Surly Endomorph Tire – The Original Fat Rear Muscle

Meet the Surly Endomorph, the tire that started it all for fat bikes. This beast features a shred-your-face-off, run-over-anything, kung-fu-grip knobby tread that doesn’t just look mean — it is mean. Designed for the rear wheel, the Endomorph’s tall, widely spaced knobs dig deep into snow, sand, and soft dirt, while their siped edges flex for extra bite and control.

The round, supple casing delivers a smooth, stable ride across unpredictable terrain. Its tread wraps well around the sidewalls to keep traction steady when you’re leaned over or dealing with off-camber surfaces. And thanks to those wide knob gaps, the tire clears mud and debris like a champ, so your grip never quits.

Built to pair with wide rims — from 50mm to 100mm, ideally 65mm — the Endomorph defined what fat traction feels like before fat bikes were even cool.

Key Features

• Aggressive, tall, and siped knobs for maximum grip

• Wide tread spacing for self-cleaning performance

• Round, supple casing for smooth rolling and even traction

• Wrapped tread for solid off-camber stability

• Designed for rear use in sand, snow, and other soft surfaces

• Proven Surly durability and attitude

Specifications

• Tire Type: Clincher (Wire Bead)

• Bead Seat Diameter (BSD): 559 mm (26")

• Recommended Rim Width: 65 mm (compatible 50–100 mm)

• Intended Use: Rear Fat Tire

• Tread Pattern: Tall, siped, wide-spaced knobs

• Casing: Supple, round-profile

• Tubeless Ready: No