The drivetrain is the centrepiece of your bike, the complex dance of components that turns your legs' watts into forward motion. It can look complex and daunting, but to the uninitiated, it is a pile of greasy bits. Yet knowing the very basics of how your drivetrain works is the key to becoming a more confident, efficient, and knowledgeable cyclist.
This guide will help to demystify the bicycle drivetrain by laying out the basics of how it works, the main component players, and what goes into the quality of the experience, ultimately equipping you to choose the right setup for your riding and even sample what's different with electric bikes.
The Principle: How It Works
A bicycle drivetrain is all about mechanical and, thus, energy efficiency. The entire thing is meant to convert the rotational force you apply to the pedals into turning the rear wheel. This is made possible by a combination of interconnected elements that work together.
When you press down on the pedals, you apply torque to the crankset. This torque is transferred via the chainrings (the big toothed cogs at the front) to the chain. The chain (a series of connected links) then grips the teeth of a cog sitting on the cassette on the rear wheel. This rotation in the cassette cog then turns the rear wheel, and you move forward.
The miracle of a multi-speed drivetrain is in the idea of gear ratios. By transferring the chain between the different-sized chainrings at the front and the cogs on the cassette at the back, you alter the mechanical advantage.
- Easy Gears (Climbing): When the chain moves to a small chainring in the front and a large cassette cog in the back, you have a low gear ratio. This means the rear wheel turns less for each rotation of the pedals. This provides an easier pedalling effort, perfect for climbing steep hills. You’re basically trading speed for more ease.
- Hard Gears (Speed): Similarly, when the chain is on the big chainring and a small cassette cog, the bike will be in a high gear ratio. Each pedal stroke now translates into more rotations of the rear wheel, and you can cycle on flat or downhill terrain even faster. However, it does need to be pedalled with more force.
Being able to adjust these gear ratios is what enables a cyclist to sustain an effort over a wide range of pedalling cadences (the speed at which your pedals spin, typically measured in revolutions per minute or RPM) across varied terrain.
The Parts: Inside a Drivetrain
A contemporary bicycle drivetrain comprises a number of important elements, and each one impacts how the drivetrain functions.
Crankset: It’s what the pedals hook to. It includes the crank arms and the chainrings. Cranksets come with one, two, or three chainrings.
- 1x (pronounced “one-by”): A single chainring configuration, popular on mountain bikes and gravel bikes for its simplicity and chain security.
- 2x: A two-chainring setup, found on most road bikes and some gravel bikes, spanning a large range of gears.
- 3x: A triple chainring system, which tends to be common among lower-end hybrid and touring bikes and offers the widest possible variety.
Chainrings: The gears mounted to the crankset. The chainrings’ tooth count determines the “gear,” or ratio.
Chain: A chain is a group of links with rollers that connects the cassette to the chainrings, transferring the power.
Cassette: A set of cogs in different sizes that attaches to the hub of the rear wheel. The number of cogs on the cassette determines the number of rear gears.
Derailleurs: The parts on the bike that transfer the chain from one cog or chainring to another when you shift gears.
- Rear Derailleur: Shifts the chain back and forth over the cassette cogs.
- Front Derailleur: Shifts the chain from one chainring to another (on 2x and 3x systems).
Shifters: Levers on the handlebars that control the derailleurs. A lever is then pulled or pushed, which pulls or pushes a cable (or sends an electronic signal) that subsequently moves the derailleur.
Bottom Bracket: The bearing set within the frame of the bike that the spindle of the crankset rides in. For directly transmitting your pedalling intention to the pavement, you need a good performance bottom bracket.
Quality Assessment: What Distinguishes the Best from the Rest
Not all drivetrains are created equal. The quality of these parts affects shifting performance, durability, weight, and the quality of your ride in general. Here’s what to look for:
Material and Manufacturing: More expensive parts are frequently constructed of lighter and stronger materials such as aluminium alloys, carbon fibre, and titanium. Accurate machine manufacturing results in smooth, fast, and reliable shifting.
Speed and Accuracy of Shifting: A good quality drivetrain will shift smoothly, quickly, and with precision under load (pedalling hard). Cheap bikes may take longer to respond to a command, or even mis-shift or shift noisily, which riders will notice.
Durability and Reliability: Better quality components are going to last longer before they need to be replaced. Look for things such as hardened steel cogs and chains coated with materials to reduce friction and minimise corrosion.
Weight: There's a reason weight matters to people who like to ride hard. Lighter tends to be more reactive and more nimble.
Number of Gears: Most of the time, more gears are better, but a single-speed bike model is likely the exception to this common rule of thumb. In modern high-end drivetrains, the emphasis is often on providing a wider range with nice, even steps between each gear.
The easiest way to determine the overall quality of a drivetrain is to peruse the groupset pecking order of the major brands. A groupset includes the drivetrain components as well as the brakes. Higher-end groupsets will bring you better performance in all of the above aspects.
The Decision Process: Choosing the Ideal Drivetrain
The best drivetrain is that which best suits your use of the bike. Consider the following factors:
Riding Style and Terrain:
- Road Riding: If your rides are mainly paved, a 2x drivetrain with a cassette that has close-ratio gear jumps will allow you to keep a sustained cadence.
- Mountain Biking: On the mountain, when going into diverse terrain with lots of up and down, simplicity wins in the form of a 1x option offering excellent chain retention and more clearance over obstacles. The wide-range cassette gives you the low gears for climbing.
- Gravel/All-Road Riding: Gravel/adventure bikes are common for this use, often mixing both 1x and 2x gear systems. It is all about what type of terrain you ride. If you’re riding very steep, varied terrain, a 2x may provide a more complete gear range. For shallower gradients or more technical riding, a 1x can be an excellent choice.
- Commuting/Recreational Riding: This can be pretty much anything from a 1x to a 2x with a decent gear spread.
Budget: A bike’s drivetrain components make up a large chunk of its price. Entry-level drivetrains work just fine if you’re taking the bike out a few times a year, but as the price increases, you’ll also gain performance and durability. Establish a budget that you’re comfortable with, then find the best-performing groupset that falls within it.
Maintenance Tolerance: While all drivetrains are susceptible to failure, a 1x is often easier to keep in working order as a result of not having a front derailleur to fiddle with. If you want something less involved, that might make up your mind for you.
Heavy Hitters: Drivetrain Heavyweights
The three leading drivetrain brands in the cycling world each have their own qualities and product series.
Shimano: The Japanese behemoth is the biggest and best-known component maker in the bicycle business. Shimano is a name that cyclists around the world associate with quality and performance—and for good reason. Their hierarchy of road bike groupsets is Claris, Sora, Tiagra, 105, Ultegra, and Dura-Ace (in increasing order of quality). Tourney, Altus, Acera, Alivio, Deore, SLX, XT, and XTR cover the mountain bike range.
SRAM: An American company making waves in the industry. SRAM is well-known for making lightweight components and popularising 1x drivetrains on mountain and gravel bikes. They’re also a market leader with electronic eTap AXS groupsets. Their road ranges are called Apex, Rival, Force, and Red. Their mountain bike groupsets are named NX, GX, X01, and XX1.
Campagnolo: A vintage Italian brand with a glorious racing tradition. Campagnolo makes upper-echelon, performance-designed road bike groupsets that are frequently lauded for their aesthetic quality, ergonomic pleasure, and distinct 'click' of its shift levers. Their groupsets are called Centaur, Potenza, Chorus, Record, and Super Record.
The Electric Assist: Drivetrain Considerations For E-Bikes
E-bikes put more stress on the drivetrain as a result of the motor's extra power and torque. Here's what you need to know:
Durability is Key: Motor strain on drivetrains means it’s a good idea to opt for quality, reliable components. A lot of brands are starting to offer individual e-bike drivetrains that are manufactured with stronger materials in order to cope with the added load. Seek out parts that are specifically advertised as "e-bike rated" or for e-bike use.
Mid-Drive vs. Hub-Drive Motors:
- Mid-Drive Motors: These motors transmit power through the crankset, so the whole drivetrain receives power from the rider and the motor. That requires a chain, cassette, and chainring that are durable and tough. I'd highly recommend e-bike-specific groupsets if you have mid-drives.
- Hub-Drive Motors: These motors sit in the hub of the front or rear wheel and power the wheel directly, forgoing a significant portion of the drivetrain. Although this places less load on the chain and cassette, a reliable shifting system is still crucial for effectively managing your own pedalling efforts.
Gear Range: Even though the motor mitigates the necessity for a super-wide gear range in the low gears, a good range is important for maintaining the optimum cadence and getting the longest range out of the battery. A wider-range cassette might be useful for those who plan to conquer very steep hills, with or without motor help.
Shift Performance: Smooth and accurate shifting is paramount on an e-bike, since a missed or clumsy shift under the high power of the motor can be more jarring and potentially detrimental to the drivetrain components. In some e-bike systems, there’s even “shift detection” technology, which momentarily decreases motor power during gear shifts to minimise the impact of the change.
Conclusion
In conclusion, the drivetrain is the heart and soul of your ride. By learning about its principles and its parts, you can decide better when you’re buying a new bike or thinking of an upgrade. Whether you're new to the bike path or an experienced rider looking to shave off a few seconds, a properly selected and well-maintained drivetrain will be with you on every ride.
