The Brother Cycles Big Bro is a steel adventure frameset for 29in or 27.5-plus wheels. Its heat-treated, double-butted 4130 chromoly main triangle and suspension-corrected steel fork provide the basis for a rigid mountain bike, a bikepacking setup or a loaded touring build.

This generation uses Boost spacing, rail-style sliding rear dropouts and a UDH/Full Mount-compatible hanger. The sliding arrangement supports geared or singlespeed builds, while separately available Rohloff dropouts provide another transmission option. Clearance reaches 29 x 2.6in or 27.5 x 3in, although the drivetrain can affect the usable space.

An ED coating protects the frame and fork beneath the paint. Dropper routing, top-tube bag fittings, bottle and rack mounts, and triple mounts on the fork and downtube provide ways to carry equipment. Select the colour and size for this frameset listing; complete bicycles in the photographs show example builds.

Technical specifications

• Tubing: - 4130 Heat Treated Chromoly steel - double-butted main triangle, ED coated
• Brake compatibility; 51mm IS disc brake mount, 180mm max rotor size
• Dropouts: Boost 12x148mm thru axle (included)
• Gear Hanger: SRAM UDH type, full mount compatible
• Seat post diameter: 30.9mm
• Seat clamp diameter: 33.1mm (included)
• Headset: 44mm, SHIS ZS44/28.6 upper, EC44/40 lower (not included)
• Front derailleur clamp diameter: 34.9 mm top pull or high direct-mount (adapter available separately)
• Bottom bracket shell: 73mm bottom bracket, ISO threaded
• Maximum tyre clearance: 29" x 2.6", 27.5" x 3.0" (note: not all drivetrains allow for these maximum tyre clearances)
• Fork : 4130 Chromoly tapered unicrown fork, ED coated. 15x110mm Boost thru axle (included)
• Full-length cable housing guides for derailleurs and brakes
• 3 sets bottle cage mounts on all sizes
• Chainring clearance: 48-36-26t triple, 44-30t double, 38t single
• Weight: medium (18") frame 2.60kg, fork (300mm steerer) 1.37kg
• Tested to ISO 4210 MTB standard

Frame geometry

Available options

• Colour: Stealth Black, Swamp Thing
• Frame Size: Large, Medium, Small, X-large

Frame warranty

Brother provides a three-year warranty against manufacturing and material defects for the original purchaser, with proof of purchase required. Paintwork, normal wear, misuse and damage caused by neglect or modification are excluded. Refer to the manufacturer’s full warranty terms for the conditions that apply.