It was just a matter of time. In a world in which electric mountain bikes are more and more widespread, it’s normal that the big producers of components for bicycles would start to develop products designed specifically for this kind of ebikes. That’s why SRAM presented its SRAM EX1 groupset for electric mountain bikes, just a few days after Shimano unveiled its new STEPS E8000 system.

Why a drivetrain specifically designed for e-mtbs?

Is this SRAM EX1 groupset something that was really needed, or is it only another development made mainly for marketing purposes? In this case, we are more convinced by the first option. The SRAM EX1 seems to be a real step forward, for at least two reasons:

1) Resistance to stress

Almost all electric mountain bikes have central motors. The reason is that they make it possible to keep the weight of the bike as centered and as low as possible, improving manouvrability; moreover, a central motor has a much more natural feeling, which helps in controlling its power output. A central motor acts directly on the drivetrain. The stress on the mechanical components of the drivetrain (chain, derailleur, pinions…) is therefore higher than on a normal mountain bike. Depending on the assistance level selected, even European-legal 250W motors can deliver peak powers of about 450W, and a torque of 80Nm. These are important values for a “normal” drivetrain, designed to withstand the stress of a normal, non-assisted cyclist. A hardier transmission system such as the SRAM EX1 can therefore be actually useful. The e-bikers who report an unsual and fast wearing out of the drivetrain are not few.

2) More specific features

Beyond the resistance to wearing out, a drivetrain specifically designed for electric mountain bikes can be designed having in mind their particular features. All high-range electric mountain bikes now available on the market use the latest standard in drivetrains, that is 1×10 or 1×11 systems. These are drivetrains designed to offer two things:

• a range of gears as wide as possible (that is useful both for going uphill on steep slopes and for maintaining a good cadence when going fast, without having to spin)
• a smooth and gradual change from one gear to the next (that is a difference between two adjacent gears which is not too big, so that you can always find the “right” gear and have smooth accelerations).

This is what is needed on normal mountain bikes. With an electric mountain bike, thanks to the motor, there are a few differences: you can maybe make do without the easiest gears; more importantly, you don’t need such a smooth and gradual change from one gear to the next. On the contrary, thanks to the rapid acceleration provided by an electric motor, with an 11-gear transmission you find yourself having to change gears very fast, and this actually hampers acceleration, rather than helping it; it’s also annoying; as we know, the moment when you change gear is always quite delicate, it stresses the drivetrain, and it makes you lose momentum. For this reason the new SRAM EX1 groupset has a cassette with “only” 8 gears, with an average difference between gears of 21% (as opposed to about 15% for standard drivetrains). Moreover, having less gears (8 instead of 11) makes it possible to have a much straighter chainline, reducing chain wear.

Let’s have a look at all the new components in detail.

SRAM EX1 Components

XG-899 Cassette

This is basically the main new thing. As already mentioned, it’s an 8-speed cassette, with an average difference between gears of 21%. All pinions are made of steel; they are a 11-13-15-18-24-32-40-48. This cassette can be mounted on standard, non-XD freewheels.

Of course the teeth of the pinions have been shaped to help shifting gears, in conjunction with the new chain. The price of the SRAM EX1 cassette is 450€.

EX1 Chain

The chain is larger than normal, so that it’s more resistant. It has been shaped carefully in order to make it work well with the Cassette. The price is 30€.

X-Horizon EX1 Derailleur

This derailleur has been designed to withstand the high torque of an electric mountain bike, and of course to work well with the rest of the drivetrain. It weights 289 grams and costs 165€.

Shifter X-Actuation EX1

The shifter has been redesigned too. It can only change one gear at a time, in order not to stress the drivetrain. The price is 55€.

Pinions for Bosch motor

As we know, Bosch motors have some gearing on the inside which requires an unusually small chainring. Sram has therefore developed 14, 16, and 18-teeth pinions for Bosch’s motors. The new transmission is of course compatible also with the Brose and Yamaha motors.

E-Crank EX1

Two versions: 170 or 175 mm; price: 55€

In conclusion

The new SRAM EX1 groupset for electric mountain bikes (available from august 2016) is definitely a step forwards for the industry, helping in its development and maturity. Because this is the very first groupset for e-mtbs available on the market, there’s a premium price. Would we advice buying an e-mtb based on this system?

Of course, if you can afford it, choose an e-mtb with a SRAM EX1 drivetrain over one with a standard drivetrain (everything else being equal, of course). Do that especially if you know you are a power user who pushes a lot on the transmission. However, it’s important to note that also electric mountain bikes with a standard transmission can be very good bikes; you don’t need the latest and greatest tech in order to have fun in the woods. After all, thousands and thousands of bikers have had a lot of fun in the past few years with the same “old”, standard drivetrains.