Trek Rail 9.9 X01 AXS review

With the Rail 9.9 X01 AXS, Trek equips its OCLV Mountain Carbon frame with all the bells and whistles, including superb suspension for all kinds of riding, a wireless electronic drivetrain, and Bosch’s Performance Line CX 250W e-MTB drive system with a 625wh battery.

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A lot of e-bikes we test take a few laps to get comfortable on. But like many Trek mountain bikes, this one is instantly familiar, fun, and capable of cruising for multiple hours through varied terrain, hitting wooden jumps, and carving steep and loamy corners.

Trek Rail suspension

The bike is set up with a 160mm travel RockShox ZEB Ultimate fork has 38mm stanchions and loads of adjustability, paired with a 150mm travel RockShox Super Deluxe Ultimate shock with an updated Thru-Shaft damper. E-bikes in general are so heavy that it can be hard to feel the suspension as distinctly as on a non-motorized MTB. But this bike’s superior suspension was something all testers felt positively about.

Trek says that RE:aktiv with Thru Shaft works faster than a normal shock, so it tracks the ground better for superior control. The tracking is exceptional, and the planted feeling of this bike never wavers. SRAM Code RSC hydraulic disc brakes with 200mm rotors help keep speed under control.

Trek Rail drivetrain

The SRAM drivetrain has a 32-tooth climbing gear, which helps conserve battery on uphills so you can ride longer before recharging. The four-piston Shimano XT brakes are a personal favorite, and they feel comfortable, familiar, and powerful riding ski area descents.

The wireless SRAM X01 Eagle AXS drivetrain is smooth once it is dialed in, and the RockShox Reverb AXS dropper post functions perfectly. Both eliminate clutter on the handlebar, which is aesthetically pleasing, and less prone to mishaps when pushing hard on this bike.

The carbon rims are stiff and help the bike feel snappy and responsive. A flip-chip lets you tweak geometry to be slightly more downhill-oriented or slightly more trail-oriented. I left it in the lower position for the best performance — and most fun — riding downhill.

Bosch’s Performance Line CX 250W e-MTB drive system is currently the most widely used. It’s operated with a full-color Kiox controller that displays ride info, connects with Bluetooth-enabled devices, and can help prevent theft. Trek mounts it on the top tube, not the handlebar. But until I got used to the particulars of electronic MTB shifting and the motor controls, the handlebar felt cluttered.

Bosch’s system uses the most energy-dense battery available, in this case, a 625 Wh battery, which stores more energy per pound of battery than others. It is also very good at torque management. When applying power to the pedals, sensors detect the input, and there is no lag or delay in the assist engaging or disengaging when not pedaling, so the bike doesn’t feel like it surges overwhelmingly.

Steering limiters on the front end prevent the handlebar from turning to the point of damaging the frame—a feature increasingly common on big-travel enduro bikes. A kickstand mount is fairly uncommon on enduro bikes, but this bike has one, which seems curious and speaks to the notion that e-bikes are still trying to find themselves, both on the trail and off.

Trek Rail 9.9 X01 AXS verdict

This fun, versatile, and capable bike is a great do-everything ride. The battery outlasts other bikes, which is a combination of a smaller 32-tooth front chainring which lets you pedal steeps with less assist, and the powerful Bosch system. The Rail 9.9 X01 AXS is a bike that all testers love for all types of riding.