# SRAM EX1 - eBike specific drivetrain



## jazzanova (Jun 1, 2008)

https://dirtmountainbike.com/news/s...specific-drivetrain-updated-guide-brakes.html

HOT ON THE HEELS OF SHIMANO LAUNCHING ITS FIRST EBIKE MOTOR, SRAM INTRODUCES ITS EMTB SPECIFIC DRIVETRAIN (WHICH WE'RE PRETTY SURE IS A WORLD FIRST) AND SOME UPDATED GUIDE BRAKES.
Previously on an eMTB you would have to use a standard drivetrain and brake set and hope that it could handle extra demands of an electric mountain bike. Thanks to SRAM that will no longer be the case.

SRAM EX1 DRIVETRAIN
SRAM has traditionally designed drivetrains around high cadence-low torque usage. The introduction of eMTBs has turned this on its head as riders can now pound up hills putting down a high torque and turning their cadence right down to achieve the same power output.

Because of this, SRAM has put most of its focus into the cassette and chain on the EX1 drivetrain. The cassette is an eight speed with a whopping range of 11 - 48t (436 per cent) which is almost Eagle levels of spread.

The steps between the cogs are about 30 per cent, which is much bigger than any current drivetrain, SRAM claims this makes them more "purpose-driven" as you can be less subtle about things with the saving-grace of a motor to back up your legs.

It's also worth noting the EX1 shifter only allows one shift at a time so you won't suddenly find yourself under powered or spinning out thanks to a mis-shift - this will hopefully mean fewer snapped chains as well.

The cassette is complemented by the new EX1 chain that is wider than a standard chain and therefore claimed to be more robust. It also wraps around a bigger proportion of the climbing gears to reduce wear.

Finishing off the drivetrain is a new crank that is compatible with Bosch, Brose and Yamaha motors. There are also Bosch compatible sprockets available with 14, 16 or 18 teeth and 34-tooth chainrings for Brose and Yamaha motors.


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## fos'l (May 27, 2009)

Really interesting; thanks.


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## WoodlandHills (Nov 18, 2015)

More proof that eMTBs are just a passing fad, LOL I wonder why SRAM isn't paying attention to their core customers, the ones who have been buying their products through thick and thin and who are against any sort of ebike access to MTB trails. It is almost like they didn't want to get stuck fighting for share in a static market and decided to expand the size of the MTB business and thus their profits. I guess they've joined that other sell-out: Specialized........


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## Harryman (Jun 14, 2011)

SRAM's biggest market is OEM, so you can bet that they want to stay on the bikes their OEM partners are selling. Ebikes are not a small market elsewhere, and it'll only grow here, it's no surprise. They are more aggressive than Shimano and most other companies which leads them to usually be the first major player in sub markets and with innovative gear. I'm sure Shimano will release a similar line six months from now. 

I wouldn't be surprised to see them roll out ebike power plants and transmissions considering their experience with their Hammerschmidt crank and internally geared hubs. If you don't have to be overly concerned with weight, internal gears with a beefy chain make far more sense than the fragile stuff we use on bikes.


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## formula4speed (Mar 25, 2013)

I'm surprised you don't see more IGHs like the Alfine 8 on E-bikes. You don't as much low end as you could with a double crankset and cassette, but you have a motor to make up for that. The weight would also seem like less of an issue since you are carrying the motor and battery along.

Being self contained and being able to shift at a stop is pretty sweet.


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## WoodlandHills (Nov 18, 2015)

The Alfine8 won't last very long with a mid-drive and the Alfine 5 is considered to be marginal. The Nexus 3 is very popular as is the Sturmey Archer 3-speed. I've had very good results with Nexus 3s and am currently waiting for a docs release to continue riding with the new SA 5-speed, the C-50. It's claimed to be an all new "heavy duty" design and I have heard that it was intended for ebikes from the get-go.

The Rholoff will hold up, but who really needs that many gears on an ebike? There are a few preconceived notions that have to be dropped when one transitions to an ebike, among them being the lightness fetish and the whole 20+ gear drivetrain thing. Having an extra 750w to input into the chain changes things.....


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## Walt (Jan 23, 2004)

WoodlandHills said:


> Having an extra 750w to input into the chain changes things.....


But they're just like normal mountain bikes.

-W


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## formula4speed (Mar 25, 2013)

WoodlandHills said:


> The Alfine8 won't last very long with a mid-drive and the Alfine 5 is considered to be marginal. The Nexus 3 is very popular as is the Sturmey Archer 3-speed. I've had very good results with Nexus 3s and am currently waiting for a docs release to continue riding with the new SA 5-speed, the C-50. It's claimed to be an all new "heavy duty" design and I have heard that it was intended for ebikes from the get-go.
> 
> The Rholoff will hold up, but who really needs that many gears on an ebike? There are a few preconceived notions that have to be dropped when one transitions to an ebike, among them being the lightness fetish and the whole 20+ gear drivetrain thing. Having an extra 750w to input into the chain changes things.....


When I was in Switzerland I toured the Flyer Bike factory and they had a rental fleet of city bikes that were mid drive and I'm pretty sure they were using the Alfine 8. Maybe just a lack of better options. If I recall correctly all the mountain bikes used a "normal" drivetrain. Anyway, I rented one of the city bikes with the 8 speed IGH and it was enough range even with the monster hills they had in Switzerland. If they start making even more durable IGHs I'll be interested for my regular bikes (Rohloff not withstanding).


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## fos'l (May 27, 2009)

I rode the Sturmey Archer 5-speed on a Faraday, and it complied nicely with the 250w motor. Accelerated quickly to 20 mph and good range with only a 43V, 243 w/h battery.
Interested in how this 5-speed works for Woodland Hills (heal quickly) off road, since that could be an interesting build option.


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## Le Duke (Mar 23, 2009)

When are you getting your e-Geometron, jazzanova?


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## jazzanova (Jun 1, 2008)

Le Duke said:


> When are you getting your e-Geometron, jazzanova?


Well that would be some special bike, don't you think?


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## Le Duke (Mar 23, 2009)

Yep. Why pedal poorly, when you don't have to pedal at all?

Sent from my XT1585 using Tapatalk


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## jazzanova (Jun 1, 2008)

Le Duke said:


> Yep. Why pedal poorly, when you don't have to pedal at all?
> 
> Sent from my XT1585 using Tapatalk


There you go!


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## Francis Cebedo (Aug 1, 1996)

I rode this drivetrain a bit during the launch. Really awesome, specially the cassette.

Anybody finding weaknesses with existing drivetrains for e-bikes??


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## Harryman (Jun 14, 2011)

It depends on how you define an ebike, on a 250W ebike existing drivetrains seem to fair fine, on 1000W ebikes, the increased power and tourque added to a not straight chainline seems to eat 10 speed chainrings, cassettes and chains fairly easily. Which makes sense. Most people seem to go with internally geared hubs or just a few cogs out back and a heavy duty ebike specific chainring. Strength over weight is the best idea. 

Being a gear guy, I've been following a number of build threads on the ebike forums.


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## fos'l (May 27, 2009)

I've been employing 11-17-28 cassette gears with 8-speed spacing on my mid-drive and wear has been negligible. Don't seem to need many gears with a motor.


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