It feels like cheating: The Trek Domane+ SLR9 AXS road bike, reviewed

One of the things I love most about working at Ars Technica is the lunchtime bike rides. My home in the northwest suburbs of Chicago lies two miles from the Des Plaines River Trail and about three miles from the North Branch Trail. When the weather cooperates, I'm generally furiously pedaling through the woods on my Trek Checkpoint ALR 5 gravel bike.

So when Trek offered me the chance to ride its top-of-the-line Domane+ SLR 9 AXS e-bike, I jumped at the opportunity. Yes, the weather can be dodgy during seasonal transitions, but I'd be facing the changing temps and gusting winds astride a carbon-frame gravel bike with carbon wheels… and a 50 Nm electric motor paired with a 360 Wh battery in the downtube.

But even as I picked up the Domane+ from a local bike shop, one question kept popping up. Why would I want to ride an electric road bike?

I ride for a number of reasons. I enjoy it, I like being out in nature, I like riding with friends, and it's fantastic exercise. The Domane+ would hopefully make the riding experience better, but I wouldn't be getting the full aerobic benefit from my rides with a motor doing some of the work. Electrified commuter bikes, cargo bikes, beach bikes, and even mountain bikes have built-in use cases. But for a guy who loves burning calories on a bicycle, the existence of this $13,000 e-bike is something of a head-scratcher.

The Domane+ SLR 9 AXS starts at $12,999. Along with the aforementioned Checkpoint, Domane is one of Trek's two gravel bike lines. There are subtle differences in geometry between the two, but the main difference is that the Checkpoint comes with 40mm tires, while the Domane has 32 mm standard.

The top tube has a built-in display. You can see the boost buttons on the interior of the drop bars.

Credit: Eric Bangeman

A close-up of the boost buttons.

Credit: Trek

As one would expect from a bike with this price tag, the Domane+ has been bedazzled with top-of-the-line components. Starting with the gear you'd find on a regular bike, this Trek has Bontrager Aeolus RSL 37V OCLV carbon wheels, SRAM Red 12-speed wireless electronic drivetrain, 40 mm Bontrager GR1 Team Issue tires, and an LED display with Bluetooth and ANT+ connectivity built into the top tube.

At first glance, the Domane+ doesn't look like an e-bike. With the battery parked inside it, the downtube is thicker than the non-electrified Domanes, and there are a couple of buttons on the handlebars for controlling the motor, which is located inside the bottom bracket. The difference is noticeable once you pick the Domane+ SLR 9 AXS up: it weighs 26.97 lb (12.16 kg), over 10 lb (4.5 kg) more than its human-powered counterpart (and about 4.5 lb more than my aluminum-frame Checkpoint ALR 5).

The wireless shifting is almost flawless.

Credit: Eric Bangeman

The 50 Nm motor inside the bottom bracket is powered by an integrated 360 Wh battery that can provide 250 W of power continuously, with 300 W of peak power. The Domane+ has three assist modes. Eco adds 75 W of power to your pedaling efforts, Mid gives you 150 W, and the High setting 300 W. With boosts up to 28 mph, the Domane+ is a Class 3 e-bike. Some states and municipalities have restrictions on Class 3 e-bikes, so be sure you're aware of the laws where you live.

Built into the top tube is an LED screen that can display speed, battery level, estimated range, and how many watts you're cranking out. As a bike computer, it's rudimentary, so I purchased a phone mount. While that allowed me to ride with the Trek Central app open, which can show all the data you'd want on a ride, it also partially obscured the LED on the top tube.

The Dashboard of the Trek Central app. Once you pair the Domane+ with your phone, you can configure your ride to your liking.

Credit: Eric Bangeman

Before my first ride, I paired the bike with the Trek Central app, which is available for iOS and Android. My first attempt failed, as the app had yet to be updated with the specs for the Domane+ SLR 9 AXS. Once I downloaded the updated copy, I could go through setup to tweak the bike to my liking.

Trek Central's built-in tutorial makes setup and tuning simple. Using sliders, I was able to adjust the amount of boost and how quickly it comes for each mode. After some experimentation, I ended up leaving the default settings intact, with the exception of High mode. Since I have to deal with a fair number of stoplights on some of my routes, I maxed out the pedal response to High, so I could get a quick boost when the lights turn green.

To put the Domane+ through its paces, I took a couple of rides on a gravel trail I frequent that has some rough sections. I also rode the same 15-mile road-only route on different boost settings over three consecutive days with very similar weather conditions.

Regardless of whether the motor is engaged, the Domane+ is a killer ride. The carbon frame, fork, and wheels mean the bike absorbs some of the shock from nasty frost heaves and rutted trails—much better than the aluminum-framed Checkpoint that is my regular ride. Shifting with the eTap is mostly instantaneous and buttery smooth, although there were a couple of times I noticed a brief delay when shifting into the highest gear. In terms of the riding setup, my chief complaint with the Domane+ is that it has a single 42T chainring on the front. I found myself missing the 50T chainring on my usual ride, as I ran out of gears on the Domane+ during some sprints, even with the motor switched off.

The lowest level of boost is subtle but noticeable. With the default ride settings, I averaged 16.5 mph on the route—about the same pace when I'm doing all of the work. Riding the circuit on boost level two upped my pace to 18 mph. With the boost maxed out, I was at 20.7 mph. The location of the boost buttons on the handlebar makes it easy to move between assist levels.

Unfortunately for my activity tracking, my Apple Watch assumed the faster speeds meant I was doing more work—even though my average heart rate dropped from 122 bpm on the lowest boost setting to 117 bpm at the highest. If you're the kind of person who meticulously tracks their workout data (I am one of those people), you will likely find this confounding.

Trek pegs the range of the Domane+ at 60 miles in Eco mode. (An optional range extender will give you another 30 miles of range in that mode.) That jibes with my experience on the bike. A 15.1-mile ride on Eco mode used 24 percent of the charge; riding the same route with assist on high, I was left with 38 percent of the battery at the end of my ride. With the electronic shifting being powered by the battery pack, Trek makes it difficult to completely drain the battery.

If there's a downside to the Domane+, it's the data. Between the display built into the top tube and the Trek Central app, you've got a pretty good bike computer, but with two minor frustrations. First, the app's layout limits some of the data shown during your ride. When riding, I'm most interested in knowing my speed, distance traveled, cadence, and power output. While the app dashboard is configurable, I couldn't tweak it to show me all four data points at the same time. The other irritation is that the Trek uses extremely advanced math (GPS) to calculate how far you've ridden, not simple math (number of wheel rotations), which is less accurate. When the Domane+ said I'd ridden 10 miles, I had ridden 10.4 miles, according to the bike computer on my other bikes.

Aside from those quibbles, the app is super useful. There's a ride-planning feature built-in that offers route guidance, and it's integrated with Strava and Komoot so you can share your rides across different apps. That said, you'll need to buy a bike computer if you want access to all the data, all the time.

On gravel and other rough surfaces, the Domane+ with its 700x40 knobby tires gobbles up the trails. I can only dream how it would ride with 29 mm slicks instead on a good road.

My test ride with assist set at Eco.

Credit: Eric Bangeman

There were times I really appreciated the helping hand from the motor, especially going up what passes for hills in northeastern Illinois. Setting the highest level of boost to kick in immediately was a winning move at stoplights. During one gravel-trail ride, the skies opened up on me. I hopped off the trail at the first opportunity and onto a busy, four-lane road so I could get home as quickly as possible. With boost on High, I could sprint the three or so miles home, topping 30 mph most of the way.

I loved riding the Domane+. And if I lived somewhere with hills and mountains or made regular long rides in groups, I might want one for myself. But exercise is a big part of why I ride, and I felt that the motors got in the way of that. It also bugged me that my fitness tracking was off—despite my heart rate being consistently lower, the iPhone Fitness app consistently showed me burning more calories than I actually did. The Domane+ SLR9 is a brilliant piece of machinery, but it's not for me.

As the saying goes, all good things must come to an end. That was the case for the stretch of unseasonably warm weather. I walked out to the garage shortly after noon. The sun shone brightly, and a gusty southerly wind had warmed the Chicago suburbs into the mid-70s. The following day—not to mention most of the 10-day forecast—promised highs in the 30s and 40s, and the bike was due back at the shop.

Despite the wind, I was determined to make my final ride on the Domane+ SLR 9 AXS entirely human-powered. As I turned off quiet residential streets and pedaled south into the gale, my speed slowed, and I felt the effects of my first heavy exertions. I moved my hands down to the bottom of the handlebars and tried to be as aerodynamic as possible as I pedaled furiously into the gusting wind.

As I downshifted, I glanced at the boost button. The Domane's motor had given me a leg up on windy days before, and the temptation was strong. But I wanted my last ride with this brilliant bike to be mine and mine alone. After three miles of strong headwinds, I turned west, and the headwind became a crosswind. A mile later, I was riding north with a strong tailwind. I shifted into the highest gear and felt like a boss as I passed 30 mph. As the miles ticked by, I drank in the sunlight and felt the burn, relishing the sensation of being at one with the machine and the smoothness of the ride.

It was only during the last couple of miles that I remembered the electric motor was even there.