Bike Gears Explained with a Diagram

The short version

Most bikes with gears use a derailleur system. The pedals turn one or more toothed rings at the front (chainrings). A chain connects them to a stack of toothed rings on the rear wheel (the cassette). Two shifters move the chain between those rings, and the combination you pick decides how hard the bike is to pedal.

A text diagram of the drivetrain

Looking at the bike from the right-hand (drive) side, with the front on the left:

   Shifters (handlebar)
   left = front derailleur   right = rear derailleur
        |                         |
        v                         v
  [Front derailleur]        [Rear derailleur]
        |                         |
  (Chainrings)==== chain ====(Cassette cogs)
   on the crank                on the rear wheel
   with the pedals             small cog = hard
   small ring = easy           large cog = easy

Read it as two sets of gears linked by one chain. On most bikes with a front derailleur, the left shifter changes the front set and the right shifter changes the rear set.

The parts, front to back

Chainrings. These are the toothed rings bolted to the crank arm. Road bikes often have two, many mountain and gravel bikes have one, and older or touring bikes sometimes have three. For the full naming rundown, see bike gear names.

Cassette. The stack of rear cogs. Current cassettes commonly have somewhere between 7 and 12 cogs, with the smallest cogs furthest from the wheel and the largest closest to the spokes. Some cheaper or older bikes use a freewheel, which screws onto the hub instead.

Chain. One chain runs across both sets of gears. It needs to suit the number of rear cogs on your bike.

Derailleurs. The rear derailleur moves the chain across the cassette and keeps tension on it. The front derailleur, where fitted, moves the chain between chainrings.

Shifters. On flat-bar bikes these are usually trigger or twist shifters. On road bikes they are usually built into the brake levers. They pull a cable (or send an electronic signal) to the derailleur.

How the gear count is worked out

Multiply the number of chainrings by the number of rear cogs. A bike with 2 chainrings and an 11-speed cassette is often sold as having 22 gears. In practice some combinations overlap, so the number of truly different gears is smaller. We go into this in how many gears a road bike has.

Which gears are easy and which are hard

• Easy gear (low gear): small chainring at the front, large cog at the back. Each pedal turn moves the bike less, so pedaling takes less force.
• Hard gear (high gear): large chainring at the front, small cog at the back. Each pedal turn moves the bike further, which suits fast riding on flat or downhill ground.

“Gear 1” is generally the easiest gear on bikes with numbered shifters. Numbering can differ by brand and shifter, so check the markings on your own bike. For choosing a gear on a climb, see which bike gears to use on hills.

How to shift properly

• Shift before you need to, for example before a hill gets steep.
• Keep pedaling while you shift, but ease off the pressure on the pedals.
• Use the rear shifter for small changes and the front for bigger jumps.
• Avoid the extremes, such as the big chainring with the biggest cog, or the small chainring with the smallest cog. This “cross-chaining” can be noisy and may wear parts faster.

When gears misbehave

Skipping, noisy or reluctant shifting usually points to cable tension, a worn chain or cassette, or a bent derailleur hanger. See why your bike gears keep slipping for a step-by-step way to narrow down the cause.

Where to go next

• Learn the correct terms in bike gear names: chainrings, cogs and sprockets.
• Thinking of converting a one-speed? Read about adding gears to a single speed bike.