Bicycle Drivetrain Guide
developed by the several companies.
Another important aspect of bottom bracket compatibility is whether your bicycle has an Italian or English threaded bottom bracket. The shell diameter of an Italian bottom bracket is larger, threaded 36 mm x 24 tpi, and its threads are both normal (or right-handed). English bottom brackets are threaded 1.370-inch x 24tpi, with the right cup having a reverse thread and the left cup having a regular thread.
Chain
The chain connects the chainring to the rear sprocket, transmitting power from the rider to the rear wheel. Current bicycles use roller chains (with few exceptions) that are categorized by pitch and width. The chain’s pitch is the distance from roller to roller and is typically 1/2 inch on modern bicycles. The width is measured between chain plates and is either 1/8 inch for derailleur-less bikes and 3/32 inch for multi-speed, derailed bikes.
Another specification of a bicycle chain is based on outer width: the outside distance between chain-link plates. There are two main standards: Campagnolo and Shimano. Shimano uses the same width chain for all drive trains with eight or fewer gears in the rear cassette or freewheel and a different width each for its 9- and 10-speed groups. Campagnolo uses three widths presently: 9, 10 and 11. As the number of sprockets in the rear increase, the width of the chain must decrease, providing enough clearance for the extra gears. Other companies manufacture chains that are designed to work with the Campy and Shimano systems.
Derailleurs
On multi-speed bicycles, the derailleur moves the chain from one sprocket to another. They are actuated by a cable pulled from the shifters, typically mounted onto the handlebars (and sometimes down tubes) of the bicycle.
Front derailleur
The front derailleur moves the chain from chainring to chainring and acts as a chain guide, keeping the chain aligned. There are several chainring characteristics to consider when shopping for a front derailleur. The most important is double or triple (whether there are two or three chainrings attached to the crank). A triple front derailleur is designed with a deeper inner cage than a double derailleur to be able to push the chain up from the small ring.
Another key characteristic is chainring size. Certain derailleurs’ cage diameters limit the maximum number of teeth possible on the large ring. The final characteristic is 8/9/10-speed compatibility. The width between the inner and outer cage varies between designs and may not work well when used with the wrong gearing.
Rear derailleur The rear derailleur acts as a chain guide and chain tensioner. As the chain moves from a large sprocket to a smaller one, it needs less chain to cover the circumference. The rear derailleur has a spring mechanism that pulls in that extra length of chain, known as “chain wrap.” The rear derailleur also moves the chain from cog to cog and is one of the more active components of the bicycle. As you pedal and drive the chain around the chainrings and rear sprockets, the chain continuously runs through the rear derailleur.
Rear derailleurs are classified in the same manner as front derailleurs–first by speed: 8/9/10, then by double or triple (it is actually the difference between the largest and smallest chainring added to the difference between your largest and smallest cog). Typically, with a double chainring you can use a short cage and with a triple you would need a long cage. The longer cage helps take up the extra slack that appears when in the small ring.
Rear sprocket
The rear sprocket is the chain’s rear interface with the bicycle. On a single speed (fixed gear included) you only use one rear sprocket, or cog. Multi-speed bikes have a cluster of cogs called “cassettes” or “freewheels.”
A freewheel is a group of cogs fixed to a “freewheel” mechanism that allows you to coast; there is a ratcheting mechanism that allows the rear hub to spin as you coast, or ride without pedaling. A bike cassette is designed to be used with a rear hub equipped with a freewheel mechanism to which you attach the cogs.
Typical freewheels come in 5- to 7-speed versions, and cassettes are 8/9/10/11-speed, with few exceptions. Cassette cogs are designed to be set up in a particular orientation to aid in shifting; any variation of this orientation can cause serious shifting and safety issues. Cassettes are designed to be used with the appropriate chain, and the wrong chain won’t ride on the teeth properly, resulting in a very poor and annoying ride.
Rear hub
The rear sprocket is attached to the hub directly (in the case of a fixed gear), or via a freewheel mechanism. The power from the front chainring is transmitted via the chain to the rear sprocket and into the rear hub, the central point of the rear wheel. The two main characteristics of a rear hub are hub type (cassette, freewheel or