Bicycle Drivetrain 101: How to Shift Gears on a Bike
The combination of two different sized cogs and a chain lets you power down hills, cruise on the flat and climb up a gradient. What a great invention. But, changing gears is a matter where the chain runs between many different cogs. These cogs are both turning between your feet and attached to the rear wheel, giving the rider a sometimes bewildering number of gears to choose between.
The drivetrain of the bike consists of all the bits that you use to push (or pull) the bike along, we’ll get to the different terminology. The key components are:
Chainset consists of number of different parts – cranks, bottom bracket (together called crankset) and chainrings. It is the name given to a group of components that rotate when you turn your pedals, to drive the bike’s chain and turn the rear wheel to propel the bike along.
The chainset has two sides, it connects via the chain to the drive wheel of the bike. Two crank arms are mounted either side of the from at 180 degrees to each other. In between is a spindle which passes through the bottom bracket in the frame, which is simply a set of bearings on which the cranks rotate.
Also mounted on the bottom bracket is the chainrings. Your bike may have one, two or three chainrings. A bike with only one chainring will not have a front derailleur. Chainrings form part of the chainset, and are typically mounted on to a four- or five-arm metal ‘spider’ that rotates with every turn of the pedal.
Freewheel or called cassette is the cluster of sprockets on your bike. The freewheel is normally situated on the rear hub of your bike. On a cassette, each different number of teeth on different sprocket, which provides power are not same.
The number of cogs on freewheels vary, but 7 or 8 are common. The range of gears on your cassette, combined with the size and number of your front chainrings, gives you your bike’s gear ratio or ‘gearing’. A 21 speed bike has 3 chainrings and 7 cogs.
Derailleur often referred to as mech. A bicycle can have either front and rear derailleur, but a single-speed will both not. There are two main brands to choose from when selecting a groupset: Shimano and SRAM.
The front derailleur pushes the chain between the two or three chainrings on the chainset to change gears. The rear derailleur shifts the chain across the different sprockets on the cassette to achieve higher or lower gears and is spring loaded to take up the chain slack.
How the gears work
As outlined above, you probably have two sets of gears on your derailleur-equipped bicycle. The front derailleur moves the chain across the chainrings. The rear derailleur moves the chain across the cogs of the freewheel.
Your point of contact with your gear systems is a ‘shifter’ of some type. A cable connects each shifter to its derailleur. Tension on the cable pulls the derailleur one direction, and a spring in the derailleur pulls it in the other direction.
Many shifters are marked in some way, often numbered or with an ‘H’ for the high gear and an ‘L’ for the low gear.
The front derailleur is controlled by the left hand side (LHS) shifter of your handlebars. The ‘1’ or ‘L’ refers to the innermost chainring (closest to the bike), this chainring delivers the least resistance and is useful for very steep inclines or soft terrain. Smaller chainrings are easier to pedal in, but less power is transferred to the rear wheel.
The ‘3’ or ‘H’ refers to the outermost chainring(closest to the pedal)., this chainring produces the most resistance and is useful for maintaining speed. Conversely the largest chainring provides more power to the rear wheel, but is harder to pedaling.
- The rear derailleur is controlled by the right hand side (RHS) shifter of your handlebars. On a 7 speed shifter, ‘1’ or ‘L’ refers to the the biggest sprockets, this cog gives the least resistance. That is to say That bigger sprockets are easier to pedal in and are used for setting off from stationary and riding up hills. ‘7’ or ‘H’ refers to the outermost cog, which produces the most resistance.
This can be confusing for some people that the highest gears correspond to the physically largest chainring but the physically smallest cog. It is better to ignore the size of the gears and remember that the inner gears are lower and the outer gears are higher in both front and back.
Riding a bike with gears can be quite a daunting experience. With practice and understanding, though, the relationship between you and your steed can become a truly satisfying experience. Try not to be daunted by your gears.
When & Where & How to Use
Don’t be afraid to experiment with different gear combinations. Change through the gears one or two at a time, a little understanding can go a long way.
Every shifter/derailleur combination is different, develop a feel for yours. As you get familiar with the feel of the gears, you can begin to anticipate what gear combination will be best for upcoming terrain and obstacles.
Here are a few hints and tips：
- For: Uphills and headwinds
Use: Small or middle front chainring + bigger rear cogs
- For: Downhills
Use: Large front chainring + a range of rear cogs
For: Flat terrain
Use: Small or middle front chainring + smaller rear cogs
Many beginners are unaware that certain combinations of gears should not be used. There are 2 most extreme combinations of gears to avoid.
- Riding with the chain in the largest chainring and the largest sprocket.
- Running the chain on the smallest chainring and smallest sprocket.
This results puts a lot of stress on the chain, rapidly increased component wear and potentially the chain coming off and jamming, even on an otherwise correctly set-up and maintained bike.