Mountain bikes finally go wireless

Over the past decade there has been a massive simplification of the number of gears on mountain bikes. Whereas 27- or 30-speeds were once the norm, most contemporary riders use only 11 or 12 gears. Lighter bikes, fitter riders, and – most importantly – much larger rear cassettes, have enabled mountain bikers to revert to running a single chainring instead of a double or triple.

Despite the elegance of these single chainring systems, one feature has not changed: the cable-operated nature of all mountain bike drivetrains. Cables stretch or snap, and are generally way too vulnerable in an off-road riding and racing environment with exposure to rocks, roots and branches. The cable-operated drivetrain is also extremely finicky to calibrate, with the larger rear cassettes requiring extreme dexterity and intuition to perfectly align a chain and prevent annoying chain jumps or ghost shifting.

The solution? That would obviously be abandoning the cable-tension system altogether. And 2019 is the year this has finally happened.

Look Ma, no cables

Eight years after the first road cycling drivetrains, SRAM has introduced the first electronic shifting mountain bike groupset. Called AXS, it’s the culmination of an exhaustive six-year development cycle. Crucially, it’s truly wireless. Literally. Requiring no cables.

So how does it work? A wireless transmitter on the handlebar-operated shifter signals the appropriate gear selection to the rear derailleur, which now uses a tiny electric motor to shift the chain up and down the cassette, instead of cable tension. The promise is virtually lag- and skip-free shifting, even after hundreds of kilometres of riding.

The obvious question with anything electronic is battery life. Endurance for the electronic system is split into two gradings. The AXS handlebar shifter has an operational signalling life of two years before it requires a battery replacement. The system’s harder-working component, its rear derailleur, requires recharging every 20 hours.

But how does the rear derailleur convert battery power to instantaneously manipulating a chain that is being driven under strain by a rider? SRAM has engineered the AXS rear derailleur to operate a tiny onboard gearbox, with the little gears meshing to provide enough leverage to move a torque-laden chain to whichever gear the rider selects. One of the system’s most pronounced advantages is that it will shift cleanly and without hesitation while pedalling over rough terrain, an area where traditional cable-operated systems can prove frustratingly hesitant and annoying.

What’s the catch?

Of course you’re wondering about possible disadvantages. Well, you need to remain mindful of keeping the rear derailleur charged. And then there is the expense. As with any new technology, early adopters will pay a price for their vanguard mountain bike gearing privilege. Prices for the AXS drivetrain should trade at a 40% premium to comparable cable-operated systems for this season.

And although electronic shifting is a breakthrough of sorts for mountain bike drivetrains, the fact remains that with an exposed derailleur and rear cassette, riding damage and abrasion are still unaddressed issues. However, these could be solved by the adoption of proper sealed gearboxes, which remain inexplicably beyond the product strategy of large cycling component manufacturers.

The potential durability of a gearbox system would mean the end of that continuous maintenance revenue stream generated by riders having to replace chains and chainrings every few hundred kilometres…

Subaru Southern Africa sponsors Team Pyga Euro Steel. You can learn more about this MTB team here.