Basic Guide: Electronic Drivetrains
For most of cycling history, drivetrains were pretty straight forward. They were fixed gears. Then, in the 1937, the first derailleur systems were introduced in the Tour de France, and cycling has never been the same since. The technology was revolutionary, and since then it’s been the mostly evolutionary process of adding a new gear every few years.
The last few years, however, have seen another, equally game-changing development in drivetrain technology: electronic road drivetrains. Electronic drivetrains forgo the traditional cable-pull method of operation in favor of computerized servo motors to move the chain across the gears. Sure, Mavic gave this a shot in the 90’s with their Zap and Mektronic systems, but the technology wasn’t ready for primetime yet. Modern electronic systems from Shimano, SRAM and Campagnolo have brought revolutionary levels of technology to cycling that have already changed the way we think about performance, and still promise big things to come.
Electronic systems, as stated above, use electronic wires linked to derailleurs with servo motors to change gears. This has several advantages.
- Servos are far more powerful than any mechanical system, and therefore give the rider the ability to shift under power, or while climbing, without dropping a chain.
- The system is computerized, so it’s self-adjusting. That means that you don’t have to worry about chain rub or extreme chain angles, since the computer can automatically trim the front derailleur as you shift the rear derailleur.
- The shifters require only a slight button tap to change gears, this means shifting is more precise. Also, several models of electronic drivetrains offer the ability to sweep most or the entire cassette by simply pushing and holding down the shift lever.
- Many accessories are available for electronic systems, including auxiliary “climber” or “sprinter” shifters, so you can shift from almost any hand position.
If you’re in the market for a new electronic system, or just want to see what all the hype is about, then read on below for a breakdown of the different available electronic drivetrain systems.
Shimano’s electronic system is called Di2, and it comes in both Dura-Ace and Ultegra varieties, as well as time trial editions. Shimano’s system consists of shifters, front and rear derailleurs, a battery, battery charger, control unit, and wiring harness. Di2 systems can only be used on framesets that are built for electronic drivetrains (these will have battery mounts, and specific wiring ports instead of cable stops). The big selling point for Di2 are the many accessories are available for Di2 systems, including secondary “climbers” shifters which mount on the bar flats, or “sprinter” shifter that mount on the bar ends, each of which can be custom programmed to shift how you want them to. Shimano claims that their Di2 batteries will last for about 1000 miles per charge. Charging time is claimed at 90 minutes.
The other nifty thing about Di2 is that you can mix and match systems to suit your budget or needs. Ultegra 6770, Ultegra 6870, and Dura-Ace 9070 all use Shimano’s E-Tubes wiring system, and can be cross compatible with one another, just be wary of trying to mix and match 11-speed and 10-speed components. Unfortunately, the original Dura-Ace 7970 system uses a different wiring harness. All Di2 systems can only be used with compatible Di2 components, and can not be used with any mechanical parts (except the crankset and brakes).
Campagnolo’s electronic system is called EPS, and is available in Super Record, Record and Chorus varieties, as well as a time trial version for each group. Functionally, all three systems are exactly the same, the only thing that changes are the weight and materials used. The system consists of shifters, front and rear derailleurs, a battery, battery charger, DTI control unit, and wiring harness. EPS systems can only be used on framesets that are built for electronic drivetrains (these will have battery mounts, and specific wiring ports instead of cable stops). The standout feature for the EPS system is that it gives the rider the ability to “sweep” the entire cassette by simply holding down the shift lever, and has a Bluetooth/ANT+ enabled junction box. This allows the drivetrain to communicate wirelessly with the MyCampy smartphone app and a Garmin head unit, so the user to customize shift settings, track component wear, battery levels, see current gear selection, and more (these feature are only available with the V3 DTI unit and battery). Campagnolo claims that their EPS batteries will last for about 1000 miles per charge. Charging time is also about 90 minutes.
Record and Super Record are cross-compatible, while Chorus is not. All of the EPS groups are handmade at Campagnolo’s factory in Vicenza Italy. Campagnolo systems are not cross compatible with Shimano systems. All EPS systems can only be used with compatible EPS components, and can not be used with any mechanical parts (except the crankset and brakes).
SRAM introduced their eTap electronic groupset last year to rave reviews. eTap is the world's first completely wireless electronic drivetrain and fundamentally rethinks how a groupset operates and shifts. By virtue of being wireless, eTap is incredibly easy to install and is compatible with almost any frame. It also looks super clean, with a clutter free cockpit devoid of all but the brake cables. To transmit the shift signal, SRAM developed their own ultrasecure Airea wireless protocol. Airea is a 128-bit encrypted signal that was developed in conjunction with engineers, computer security experts, and even hackers. It's designed to be unbreakable, and interference-free, so you never have to worry about losing a shift to interference from other radio operated devices (like garage door openers, phones, etc...) or worry about someone hijacking your system. Since the signal moves at the speed of light, you also get ultrafast shifting with the reliability and speed you've always expected from SRAM. The shifting also works slightly differently than how you're used to, with an F1-inspired paddle system. The right shifter moves to a harder gear, the left to an easier one, and pressing both at (roughly) the same time shifts the front derailleur.
Each derailleur gets it's own battery, which is good for about 100 hours per charge. The batteries are also interchangeable, so if one dies you can simply swap them out mid-ride. The shifters operate on CR2032 coin batteries, and should be good for about 6 months each.