Cannondale had one goal with the Moterra SL: To create the lightest, full-power electric mountain bike ever made. The barriers are many, but there's one big one: A powerful motor combined with a battery that has extensive range can add enormous weight and stress to an agile, lightweight frame.

To engineer around that paradox, Cannondale needed to strengthen the frame while cutting weight. The company turned to a solution they designed a long time ago, which takes its cue from Formula One race cars. The Moterra SL uses what the company calls a FlexPivot, which it first used in its Scalpel XC race bike. Instead of using the bearings and hardware of a traditional Horst link suspension system, they substituted a thin, ultralight piece of carbon that can flex in the bike's chainstays—the tubes that hold on the bike's bottom bracket. These flexors not only look clean and eliminate maintenance, but they also allow engineers to fine tune-the suspension.

FlexPivot technology can only go so far, however, in explaining how this 45-pound bike provides serious power without feeling like a Sherman tank. Cannondale took a deep dive into kinematics, a physics term that translates to “the motion of systems composed of joined parts.”

Three Times a Charm

There’s a lot of joined parts in this bike. The Moterra SL comes in three builds that range from the top-end Lab71 to the low-end SL2 that I tested, which sells for half the price. All have carbon frames that officially fall under the all-mountain category, but their slack head-angles make them feel almost like an enduro bike.

All are mullets (29-inch wheel in the front, 27.5-inch wheel in the rear), with a FlipChip to convert it to a full 29-inch bike. All are powered by a custom, high-energy-density 601-Wh internal battery and a Cannondale-tuned Shimano EP801 motor (with 85 newton-meters of torque) that offers four power modes—Eco, Trail 1, Trail 2, and Boost—and can be further fine-tuned in the companion app.

One cool aspect of the e-design is that, if the computer on the handlebars feels too busy and cumbersome, there’s an easy push button on the top tube that allows the rider to change power modes with ease. That lets you ditch the computer altogether and ride with a clean cockpit.

The SL2 build that I tried has a quality mashup of components: a Fox Performance 36 fork with 160 mm of travel; an Acros Adjustable Angle headset, which is nice for further fine-tuning the fit; a Fox Float X Performance Elite rear shock with 150 mm of travel; a Shimano XT derailleur (which is not specific to electric mountain bikes; I’m going to come back to this), and Shimano Deore for shifters, chain, rear cogs, brakes, and brake levers.

This is an enticing package. Because I'm not much of a downhiller myself—I'm more of an XC person—I asked a few more aggressive mountain bikers to take it out. They happily obliged and had an absolute blast, until the derailleur cage sheared off on a bedrock section of singletrack. To be fair to Cannondale, I’m not quite sure what it was. The derailleur could have been faulty, or it could have hit something in the trail. Or it could be the result of slightly misjudging the capacity of an unfamiliar, powerful new e-mtb.

But the broken derailleur did give me pause. While Shimano XT may be a fine option on an acoustic mountain bike, there’s so much more torque on the chain under the power of an e-mtb. A non-e-mtb specific derailleur is more likely to result in a broken chain. I confirmed this later with a local bike mechanic. His shop sees way more mechanicals—what bike people call, you know, just general malfunctions—on e-mtbs with components made for acoustic mountain bikes than on those with e-mtb-specific components.

On the Road Again

Back on the trail with a new derailleur and change ring installed, courtesy of my local bike shop The Ski Hut, I took the SL2 on one of my shorter after-work rides—a 10-mile singletrack circuit close to my house with about 1,200 feet of climbing. This ride has some flow trail and a respectable 3-mile loop of tight wooded singletrack made up of rough bedrock traverses, dirt berms, and some rocky technical features. It’s not a double-black extreme loop, but there’s enough challenging stuff to keep it interesting.

Off the bat the bike’s power was impressive. On flowy trails it flies like a colt out of the barn, even in Trail 1 mode, which I found to offer ample power on almost every type of singletrack terrain I rode throughout my month-long test. The bike, and I, faltered a bit in tight, technical uphill singletrack. In some cases, it felt too big and bulky to finesse precise lines.

On one set of switchbacks that involved climbing over uneven bedrock corners or loose gravel, all of which require you to nail a tight line, I noticed the bike’s wide turning radius combined with its power to throw me off the line, and hence, off the bike. This overpowered sensation has a lot to do with the very slack head-tube angle—that is, the fork sticks out a little farther. A slack head tube is great for pedaling at speed and while descending, but it’s not as maneuverable on steep climbs in tight terrain. To fix this, the Moterra SL has adjustable headset cups that can change the bike’s geometry.

On subsequent rides in similar terrain, I was surprised to be striking my pedals on the ground in places I generally don’t on my acoustic xc mountain bike. Again, that has a lot to do with the SL2’s slack geometry combined with a 27.5-inch rear wheel that is purposely low and planted. This lower center of gravity makes the bike more stable and controllable at speed, which is Cannondale’s priority. But there’s a fix for this, too: Swap out the 27.5-inch rear wheel for a 29-inch one.

This bike is at its best when it’s allowed to go full send, instead of trying to reign it in. If I were a different and more aggressive rider, I would be able to power up any hard-rock feature, surrounded by hardwood trees, with a 50-50 chance of breaking my head. As for battery power? Most of my rides were in the 10 to 20 mile range, and I always came home with one less bar than I started, using roughly 20 percent of the battery juice, indicating big rides are fully in this bike’s capacity.

The real fun with the SL2 is letting it fly in wider, more open spaces. It is a powerful, stable beast on the kind of terrain it’s built to inhabit, which is big mountain stuff—long fire road climbs and steep, advanced downhill terrain that put its deftly engineered kinematics to the ultimate test. If mountains aren’t close by, take it to the local bike park. You won’t be needing a chairlift assist.