Bicycle Gear Ratio & Speed Calculator
ガイド
Bicycle Gear Ratio & Speed Calculator
See exactly how fast you will roll in every gear on your bike. Punch in your chainring and cassette teeth, pick a wheel size, and the calculator builds a colour-coded grid of speed, gear inches, development and ratio for every chainring × sprocket combination — useful when shopping for a new groupset, planning a build, or hunting down duplicate gears you never use.
使用方法
- Enter your chainring tooth counts as a comma list (e.g.
50, 34for a 50/34 compact crank). - Enter your cassette sprocket tooth counts smallest first (e.g.
11, 13, 15, 17, 19, 21, 24, 28, 32). - [表示モード]を選択してください wheel size preset that matches your tyre, or choose カスタム and type the rolling circumference in millimetres.
- をドラッグして cadence slider to your usual RPM (recreational ≈ 75, road ≈ 90, racers 100+) and pick km/h または mph.
- を使用して、よく使用されるヘッダーをデフォルト値とともに挿入します。認証セクションで認証タイプと認証情報を設定し、カスタムヘッダーを手動で追加します。curl、Postman、またはコードで使用するための完全なヘッダーセットをコピーします。 Grid Shows dropdown to swap between speed, gear inches, development, or raw ratio. The summary table updates with low/high gear, gear range and top speed live.
- Cells highlighted in amber are overlapping gears between your chainrings — gears that duplicate within 5% and can be skipped when shifting.
機能
- Every combination at a glance – chainring × sprocket grid with all gears side by side, not one at a time.
- Multiple metrics – switch the grid between speed, gear inches, metres of development, or gear ratio.
- Wheel size presets – 700×23/25/28/32/38c, 650b gravel, 26″, 27.5″, 29″ MTB, 20″ BMX, 16″ folding, plus a custom circumference field.
- Speed at your cadence – slider from 40 to 120 RPM with km/h or mph output.
- Overlap detection – cells across chainrings within 5% ratio are flagged amber so you can spot duplicate gears.
- Lowest and highest gear highlighted – easiest climbing gear in green, top-speed gear in orange.
- Live summary – wheel circumference, total combinations, gear range percentage, and top/bottom speeds at the selected cadence.
- クライアントサイドのみ – no uploads, no accounts, nothing leaves your browser.
よくある質問
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What is a gear ratio on a bicycle?
Gear ratio is the front chainring tooth count divided by the rear sprocket tooth count. A 50t chainring with a 25t sprocket gives a ratio of 2.0, meaning one pedal revolution turns the rear wheel two full times. Higher ratios travel further per pedal stroke but require more force; lower ratios spin faster for the same effort, ideal for climbing.
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What are gear inches and why are they used?
Gear inches is the effective diameter of the rear wheel if the bike had no gears: wheel diameter (inches) × gear ratio. It dates back to high-wheeler bikes where you simply quoted the wheel size. Today it is a wheel-size-independent way to compare gearing — 100 gear inches feels the same on any bike, whether 700c road or 29er MTB.
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What is development (or roll-out) and how does it differ from gear inches?
Development is the distance the bike travels in one pedal revolution, measured in metres: wheel circumference × gear ratio. It is the European equivalent of gear inches and is more intuitive for actual cycling — a development of 8 metres means each pedal stroke moves you 8 metres along the road.
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Why do some cassettes have overlapping gears between chainrings?
On a 2x drivetrain (two chainrings), some chainring/sprocket combinations end up with nearly identical ratios — for example 50/19 and 34/13 both give ratios near 2.6. These are 'overlap' gears: shifting between them changes nothing in feel or speed. Modern 1x drivetrains were designed to eliminate this duplication, simplifying gear choice at the cost of bigger jumps between gears.
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