Snapped chains, noisy shifting and excessive wear – E-MTB drivetrains have long lagged behind the rest of the industry, and we’re all aware of the common short-comings of the current situation. However, with the launch of the world’s first E-MTB-specific drivetrain system, the SRAM EX1, the US brand is looking to revolutionise the market with its innovative features, ginormous gear range and just eight gears.

The world’s first E-MTB-specific drivetrain system: the SRAM EX1. This article has the lowdown.
The world’s first E-MTB-specific drivetrain system: the SRAM EX1. This article has the lowdown.

Amassing huge amounts of data, clocking up thousands of test kilometres and sitting through hours of meetings with motor manufacturers such as Bosch, SRAM’s hard earned research led them to focus their minds on two crucial topics: what are the specific demands on an E-MTB drivetrain and what are the failures of the current drivetrains?

The brand new SRAM EX1 drivetrain system emerged with only 8 gears, and an 11-48 tooth gear ratio giving a satisfying 436% gear range.

Während der Entwicklung musste sich die neue SRAM EX1 sowohl in der Praxis …
During development the SRAM EX1 endured the trails for data acquisition …
… als auch im Labor beweisen.
… and was put through its paces in the lab too – all in the name of performance.

SRAM EX1 – Fewer gears, better performance?

After analyzing their data, it dawned on SRAM that the current drivetrain issues are only in part due to the higher load on the E MTB drivetrain. In fact, the frequent snapped chains and excessive component wear we all have experienced is primarily due to multi-shifting, when we shift through multiple gears at once, doing so under the load of our electric motors. While on a conventional mountain bike you tend to shift gears at a low torque with high cadence, E-MTBs have a much more linear power curve and shifting is usually carried out under a high torque, meaning that it was only a matter of time before a key player in the drivetrain market designed something specific for this. Consequently, SRAM’s new EX1 E-Block cassette renders the need to double shift redundant, as each gear has a 30% wider ratio than the previous (13 %). Paired with their newly engineered cog architecture to generate faster and smoother shifting [both up and a down the cassette], a revised chain and narrower cassette to give a straighter chain line. All of which drastically minimizes wear and tear on the drivetrain, whilst shifting performance is significantly improved.

Prüfstände im SRAM-Test-Lab.
SRAM’s test lab has multiple test rigs.
Im Todesstern muss die Schaltung ihre Dauerhaltbarkeit beweisen.
In the Death Star test rig, the new drivetrain’s durability was put to the test.
Nebenan wird mit einer Highspeed-Kamera jeder Schaltvorgang penibel beobachtet und analysiert.
Then a high-speed camera allows engineers to scrutinize every aspect of the shifting.
Erste Fahrversuche werden direkt im Labor durchgeführt.
The initial tests with a motor were carried out in the lab.

SRAM EX1 – Bigger gear range, more battery life, more fun

At the heart of this new drivetrain system is SRAM’s EX1 E-BLOCK cassette, offering a massive gear range of 436 %. For Bosch motors, the EX1 offers 14, 16 and 18 tooth sprockets and has a 34-tooth chain ring for Brose and Yamaha mid-ship motors, meaning that long and steep climbs can be conquered. And thanks to the higher cadence due to running a smaller gear, your battery’s range is increased too.

Die fünf großen Ritzel der SRAM EX1 werden aus dem Vollen gefräst. Das aufwendige Verfahren spart Gewicht und erhöht die Haltbarkeit.
The largest five sprockets on the SRAM EX1 cassette are machined from a billet of case-hardened tool steel, a complex process that saves weight and increase durability.

SRAM EX1 – Familiar technology optimised

Not everything on the new SRAM EX1 drivetrain system is brand new; certain technologies have been borrowed from conventional mountain bikes and adapted for E-MTBs. Here’s an overview:

Das heutige Schaltwerk hat nur noch wenig mit diesen alten Funktionsmustern gemein.
The EX1 derailleur shares some traits with these former models.

SRAM EX1 derailleur

The derailleur looks remarkably similar to SRAM’s current 1×11 derailleurs, having taken functional cues from their X-HORIZON technology (that minimised ghost shifting and chain bang) but adapting them for use on E-MTBs by creating a longer cage, larger pulley wheels and a more powerful clutch mechanism.
Price: 165 €

Das Schaltwerk unterscheidet sich nur im Detail von den bereits bekannten SRAM 1x11-Schaltwerken.
It’s all in the details: the derailleur for the EX1 has been thoroughly redesigned although it looks very similar to the SRAM 1×11 derailleurs.

SRAM EX1 shifter

The EX1 shifter looks a lot like the ever-familiar SRAM shifters, however, in action its shifting is defined and precise, preventing double-shifting and thus minimizing drivetrain system wear.
Price: 55 €

SRAM EX1 cranks

The aluminium cranks are specifically made and are compatible with both ISIS bottom brackets as well as Bosch and Brose mid-ship motors.
Price: 55 €

Sehr schick! Die neue SRAM EX1-Kurbel am Moustache E-Mountainbike.
Very nice! The new SRAM EX1 cranks shown here on a Moustache E-MTB.

SRAM EX1 chainring

The steel chainring features the recognized X-SYNC tooth profile, guaranteeing chain management and reducing wear. It’s available with 14, 16 and 18 tooth sprockets for Bosch mid-motors and 34-tooth chainrings for Brose and Yamaha motors.
Price: 20 €

SRAM EX1 chain

Marginally wider but much more robust, the SRAM EX1 chain now features rounded edges to increase shifting precision and boost durability. In event of a defect, the drivetrain can be run with a SRAM 10-speed chain if needed.
Price: 30 €

SRAM ex1 schaltung drivetrain 8 gaenge e-mountainbike (1 von 24)

SRAM EX1 cassette

The cassette is at the core of the drivetrain, with 8 sprockets, and an 11-48 ratio giving a 436 % gear range. Thanks to the optimized tooth profile, shifting is improved, sticking to the SRAM E-MTB principle of one gear at a time – precisely and intuitively. The first three sprockets can be replaced individually, and the cassette is compatible with regular freehub bodies (not XD).
Price: 450 €

Herzstück der Gruppe: die SRAM EX1-Kassette mit 11–48 Zähnen.
Core of the drivetrain: the SRAM EX1 cassette with 11-48 teeth.

Availability of the SRAM EX1

Right now the drivetrain is only available to manufacturers, and will be sold on E-MTBs from summer 2016. As it stands, there are some pretty impractical legal barriers for retailers to mount different parts onto e-bikes. The EX1 has been released by SRAM as Original Equipment for use on E-MTBs. So it’s down to the manufacturer of the bike to decide whether they use it on their models. If you’re in any doubt, it’s worth asking qualified specialist retailers which components are permitted to be swapped. In order to fully benefit from the EX1’s potential, unleashing its performance, the dealer will have to alter the stored gear range in the motor control to make it compatible to the big cassette if you’re fitting the EX1 drivetrain system.

The SRAM EX1 drivetrain in reality

We’ve been out testing the SRAM EX1 exhaustively on Finale Ligure’s awe-inspiring and challenging trails, as well as on our mega diverse local trails. Check out our SRAM EX1 review to see if the world’s first E-MTB-specific drivetrain lived up to the hype.

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Words: Christoph Bayer & Robin Schmitt Photos: Christoph Bayer & Victor Lucas