Much ado about 12-speed, part 2: Why SRAM’s new road drivetrain is potentially brilliant

Around a month ago, the prototype 12-speed second version of SRAM’s wildly popular Red eTap wireless electronic road bike drivetrain was spotted on Team Katusha’s race fleet during the Saitama Criterium in Japan. The real innovation here, however, isn’t in adding the 12th cog. It’s how SRAM changed everything else to suit.

Italian stalwart Campagnolo released its 12-speed Record and Super Record groupsets in early 2018. However, due to its heavy traditionalist racing approach to development, it kept to a relatively narrow spread of 11-29T and 11-32T cassettes, paired with traditional 50/34T, 52/36T, and 53/39T chainring options. This feels like a huge missed opportunity.

Poring over the SRAM prototype groupset shows that the firm seems to have an ear firmly to the ground with how it developed this drivetrain. I’ll explain why.


These days you can’t talk about a new groupset without playing “count-the-sprockets” on the back wheel, and the Red eTap prototype doesn’t disappoint. As usual, Red-level cassettes are machined from a single steel billet for light weight and strength, then bound with elastomer rings in between cogs to dampen shift noise.

Photo credit: Kei Tsuji/CyclingTips

What’s peculiar to SRAM is where the company decided to add its 12th cog: at the very top end. Just like with the Eagle 1×12 mountain bike groupsets, these new cassettes top out with a 10-tooth cog, instead of the 11T high gear limit of the thirty-year-old Shimano freehub. SRAM can afford to do this because it’s had its XD driver body out since 2015, when it first debuted along with its 1×11 road bike and cyclocross drivetrains – and this is the foundation that allows use of such a small cog.

For the 12-speed version of Red eTap, SRAM eyes more widespread adoption of XD, which now sprouts 1.85 mm more width in XD-R form – just as Shimano freehubs did when moving from 10 to 11 cogs on road bikes.

XD-R hub driver body aside, this change seems…relatively tame. Or is it?


Photo credit: Kei Tsuji/CyclingTips

Borrowing a trick from the mountain bike world, SRAM adopted direct-mount fitment for these 12-speed eTap prototype cranks. This means there is no more chainring spider and BCD (bolt circle diameter) to account for when making chainrings; they attach to the crank via a splined interface and a few bolts.

Direct-mount cranks are nothing new, but the chainrings certainly are. Instead of the usual options, SRAM fields two strange double combos: a 50/37T and a 48/35T. Doing the math yields a 13-tooth difference for both options, which is much less than the 16-tooth maximum that your usual front derailleur is limited to. As I can attest with my old FSA Omega 46/36T cyclocross crank, a smaller difference between chainring sizes automatically reduces the shock of an upshift to your legs. The smaller gap between chainrings can help with front shifting, an area where SRAM has historically lagged behind Shimano and Campagnolo.


Photo credit: Kei Tsuji/CyclingTips

Remember that it doesn’t matter how many gears you have on the bike; it’s the spread of gear ratios that’s more important. This is where SRAM really shines with the 12-speed Red eTap prototype; it doesn’t make maximum sense until you combine chainrings and cassette together.

The 50/37T chainring option is meant to replace the 53/39T. How so? Let’s pair it with the new 10-28T cassette as an example, and have this installed on a fictional bike with 700C x 28 mm tires. The 50×10 combo gets you a top gear of 133.46 gear inches, while on the other extreme, the 37×28 provides a low gear good for 35.23 gear inches.

By comparison, if we repeat this with the ubiquitous 53/39T x 11-28T drivetrain, the 53×11 combo yields a top gear of 128.66 gear inches. On the other end of the scale, a 39×28 low gear is good for 37.1 gear inches. SRAM have cleverly increased the gear ratio spread by two gear inches in either direction.

Using the same cassette and wheel/tire size, how does the new 48/35T double chainring combo fare against the popular 50/34T option?

50/34T x 11-28T nets you a low gear of 32.3 gear inches and a top gear of 121.45. SRAM’s new 48/35T x 10-28T drivetrain option provides a low gear of 33.37 gear inches and a top gear of 128.13. This almost matches the low gear of the 50/34T x 11-28T combo, while bettering top end by 7 gear inches…and you’d have to be travelling really fast or going downhill to spin out either top gear combination.


All this, however, is leadup to what I think is SRAM’s master stroke: the new cranks are definitely friendlier for more riders.

Gravel, touring, urban, cyclocross, and adventure cyclists all know the merits of a crank that has chainrings smaller than the usual 50/34T “compact” range. Weight aside, I was surprised just how usable Hyro’s original 46/36T cyclocross cranks were, only really being let down when climbing very steep inclines. My old 46×12 top gear combination was sufficient for high-speed cruising on the flats, and very good for commuting. The new SRAM Red chainrings and that new 10T cog go quite a bit into offering drivetrain options satisfying both the gravel/adventure riding crowd and the criterium racer set.

What’s more, because of the popularity of larger cassettes and the move to direct-mount chainrings, SRAM has no technical hurdles stopping it from offering even lower gearing on its cranks. The “magic” 46/30T gravel option might not be an impossibility.

Photo credit: Kei Tsuji/CyclingTips

Other changes on the prototype Red eTap groupset may or may not be indicative of the finished product. There’s the asymmetrical chain, where the plates are straight on the outside instead of scalloped. James Huang of CyclingTips muses the new rear derailleur may be hiding a “Type 3” friction clutch mechanism, similar to what Shimano did with its Ultegra RX units. They’re all just icing on the cake: the gearing is the real story I think.

We will know more details when SRAM makes its formal announcement in January 2019.


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