls out farther per revolution than a narrow one on the same rim, so measuring the actual outer diameter (see the FAQ below) gives a more accurate gain ratio than assuming a chart value.
• Forgetting that crank length shifts the number too. Swapping to a longer or shorter crank changes gain ratio even if the chainring and cog stay exactly the same — a factor riders sometimes overlook when comparing “the same gearing” across two different bike setups.

The Formula

$$\text{Gain Ratio} = \frac{\text{Chainring}}{\text{Cog}} \times \frac{\text{Wheel Radius}}{\text{Crank Length}}$$

Worked Example

1. $50 \div 14 \times (350 \div 172.5) = 7.25$

Useful to Know

Sheldon Brown’s own reference examples show why gain ratio — not gear ratio — is the number worth comparing: a road bike’s 53-tooth chainring over a 19-tooth cog (with 170mm cranks and a 680mm wheel diameter) works out to a gain ratio of about 5.58, while a mountain bike’s 46-tooth chainring over a 16-tooth cog (with a 26-inch wheel and shorter cranks) comes out to about 5.54 — nearly identical, despite completely different gearing numbers, wheel sizes, and crank lengths. That’s the entire point of gain ratio: two bikes that “feel” the same to pedal can have wildly different chainring/cog numbers once wheel size and crank length are taken into account.