Soma Fabrications

Jawbone B-Type Frame

The Soma Jawbone B-Type Frame is a versatile and rugged drop-bar mountain touring and bikepacking platform, designed to handle off-road adventures, long-distance touring, and multi-day expeditions. Constructed from Tange Prestige heat-treated butted CrMo steel, this frame delivers durability, comfort, and reliability on rough terrain while offering flexible drivetrain and tire compatibility.

Key Features:

• Tange Prestige Heat-Treated Butted CrMo Steel - Provides a strong yet compliant ride quality, perfect for extended adventures.
• IRD Broski Sliding Dropouts - Allows for multiple drivetrain setups, including traditional derailleurs and Rohloff geared hubs (135mm QR stock, 142 x 12mm thru-axle inserts available separately).
• Disc Brake Compatibility - IS mount disc brake tabs for powerful, all-weather stopping performance.
• Drivetrain Flexibility - Front derailleur compatible (bottom pull) for riders who prefer a multi-gear setup.
• Optimized Headtube Design - 44mm headtube fits 1-1/8" steerer tubes, with the option to run tapered forks using an EC44 lower cup.
• Adventure-Ready Mounting Points:
• • Rear rack and fender eyelets for cargo hauling.
  • Two sets of bottle cage bosses for hydration needs.
  • One set of cargo cage bosses on the downtube for extra gear storage.
• Tire Clearance for Versatility:
• • 27.5 x 47mm up to 2.6 tires for trail-ready capability.
  • 700c x 38mm up to 29 x 2.25 tires for mixed-terrain touring and gravel riding.
• Component Compatibility:
• • 27.2mm seat post size
  • 28.6mm front derailleur clamp size
  • 29.8mm seat collar
• 73mm English threaded bottom bracket for a durable and easy-to-service setup.

Built for Adventure
Whether you're planning an epic off-road tour, bikepacking expedition, or gravel adventure, the Soma Jawbone B-Type Frame provides the perfect balance of strength, comfort, and adaptability for riders who demand versatility and durability in their build.