The groupset wars are alive and well in 2020, and when it comes to electronic shifting, you have three options, Shimano Di2, SRAM eTap, and Campagnolo EPS — the former two make up the lion’s share of the market for battery-powered gear changes.
If we're honest, there isn’t a bad electronic groupset that we know of, they all shift from cog to cog with lightning-quick speed and accuracy — if they are set up properly — and require minimal upkeep except for keeping things clean, charged and lubed, and replacing moving parts as they wear out.
With that, choosing between a Di2 and eTap groupset is becoming increasingly difficult, with each system have its strengths and weaknesses. Below are the factors we would use when it comes to choosing the right road bike groupsets.
Both SRAM and Shimano have different commands for moving the gears up and down the cassette and chainrings. Shimano was the first of the big three-component brands to introduce electronic shifting, although Mavic beat them to the punch way back in 1992 with the now discontinued Zap group.
The layout of the Di2 shift buttons almost mirrors its mechanical shifting; two small shift buttons are situated just under the blade of the brake lever. For experienced riders, and those who have spent any time using a Shimano equipped bike, the transition to Shimano Di2 will be seamless and intuitive, and shifts are met with a tactile click. The only minor criticism we have of the Di2 shifting layout is that with thick gloves on, it’s hard to feel the difference between the buttons.
When SRAM launched its first electronic groupset, it came at the shifting problem with a clean slate. Instead of mimicking the DoubleTap system used for its mechanical groupsets, the brand opted to make the right paddle shift to a harder gear, the left paddle shift to an easier gear, and both at the same time shifts the front derailleur. This layout is extremely intuitive, and there has been plenty of reporting on how easy this system is to explain to beginners or inexperienced riders. The trouble with this argument is, beginners and inexperienced riders are likely shopping well below the price bracket of an eTap or Di2 equipped bike.
Both systems have some degree of autonomous shifting; as you move up or down the cassette, the groupset will shift at the front to prevent overlapping gear ratios — Shimano calls this Synchronized (Syncro) shifting, and SRAM calls it Sequential Shifting. Both also have semi-automatic versions which will shift a few cogs up or down and the rear as you change at the front to prevent jumps in gearing.
When it comes to shifting speed, as in how quickly each group moves the chain to the next cog, Shimano has the slight edge here, but we are talking fractions of seconds. This is likely due in part to the fact that eTap has to wait a millisecond to see whether you are just pressing one shift paddle or both.
eTap is entirely wireless, so each component needs to have its own battery, while Di2, with its wires, can run everything off one single battery housed in the seat tube.
eTap uses disposable coin cells in the shifters, and rechargeable batteries in each derailleur. As each derailleur has it's own battery pack, visually they aren't quite as svelte as their mechanical or Shimano compatriots. SRAM says the shifters should have juice for about two years, depending on use, while the eTap batteries will need to be charged after about sixty hours of ride time, again depending on how much you shift. Typically, the battery on your rear mech will die first because that’s where the most shifting happens; if you do get caught out, you can always swap in the battery from your front derailleur to get you home.
Shimano’s Di2 battery is claimed to last about 2,000km between charges, depending on usage. When your Di2 battery does start to go flat, you will lose front shifting to preserve enough power to get you home before your bike is converted to a single-speed.
Having spent quite a bit of time on both systems, I have found myself caught out more times with a dead battery with Di2 than eTap. The battery lasts such a long time, I simply forget it’s there until the front derailleur stops working, whereas the comparatively short battery life of the eTap batteries is a blessing in disguise because you’re unable to forget they exist.
With the latest eTap groupsets, SRAM added a 12th cog to the rear cassette, and with it, a new approach to gearing it called X-Range. This new system traded the traditional gearing combinations for smaller chainrings and wide-range cassettes.
Based around a 10t small cog, the new eTap 12-speed cassettes come in 10-26T, 10-28T, and 10-32T ranges which work with the standard eTap derailleur. SRAM just launched it’s new wide gearing 10-33T and 10-36T will only work with the new Max AXS rear mech. If you want to go super wide range at the back, the eTap AXS road components speak the same language as the Eagle AXS MTB components and can be mixed and matched. At the front chainrings are available in 46/33T, 48/35T and 50/37T. At the Red level, the chainrings are a single piece, which may reduce weight and improve shifting, but when you wear one out, your wallet is going to take quite a hit — especially if you have the chainring integrated Quarq power meter cause that will need to be replaced too. The Force crankset and power meter are a more standard layout.
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The new Force Wide sees lower gearing and a 43/30T crankset but also pushes the chain line out to 47.5mm from 45, improving clearance for gravel tyres and compatibility with mountain bike bottom bracket standards.
With the Orbit Fluid damper in the rear derailleur, you can run 1x gearing from 36T to 48T.
Shimano’s gearing is a bit more traditional, with 11 cogs at the back and cassettes ranging from 11-25T all the way up to 11-34T in the Ultegra spec, though you’ll need a long-cage derailleur to access the wider gearing, both for the second-tier Ultegra Di2 group, and Shimano's GRX gravel groupset.
The chainrings come in 53/39T, 52/36T, and 50/34T options all which have the same four-bolt layout and are interchangeable.
Both electronic drivetrains come in rim and hydraulic disc brakes, and both work pretty darn well. At the levers, both SRAM and Shimano offer reach and bite point adjustment, and road-specific disc rotors in 160mm and 140mm sizes.
Shimano's rim brakes seem to have a stiffer caliper than SRAM’s and offer a bit more power and modulation. SRAM also doesn't make a direct mount rim brake.
SRAM hydraulic brakes are best known for their sizable master cylinder at the hoods. The early versions of SRAM hydro brakes were pretty ugly, but the skyscraper of a master cylinder did give you something to hold onto when things got spicy. The eTap hydraulic levers are still noticeably taller than their Shimano counterparts, but the aesthetics have improved tenfold.
Shimano has done a fantastic job of hiding the master cylinder in its hydro brakes, and ergonomically, they are pretty darn close to their cable-driven stalemates. The brake pads on Shimano disc brakes sit a bit further into the caliper when the pistons are retracted, so there is more clearance between the rotor and the pads as you roll along, meaning there's less noise from road grit that gets picked up by the rotor or a disc that's come out of true.
While they take a different form, both brands' brakes work, offering oodles of power and modulation. They feel different, but which is best for you will come down to personal preference, and over time you will get used to whatever is bolted onto your bike.
Maintenance and cables
The main advantage of electronic drivetrains is that there are no gear cables to gum up or snap. With more of the best road bikes moving towards entirely hidden cables, this means less time trying to fish cables and housing through frames, handlebars and stems.
One of the main advantages of SRAM’s eTap system is that it’s wireless, meaning setting up derailleurs is pretty much as simple as bolting them on. You still have to run brake hose/cables and housing, though for hydraulic discs you will probably only ever need to do it once when building the bike.
With Shimano Di2, you will still have shift cables and junction boxes to contend with, but unless you are building up a frameset, this will be taken care of before your bike leaves the showroom floor.
Just about every electronic nowadays has some sort of connectivity for firmware updates, diagnostics, and customization. In this department, SRAM noses ahead of Shimano because each eTap compound speaks Bluetooth, and can be accessed through the SRAM AXS app.
To make a wireless connection to a Di2 drivetrain, you’ll need to purchase an E-Tube Wireless D-Fly unit, which connects to the E-Tube phone app; or you can plug a USB cable into the charging port for a wired connection to a Windows-only desktop application.
With the ~three-year product cycles we see with componentry in the bike industry, we would hazard a guess that the next Shimano road groupset launch is due in the next year or so, and we would also say it’s a safe bet that Bluetooth connectivity will be integrated.
Beyond the Syncro shifting and Sequential Shifting we talked about at the top, another advantage to electronic drivetrains is the ability to add satellite shifters. Whether it be the ability to shift from the tops or the drops without moving your hands, SRAM and Shimano both offer this functionality.
SRAM calls it satellite shifters Blips, these are round buttons which are wrapped under the bar tape and plugged directly into the shifter.
Shimano has a range of satellite shifters, from sprint shifters found in the drops, to climbing shifters which can be zip-tied to the tops. The top of the hoods also have a hidden button, which can be programmed to interact with lights and computers via ANT+.
When SRAM added a cog to its rear cluster, the cassettes, chainrings, and chains were no longer interchangeable; not only with Shimano components but the vast majority of third party offerings from brands like FSA, KMC, Praxis and the like. The 10T cog also means the brand swapped from the traditional HG freehub body to an XD-R driver. Friction testing has also shown the new Flat Top chain is a bit slower than a traditional chain, though longevity is said to be increased.
With that said, AXS components are cross-compatible, so if you want a 10-50 rear cassette and a 48T front chainring, you can bolt an AXS eagle rear derailleur on and pair it to your Force AXS or Red AXS shifters. With the Orbit Fluid Damper, which performs the same task as a roller bearing clutch, the same rear mech can be used for both 1x and 2x setups. The new DUB bottom bracket also vastly improves frame compatibility.
Shimano, on the other hand, uses a standard 11-speed chain, the HG freehub body, and you can swap in pretty much any chainrings you’d like — we do wonder if the next generation of Shimano drivetrain components will use the Micro Spline freehub if they make the jump to 12-speed.
Drivetrain weights are a bit hard to pin down due to the variability, not only in chains, cassettes, crank lengths, etc but also how long the cables, housing, or brake hose having an effect on what lights up on the scale.
SRAM and Shimano electronic drivetrains both come in a little over 2000g, with the claimed weights coming from Shimano trending to be about 200-300g lighter. However, these weights don’t include the battery or cables. In reality, the difference in weight will be pretty trivial. Once they are bolted onto a bike, there is no way you will be able to feel the difference in grams from a Dura-Ace Di2 group to a Red eTap AXS group, or between Ultegra Di2 and Force eTap AXS.
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