Much ado about 12-speed

A long time ago, I wrote about my dad’s Peugeot P8 road bike, manufactured circa 1981. While that was a “ten-speed” bike, it was down to having a five-cog freewheel at the back and two chainrings up front: a so-called 2×5 (two-by-five) drivetrain.

My father’s Peugeot P8 road bike, circa 1981.

Almost forty years later, we say a 10-speed drivetrain refers to ten cogs at the back…and that’s not even the state of the bicycle drivetrain art. We’re now at 12-speed drivetrains, starting on mountain bikes with SRAM’s XX1 and X01 Eagle in March 2016, and Campagnolo on the road bike side with its 2018 Record and Super Record groupsets. While retaining 11-speed on the road, Shimano has followed suit with XTR M9100 being offered with either 11 or 12 cogs on the back wheel.

SRAM’s XX1 Eagle 1×12-speed drivetrain for mountain bikes, revolving around a 10-50T cassette the size of a dinner plate. Photo credit: BikeRumor.

Why this march toward ever more cogs on the cassette though? I take a look at the arguments for and against this proliferation.


With road cycling and racing, the historical focus was primarily on keeping a tight spread of gears on the cassette. This is to help keep a rider’s pedaling cadence as constant as possible, with the smallest possible jumps between the next easier and harder cogs to minimize “shift shock.” Not long ago, it wasn’t unusual to have 11-23T and 11-25T cassettes, which have a very narrow gearing range (the difference in size or number of teeth between easiest and hardest cogs), but are ideal for criterium races in the flats. Heaven help you if you had to climb a long steep hill though…while you have a second smaller chainring to help, if that gearing isn’t low enough, it’s either you grit your teeth and grind your legs pedaling away, or you get off and walk.

Shotgun in San Mateo, Rizal province. Not the kind of terrain you want to climb if your bike’s cassette tops out at a 25T cog.

Lately, however, people have woken up to the realization that not all road cyclists are into racing or grinding away uphill at a low cadence. Some of them just want to be able to keep riding their bikes, staying in the saddle, and spinning their way up…slowly but steadily. I would say it’s at the 10-speed level that gearing becomes an acceptable compromise between wide range and cadence control.

Both my bikes have Shimano Tiagra 12-30T 10-speed cassettes.

Looking at Shimano’s Tiagra 4600 and 4700 road bike groupsets is a good way of seeing how things have changed. Both are 10-speed, but Tiagra 4600 topped out with a 12-30T cassette option. Tiagra 4700, by contrast, offers 11-32T and 11-34T cassettes. Just five years ago, a cassette with a 34T cog was mountain bike material.

With its professional-grade Dura-Ace R9100 11-speed groupset, launched in 2017, Shimano even offers an 11-30T cassette option too. Sacrilege?


At the launch of Cannondale’s revamped 2018 F-Si, its premier cross-country hardtail mountain bike. Photo credit: Cannondale/BikeRumor.

Mountain bikers aren’t as concerned with cadence control as road cyclists are. While smoothness is still key, it seems applied in a different way compared to the souplesse roadies swear by – more to maximize grip at the tire/ground interface, and less for smooth pedaling. They’re more concerned about outright gear range, instead…and the simple reality is not all combinations of chainring and cog are distinct, nor usable (due to cross-chaining). On a 2×11 groupset, for example, one usually has only 14 or so distinct gears – the rest are duplicates.

The cockpit of a Rocky Mountain Instinct 999 MSL from 2014, featuring extra switches for the Rock Shox Reverb dropper post and the remote CTD adjustment for the rear suspension. Photo credit:

The way technology has exploded on mountain bikes in the past six years, there are so many controls and levers festooned on handlebars to think about: shifters, brakes, dropper posts, and remote suspension lockouts. Bombing down a trail at high speed, it can be mental overload to simultaneously read the trail’s features, plan your approach accordingly, shave off speed, work your shifters…you get what I mean.

SRAM’s effort to kill off front shifting, with its “1x” philosophy and the release of the original XX1 groupset in 2012, was a bid to simplify things, I think. You end up performing all gear changes with just one lever. It also freed mountain bike frame designers by reducing the variables contributing to “chain growth,” where compression of the rear suspension changes the distance between bottom bracket and rear axle. I don’t know all the details, but it seems to have an effect on the handling of the bike.

A look at the alternating narrow-wide tooth profiles of an XX1 chainring. Photo credit: BikeRumor.

To ensure that such 1x drivetrains did not lose the gearing range of an equivalent 2x system, SRAM made its cassettes with huge range – 10-42T on the original 1×11 stuff, then growing to 10-50T on 1×12 Eagle. Having 11 or 12 cogs with no front shifting comes pretty close to the 14 or so distinct cogs of a typical 2×10 or 2×11 drivetrain.

To combat chain drop, it adopted chainrings with tall teeth and narrow-wide tooth profiling, as well as a one-way friction clutch mechanism on the rear derailleur, which itself is restricted to horizontal operation only. These same tricks to improve chain retention make 1x drivetrains ideal for the short but frantic action of cyclocross racing, where the longest a race lasts is an hour.

While we’re on the subject of off-road things, the growing adventure/gravel bike category is sort of a middle ground of the demands of road bikes and mountain bikes. A single-chainring drivetrain is simpler and guards against chain drop, but many gravel riders insist on a double crankset for the increased gear range and options, especially for much longer events.


Shimano’s Hyperglide freehub body. In its original form, it doesn’t really support more than 10 cogs.

The jump toward more cogs introduces its own problems and growing pains. Honestly, this is a bit of a mixed bag and a minefield all on its own.

First things first: Campagnolo’s 12-speed cassettes will work on wheels and freehub bodies splined for Campagnolo 11-speed. End of story there.

Shimano’s classic Hyperglide freehub body, with its 13 splines, has been around for 30 years. Part of its universal appeal is that it is an “open” design: most hub makers worth their salt use it. Heck, even their competitor SRAM does. Unfortunately, it’s got limitations.

A DT Swiss wheel with an 11-speed road freehub. It is 1.85 mm longer than the original Shimano Hyperglide design, but is otherwise identical. Photo credit:

As drivetrains have gained more and more cogs in their cassettes, the original design no longer accepts more than 10 cogs, at least on road bikes. For 11-speed road bike gruppos, the freehub body had to be extended by 1.85 mm to accommodate the 11th cog; these hubs can still be used with 8/9/10-speed cassettes with an appropriate 1.85 mm spacer.

On the mountain bike side, Shimano did something clever: it dished the largest cog on its 11-speed cassettes so that it could still fit on a 10-speed freehub body and sit on top of the spokes. It also offers a pair of 11-34T 11-speed cassettes, designated “CS-HG700-11” and “CS-HG800-11”, which are meant to work with road bikes with 10-speed freehub bodies.

A 3D model of a rear hub with SRAM’s XD Driver freehub body fitted. The hybrid design has short splines, but also has screw threads, like rear hubs of old. Photo credit: BikeRumor.

The second limitation of the Hyperglide freehub body is it will not accept a cog smaller than 11T. When SRAM came out with XX1 and its 10-42T cassette, it introduced its XD Driver, a different freehub body with a slimmer end, which will fit even a 9T cog. The XD Driver and its XD-R road bike counterpart are also open standards, so many companies offer an XD/XD-R replacement freehub unit for their rear hubs.

To fit a 10T cog, Shimano had to come up with its new Micro Spline freehub body. Photo credit: BikeRumor.

With XTR M9100, Shimano faced the same dilemma, and thus did away with the Hyperglide freehub. They replaced it with the Micro Spline design, which has 23 smaller splines and is actually shorter.

There are two unfortunate consequences with Micro Spline: there is no backwards compatibility with cassettes made for Hyperglide freehubs; and Micro Spline is, as of this writing, a “closed” design. Shimano has chosen to withhold use of the design, leaving only itself and development partner DT Swiss as beneficiaries. This means nobody else can use it, although if you have DT Swiss hubs, you could upgrade them to Micro Spline if you want.


Another issue with ever increasing cog counts is that the chain has had to get narrower and narrower to match. This started with 9-speed, where manufacturers simply crammed one more cog in the space that used to be allotted for eight, and has continued to this day.

Another issue specific to 1x drivetrains is the chain line. We’re avoiding cross-chaining in the traditional sense of using big chainring and biggest cog or small chainring and smallest cog, but even with a single chainring up front, the sheer number of cogs out back means the chain can assume some pretty extreme angles as you shift and pedal.

While Shimano, SRAM, Campagnolo, and third-party chain makers like KMC and Taya have stepped up their game in quality, some people still think that making chains so narrow should have some disadvantage in terms of longevity. All I can say here is: your mileage may vary.


Campagnolo’s 2018 12-speed Super Record cassette, rear derailleur, disc brake, and chain. Photo credit: BikeRumor.

It baffles me that Campagnolo ignored the no-compromises approach that 12-speed brings. With that many cogs, a rider should no longer have to choose between close gear spacing and wide range. However, their largest cassette option is 11-32T. Not making a wider range cassette is a huge missed opportunity, I think – one that would have endeared them to gravel cyclists. Maybe when the tech trickles down to Chorus or Potenza level…

What does XTR M9100 mean for Shimano’s road bike transmissions? Right now, I wouldn’t be too worried. While the design has other benefits, the whole point of Micro Spline is fitment of a 10T cog, which I doubt anybody would use except for die-hard 1x fans. With Dura-Ace R9100, Ultegra R8000, and 105 R7000 still relatively fresh, I feel we may not need Micro Spline on the road just yet.

For my riding, I’m not concerned about having the most cogs. There is merit to having more, but more important to me is the gearing range spread across those cogs. While I haven’t had to use my 30T largest cog very often, I’m pretty sure my heavy carcass would welcome any larger cog available if I had to climb stuff like Shotgun or Pico de Loro.


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