June 25, 2024

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Trek Domane + SLR9 with eTap before an epic ride.

Trek Domane + SLR9 gravel bike review – Ars Technica

Zoom in / Trek Domane + SLR9 with eTap before an epic ride.

Eric Bangman

One of the things I love most about working at Ars Technica is riding my bike at lunchtime. My home is located in the northwest suburbs of Chicago about two miles from the Des Plaines River Trail and about three miles from the North Branch Trail. When the weather cooperates, I generally ride hard in 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 e-bike, I jumped at the chance. Yes, the weather can be dodgy during seasonal transitions, but I’ll battle the changing temperatures and high winds on a carbon-framed gravel bike with carbon wheels…and a 50Nm electric motor paired with a 360Wh battery in the downtube.

But even when I got my 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 love being in nature, I love riding with friends, it’s a great workout. Hopefully the Domane+ will make the riding experience better, but I wouldn’t get the full aero benefit from my rides with an engine doing some of the work. Electrified commuter bikes, cargo bikes, beach bikes, and even mountain bikes all have built-in use cases. But for the guy who likes to burn calories on a bike, having this $13,000 e-bike is a head-scratcher.

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

The top tube contains a built-in screen.  You can see the boost buttons inside the drop bars.
Zoom in / The top tube contains a built-in screen. You can see the boost buttons inside the drop bars.

Eric Bangman

Close up of the boost buttons.
Zoom in / Close up of the boost buttons.

a trip

As one would expect from a bike at this price, the Domane+ has dazzled with the latest components. Starting with the gear you’d find on a regular bike, this ride has Bontrager Aeolus RSL 34 OCLV carbon wheels, a top-of-the-line Dura-Ace Di2 12-speed wireless electronic drivetrain, a Bontrager RC hard case, 32mm light tires and an LED display with connectivity. Bluetooth and ANT+ are built into the top tube.

At first glance, the Domane+ doesn’t look like an e-bike. With the battery housed in, the down tube is thicker than non-electrified Domanes, and there are two pairs of buttons on the handlebars to control the motor, which is located inside the bottom bracket. The difference is noticeable once you pick the Domane+ SLR 9 up: It weighs 25.91 lbs (11.75 kg), nearly 10 lbs (4.5 kg) more than its human-powered counterpart (and about 4.5 lbs more than my aluminum fender).

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Wireless transmission is almost flawless.
Zoom in / Wireless transmission is almost flawless.

Eric Bangman

The 50Nm motor inside the bottom bracket is driven by a built-in 360W battery that can deliver 250W of power continuously, with 300W of maximum power. Domane+ has three auxiliary modes. The Eco adds 75 watts of power to your pedaling efforts, the Mid gives you 150 watts, and the High setting gives you 300 watts With boosts to 28 mph, the Domane+ is a Class 3 e-bike. Some states and municipalities have restrictions on Class 3 e-bikes, So make sure you are aware of the laws where you live.

On the top tube is an LED display that can display speed, battery level, rated range, and how many watts you’re cranking. As a bike computer, it’s rudimentary, so I bought a phone holder. While that allowed me to ride with the Trek Central app open, which can display all the data you want on the ride, it also partially blocked the LED in the top tube.

Trek Central app control panel.  Once you've paired the Domane+ SLR9 with your phone, you can configure your ride to your liking.
Zoom in / Trek Central app control panel. Once you’ve paired the Domane+ SLR9 with your phone, you can configure your ride to your liking.

Eric Bangman

Before my first ride, I paired the bike with the Trek Central app, which is available for iOS and Android. My first attempt fails, because the app has not yet been updated to Domane + SLR 9 specs. Once I download the updated version, I can proceed with setup to modify the bike to my liking.

Trek Central’s built-in tutorial makes setup and tuning simple. Using the sliders, I was able to adjust the amount of boost and how quickly it happened for each mode. After some experimentation, I ended up leaving the default settings intact, except for High mode. Since I have to deal with quite a few stop signs on some of my tracks, I override the pedal response to High, so I can get a quick boost when the lights turn green.

To put the Domane+ through its paces, I rode a few rides on a gravel trail I’d frequent that had some rough sections. I also rode the same 15-mile route just on different boost settings over three consecutive days with very similar weather conditions.

Regardless of whether the engine runs, the Domane+ is a killer ride. The carbon frame, fork and wheels mean the bike absorbs some of the shock from bad frost climbs and winding trails—much better than the aluminum-framed Checkpoint that is my usual ride. Shifting with the eTap is instant and buttery smooth, though there were a few times I noticed a brief delay when shifting into top gear. In terms of ride setup, my main complaint with the Domane+ is that it has a single 46T chainring up front. I found myself missing the 50T chain on my regular ride, running out of gears on the Domane+ during some sprints, even with the engine off.

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The lowest level of boost is subtle but noticeable. With the default riding settings, I averaged 16.5 mph on the road—about the same speed when I’m doing all the work. Riding the circuit on the second boost level brought my pace up to 18mph. With the max boost, I was at 20.7 mph. The location of the boost buttons on the steering wheel makes it easy to switch between assistance levels.

Unfortunately for my activity tracking, the Apple Watch assumed that faster speeds meant I was doing more work — though my average heart rate dropped from 122bpm on the lowest push setting to 117bpm on the highest. If you’re the kind of person who meticulously tracks exercise data (I’m one of those people), you’ll likely find this confusing.

Trek caps the Domane+’s range at 60 miles in Eco mode. (An optional range extender will give you another 30 miles of range in this mode.) Driving 15.1 miles in Eco mode used up 24 percent of the charge; Riding on the same road with high assist left me with 38 percent of the battery at the end of my ride. With electronic shifting powered by the battery pack, Trek makes it difficult to completely drain the battery.

If there’s a downside to Domane+, it’s the data. Between the display built into the top tube and the Trek Central app, you’ve got a decent bike computer, but with two minor frustrations. First, the app’s layout limits some of the data that appears during your ride. When riding, I’m more interested in knowing my speed, mileage, cadence, and power output. While the app’s dashboard is configurable, I wasn’t able to modify it to show me all four data points at the same time. The other interesting thing is that Trek uses highly advanced math (GPS) to calculate your distance traveled, not simple math (the number of wheel revolutions), which is less accurate. When the Domane+ said I had ridden 10 miles, I had covered 10.4 miles, according to the bike computer on my other bike.

Those quirks aside, the app is very useful. There’s a built-in ride planning feature that provides route directions, and it’s integrated with Strava and Komoot so you can share your rides across different apps. However, you will need to purchase a bike computer if you want access to all the data, all the time.

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On gravel and other rough surfaces, the Domane+ with its knobby 700×35 tires devour trails. I can only dream about how you’d ride with 29mm slicks instead on a good road.

My test ride was tuned in with the help on Eco.
Zoom in / My test ride was tuned in with the help on Eco.

Eric Bangman

Same route but with a higher boost throughout.  Notice the dramatic elevation changes in the suburbs of Chicago.

Same route but with a higher boost throughout. Notice the dramatic elevation changes in the suburbs of Chicago.

Eric Bangman

There were times when I really appreciated a helping hand from the motor, especially going up hilly passes in northeastern Illinois. Setting the highest level of kick boost right away was a winning move at the traffic lights. During one of the rides on the gravel trail, the heavens opened up on me. I jumped off the trail at the first opportunity and onto a busy four-lane road so I could get home as quickly as possible. With a boost on High, I could run the three miles or so home, topping out at 30 mph most of the way.

I loved riding Doman +. And if I live somewhere with hills and mountains or do regular long rides in groups, I might want one for myself. But exercise is a big part of why I ride, and I felt like the engines got in the way of that. It also bothered me that my fitness tracking was off — despite my constantly dropping heart rate, the iPhone Fitness app consistently showed me burning more calories than I actually was. The Domane+ SLR9 is a fine piece of machinery, but it just isn’t for me.

As the saying goes, all good things must come to an end. Such was the case for a stretch of unseasonably warm weather. I went out to the garage a little later in the afternoon. The sun was shining, and a gusty south wind warmed the Chicago suburbs into the mid-1970s. The next day—not to mention most 10-day forecasts—promised highs in the 30’s and 40’s, and the bike was due back in the shop.

Despite the wind, I was determined to make my final trip on my fully human-powered Domane+ SLR 9. As I closed the quiet residential streets and plodded south into the storm, my speeds slowed, and I felt the effects of my first heavy exertions. I moved my hands down the handlebar and tried to be as aerodynamic as possible as I pedaled hard into the gusting wind.

When I was slower, I glanced at the boost button. Douman’s drive had given me a leg up on windy days before, and the temptation was strong. But I wanted my last ride with this awesome bike to be mine alone. After three miles into a headwind, I turned west, and the headwind became a crosswind. A mile later, I was pedaling north with a strong tailwind. I shifted to the highest gear and felt like a boss when I got over 30 mph. As the miles went by, I drank in the sunshine and felt the burn, enjoying the feel of my presence with the machine and the smoothness of the ride.

I remembered that the electric motor was only there for the last few miles.