Why an e-bike-specific group?
We’ll just get to the heart of the matter and ask/answer that question. No, it is not required, as e-bikes can manage out there with any old drivetrain, brakes, and suspension. But spend some significant time on an e-bike and one will realize that there are quite a few compromises with current systems. The experience can get a whole lot better and SRAM is well ahead of the curve in addressing the issues.
Those issues can be boiled down to the following:
- Shifting under power is rough and clunky
- The shift steps don’t make enough of a difference
- The durability of the drivetrain
- Brakes don’t have enough power to stop bike precisely
These are all due to two things: The e-assist can double the power of the rider and riders are trained to ‘soft-pedal’ while shifting but the assist motor can be kicking in while the rider is shifting. Also, e-bikes are heavier by about 20-25 pounds of un-sprung weight and it can affect the ride, as the brakes are stressed and the bike pushes into corners or fades in long descents.
The heart of the system
The heart and soul of the SRAM EX1 system is its E-BLOCK cassette, which is designed to provide the optimum E-MTB gear range, as well as increased battery longevity and component wear life. Its 11-48, 8-speed design allows a 436-percent gear range. Based on its testing, SRAM believes this is the ideal e-mountain bike gear range.
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.
Shifting performance and feel is signature SRAM. As stated previously, the trigger shifter has been designed to shift once at a time — not multiples — but the action is positive and exact. The EX1 derailleur employs the rugged, X-Horizon design seen in XX1 and X01 derailleurs, with a redesigned clutch, cage and pulley design specifically for the 48-tooth cog.
Guide RE combines SRAM’s Guide R lever assembly with a powerful 4-piston caliper derived from the gravity-focused Code brakes. Highlights include:
- Guide R lever assembly with Guide technologies
- 4 piston caliper derived from the Code gravity specific brakes
- Sintered pads for better pad life in intensive use
- Weight: 415g (based on direct mount, 800 hose, 160mm CL Rotor)
The rest of the goods
EX1 X-Horizon Rear Derailleur
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.
EX1 X-Horizon Features:
- 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
EX1 X-Horizon Specifications:
- Speeds: 8
- Cable pull ratio: 1:1
- Max tooth: 48
- Color: black
- Pulley bearings material: Steel
- Cage material: Aluminum
- Weight: 289g
EX1 X-Actuation Trigger Shifter
Eight speeds are key for optimizing for the e-assist with 30% gearing changes on each shift, alleviating double shifting and over shifting. Single precise gear changes increase battery life and help to decrease component wear.
EX1 X-Actuation Specifications:
- Speeds: 8
- Max upshifts/downshifts: 1
- Multi-position: Yes
- Part weight: 122g
The high torque loads of E-MTBs require tough components. The straighter chain line EX1 offers allows the use of a chain that is wider and more robust than those found on drivetrains not specifically engineered for E-MTBs. The 8-speed EX1 chain has been engineered to run quiet across the gear range and transmit more power to the rear wheel.
EX1 Chain Features and Benefits:
- EX1 chain is wider and designed for the high-torque, heavy-duty use of E-MTB
- Compatibility: 8-speed
- E-Block cassette: $390
- Rear derailleur: $142
- Shifter: $48
- Chain: $25
- Brakes: $133 each
- Crank: $50
- Sprocket: $20
We’ve been riding e-bikes on the roads and OHV trails for a couple years now and we have noticed several weaknesses of commuter systems adapted for dirt trails. Most notably, the systems simply cannot handle the dirt, torque, shifting requirements needed for steep, dirt trails. SRAM is ahead of the issue here and is solving several problems that we have noticed. The shifting performance of the EX1 is simply incredible as the rider can shift under power at 20%+ grades. Precise, consistent braking is now available in spades too. Next stop, optimized suspension.
For more information visit www.sram.com.