Electric bikes eh? There are those that hate them so much that we can actually talk about them here in the very first sentence, metaphorically behind their backs since they won’t even have clicked on the link to get here. There are others who would recognise that there’s little point in making like an ostrich since e-Bikes are already here and are already huge business around the globe. Whatever your opinions they are here to stay, whether you choose to ignore them or not.
So, it’s no surprise that in light of their massive sales growth that mainstream component manufactures are getting on board with modified components designed specifically for the quirks and requirements of ebikes. Today, SRAM have announced an entire groupset aimed at not just ebikes but specifically eMTBs.
Up until now pretty much all the components on an ebike have been the same kit you’d hang on a standard MTB. But ebikes work and ride very differently to ordinary bikes. For a start the engines for both behave very differently, your legs being the sole power source of a standard bike.
Legs V Motors
Gearing on your bike is tuned to the fact that your legs, as the engine, put out varying amounts of power and torque depending on how fast and on what gradient you happen to be riding. At high torque moments you are likely to be riding pretty slowly and up a steep gradient. You’ll probably be ‘spinning’. At high RPM you can put a lot of torque through the groupset and because you are putting in a lot of torque to each pedal stroke the difference (step) between gears can be much larger. At the other end of the scale where you are riding fast in a higher gear, your RPM is likely much lower. At low RPM the amount of torque you can put through the pedals is less and so the steps between gears are smaller.
Look at your cassette. Down at the bottom you have 11 then 13 teeth – a 2 step difference. At the other end on the big rings you can jump from 36 to 44, because at this end your legs will be pushing high torque at higher RPM so you can deal with the big jump in teeth. If you look at the profile of your cassette you’ll see it’s a curve. Power output from your legs is not linear and so this curve in the cassette profile kind of matches what your legs can do. There are lots of variables and lots of riders ride their bikes in different ways but the important thing to note is that fact that the human body puts out different amounts of torque at different RPM.
Motors Are Not Legs
Now, lets consider an electric motor. Here the torque is pretty much constant no matter what speed it is turning and so there’s no need for compensatory and varied steps between gears. This means that the gearing where an electric motor is involved can be much more linear with more even steps between the gears, especially at the lower end. Now of course, your legs are still a necessary contributing power source on an eBike – the motor does not do all the work – and so the gearing should be not totally linear and you can see from the image above that there’s still a tight grouping of the smaller ‘faster’ gears. But the rest of the gears are much more evenly stepped.
SRAM have recognised the requirements here when you mix legs and motors and have developed the EX1 groupset. They claim each component from cranks to chain has been developed with the specific requirements demanded by use on an ebike. So we have features like a reduced size, but more linear 8 speed cassette – There’s no need for gentler steps or more gears when you have a motor to pick up some of the extra torque needed. The cassette is also narrower which helps keep a good chainline from the single ring at the motor end of things.
From the SRAM press release:
“Until the development of EX1, the E-MTB was seen simply as a mountain bike plus electric assistance. Though that definition is not strictly incorrect, the whole, in this case, is significantly greater than the sum of its parts. The experience an E-MTB provides its rider and the demands placed on each element of the entire system are incredibly different than with a traditional, non-electric-assisted mountain bike. Therefore, the thinking simply has to be different.”
XG-899 E-BLOCK™ CASSETTE
“E-BLOCK™ shifting technology is a fundamental redevelopment of external drivetrain shifting. On the E-BLOCK™ cassette, the chain has a defined link position on each cog. Cog architecture has been engineered to work with both inner and outer links of the chain, which allows extremely refined shifting for both inboard and outboard shifts. The result is precise and robust shifting performance in any situation, even with full motor support.”
FEATURES AND BENEFITS
- 11-48t, 8-speed cassette machined from case-hardened tool steel
- Ideal mid-ship motor gear range
- Increased chain wrap on climbing cogs
- Symmetric shifting geometry allows fast, precise gear shifts
- Optimal inboard and outboard shifting performance
- The big steps between cassette cogs is a completely new cassette technology engineered specifically for the demands of E-MTB
- Non XD™ driver body compatible
- Speed – 8
- Gearing – 11-48t
- Cog finish – black
- Technology – XG
- Cog sizes – 11t, 13t, 15t, 18t, 24t, 32t, 40t, 48t
- Cogs on cluster – 5
There’s a stronger chain to deal with higher torque you can put in to it as a result of you plus motor dragging it around.
EX1 X-HORIZON™ REAR DERAILLEUR
There’s a rear mech designed for the reduced steps (8) over a wider range (11 – 48) and it’s clutched to deal with the fact that with a motor to hand it’s possible to put a huge amount of power through the system in a very short time, which can have consequences if you happen to be mid shift at the moment you put the hammer down.
“The EX1 derailleur capitalizes on the robust build and precise shifting attributes of the X-HORIZON™ design, to create the world’s first derailleur specifically made for E-MTBs. Engineered to handle high-torque, low-cadence shifting across the 11-48 tooth E-BLOCK™ cassette, the EX1 derailleur gives E-MTB riders clean, confident shifts, so they can spend more time enjoying the ride.”
FEATURES AND BENEFITS
- Proven SRAM X-HORIZON™ design that reduces shift force, ghost shifting and chain slap
- 12-tooth X-SYNC™ pulley wheels
- The EX1 derailleur is purpose built for E-MTB
- Speeds – 8
- Cable pull ratio – 1:1
- Max tooth – 48
- Color – black
- Pulley bearings material – steel
- Cage material – aluminum
- Weight – 289g
The crank arms have been designed for the BB mounted motors from Yamaha, Bosch and Brose. The Bosch version has it’s own 14/16/18 tooth tiny chain ring integrated.
Lightweight, durable, stiff and designed specifically to work with Bosch and Brose mid-ship motors, EX1 crankarms are purpose built for the high-torque
CRANK FEATURES AND BENEFITS
- Proven SRAM technologies adapted for the demands of midship-motor E-MTBs
- Compatible with Bosch, Brose and Yamaha bottom bracket interfaces
- BB compatibility – ISIS
- Crank arm length – 170mm, 175mm
- Color – black
- Crank arm material – aluminum
EX1 X-ACTUATION™ TRIGGER SHIFTER
The shifter moves in single shifts only, since the steps between each gear is much more even but also larger, there’s no need to grab a ‘handful’ of gears in those panic shift moments. The motor can take the brunt there.
“It has the proven SRAM shifter technology and authoritative lever feel, but the EX1 shifter has been engineered to deliver one perfectly accurate shift at a time, alleviating double shifting and over shifting. Single precise gear changes increase battery life and help to decrease component wear.”
FEATURES AND BENEFITS
- X-ACTUATION™ for precise and dependable performance
- Single shifts reduce over shifting and increase battery performance
- Speeds – 8
- Compatibility – 8-speed rear derailleur
- Cable pull ratio – X-ACTUATION™
- Color – black
- Cable length – 2200mm
- Shifter type – trigger
- Matchmaker compatible – yes
- Max upshifts/downshifts – 1
- Multi-position – yes
- Part weight – 122g
Guide RE Brakes
There’s even a new set of Guide brakes for eBikes designed to be able to deal with the extra mass (they are really heavy) of an ebike.
More from the SRAM press release:
“The 8-speed design incorporates big (30-percent average) steps between gears. The big steps, in combination with the EX1 group’s single-action shift lever, reduces riders’ tendency to double shift. The single-shift design significantly helps chain and cassette wear.
The cassette, machined from case-hardened tool steel, is narrower than a 10- or 11-speed cassette, which helps maintain a straighter chain line throughout the gear range. Engineers were then able to pair the cassette with a slightly wider, tougher chain to increase durability—which is critical in the E-MTB environment, where shifting is typically done at very high torque and low pedaling cadence, versus the low-torque, high-cadence environment of traditional mountain biking.
The E-BLOCK™ cassette uses a non-XD™ driver body. The larger virtual front sprocket provided by a midship motor all but eliminates the need for a 10-tooth cassette cog, so the E-BLOCK™ design’s focus is the larger, “climbing” cogs. By combining the proper climbing gears with motor output, battery power is optimized, and lasts longer given the same conditions.”
So there you have it. They may be first out with an off road eBike groupset but they won’t be the last.