April 16, 2021
Unless you've been living under a rock, there's no way you missed the announcement of SRAM's new Rival eTap AXS wireless shifting groupset - the marketing took over most of the bicycle industry media on launch day. With wireless shifting now available in SRAM's budget Rival group for the first time, electronic shifting is more affordable than ever.
I thought it was a great time to take a look at how SRAM's eTap AXS electronic shifting components stack up against Shimano's Di2 product line. Here are my thoughts on the pros, cons, and how to choose between the two brands.
Shimano's Di2 (pronounced "dee-eye-two") was launched way back in 2009. That generation of components is obsolete now, but the name - digital integrated intelligence - lives on in the current Dura-Ace and Ultegra Di2 groups, and recently become available in GRX, Shimano's dedicated group for gravel, adventure, and cyclocross bikes as well.
AXS (say "access") from SRAM is far newer, only hitting the market in 2015. SRAM beat Shimano to the punch, however, with the wireless portion. When this article was written, Di2 was wired - in August, 2021, Shimano announced that their new Dura-Ace and Ultegra groups would be wireless, as well as moving to 12 speed. I've left the remainder of the original article online, below; you'll notice it refers to wired Di2, which is accurate regarding the product on the market today, but will be obsolete when the new wireless Dura-Ace and Ultegra hit the market in October.
The most obvious difference between Di2 and eTap AXS is the wires (or lack thereof.) Shimano's Di2 groups connect the derailleur(s), shifters, and battery pack together with wires. You may not see them, because on higher-end bikes the wiring and battery are typically hidden inside the frame tubes, but they're in there. This means when setting up a new bike, you need to get the correct length of wiring, and then route those wires through the frame, which adds complexity and time. Because there is only one (rechargeable) battery, the entire system charges at once when you plug into the charging port.
SRAM's eTap AXS components, in contrast, are wireless. The derailleurs and shifters each contain their own battery, and the connection between them happens over an encrypted, wireless protocol. There are no wires to route through the frame, which simplifies setup. That does mean, however, that you need to manage each battery independently - four in total, if your bike uses a front derailleur. Each derailleur has a removable, rechargeable battery that can be charged independently, while the shifters use disposable CR2032 coin-style batteries.
Remember that we're only taking about wireless or wired shifting, which is exciting - no cables to stretch or become contaminated with dirt, affecting shifting performance. Your brakes, however, must still be connected by hydraulic lines and filled with brake fluid. So while wireless may save you time, from not having to route wires through your frame, you'll still need to route the hydraulic lines, on both Shimano and SRAM systems.
Shimano offers more configuration options than SRAM. On an eTap system, clicking the button on the right shifter switches to a harder gear, while the button on the left shifter switches to an easier gear. On bikes with double cranksets, hitting both buttons at the same time moves the chain between the two chainrings. Shimano shifters have up and downshift buttons on both sides of the bike, so the user can manage the up and downshifts in a more traditional manner, as users might remember from mechanical shifting bikes they owned previously.
Shimano also offers a configurable option called Syncro shift, for users who want wide-range double cranksets but the simplicity of up and down shifting with one hand. In this mode, one button press can signal the rider's intentions, and the system can shift both the front and rear derailleurs at the same time, automatically. Clever.
SRAM eTap AXS wireless road components use the same 12 speed cassettes as their Eagle AXS mountain bike group. For cyclocross and gravel riders, this creates some interesting drivetrain choices and possibilities, because the components are cross-compatible.
Shimano, in contrast, sticks with 11 speed cassettes for the Dura-Ace, Ultegra, and 105 groups, even though Shimano's enthusiast-level MTB components are now 12 speed. This means that there is minimal cross-compatibility between the road and MTB components.
Shimano's Di2, because it has no radio transmitters or receivers to power, has a longer battery life than eTap AXS. On an eTap AXS system, the radio functions consume battery life. Although the batteries still last a very long time, the battery life is still much shorter than on a Di2 system.
SRAM claims about 600 miles (1000 kilometers) for the eTap AXS system, while the published lifespan on Di2 is double or triple that. In reality, the battery life on both systems is so long that even serious distance riders likely never need to charge more than once a week.
Because the eTap system uses separate, hot-swappable batteries on each derailleur, it's possible to simply carry spares on a long trip - for example, on an extended gravel backpacking trip where you don't have access to charging. That's not possible on a modern Di2 bike with internal batteries that can't readily be hot-swapped. But keep in mind with Shimano this is likely a moot point, since the battery life is so long in the first place there's no need for spares.
Note that eTap ASX shifter levers use separate, disposable coin-type batteries that can't be recharged. Having one of those die on an extended trip is very unlikely, but it might be a good practice to carry spares in your tool kit, just in case.
One of the most interesting parts of the SRAM eTap Rival AXS announcement was the crank-based power meter from Quarq. It's cleverly hidden inside the "DUB" crank spindle, and I was impressed by how low the upcharge is to upgrade to power monitoring when buying a Rival eTap AXS group or Rival eTap AXS-equipped complete bike.
The power meter is not offered on the traditional GXP cranksets, however, so this won't work on your bike if you have a traditional English threaded bottom bracket - an oversized BB30 / PF30 etc. shell is needed.
It's not surprising that setup and maintenance of electronic shifting would happen in a mobile app. Electronic shifting clearly appeals to a younger, early-adopter crowd who is comfortable with smartphones and an app ecosystem.
SRAM's AXS app allows you to do common tasks, like firmware updates, system setup, checking the battery charge, etc. from your iPhone.
Shimano's E-Tube Mobile app performs similar functions, but it's worth noting that it requires a bluetooth module on the bike - which isn't normally included with road groups, although it can be added.
At the top-end of SRAM's product line, we find the Red eTap AXS group, which competes against Shimano's Dura-Ace Di2 group. One step down we find SRAM Force eTap AXS and Shimano Ultegra Di2. Historically, SRAM's Rival (mechanical shifting) group has competed with Shimano's 105 group, which also used mechanical shifting - no electronic option on either of those groups. That changed, however, when SRAM introduced their wireless, electronic Rival eTap AXS group - Shimano does not have a Di2 electronic option at the 105 level.
I expect Rival eTap Di2 to be very popular as the OEM equipment on complete bikes from major brands, since it's the only electronic group available at this price point. Specialized, Trek, Ridley, Colnago, and many others have already announced spec and pricing. You can expect to pay from $3,000 to $5,000 for off-the-shelf bikes equipped with Rival eTap AXS.
If you're shopping for a grouppo to outfit a frame and fork you already own, expect to pay $1,200 - $1,600 for SRAM's Rival eTap AXS, depending on whether you want a 1x or 2x drivetrain, and the power meter option.
Shimano's wired Di2 offers amazing shifting quality, but there's no question that making it wireless would simplify setup and assembly. Shimano's patent filings suggest a wireless, 12 speed Dura-Ace Di2 group could be in the cards, but keep in mind, Shimano has many patents and R&D projects that don't necessarily become real products offered to the public.
The move toward wireless shifting means that frames and forks can change, as well. We're already seeing frames designed specifically for wireless - entirely lacking shifter cable routing ports. If your next dream bike is wireless-specific, the choice may be made for you.
Let's get this out of the way - Shimano's Di2 and SRAM's eTap AXS products are both excellent, and you can't go wrong with either. Dura-Ace and Red are pro-level components that have proved themselves on the World Tour, and an amateur cyclist would be lucky to have either. Ultegra and Force offer 98% of the performance at a fraction of the cost for enthusiasts who want more bang for the buck, and with the introduction of Rival eTap AXS, there's now a budget option for price-sensitive riders who want to jump into electronic shifting that didn't exist before.
That being said, there are some specific factors that might steer a rider toward Shimano or SRAM:
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