gravel bike with 650b wheels 3T Ultra Boost Eagle AXS Flatbar 650b eBike

The 3T Ultra Boost Eagle AXS Flatbar 650b takes 3T's Exploro Ultra carbon platform — engineered around aero tube shapes and a pure-road-length carbon fork — and orients it toward the rougher end of mixed-terrain riding. Where the drop-bar versions of the Ultra Boost are built around speed on fast gravel and open roads, the flat-bar 650b configuration is built for riders who want access to more technical terrain. The flat handlebar and wider 650b wheels are the two choices that define this bike's character, and both serve the same underlying goal: a capable, confident gravel eBike for rides where pavement is the exception.

3T's REALFAST aerodynamic architecture is present throughout the chassis. The wide downtube shields the water bottle from oncoming airflow while redirecting air around the rider — a design choice that holds its value whether you're on pavement or gravel. A close-fitting rear wheel cutout keeps the frame profile tight. Double drop chainstays provide lateral stiffness without compromising tire clearance; the Pirelli Cinturato Gravel M tires that come standard measure 650b x 50mm. The aero seat tube accepts dropper posts, which is a relevant detail on a bike that will regularly encounter technical descents. Frame construction is unidirectional pre-preg carbon with a high-modulus/high-strength performance blend layup, and the fork is 3T's Fango RaceMax Integrale with a compact crown.

The geometry is tuned for the flat-bar 650b mission. Head tube angle is notably slack in the smaller sizes — 68.5° at 48cm, stepping up to 72.5° at 56cm and above — which gives the front end a stable, planted feel on loose surfaces. The 74° seat tube angle is consistent across all sizes, and 419mm chainstays run uniform throughout the range. The 3T Flatbar LTD runs 700mm wide with a 9° sweep and 30mm of rise, keeping the rider upright and in control. The 3T Apto Stealth stem is sized by frame: 80mm in S, 90mm in M, 100mm in L, 110mm in XL.

Motor and Range

The Mahle X20 motor system produces 55Nm of torque with a 350Wh Mahle iX350 battery. 3T rates range at over 150km on a single charge, and an optional battery extender is available for longer efforts. The Mahle system is designed to feel light and natural in assist — proportional power delivery that doesn't overwhelm the rider's input at lower speeds — with customizable power modes. The motor integration is specific to this platform: front and rear thru-axles run 100x12 and 142x12 in dimensions designed for the X20 system.

Drivetrain and Components

Shifting is handled by SRAM GX Eagle AXS wireless levers paired with an SRAM XX1 Eagle AXS rear derailleur — electronic, wireless, 1x12-speed. The cassette is SRAM NX Eagle at 11-50T, providing a wide range suited to sustained climbs and loaded terrain. The crankset is SRAM Force D1 at 42T or SRAM Rival at 40T depending on availability, with crank arm lengths scaled by frame size. Hydraulic disc brakes are SRAM with SRAM Level LT or LTM levers and SRAM 160mm rotors front and rear. The saddle is a Brooks Cambium C17 — an appropriate choice for long mixed-terrain days. A 3T Carbon 27.2mm round seatpost with zero offset completes the cockpit, and a 3T nylon front-load bottle cage comes standard.

Design Benefits

1. REALFAST aerodynamics on a gravel eBike — wide downtube, close-fitting rear wheel cutout, and double drop chainstays keep drag low even with 650b x 50mm tires mounted.
2. Mahle X20 motor system — 55Nm of torque, 350Wh battery, and 3T-rated range of over 150km per charge with an optional extender for longer routes.
3. Flat bar for technical terrain — 700mm wide, 9° sweep, 30mm rise puts the rider in an upright position with more control leverage in rough conditions than drop-bar hoods allow.
4. 650b x 50mm tire clearance — Pirelli Cinturato Gravel M tires come standard; the wheel size and volume combination handles loose, rocky, and uneven surfaces that push the limits of 700c gravel setups.
5. SRAM Eagle AXS electronics — GX Eagle AXS wireless shifters and XX1 Eagle AXS rear derailleur give reliable electronic shifting across the 11-50T range without cables to maintain.
6. Dropper-post compatible seat tube — the aero seat tube accepts dropper posts for riders who want active saddle height management on technical terrain.
7. Brooks Cambium C17 saddle standard — a saddle designed for all-day comfort on mixed surfaces, appropriate for the long-duration riding this bike is built around.

The Ultra Boost Eagle AXS Flatbar is available in Black/White in sizes 48 through 61cm. It suits riders who want an eBike that doesn't compromise on speed or aerodynamics to deliver off-road capability — the REALFAST platform is still present, and the Mahle X20 motor extends the range of where that platform can go. If your rides regularly cross into terrain where a drop bar limits your control and 700c wheels limit your clearance, this is the version of the Ultra Boost built for that.