The Drivetrain:
What moves your bike.Welcome friends to "The Drivetrain" page of Get-Into-Cycling.com. Have you ever wondered how all the parts of your bike work to move your bike forward? In this section you will see a brief description of all the major components and their purpose.....all in plain, easy to understand English!From the chain to the cranks. From the pedals to the gears. Everything you needed to know about the drivetrain or your bicycle (well at least the basics) without having to get a degree in Engineering. _________________________________________________________________ Crankset
The crankset is what transfers the power of the cyclist to the wheels to move the bike forward. The crankset is composed of several major components: The crankarms, chainrings and a device called a bottom bracket which ties both sides of the bike's crankarms together.
This photo shows a crankset known as a double crankset, because it has two chainrings.
This photo shows a crankset know as a triple crankset, because it has three chainrings. Triple cranks are used on sport bikes, touring bikes as well as on mountain bikes. _________________________________________________________________
This is a photo of a bottom bracket (aka "bb"). This device "ties" both crank arms together so that they work as one unit. Very critical to the balance of the drivetrain. This particular bb is known as a "sealed" mechanism. It is designed as a single use item, meaning that once it has reached the end of its service life, it is discarded for a new one. The term, plug and play comes to mind..... Older bicycles have bb mechanisms that are serviceable: Bearings and shaft can be replaced or cleaned and regreased. Additionally, not all cranks will fit on all bb's. There are also now numerous types of mountings for crankarms and bb's: Cottered: This is an older style mounting that attaches the crank arm to the bb spindle using a pin bolt. They've been referred to as "Frankenstein Bolts" because they resemble the bolts that stick out of Frankenstein's neck.
One Piece: This is more of a crankset description than a bb. This is found on more less expensive bicycles. It is a single piece of bent steel that combines the crankarms, chainrings and bb spindle together in one piece (see photo above). The bb housing is also a little larger for these types of bikes.
Square tapered: This was once the common mounting for a crank arm to a bb. The spindle has four flat surfaces and the crank arm is attached to it via a single crank bolt. The photo above shows two examples of square taper bb's (an older style which can be taken apart and a newer sealed version).
Splined (example: ISIS, Shimano Hollowtech, etc.): These are fairly newer mountings and use slines or teeth to mount the crank arm to the spindle. The photo above is an example of a Shimano Hollowtech splined bb, an ISIS splined bb, along with a couple of traditional square tapered bb's. It is also secured with one bolt (or other design). This design is claimed to distribute more of your pedaling power to the wheels and not flex like a square tapered design and is lighter in weight. Be advised: NOT all splined cranks will work with one another so make sure you have the correct types for your bike if replacing or upgrading your bb or cranks. Compare the differences between a square taper, an ISIS bb and a Hollowtech bb in the photos below.
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Chain
In order to transfer your pedaling power to the wheels, your crank must be connected to the wheels. That connection is the chain. The chain pulls the wheel forward thus propelling the bike. Very critical to the drivetrain system. _________________________________________________________________ Cassette or Freewheel
The final connection of your chain to propel your bike forward, and an essential part of the efficiency of the drivetrain system, is a device called a cassette or freewheel. It is the cluster of gears located on the rear wheel of your bike. Each gear is called a cog and has a varying number of teeth. Cassettes and freewheels do the same job, that job being the transfer of power from the chain to the wheels. The only difference between the two is this: Cassettes come off the hub as separate cogs and spacers. Freewheels come off the hub as an entire unit. If your bike only has one cog or gear, that is referred to as a single speed. _________________________________________________________________ Front and Rear DerailleursThe job of the derailleurs in the drivetrain heirarchy is to shift the chain to various gears on the rear cassette/freewheel or the chainrings on the crank. This allows you to be able to choose the most optimum gear choice for climbing, flat terrain, speed or torque.If you have a single speed, than derailleurs do not apply to the drivetrain of your bicycle obviously. But you may have a bike equipped with an internal speed hub. The shifting and gearing mechanisms are built inside the hub rather than using a cassette and derailleur setup.
This is a photo of a front derailleur. _________________________________________________________________
This is a photo of a rear derailleur. _________________________________________________________________ ShiftersThat's great the derailleurs move the chain, but who controls the derailleurs? Well, the shifters do that job (actually YOU move the shifters...they haven't come up with mind-controlled shifters yet). The shifters can be mounted on the downtube of the bike, the stem or on the handlebars. There are two styles of shifters: Index and friction.-Index Shifters: Index shifters (or "click" shifters) have been the standard shifter for nearly all bicycle for the last 20+ years. They have existed longer than that, but did not really catch on in popularity until Shimano introduced their version of index shifting, called "SIS" or Shimano Index System. After that, every component manufacturer followed suit. Basically index shifters allow you to change gears on your drivetrain precisely without having to fine tune or "hunt" for the gear. Each click of the shifter moves the chain exactly to the next gear. Just shift without thinking about it. Most index shifters will even allow you to shift to "friction" mode for all you "old school" types. -Friction Shifters: Friction shifters were once the common shifter for bikes. The advantages of friction shifters is its simplicity (no indexing mechanism to wearout or break) and lighter weight. With the advent of index shifting, however, friction shifting has gone the way of the condor. But just like the condor, there are still "a few" cyclist who prefer friction shifter's no-nonsense approach, versus indexing. Many even claim that with proper adjustment of both the shifters and derailleurs, you can shift faster and just as accurately with friction shifters. We believe them.....
This photo shows a set of combination shifter and brake levers. The standard for control for the drivetrain of the modern road bicycle. _________________________________________________________________
This photo shows a downtube shifter. These were once common place on every mid-to-high level road bike until around 1990 when the combination shifter/brake lever appeared. _________________________________________________________________
This photo shows a shifter called a twist shifter. Twist shifters came into popularity around the late 80's, early 90's from a company called SRAM, when they developed the "Grip Shift." These shifters are primarily on mountain or comfort/hybrid bikes, although SRAM also developed a version for road in the early 90's. _________________________________________________________________
The photo above shows a shifter called a bar end shifter. They are avalable as both a friction or index model. These shifters are used primarily on touring bikes and on time-trial/triathalon style bikes. _________________________________________________________________
The photo above is an example of a modern mountain bike shifter, sometime mistakenly referred to as a "thumbshifter." First generation mountain bikes had the true "thumbshifters" (see photo below): Basically a single lever that was mounted on the top of the handlebar or now referred to as "top mount." The one above is called an "underbar" or "below the bar" shifter and uses two levers: One to upshift, the other to downshift.
PedalsSo how do you put the power down on the bike? Well that's where the pedals come into play. This is the part that really connects you to the bike in terms of transmitting power....it all starts at the pedals. The "pistons" of the drivetrain. Pedals come in various flavors.....just like ice cream. There are pedals that have clips and straps. There are pedals that use a cleat system called clipless pedals. And then there are standard platform pedals (no platform shoes included.....you'll have to get those at a thrift store along with your 8-track tapes).Without pedals, you could not power the rest of the drivetrain.
This is a photo of a road style clipless pedal. Below is a photo of the cleats used on a road-specific cycling shoe to attach to the clipless pedal.
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This is a clipless pedal for a mountain bike. _________________________________________________________________
This is an example of a platform pedal. This particular type is designed for mountain bikes. The Drivetrain: Return to Bike Anatomy Home
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