This tool works best on a wider screen — the comparison tables need horizontal space to be useful.
70 rpm
175 W
235 lbs
Units
Current drivetrain
Numbers must be in ascending order
Proposed drivetrain
Numbers must be in ascending order
What you gain
What you lose
The verdict
| Gear | Sprocket | Speed | Max Grade | Jump % | ||||
|---|---|---|---|---|---|---|---|---|
| Current | Proposed | Current | Proposed | Current | Proposed | Current | Proposed | |
Speed across all gears — current vs proposed
Current drivetrain
| Gear | Ratio | Gear Inches | Dev (m) | Gain Ratio |
|---|
Proposed drivetrain
| Gear | Ratio | Gear Inches | Dev (m) | Gain Ratio |
|---|
About the numbers. Speed uses nominal wheel diameter at your set cadence. Max grade is calculated from your power output and system weight — a realistic sustained effort, not a theoretical maximum. Gear inches = wheel diameter × ratio. Development = wheel circumference × ratio. Gain ratio = (wheel radius ÷ crank length) × ratio. Jump percentages are tooth-count steps between adjacent sprockets: green ≤18% smooth, amber ≤28% noticeable, red >28% large. Grade is shown to one decimal place. Grades above 30% are shown as >30% — steeper than any paved road.
Why this exists
I was spending weeks researching a drivetrain upgrade and I couldn't find a single tool that answered the actual question: what exactly do I gain, and what do I lose? Every calculator showed me the numbers for one setup. None of them compared two.
Making it worse — when I asked mechanics to explain the difference, the answers were technically correct but impossible to understand if you're not already fluent in drivetrain specs. There was a gap between the knowledge and the communication of it.
BikeGearCalc.com is that gap closed. Enter what you have and what you're considering, and see everything laid out side by side in plain terms.
Understanding the numbers
The five terms that matter most.
Gear Inches
Picture a giant old-fashioned penny-farthing with one huge wheel. Gear inches tells you how big that wheel would need to be to match your gearing. The standard US way to compare setups across different bikes. Bigger number = harder gear.
Development (meters)
How far your bike travels with each complete pedal stroke. If your development is 6.5m, one full crank revolution moves you 6.5 meters forward. More useful than gear inches for comparing bikes with different wheel sizes.
Gain Ratio
The fairest way to compare gearing across different bikes. Unlike gear inches, gain ratio also accounts for crank arm length — so bikes with different wheel sizes and cranks can be directly compared. A gain ratio of 5.0 means for every inch your foot moves, your bike moves 5 inches forward.
Max Grade
The steepest hill you could realistically sustain in that gear, based on your power output and weight. A 10% grade means the road rises 10 feet for every 100 feet forward. Casual riders: 100–150W. Regular riders: 150–220W. Fit enthusiasts: 220–300W.
Jump %
How big a step each shift is between adjacent gears. Under 18% is smooth. Around 28% is noticeable. Above 30% is a large step most riders feel clearly. Wide-range cassettes tend to have bigger jumps in the middle — that's the tradeoff for a big bailout gear at the bottom.