How does mechanical shifting work?
Mechanical shifting systems move the chain up and down the cassette and chainrings via a steel cable set to a certain tension that runs from the left handlebar shifter to the front derailleur, and the right shifter to the rear derailleur.
When a cyclist changes gears by manipulating mechanical shifters, it affects cable tension, which in turn affects spring pressure inside the front and rear derailleurs set to certain forces and travel limits. When this tension, or the limit settings, are out of balance, shifting performance is poor. Gears skip and the chain makes a lot of noise which can be very irritating on a long ride.
How does Shimano’s Di2 electronic drivetrain work?
With an electronic setup like Shimano’s Di2, there are no cables, well, not physical cables anyway. The system works on an internal cable routing network of electronic wires linked to a series of junction boxes that serve a relay and a command centre.
One is typically inside the bike’s frame, near the bottom bracket shell, and the other, positioned hear the handlebars for easy access. They are how you recharge the batter and change certain setting such as trimming the chain.
The derailleurs move the chain with the power from one central battery, usually stored in the seatpost, or individual batteries on each component, depending on the brand. Electric motors in each derailleur receive a signal from the shift levers, via a junction box , which then directs them to move the chain either up or down the cassette or chainrings.
How does SRAM’s eTap AXS electronic drivetrain work?
To differentiate themselves, SRAM has gone with a fully wireless system to control their eTap AXS electronic drivetrains. This means that there are no internally routed wires or cables in the frame (to possibly rattle around!) other than those necessary for rim or disc brakes.
The battery power in eTap comes from no one source, but individual batteries in each component of the electrical drivetrain. The shifters work on small coin cell watch batteries stored under a hatch under the hoods of each shift lever. With normal use, these batteries only needs to be changed once every two years.
The front and rear derailleurs have independent batteries that clip in and out for charging. Their battery life is not as impressive as other brands, but removal and charging is fast and easy. The entire system communicates on a special bandwidth that SRAM owns, which eliminates the need for any junction boxes.
Let’s look at a few reasons you should get electronic shifting.
What are the advantages of electric gears?
What makes electronic drivetrain shifting so much more beneficial for the amateur and professional cyclist? It’s that with mechanical derailleurs, you need to shift at the right time to keep from grinding gears or dropping the chain. With an electronic gears, you can even change the left and right derailleurs shift on to the side you want, you aren’t stuck with a fixed left or right.
Whereas, with electronic shifters, you don’t have to worry about waiting to shift from the small to the big chainring or vice versa. And because electronic drivetrains are battery-powered, shifts can be performed at any time, no matter what speed you’re riding at, and even under load. Every shift will be crisp and accurate, up to four or more gears at a time.
As with any other cycling innovation that is relatively new to the mass market, electronic groupsets are still fairly expensive so you have to be a committed cyclist with a desire to upgrade your performance at (almost) any price.
The top three electric gears for road bikes
Three manufacturers dominate the market for road bikes: Shimano, SRAM and Campagnolo. Campagnolo (aka Campy) uses a wired system they call EPS with a series of junction boxes like Shimano Di2. The difference between the two brands is how Campy downshifts. There is a small thumb lever on the internal portion of the hoods for that purpose instead of a second smaller lever on the shifter.
Shimano produces Di2 in Dura Ace and Ultegra for the moment, but a 105 Di2 groupset is on the way. Both the Dura Ace and Ultegra Di2 groups are available in disc or rim brake. SRAM offers three eTap AXS electronic drivetrains for purchase, RED, Force and Rival. And finally, Campagnolo EPS, offers three as well, Super Record, Record and Chorus electronic groupsets.
Many consider Campagnolo the most prestigious of the Big Three electronic groupset manufacturers and boasts a long and storied history. It’s also the most expensive because it caters only to the mid and high sectors of the market. The UCI ProWorldTeams UAE Team Emirates and Citroën-AG2R use Super-Record EPS.
Possible disadvantages to electric gears
Once you’ve decided that you are done with mechanical systems on your road bike, and you absolutely must have electronic shifting, inform yourself of the possible disadvantages because nothing is perfect. Take maintenance for example. I used to be possible for me to fix my own car if the problem was not major. That’s no longer true, and the same is true for my bike today.
Shop around for the best prices if you’ve decided to make the switch. Or you wait until the technology trickles down to lower priced groups like 105 and Rival that offer excellent quality to price ratio. I can foresee a time in the not-too-distant future when the only place you’ll be able to buy a bike with a mechanical shifting system is in an antique shop.
Further reading on the topic of electric gears
We’ve been thinking and writing about electric gears for a while. Check out some of our favourite stories on this topic!