Bicycle Drivetrain Guide
Bicycle Drivetrain Guide
Your bicycle’s drivetrain is comprised of all of the parts that power the bicycle and make it go. Bike pedals move the cranks, which turn the bottom bracket and the chainrings, which drive the chain that spins the rear sprockets, turning the rear hub, which moves the wheel and propels the bicycle forward. The crisp movement of these parts and the ability to minimize effort while maximizing speed is the heart of cycling. It is essential that drivetrain be clean, true and well-maintained in order to more fully enjoy riding your bike. When one of these parts gets out of whack, the rest soon follow.
It is also important to get individual components that are compatible within the system (e.g. typically Campagnolo and Shimano parts are not inter-compatible). Many times the difference between 9- and 10-speed parts is enough to make them incompatible as well. The collective term for a complete bike drivetrain kit is “group” or “gruppo.” Multi-speed drivetrains are classified by the number of cogs in the rear cassette. A modern day 10-speed bicycle can have as many as 30 “possible gears,” with 10 in the rear and three in the front, but still have a 10-speed drivetrain.
Pedals
Your bike pedals are your power connection to your bicycle. As you pump your legs and turn your feet, you cause the cranks to turn. Proper pedal choice is important for comfort, control and safety on the bike. Many recreational and enthusiast cyclists prefer the adaptability that platform pedals offer. They allow you to ride in any type of shoe and give a sense of security to a novice rider who is cautious of locking the feet into clipless pedals. Many platform pedals can be adapted with a toe cage to give more control and power while retaining the sense of security associated with platforms.
Racers and more advanced riders often prefer “clipless” pedals. These pedals are used in conjunction with matching cleats that are attached to special shoes. The cleats lock into place in the pedal, offering a secure attachment of rider to bicycle. Most cleats easily release the shoe by a simple twist of the ankle, and they are quite easy to use with some initial practice.
Cranks
The cranks connect the pedals to the bottom bracket and hold the front chainrings. They connect to the axis around which your feet spin and transmit your power to the bike. Cranksets come in many different lengths based upon bicycle frame size and the rider’s leg length. They are generally made out of aluminum, but some low-end cranks are made of steel, and some high-end cranks are made of carbon fiber. These cranksets are marketed to top-level racers and generally carry the appropriate price tag. Cranks attach to the bicycle at the bottom bracket. There are several types of cranks/bottom bracket interfaces, and it is important to know their differences.
Chainrings
Chainrings are the forward chain interface with the bicycle. They contain teeth that hold the chain and drive it forward. Chainrings come in a wide range of sizes, identified by the number of teeth and application. Typical mountain bikes use three chainrings; road bikes generally have two to three. Single-speed and fixed-gear bicycles use only one chainring. Chainrings are typically made of aluminum, with some being made of steel and a handful of boutique brands making them out of carbon fiber.
What makes a proper chainring is dependent upon many factors: number of teeth, single/double/triple configuration, 8/9/10/11 speed use and bolt circle diameter. Once all of those factors have been determined, you can choose the group level or brand that best suits your needs.
Bottom bracket
The bottom bracket is the cranks’ interface with the bike. It contains bearings around which an axle rotates; this axle is connected to the cranks. Current bottom brackets come in varying interface types. Traditional bottom brackets have loose ball bearings with their accompanying cups and cones and an axle locked in place with locknuts, typically on the left side of the BB shell. More recent cartridge bottom brackets are built as one piece with cartridge bearings press-fit onto the axle and fit into the frame with “cups” that thread into opposite sides of the shell.
Many bike parts companies have most recently been developing bottom brackets without an axle. The axle is built into the cranks and runs through bearings that are press-fit into cups that thread into the bottom bracket shell. The other end of the axle then attaches to the opposite crankarm. Different brands have different bearing sizes and only work with their respective cranks.
Bottom brackets come in many different interfaces developed by the different component manufacturers. Cup and cone BBs are generally “square taper.” Cartridge bottom brackets are one of two versions of square taper (International Standard or Japanese Standard) or one of the many versions of splined BB