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Bike Gears Explained: Ratios, Gear Inches, and How to Shift Smarter
Gears exist to solve one problem: your legs produce power efficiently only in a narrow cadence band (roughly 70–95 rpm for most riders), while the bike needs to travel anywhere from 4 mph up a wall to 40 mph down one. Gearing is the transmission that keeps your legs in their happy band across that entire range.
The ratio
Divide chainring teeth by cassette-cog teeth. A 50-tooth chainring with a 25-tooth cog is a 2.0 ratio: each pedal revolution turns the rear wheel twice. Bigger ratio = faster and harder; smaller = slower and easier. A typical modern road "compact" setup (50/34 chainrings, 11–34 cassette) spans from 1.0 (34/34 — a genuine climbing gear that lets you spin up 10% grades) to 4.5 (50/11 — for descents and sprints).
Gear inches: comparing across bikes
Ratio alone ignores wheel size, so the classic comparison unit is gear inches: ratio × wheel diameter (~27 in for road wheels). Rough guide: under 30 gear inches is steep-climbing territory, 40–70 covers everyday riding, 100+ is high-speed. At 90 rpm, a 70-inch gear moves you at about 18.7 mph — speed = gear inches × cadence × 0.00297.
Practical shifting rules
- Shift before you need to. Drivetrains shift badly under full load; ease the pedal pressure for one stroke as you shift, and downshift before the hill bites.
- Avoid cross-chaining. Big ring + biggest cog (or small ring + smallest cog) runs the chain at a harsh angle: noise, wear, and wasted watts. Use the front derailleur to stay in the middle of the cassette.
- Front for terrain, rear for fine-tuning. The chainring is your range selector (flat vs. climbing); the cassette trims cadence within that range.
- 1x drivetrains (one chainring, wide 10–50-ish cassette) trade some range and larger jumps between gears for simplicity and reliability — the reason they own mountain and much of gravel biking.
Do you have the right gears?
If you regularly grind below 60 rpm on local climbs even in your easiest gear, you need lower gearing — a bigger cassette (say 11–34 instead of 11–28) is usually a cheap change. Nobody ever lost a ride because their easiest gear was too easy. Gearing and cadence are two halves of one system: see cadence explained, and check what your gearing means for climbing speed with the calculator.
Keep exploring
Put these numbers to work with the free CalculateBike speed and calorie calculator, browse the cycling gear guide, or read more cycling articles. Prefer two feet to two wheels? Our sister tools CalculateSteps and CalculateRun cover walking and running.