In a world where more cogs is often seen as better – SRAM just launched their 12-speed Eagle groupsets, after all – it's interesting to see a manufacturer taking a different direction. And that's what SRAM have done with their new launch, EX1, a groupset designed specifically for the transmission requirements of electric mountain bikes.
"In the early days of mountain biking, riders were forced to settle for products that had been designed for use on road bikes. Modifications were made, but the roots of the design were not completely purpose built, not mountain biking specific", say SRAM. "SRAM EX1 is poised to have the same impact on the E-MTB world. EX1 is the first and only drivetrain available today that was designed from the ground up specifically for e-MTBs."
So, what have SRAM done to make this groupset e-bike specific? Well, the extra torque of the motor puts a lot of strain on the chain and cassette, and because the motor is adding a significant amount of power there's not quite as much need for closely-spaced gears. So, SRAM have knocked the number of cassette sprockets down to eight, given the cassette a wide (11-48T) range with big gaps of around 30% between gears, and joined them to the motor with a heavier-duty chain.
The cassette is machined from tool steel: steel is much more hardy than alloy and the weight penalty is neither here nor there on an e-MTB. It's also narrower than a standard MTB cassette which means that the chain line at either end of the range isn't as extrame, which should reduce wear. It fits on a standard splined freehub, there's no need for SRAM's XD freehub body.
The groupset is designed for single shifts at a time rather than multiple shifts which are more likely to damage the chain when it's driven by the motor. To that end, the new front shifter only allows a single sprocket shift per action, as opposed to the multiple shifts that are possible with a standard mountain bike shifter.
The derailleur is new, though it uses the same X-HORIZON design as SRAM's other mountain bike mechs. It's specifically designed for the job of shifting on an e-MTB though, which means it's optimised for low-cadence shifts under heavy load, which is what you tend to get when you're riding under power.
The new EX1 transmission components are paired with new brakes: SRAM Guide RE. They're not new, exactly, more a fusion of tried-and-tested components already made by SRAM. They use the Guide R lever and pair that with a 4-piston calliper derived from the Code range, which is popular with downhillers and provides more power than the Guide R calliper that's normally paired with the lever.