A Guide to Bicycle Drivetrains: How do Gears Work

Just like it’s important to shift gears properly when driving a car, it’s important to shift gears properly when driving a bicycle. In fact, it may be even more important when riding a bike, as there’s no engine to propel you forward, but instead, you have to do it using your legs. So, if you find riding up a hill in third or fourth gear challenging, consider going in first or second. But that’s common knowledge for most people, and it’s not the point I’m trying to make here. Instead, I want to put the emphasis on the importance of having the right drivetrain and more specifically, the cassette of your bicycle.

Bicycle Drivetrains Explained

speed cassette close up
source: livestrong.com

Most bikes today come with external drivetrains, which are simple, lightweight and efficient. The gears are changed on the cassette, using a derailleur, which moves the chain up or down the cassette. as the derailleur shifts, it forces the chain against steps or ramps, moving the chain to a smaller or bigger sprocket on the cassette. The bike can also have a front derailleur to shift the chain between different chainrings attached to the cranks. The gears located at the front provide more gear jumps, changing the range of gears to suit higher-speed, lower-speed or flat terrain driving. The cassette, on the other hand, allows you to choose the gear more precisely within that range. Typically, the rear of your bike will have a 6 or 8 speed cassette.

Hub Gears

Hub gears are used by commuters who want a more robust and maintenance-free bicycle drivetrain. You’ll have to service them every 3 000 to 5 000km. The derailleurs are the only part that’s slightly exposed and susceptible to wear. Having everything packed away inside the rear wheel allows you to have peace of mind, even during winter, that your gears are well-protected. Hub gear systems range from 3 to 14 gears, so you have plenty of choices no matter what terrain you drive on. However, they are heavier, and changing a puncture is more difficult.

How do Gears Work?

bicycle drivetrain on orange bike close up
source: cycletechuk.com

The gears convert your crank input into back wheel output. In other words, how hard you pedal is converted into different speeds at the rear wheel based on the gear you’re in. The gear development (the amount of power you create with each stroke) is represented in gear inches (how far your bike goes forward with each rotation of the cranks). This will give you a general idea of how easy or hard the gears are, with ranges around 20 inches (~50cm) being easy, 70 inches (~177cm) being medium, and anything above 100 inches (254cm) being hard.

There’s another term – gear range – which is typically expressed in percentages and describes the overall range provided by the system. For instance, a 400 per cent range provides a 4:1 ratio. Pedalling in the highest gear will move you 4 times faster than it would in the lowest gear. In external drivetrains, the gear range is calculated using the ratio of the smallest and largest chainring teeth at the chainset and multiplying them by the ratio of the smallest and largest sprockets on the cassette.

mountain bike speed cassette close up
source: chooserly.com

Cranks are available in different forms for road bikes, such as standard, triple, compact and super compact. Triple cranks used to be the most popular type, and they featured three chainrings. Nowadays, though, most bicycles feature two chainrings that are either on a compact or standard crankset. The standard crankset is better suited for high speeds. Compact cranksets provide a higher range of gearing, making them suitable for riders riding at high speeds and for those climbing steep inclines. lastly, super-compact chainsets use even lower ratios than compact chainsets, making them ideal for climbing.

Mountain bike chainsets generally use smaller chainrings to deal with off-road terrain. Most of them are equipped with a single chainring that’s paired with a wide range cassette at the back. The arrangement is referred to as a one-by setup. To get an idea of how many gears you have, you’ll have to multiply the number of cogs on the cassette with the number of chainrings at the front. However, similar gears may be duplicated based on which sprocket and chainring combination you’re using. Also, it’s inadvisable to use some gear combinations as they can put the chain at an awkward angle.

Cleaning Your Drivetrain

man cleaning bicycle drivetrain
source: roadcyclinguk.com

If you want your gears to shift and run smoothly, you should keep them clean. This can also help you prolong the lifespan of your drivetrain, and you’ll notice potential issues before they become a problem. As aforementioned, hub gears require less maintenance, although you may have to adjust the cable tension every now and then, as it tends to stretch. Clean and lubricate your chain regularly, and make sure you remove any debris that’s stuck to it. And last but not least, make sure you clean your 8 speed cassette with the help of a brush.