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Unites • SI

Gears

Guide & Objectives

Simulate, compare, and optimize your bike drivetrain. Accurately analyze the impact of changing your chainring, cassette, or tire size on your speed and cadence.

1

Objective

1 - Visualize your gear ratios. 2 - Compare two configurations (A vs B). 3 - Find the ideal gearing for your riding style.

2

How to use

1. Select your components from the catalog or enter them manually. 2. Adjust your target speed. 3. Observe the linear and kinematic graphs.

3

Value

1 - Visualize your transmission and compare different configurations. 2 - Optimize your gear ratios. 3 - Generate a PDF report of your technical choices.

Understanding gear ratios

A gear ratio refers to the chainring/sprocket combination in use at any given moment — the pair holding the chain. It is not an abstract value: it determines the distance covered per pedal revolution, otherwise known as your gear development.

Gear development: the key metric

Gear development (expressed in metres) is the distance travelled per complete pedal stroke:

Development=Chainring teethSprocket teeth⋅(Tyre circumference)=ZchainringZsprocket⋅(π⋅Dwheel)\text{Development} = \frac{\text{Chainring teeth}}{\text{Sprocket teeth}} \cdot (\text{Tyre circumference}) = \frac{Z{chainring}}{Z{sprocket}} \cdot (\pi \cdot D_{wheel})

Where:
Chainring teeth: number of teeth (dimensionless)
Sprocket teeth: number of teeth (dimensionless)
Tyre circumference: expressed in metres (m)

With:
A 50-tooth chainring
A 17-tooth sprocket
A 700×25c tyre (circumference 2.105 m)
the development is:

Development=Chainring teethSprocket teeth⋅(Tyre circumference)=5017⋅(2.105)=6.19 m\text{Development} = \frac{\text{Chainring teeth}}{\text{Sprocket teeth}} \cdot (\text{Tyre circumference}) = \frac{50}{17} \cdot (2.105) = 6.19 \text{ m}

The bike covers 6.19 m per pedal stroke. At a cadence of 90 rpm, this corresponds to approximately 34 km/h — a solid pace on flat terrain.

Single chainring or double chainring

The choice between a single and a double chainring depends primarily on your bike, your groupset brand, but also on your usual terrain and riding style:

Double chainring (compact, semi-compact, standard) — The most common setup in road cycling today. Ideal for versatile road riding. A 50/34 compact offers a wide range: small ring for climbing, big ring for flatter sections.
A double chainring setup can be slightly heavier, as it requires more components: two chainrings and a front derailleur, resulting in marginally greater overall weight.

Single chainring — Popularised by gravel, and increasingly adopted on road bikes, including recently in the professional World Tour peloton. It eliminates the front derailleur and simplifies the drivetrain. In return, a wide-range cassette is required, often starting at 10 teeth (SRAM) to compensate.
Gear jumps between sprockets are larger, and the efficiency of a 10-tooth sprocket is slightly reduced.

Choosing your cassette for the terrain

The cassette determines how finely you can step through your gear range:

  • Flat or rolling roads: An 11-25 or 11-30 cassette provides tight steps for maintaining a steady cadence at high speed.
  • Hilly roads with climbs: An 11-32 or 11-34 makes climbing easier without sacrificing the top gears on the flat.
  • Gravel / bikepacking: An 11-34 or 10-44 (with a single chainring) handles accumulated elevation gain and the weight of loaded gear.

The right gear only works alongside the right cadence

Cadence refers to the number of revolutions per minute of the pedals. It is expressed in revolutions per minute (rpm) — the standard unit used worldwide.
A high gear demands greater muscular effort but a lower pedalling frequency. A low gear protects your knees and adapts better to steep climbs, at the cost of a limited top speed. Most road cyclists target a cadence between 85 and 95 rpm — the zone of optimal muscular and cardiovascular efficiency.

Use the simulator below to compare two drivetrains side by side and find the configuration that matches your terrain and goals.

Catalog Filters

Brands
Speeds (Cassettes)

Paramètres

tr/min

A Reference Configuration

Select a configuration...
Select a configuration...
Circ: 2.105m
Waiting for configuration...

B Compared Configuration

Select a configuration...
Select a configuration...
Circ: 2.105m
Waiting for configuration...
Warning and Disclaimer

The proposed combinations in this tool (especially custom inputs) do not guarantee the mechanical compatibility of your drivetrain.

Always verify your rear derailleur total capacity and maximum front chainring difference before installation.

Displayed speeds are theoretical and based on the estimated rolling circumference of your tire.

Learn More

Gear Ratio (Sprocket)

The gear ratio defines the number of revolutions the rear wheel makes for one complete revolution of the crankset. Example: a ratio of 2.0 means the wheel rotates twice as fast as your legs.

  • ZchainringZ{chainring}: Number of teeth on the chainring (number of teeth, unitless)
  • ZsprocketZ{sprocket}: Number of teeth on the sprocket (number of teeth, unitless)

Gear Ratio

Gear ratio is the actual distance traveled by the bicycle with each revolution of the crankset. It depends on the circumference of the wheel (which varies according to the rim diameter and tire width).

Dev=Ratio⋅(π⋅Dwheel)Dev = Ratio \cdot (\pi \cdot D_{wheel})
  • DwheelD_{wheel}: Wheel diameter, including tire (mm)

Linear Speed

The cyclist’s speed is the product of the gear ratio and the pedaling cadence (in revolutions per minute).

V=Dev⋅Cadence⋅0.06V = Dev \cdot Cadence \cdot 0.06
  • VV: Linear speed (km/h)
  • DevDev: Gear ratio (mm)
  • 0.060.06: Conversion from millimeters per minute to kilometers per hour: (601000⋅1000\frac{60}{1000 \cdot 1000})

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