SRAM EX1 electric mountain bike drivetrain group

Hot on the heels of Shimano’s XT-level off road e-bike group, SRAM is introducing EX1 for motor-assisted mountain bikes. Why? Because they wanted to create a complete group that addressed the unique demands placed on equipment by an e-MTB. And because that market is growing rapidly regardless of how some folks feel about it and this gives them a complete group to offer as OEM spec.

Marcus Schneider, SRAM Germany’s general manager and e-bike product manager, says “most every e-bike out there now is using standard drivetrain and brake parts. And they’re good, but we thought we could do better.”

What’s different about an e-MTB? Well, there’s more weight, which puts more demand on the brakes, because you still need to stop in the same distance. And with drivetrains, when you shift on a traditional (i.e. human powered) bike, you typically let off the gears slightly, particularly when climbing. But with an e-bike, the motor is continuing to propel the drivetrain forward, so it needs to be able to shift under power.

And when you first hop on a traditional bike, it’s common to shift a bunch of gears at once to get it to the right starting point. And there are plenty of gear steps to help you find just the right one for your human powered bike. But with an e-bike’s immediate torque and power on tap, they didn’t need as many gear steps. In fact, all those extra gears could actually create chain management issues. So, they only needed eight cogs…

SRAM EX1 electric mountain bike drivetrain group

For standard bikes, each gear step is about 14-17%. Their new E-Block cassette pushes that to about 30%. That let them use fewer cogs -eight, to be exact- while still offering a massive gear range. It’s an 11-48 spread, using 11/13/15/18/24/32/40/48t tooth counts. The benefit to that is they could make a narrower cassette, which maintains a better chainline regardless of which gear you’re in.

SRAM EX1 electric mountain bike drivetrain group

They also added more aggressive chain management features to the cassette, using the shapes of the inner and outer chain plates to enhance shift quality and speed. They shaped the spider section of each cog to better counter chain forces. It’s a cluster build, putting the five largest cogs on a cluster plus three individual smaller cogs, which slide onto a standard freehub body with a spacer behind it to fill the gap between the it and the hub’s spoke flange.

sram-EX1-e-bike-electric-mountain-bike-drivetrain-group08

Since the gear gaps are now larger, the shifters were tweaked to limit shifts to just one at a time so the chain wouldn’t jam up or skip over the larger tooth jumps. They look exactly the same, but the internals are clocked to the new cog spacing.

SRAM EX1 electric mountain bike drivetrain group

The rear derailleur gets all the tech of their current X-Horizon units (clutch, etc.), but has been reinforced with a stronger pulley cage.

Connected them to the front is a new chain, PCEX1. It’s only slightly modified from their other non-hollow chains, getting an additional chamfer on the inner plates to improve shifting and chain management. They had customers always asking for stronger chains, but what they found was that once the chain management issues were solved, their chains were plenty strong enough.

SRAM EX1 electric mountain bike drivetrain group

For the cranks, they started with one of their forged alloy crank arms, then adjusted the Q-factor inward. Bottom bracket motors are wide, and with a standard crank arm, it can push the Q-factor fairly wide. They’re e-bike specific and use the ISIS mounting standard. They’ll offer alloy direct mount chainrings for the Bosch and Yamaha motor systems in 14/16/18 tooth counts, and a steel 34-tooth 104BCD chainring for Brose motor systems.

The entire system had to be designed in balance. If they made the chainrings, chain or cassette too hard or durable, it could cause the other ones to wear out to fast. So, it’s all designed in harmony to work with the rider and the extra forces put on the system by a motor. At launch, the group does not have aftermarket retail pricing. UPDATE: Yes, they will be sold separately, here’s pricing:

  • Crankset – $50 / €55 / £45
  • Direct mount chainrings – $20 / €20 / £15
  • Rear derailleur – $142 / €165 / £125
  • Shifter – $48 / €55 / £40
  • Chain – $25 / €30 / £20
  • Cassette – $390 / €450 / £345

SRAM Guide RE hydraulic disc brakes for e-mountain bikes

Bringing it all to a stop are the new Guide RE hydraulic disc brakes. They looked at all the progress they’d made with the Guide series and combined it with the power from their Code series. They used the Guide R lever, which uses their non-linked, bushing based pivot hardware and a cast alloy body. They used this, rather than their higher end levers, because it needed to be very robust in case the bike fell over and landed on it. Because, you know, motors and batteries are heavy.

SRAM Guide RE hydraulic disc brakes for e-mountain bikes

The levers are ambidextrous, able to be mounted regular or moto style depending on your preference. The DH-level four-piston, two-piece forged alloy calipers use steel-backed sintered metallic pads for better longevity. Retail for the brakeset is $133 / €145 / £112, claimed weight is 415g (800mm hose, 160mm Centerline rotor).

36 COMMENTS

  1. Interesting details on the tech and SRAM do make good arguments for 8-speed and larger gear steps.

    I just hope the new brakes are up to snuff. Riding in a tropical country like mine, a few trail buddies have had problems with their Guide brakes overheating as a system and getting strange behavior on prolonged rides under 36 deg C summer heat.

  2. I would guess the moped industry has been soft for years now so these electric mopeds have the bike industry salivating at a whole new market. That’s fine but i wish I didn’t have to see it on here.

  3. On the surface without the ebike connection, an 8 speed drivetrain with a huge gear range, better chain line and more robust components sounds pretty sweet. Does the cassette mount to a standard freehub body?
    Please double check my reading comprehension skills but it looks like this group can pair a 48t cog with a 14t ring? Wtf!? On an ebike? How can anyone with a motor still need a gear that low?

    • The front cog is turning 2.5 time faster that the crank on bosch motor, so a 14T is equivalent to a 35T, but I agree that 35/48 is still a very low ratio, especially for an e-bike

  4. this drivetrain is a dream come true for me. I LOVE 8 speed. im hoping they arent using 11sp spacing. i would use this on my regular MTB. anybody else remember those days that drivetrains lasted fiveever?

    • ” The benefit to that is they could make a narrower cassette, which maintains a better chainline regardless of which gear you’re in.”

      this would indicate it’s not the 8spd we know and love.

  5. On the Bosch system there is an internal transmission ratio of 2.5 between crank and chainring, therefore the low tooth count.

  6. 8 speed is new 12 speed 😀
    This drivetrain actually makes sense for regular low maintenance high longevity setup if you’re not too picky about the fine spread of gears.

  7. I got a buck that says I can motor up to 70kmh on my moped…. lemme see yer E-bike follow suit and I’ll think about spending 4x the money on it…. until then: keep working on it.

  8. If those are legitimately new calipers (& not just repainted Code ones) I expect we’ll either see new DH brakes soon, or sponsored riders switching to these calipers over the code caliper/guide ultimate lever most SRAM World Cup riders seem to be running these days.

  9. Because when you really, really want trail access harmed, you turn to Capitalism.

    They have what it takes to cause great damage, for the sake of a buck.

  10. I loathe seeing MTB ebike crap on here. I think they stink form the top on down. I am a big fan of ebikes for commuting, running errands, cruising about town or whatever, but they have ZERO business being on mixed use trails.

  11. How about no pedals and just a motor. The ebike thing is a conspiracy to get rid of cranks. Well maybe not, but here is my “one vote” against ebike reporting on Bikerumor in a positive manner..

  12. Wait, you mean…..
    If I throw dynamite into the lake, I get ALL the fish?!
    (deleted), I cant believe no ones done this before…

  13. Here’s what I don’t undedstand about ebike haters: Why is one form of mechanical assistance totally OK but another form of mechanical assistance isn’t? Derailleurs and 20+ gears are just as much of a crutch as an electic assist motor. In both cases you’re using a mechanical device to make pedaling easier or to go faster. Ditto for suspension. If you were really the purists you think you are you’d ride a rigid single speed (you know, like guys did in the Tour de France for several decades!)

    • Are you serious? With gears the watts you put out are constant no matter what gear you are in. Electric motors add watts. Not comparable.

  14. E-bikes have their place. Commuting, utility riding, cargo-lugging etc. are some obvious examples. I think everyone appreciates that when they become off-road electric motorbikes they can easily be used very anti-socially and spoil things for other trail users.

    • Re: “they can easily be used very anti-socially and spoil things for other trail users.”

      That’s how hikers and equestrians have always felt about mountain bikes. Hating on E-bikes won’t gain us any more favor with them.

  15. I have no interest in mopeds, but a wide range 8 speed cassette and an updated 8 speed derailleur sounds pretty good to me. I find myself skipping gears all the time on my 10 speed 11-36.

  16. First, look at that microdrive chainring. That’s gonna wear out faster than the chain. (deleted), are they trying to replicate all SunTour’s failures?

    “There’s 8-speeds because shifting under power over an 11 cassette jams it up.” Huh. Yeah, Shimano solved that like two years ago by integrating their shifter into the same system the motor is on. As you bang through the gears, the motor stutters its power in sync. OR, in the event of a non-electronically shifted drivetrain as on the Raleigh Detour IE, Shimano has optimized their chains to shift under full electric power load.

    “the shifters were tweaked to limit shifts to just one at a time so the chain wouldn’t jam up or skip over the larger tooth jumps” Cool. So having given up on making a functional front derailer, SRAM is setting the stage to lose the rear derailer, too.

    No listing of the actual Q-factor, so it’s wider than the XT group’s Q-factor for sure. Also, ISIS interface on the crank arms? Let’s dig up that dead horse so we can kick it some more.

  17. hi i want a special cassette with my own idea of adjacent ratios. just like certain types of bike have their own set up mountain ,hill climb ,road. i am in the city / road camp but being hilly need mountain ratio range and within that range i need certain conditions to accommodate my weedyness following a heart attack. so how can i get my ratio cassette rather than some body else’s

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