SRAM has been teasing a wireless version of their XX1 Eagle transmission for some time, using the wide-range, single ring setup of their mechanical groups with the eTap wireless electronic shifting trickery seen on their road groups. We reckon it's likely to land properly at some point this year, but in the meantime, here's everything we know about it so far...
Firstly, we're pretty damn sure it must be nearing a full production run as it was teased heavily during spring 2018, with a 'spy shot' being taken of the groupset on Scott rider Nino Schurter's bike by Michal Cerveny at the Stellenbosch XC World Cup. We put that in inverted commas because SRAM doesn't have a habit of letting new product be seen in the wild unless they want it to be seen in the wild - that was a deliberate product tease, likely to gauge how the public feel about the product as well as generating some hype.
What we know
Technology-wise, the picture from Stellenbosch showed a dedicated mountain bike specific rear derailleur that's very different from the wireless road RED eTap unit.
Wide ratio cassette and clutch equipped mech
First up, the parallelogram links of the mech are perpendicular to the cassette, while the road unit is angled. That's to cope with the wider range cassettes used on SRAM's single ring mountain drivetrains.
The knuckle is also much bulkier as it's obviously housing a clutch mechanism, while the jockey wheels are offset in the cage to allow a cassette with a wider range than the 32T biggest cog of the roady group. Seeing as that's a SRAM Eagle XX1 cassette in the background of the spyshot, it's likely to share the same 10-50T range and 12 ratios, but who knows if they'll pull out a wider range unit.
It's very possible that they will make a more closely spaced but narrower range block (10-42T?) that pro-cross-country riders might want to use to reduce any big jumps in cadence they need to make when moving through the gears. That might also work nicely for enduro racers who are strong enough to push harder gears but want to keep spinning at an optimal rate.
Rotating shift action with vibrating feedback
Thanks to the patent applications, we also have some idea of what the shifters will look like, but much more interestingly, how they will function. As the pictures show, they'll work by using a rotating collar that's fixed to the bar. Fixed to this collar are two paddles patent outlines that they'll work in two possible ways - one where the ring is moved forwards to engage a gear and then back to drop a gear, or another where you push the paddles a certain distance to engage a gear but then push it further in the same direction to drop a gear.
That tallies with being able to use your thumb move up the block and your index finger to go down the block, or just your thumb alone to do both - the Doubletap system seem on their road groups is functionally similar in this respect.
The patent also lays out how the shifter will give audio or haptic feedback when shifting - we imagine this will be either a beep and/or a vibration, most likely selectable through a wireless setup interface. It doesn't look like there's any visual shift indicator - that big round bit looks to us like where a coin cell battery would sit.
It's also possible that there will be eTap Blips - small shift buttons that can be positioned anywhere - a la Red eTap. These might be good for cross country racers for sticking on bar ends (assuming anyone still uses those) but we can't think where they'd be useful elsewhere on a mountain bike setup.
What we don't know
While the overall function of the mech and shifter is already pretty easy to guess at from the existing eTap systems, but it's the detail we lack.
Will it have a bigger battery?
As mountain bikes tend to live in dirt and grime, a electromechanical shift system will need to produce more grunt to move a muddy mech up a cassette than a road equivalent. That means it'll need a stronger motor, which in turn will require more battery power - or a much reduced battery life from the same sized battery, which still needs to be mounted on the mech itself.
It'll be interesting to see how SRAM handle this - battery tech is pretty advanced so it's hard to squeeze much more juice from the same size - but we suspect going bigger will be better.
Will there be e-Bike integration?
e-MTBs are becoming a much bigger deal these days, with sales leaping ahead of 'normal' bikes in some areas. Give the functionality that having a Bluetooth or ANT+ connection would give, it'd be possible for the SRAM drivetrain to work in harmony with an electric bike motor to give automatic shifting capability, likely based on cadence and power output.
SRAM has worked with Bosch on e-bike projects before, so they'd be a natural partner - especially as there's already a Bosch motor/Rohloff hub gear system that works to cut power at specific times to ease shifts. A similar system between SRAM and Bosch would smooth up derailleur shifting and also massively reduce stress on drivetrain components - extending lifespan.
Either way, we're really rather keen to see what the future holds. We'll update this article as soon as we know more...
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