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Although Wout van Aert celebrated his second Tour de France victory in 2023 by lifting his single-chainring-equipped Cervélo bike on the Champs-Élysées, this setup is not suitable for everyone unless you are gearing up for a professional race with a dedicated mechanic.

This year’s Spring Classics saw several teams and riders adopting single-chainring setups, sparking renewed debate on the merits of single-chainring drivetrains on road bikes.

paytda single-chainring systems do have advantages in certain scenarios, and the new hub gear technology could be a game-changer, the single-chainring revolution on road bikes still seems a distant prospect.

In my opinion, the current front derailleurs are simply too good, and in most cases, the benefits of giving them up don't outweigh the drawbacks.

When Does a Single Chainring System Make Sense on a Road Bike?

1x aero chainsets are becoming increasingly popular on time trial bikes.

There are several advantages (and disadvantages) to a single-chainring system on a road bike.

In scenarios where a wide gear range is not necessary, such as relatively flat rides or races, a single-chainring system can provide all the gears you need while simplifying things.

Single-chainring systems can also be more aerodynamically efficient. According to UK experts AeroCoach, switching to their ARC 1x aero chainring can save "between 1 and 4 watts at 30mph / 48kph," depending on the size of the front derailleur you remove.

This is a small gain, but increasingly, time trial and track bikes are benefiting from it.

Using a chain keeper (which helps prevent the chain from dropping off the chainring) naturally impacts any aerodynamic gains.

However, compared to a 2x setup, this configuration offers greater chain security, which can be crucial in races like Paris-Roubaix.

For example, Wout van Aert used a 1x SRAM Red eTap AXS system in both the 2023 Milan-San Remo and Paris-Roubaix, likely for this specific reason.

Depending on the setup, a single-chainring system can also be lighter. For instance, dedicated climbing bikes almost always use a single-chainring system.

Climbing bikes are typically set up with a 1x drivetrain as it can be lighter and doesn’t require two chainrings.

Disadvantages of Single-Chainring Systems on Road Bikes

So, while there are advantages to a single-chainring system on road bikes in certain situations, it also has some disadvantages.

The most obvious one is that giving up your front derailleur and one of your chainrings means a significant reduction in the number of gears and the gear range on the bike.

This can be compensated by using a wider-range rear cassette and carefully matching the chainring size for each ride. However, achieving a gear range close to a 2x system with a 1x setup involves some compromises.

The more compact cassettes used with 2x drivetrains provide greater flexibility in finding the optimal cadence.

First, wide-range cassettes (if you want to maintain a gear range similar to a 2x system) are often heavier than more compact cassettes.

What's more troublesome is that they often exhibit more noticeable "cog jump," leading to a less pleasant shifting experience.

This can be annoying because road gradients tend to be more gradual than off-road ones, and the larger gaps between gears may make it difficult to find the optimal gear and cadence in some cases.

Wide-range cassettes for 1x drivetrains, such as the Campagnolo Ekar 9-42t, offer an impressive gear range, but they also come with compromises.

Smaller cogs, like the 10t or 9t on SRAM AXS or Campagnolo Ekar cassettes, and chainrings also tend to be slightly less efficient (as the chain has to bend at a steeper angle compared to larger cogs).

While SRAM may argue that this is not truly "cross-chaining," a 1x system still forces the chain into more extreme angles at both ends of the cassette compared to a 2x system.

Both of these factors can increase friction losses in the drivetrain, which, in turn, means that a 1x system will deliver less power to the wheels than a 2x system (all else being equal).

The original 3T Strada's 1x drivetrain might be more aerodynamic, but it could also be less efficient.

So, how much of an efficiency loss are we talking about? In May 2019, VeloNews and CeramicSpeed tested the friction differences between 1X and 2X drivetrains. Let’s take a look at their testing protocol and results, then I’ll do some calculations to see how these friction losses might affect your speed.

• Testing

VeloNews/CeramicSpeed tested two different drivetrain setups:

• 1X system: Using a SRAM Force 1 rear derailleur, a 48t chainring, a PC-1170 chain, and a 10-42t cassette.
• 2X system: Using a Shimano Ultegra rear derailleur, 53/39t chainrings, an HG701 chain, and an 11-34t cassette.

The reason for choosing these systems was that they have the same gear range, allowing for a direct comparison of friction losses at the same gear ratios. Both systems were installed on a test bike capable of calculating friction losses for each gear combination. The test machine simulated a rider pedaling at 95RPM, producing 250 watts of power.

Chainline Matching: The 1X system was set up so that the 5th gear on the smallest cog provided a straight chainline, while the 2X system had a straight chainline with the 53t chainring in the 5th gear and the 39t chainring in the 8th gear.

CeramicSpeed also removed factory lubricants and re-lubed both chains with the same mineral oil. Bo

th chains ran for the same test duration.

Eslatma: CeramicSpeed previously found that friction wasn't increased when using a 1X chainring compared to even-spaced 2X chainrings. They also found that the jockey wheels of the rear derailleur didn’t affect friction.

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Here are some key conclusions from the test:

• Friction losses generally increase as the gear ratio increases.
• The 2X system was more efficient in every gear (assuming you shift to the big chainring after the 39x21t).
• Friction loss differences ranged from 1 watt (48x21t / 53x23t) to 6 watts (48x10 / 53x11).
• The 1X system had more friction loss in a perfect chainline (48x18t) compared to the 2X system (53x19t).
• Efficiency for the 1X system ranged from 96.0% to 92.4%, with an average of 95.1%.
• Efficiency for the 2X system ranged from 96.8% to 94.8%, with an average of 96.2%.

CeramicSpeed calculated that the average friction loss for the 1X system was 12.24 watts. This was determined by adding up the power losses for each gear in the 11-gear range and dividing by 11. For the 2X system, the result was 9.45 watts, meaning the average difference between the two systems was just under 3 watts.

• Why is 1X Less Efficient than 2X?

There are four primary sources of friction in the chain. The most obvious is the angle of the chain's bend, which causes more friction as the chainring and cassette teeth scrape more intensely. Chain tension, the articulation of the chain's links, and chain speed also play crucial roles.

Chain tension increases the pressure the chain exerts on the chainring and cassette. When using smaller chainrings and cogs, chain tension is higher. Chain articulation refers to the degree to which the chain must pivot at its pins, and when wrapping around smaller cogs, it results in higher friction. Chain speed refers to the rate at which gears interact with the chain per minute. This increases when the chain runs over smaller cogs.

Ultimately, the 1X system can't maintain a completely straight chainline across its gear range, and the smaller chainring leads to higher chain tension, more articulation at the chain’s links, and increased chain speed on smaller cogs.

These additional factors help explain why, even on a perfectly straight chainline, a 1X system still consumes over 2 watts more power than a 2X system. It also explains why the 48x21t gear produces the lowest friction, despite the chainline not being perfectly straight—the reduction in chain articulation and speed compensates for the slight increase in friction from a non-ideal chainline.

• How Much Does the Speed Difference Matter?

Here’s where things get interesting!

Using BikeCalc, we can determine the speed of a bike at each gear ratio, assuming a 700x44C wheel and a cadence of 95RPM. Then, we can input various power outputs (231 to 242 watts, depending on the gear) and the rider+bike weight (85kg) into a Bike Calculator to figure out the speed and time differences over 100km.

Smallest Efficiency Difference:

In 48x21t (1X) vs 53x23t (2X), you will ride at 29.12 km/h @95RPM. A 1-watt difference results in a 0.06 km/h speed advantage for the 2X system. Over 100km, the 1X system will be 25 seconds slower (0.2%).

Largest Gear:

In 48x10t (1X) vs 53x11t (2X), you will ride at 61.28 km/h @95RPM. A 6-watt difference results in a 0.14 km/h speed advantage for the 2X system. Over 100km, the 1X system will be 14 seconds slower (0.3%).

Smallest Gear:

With a 48x42t (1X) and 39x34t (2X), you will be riding at 14.49 km/h @ 95 RPM. The 2.5-watt difference results in a speed advantage of 0.15 km/h for the 2X drivetrain. Over 100 kilometres, the 1X system will add 3 minutes and 50 seconds to your ride time (0.9% slower).

The front derailleur is already excellent

Shimano’s Dura-Ace Di2 RD-R9250 front derailleur is arguably the best in its class, and most modern road bike groupsets offer excellent front shifting.

Regardless of the specific advantages and disadvantages mentioned above, the primary reason I won’t be switching to a 1X setup on my road bike anytime soon is that the current front derailleur is simply too good.

Almost all levels of modern road bike groupsets offer excellent front shifting performance. There is no doubt that electronic groupsets are currently the gold standard for front shifting. Many people (myself included) believe Shimano is the market leader in this field, but SRAM and Campagnolo are not far behind.

However, even mechanical groupsets these days offer superb front shifting performance.

Shimano’s flagship 105 R7000 groupset offers flawless front shifting at an affordable price.

Of course, improper shifting or poor setup can still cause issues, but front shifting typically doesn’t feel like a problem that needs to be solved.

Is the Classified Powershift Hub a Game Changer?

Classified’s Powershift hub is an interesting technology, seemingly performing excellently, but it’s not exactly cheap at the moment.

The Classified Powershift hub gear system is a wireless-controlled 2-speed planetary gear system integrated into the rear hub. It is often touted as the “front derailleur killer,” but I believe that this is unlikely to happen anytime soon.

It does indeed offer solutions to many of the drawbacks of the above-mentioned single-chainring systems—perhaps we can ultimately have the best of both worlds.

However, for most people, the problem is that it’s too expensive. For instance, Classified's R50 and G30 Powershift wheelsets cost £2,300 (around 20,000 RMB), which is only £25 less than the aforementioned Trek Émonda ALR 5 complete bike.

What do you actually get for all that money compared to sticking with a 2X system? A tiny improvement in aerodynamic efficiency... and that’s about it?

Of course, if Classified's hub technology eventually becomes popular and catches on, the cost may decrease over time.

Double Chainring is Still the Best Choice

For an all-around road bike, it's hard to beat the versatility offered by a 2x drivetrain.

All of my mountain bikes are single-chainring setups, but I personally think transferring this setup to a road bike doesn’t make much sense. For most people, a 2X setup remains the best option.

Given the performance and versatility offered by modern front derailleurs, the marginal potential improvements provided by a 1X system don’t seem worth it.