Road riders have been using double chainring cranks for decades but there is growing interest in 1×11 transmissions. SRAM is the first manufacturer to develop a 1×11 transmission for road use, and in this report, CTech editor Matt Wikstrom takes a closer look at the promise of the new system.

The front derailleur was a relatively late invention, appearing during the 1950s at about the midpoint in the life of the modern bicycle. Development of the device was helped along by refinement of the rear derailleur. Like early rear derailleur designs, the first front derailleurs were lever-operated but they quickly evolved to become cable-operated, and the two devices have been mainstays for road groupsets ever since.

The extra chainring immediately doubled the number of gear ratios available to riders at the time and it was only a matter of a couple of years before triple cranks were on offer. While there has been considerable refinement in the years since, derailleur design has essentially remained unchanged for sixty years, although the number of cogs on the rear hub has grown considerably.

Now that 10- and 11-speed transmissions are commonplace, riders have started re-assessing the importance of multiple chainrings. This is most evident in MTB, where there has been a general move away from triple cranksets to doubles, and more recently, single chainrings. Rear cog sizes have grown to preserve the range of gear ratios and the net result is a transmission that has no redundancies, requires less maintenance, and is easier to use.

At face value, a 1x transmission appears ill suited to road cycling—if asked, most riders would rather add more gears than give them up—but the promise of a simpler transmission that is easier to use is undeniably appealing.

SRAM believes there is merit in the system and has started marketing dedicated 1×11 transmissions for road use with some compelling arguments, but is it just a passing fad? Or is it possible that road riders draw false comfort from having a second chainring?

Let’s start with the numbers

SRAM’s road 1×11 transmissions are built around fairly large chainrings such as 48T or 50T. That number alone will frighten most riders, because they would never contemplate tackling a climb with a chainring that big. However, SRAM pairs it with a wide range cassette—11-32 or 11-36—to provide 11 discrete gear ratios that match many of those offered by a 2x transmission (see Figures 1 and 2).

For those readers that are unfamiliar with analysing gear ratios, I’ve addressed this topic in an earlier post. Converting the gear ratio into gear inches provides a simple way for comparing different gearing combinations: a large number (in gear inches) equates to a high gear that is hard to push up a hill, while a small number equates to a low gear that is easy to spin.

Figure 1 compares the gearing for a standard 53/39 crankset with a 1×11 transmission. The lowest gear ratio offered by a 53/39 double crankset in combination with an 11-26 cassette is 41 gear inches; combing a single 50T chainring with an 11-32 cassette yields a low gear of 42 gear inches. At the other end of the range, the 2x transmission offers a high gear of 130 gear inches compared to 123 gear inches for the 1x transmission.

Figure 2 shows the gearing for a sub-compact 52/36 double crankset in combination with an 11-28 cassette versus a 1x transmission 48 x 11-36. The low gear is identical for the two systems (35 gear inches) however there is a marked difference between the highest ratios (128 gear inches versus 118).

In both instances, the lowest gearing of a 1x transmission compares well with a 2x transmission, the highest gear ratios fall short, such that the 1x system limits the top-end speed of the bike. For some riders, this will be a deal-breaker, especially if they are hunting for Tour de France sprint victories or downhill KOM glory on Strava.

However, there is more to consider than just the upper and lower gear ratios of the two systems. Indeed, there is a fundamental difference in the rate of development for each transmission.

Looking at the example in Figure 1, 53/39 x 11-26 offers 16 discrete ratios with a range of 89 gears inches. As a result, there is an average of 5.6 gear inches between each gear ratio. By comparison, 50 x 11-32 offers 11 gear ratios with a range of 81 gear inches, making for an average of 7.4 gear inches between each gear ratio.

Similarly, a sub-compact 52/36 crankset offers an average rate of development of 5.8 gear inches compared to 7.5 gear inches for a 1x transmission (Figure 2). Put another way, if the rate of development for each transmission is like climbing a set of stairs, then the steps between each ratio are ~30% taller (on average) for a 1x transmission.

What does this difference mean for the rider? Seasoned riders will probably worry that the steps between the gears are too large, making it difficult to maintain a steady rhythm, but there is no golden set of ratios that will suit every rider. After all, the suitability of any given chainring and cassette combination depends upon the demands of the individual’s riding terrain as much as their personal preference. However, it is clear from the discussion above that a 1x transmission is quite distinct from a 2x transmission, and therefore, is best viewed as an alternative rather than a substitute.

1x transmission tech

There is more to a 1x transmission than simply chucking away the front derailleur and fitting a larger cassette. To start with, a long-cage rear derailleur is required to suit the larger cogs, but then there is the issue of chain retention. In the absence of the front derailleur (and any other chain retention device), a 1x transmission requires a robust and reliable mechanism to ensure that the chain does not suddenly derail.

A conventional road chainring has sculpted teeth that are designed, in places, for the chain to derail with ease. In contrast, 1x-specific chainrings are designed to “grip” the chain with alternating narrow and wide teeth. The alternating pattern is critical, because it mirrors the difference in widths for the inner and outer plates of the chain, improving the hold of the teeth on the chain.

While 1x-specific chainrings are reasonably effective on their own, they cannot contend with the extra length of chain associated with a longer derailleur cage. Any sudden rotation of the cage (eg. during rapid shifting or over uneven terrain) can create enough slack to derail the chain. Thus, 1x-specific rear derailleurs are equipped with a clutch that limits the motion of the cage at the lower knuckle of the derailleur. By keeping the derailleur cage in check, the clutch maintains extra tension on the chain to keep it secure on the chainring.

MTBers have proven that the combination of a 1x-specific chainring with a clutch-equipped rear derailleur is reliable in all but the muddiest of conditions. As such, the system should translate easily to the road, however there is room to wonder about the risk of sudden chain derailment (especially during a high-speed sprint).

At present, SRAM has two 1×11 groupsets for road use, Force 1 and Rival 1, with options for standard rim calipers, hydraulic rim calipers, and hydraulic disc brakes. Both groupsets include clutch-equipped rear derailleurs and 1x-specific cranksets with chainrings ranging 38-54 teeth (in 2-teeth increments). There are a few different 11-speed cassettes on offer (11-26, 11-28, 11-32 and 11-36) including a massive 10-42, however buyers will need a rear hub fitted with SRAM’s XD freehub body before they can fit this option.

By contrast, there is no indication from Campagnolo or Shimano that they are interested in developing a 1x transmission for road use. Shimano recently introduced an option for a 1×11 transmission with the latest iteration of its off-road XTR groupset but the company maintains that 2×10 and 2×11 transmissions offer much greater utility.

Thus, the 1x road transmission market essentially belongs to SRAM. A few manufacturers are specifying Force 1 and Rival 1 for their road bikes for 2016, but numbers are very limited. As such, early adopters will probably have to buy a groupset rather than hope for a complete bike. Australian pricing for a Rival 1 groupset starts at $1,050 (mechanical rim brakes) and $1,740 for a Force 1 groupset (also mechanical rim brakes).

Road-testing the Force 1 groupset

SRAM’s flagship 1x road groupset, Force 1, is a mid-level offering but the shape and styling of the components closely resembles Red22. I spent a week riding a Force 1 groupset with hydraulic rim brakes, and found that the braking performance was identical to Red22. The quality of shifting was also familiar and comparable, however upshifts were noticeably heavier because of the extra chain tension generated by the clutch in the rear derailleur.

I’m used to riding a bike with a compact crankset and spend most of my time in the big ring (ie 50T) on my daily rides. As such, the single shift lever on the Force 1 test rig wasn’t any kind of novelty but there was a measure of luxury in never having to worry about trimming the front derailleur.

I found that the spacing between the gear ratios was generally good (the bike was fitted with an 11-36 cassette) though there were times when a downshift, especially to the smaller cogs, could be abrupt. A few moments was all that was required to adapt; if I was feeling strong, I would push a little harder until I had the cranks turning over with ease; and if I was feeling less so, I’d surrender the effort and go back to the easier gear.

The best part about using Force 1 was riding into a climb with a high gear ratio, and with one sweep of the right shifter paddle, moving quickly to a low gear ratio. With a 2x transmission, I would spend much more time anticipating the front and rear shifts that would be needed to find a suitable ratio for the climb. The 1x transmission allowed me to leave the shifting until the very last moment, and I couldn’t help the mad glee that came with it.

Much of the same sense was waiting for me at the top of the climb, where a quick series downshifts—click, click, click, click, click—was all that was required to find a big gear to attack the descent. True to SRAM’s claims, a 1x transmission is easier to use, though Campagnolo’s thumb button—or electronics—would significantly improve the efficiency of downshifting.

Finally, I didn’t have any trouble with the chain during the review period. It was steadfast and silent, and every shift always found the next cog quickly and smoothly. After a week on Force 1, I was taking it all for granted: I had more than enough gear ratios to tackle my local roads (including some steep ascents). The gearing was like a set menu, and while there were some occasions where I would have preferred à la carte, the whole experience was completely satisfying.

Summary and final thoughts

SRAM’s 1×11 road transmission is very easy to use and promises to improve the road cycling experience for many riders. Novice road cyclists in particular will benefit from the simplicity of the system (plus it will allow them to ignore lectures from their elders on the evils of cross-chaining). Commuters too, should benefit from the simplicity of the system, both in terms of its operation and ongoing maintenance.

Racers and all-day riders are less likely to find any appeal in a 1x transmission because they will want the extra efficiency that comes with more gear ratios and a lower rate of development. That may change in the coming years though, as more cogs are inevitably added to the rear hub. In this regard, it is worth noting that Shimano lodged a patent in 1996 that outlined the design for a 14-speed transmission.

We would like to thank SRAM Australia for providing a bike equipped with a Force 1x groupset to help with the preparation of this article.