One or two chainrings: The single-chainring myth

​The choice of drivetrain determines both efficiency and riding enjoyment. The key question is: one chainring or two? The trend is clearly towards single-chainring set-ups. Even in the road bike sector, their market share is growing. Our comparison of systems shows which drivetrain type really makes sense for which terrain.

​Our take on the 1x trend

Whilst single-chainring set-ups are becoming increasingly common on real off-road terrain due to the high gear-changing frequency, double-chainring set-ups remain virtually the only option for road cycling. The industry’s push for the single-chainring trend in the gravel sector, too, lacks any sound basis. The vast majority of cyclists stick to tarmac and gravel. Here, you don’t change gears every second as you do on a mountain bike. Instead, the 2-speed drivetrain scores points with its more finely graduated gears. Therefore: your actual riding profile should be the deciding factor when making a purchase.

​The rise of the single-speed bike: a trend put to the test

In mountain biking, the single-speed drivetrain has long since established itself as the undisputed standard. On rough terrain, where the ground and gradient can change from one moment to the next and your full concentration is on staying on the line, its intuitive operation is an invaluable advantage: There’s now only ‘harder’ or ‘easier’. There’s no longer any need to think about which front gear to use. However, the cycling industry has long since extended this trend to gravel bikes and even to classic road racing bikes. Is this genuine technological added value, or is it artificially generated hype by the major component manufacturers such as SRAM, Shimano and Campagnolo, designed to create new incentives to buy?

To answer this question objectively, we need to look at the hard facts beyond the marketing claims: weight, range, gradation, cost, ergonomics, shifting performance and efficiency.

The key technical criteria in detail

1. Weight: The myth of ultra-lightweight construction

There’s no doubt about it: the single-chainring system saves on components: the front derailleur is eliminated, one chainring is saved, the shift cables for the front derailleur are no longer needed (with mechanical groupset), and the left-hand shift lever no longer requires a shift mechanism (road and gravel bikes) or becomes completely obsolete (MTB). However, if you look at a specific Shimano model range such as the Shimano GRX 12-speed gravel groupset, the weight advantage is put into perspective.

Whilst you do save weight on the crankset, derailleur and shift cable, the single-chainring system requires a massive cassette (e.g. 10–51 teeth) to ensure a gear range suitable for mountain riding. These massive sprocket sets made of steel and aluminium are significantly heavier than the closely spaced cassettes (e.g. 11–34 gears) found on a 2-speed system. All things considered, when comparing models of the same tier, the only real advantage is often just over 200 grams for the single-chainring drivetrain. That’s more of a bonus for weight fanatics.

2. Range versus gradation: the paradox in practice

This is where the biggest physical trade-off lies, which becomes particularly interesting when you look at users’ actual riding profiles:

• Dual systems offer smooth gear changes. Thanks to the combination of two chainrings and a closely spaced cassette, the gear steps are often just one or two teeth apart. Riders can fine-tune their ideal cadence to the nearest millimetre, which is essential on long flat stretches, when riding into a headwind or in a group, to remain in the low-fatigue, aerobic zone. The total gear range (bandwidth) of the Shimano GRX 2x12 system reaches an impressive 479% to 507%, with very fine gradation.
• Single-channel systems attempt to cover this gear range with a single sprocket set. Whilst Shimano’s 10-51 cassette offers an impressive 510 per cent gear range, this comes at the cost of significant gaps between gears. On tarmac, this often leaves you feeling ‘stuck between gears’ – one gear is too heavy, the next too light. With SRAM’s high-end groupsets featuring 13-speed systems, this shortcoming is somewhat alleviated, but not entirely resolved.

This is precisely where the paradox of the current gravel scene becomes apparent, because one has to ask: what percentage of gravel cyclists actually ride on genuine, rough terrain? Industry estimates suggest that 70 to 80 per cent of gravel cyclists ride predominantly on tarmac, cycle paths and fine gravel. And it is precisely on these surfaces that the supposed advantages of single-chainring drivetrains are turned on their head. This is because gear changes are less frequent there, and chain security and dirt build-up play a minor role – whereas the fine gear spacing for a constant cadence is crucial. For the main riding conditions of most gravel cyclists, the single-chainring drivetrain thus effectively becomes an artificially generated fashion trend. For manufacturers, it is a blessing: fewer components to produce, easier assembly and a ‘cleaner’ look that markets itself well.

3. The phenomenon of redundant gears

If you look at the bare figures, a 2x12-speed system sounds like it has 24 gears, whilst a 1x12-speed system offers only 12 gears. In reality, however, this difference is less significant: With a 2-speed system, the gear ratios overlap in the middle range. This means that a particular gear (e.g. the large front chainring and a large rear sprocket) feels exactly as hard to pedal as another combination (the small front chainring and a smaller rear sprocket).

If you subtract these ‘duplicate gears’, only 16 to 20 of the 24 theoretical gears in a 2x12 system are usually actually usable.

4. Chain line, misalignment and ‘prohibited movements’

Both single-chainring and double-chainring drivetrains are prone to the problem of the chain running at an angle. The more the chain runs at an angle between the chainring and the sprocket, the greater the friction and wear.

With a double chainring setup, however, the rider can usually minimise chain drift by selecting the appropriate front chainring. That is why the ‘large–large’ and ‘small–small’ combinations are known as prohibited moves: They create a particularly unfavourable chain line, can cause grinding noises at the derailleur and lead to increased wear on the drivetrain components. In practice, these combinations are therefore avoided.

With a single-chainring drivetrain, there are no prohibited gears – in principle, every gear can be used. However, this means that the chain inevitably has to cope with a greater degree of skew on the largest and smallest sprockets, as there is no second chainring to correct the chainline.

5. What does this mean for the comparison?

• Advantage of 1-speed (easy to use): Each gear is distinct. There are no overlapping gear ratios and no need to consider which front chainring would be best. All gears can be used without restriction.
• Advantage of a 2-speed system (optimised chainline and finer gear ratios): By switching between the two chainrings, it is easier to maintain the chainline over a wide range. At the same time, the more closely spaced cassettes allow for smaller gear steps – particularly in the speed ranges where you spend most of your time cycling.

6. Efficiency: What role does the chain line play?

A more favourable chainline means less friction. This is where a well-set-up 2x system offers a slight technical advantage: switching between the large and small chainrings usually helps to reduce chain drift.

With a single-chainring drivetrain, however, greater chain slippage inevitably occurs on the largest and smallest sprockets. Measurements show that this results in a slight loss of efficiency – typically a maximum of three to five watts, depending on the drivetrain, chainline and load. The same applies to the ‘forbidden gears’ in a double drivetrain. At the same time, wear on the extreme sprockets also increases slightly.

For most gravel and touring cyclists, this difference makes little difference in everyday riding. However, those who ride at high intensities on the road or battle for every watt in competition can benefit from the more favourable chainline of a 2x drivetrain.

7. Costs, maintenance, susceptibility to faults

When it comes to reliability, mechanical single-chainring systems come out on top. With no front derailleur, nothing can get stuck or become misaligned in the mud. However, the high-end single-chainring wear parts (such as SRAM’s 13-speed cassettes) can really set you back. The initial cost of single-chainring drivetrains, on the other hand, is generally a little lower. With Shimano, this ranges from 50 to 250 euros, depending on the groupset.

A comparison of the systems across the three bicycle categories

Depending on the type of bike, the requirements for the right gear system vary drastically. The following table shows where each system excels: