• Surly Big Fat Dummy bike white color side view
  • Surly Big Fat Dummy bike purple color side view
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Big Fat Dummy

Big Fat Dummy

⚠️ WARNING: This product can expose you to chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.

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All-Terrain, Fat Tire Trail Bike

Big Fat Dummy is truly a hulking beast of a bike. Maximalist bikepackers, those looking to make bikepacking a family affair, and those that help maintain their local trails will appreciate the Big Fat Dummy hauling abilities.

At first glance, it might just seem like a beefed-up version of Big Dummy, but that’s actually not the case. Specifically designed around fat tires, it has a longer toptube and slacker headtube offering the most stable, stiff, and predictable ride possible while hauling a lot of cargo.

  • Single-piece frame increases stiffness and decreases torsional flex
  • Human cargo compliant with the use of Dummy Rail Collars
  • Three-pack mounts, double water bottle bosses on seattube, internal dropper post routing
  • Clearance for 26" x 5.25" tires or 29” x 3.0” tires

Specifications

Geometry

Geometry Diagram
Reach 408 432 448
Stack 578 597 625
Head Tube Angle 69.0° 69.0° 69.0°
Head Tube Length 100 120 150
Seat Tube Length 356 432 508
BB Drop 55 55 55
Wheelbase 1532 1563 1590
Chainstay Length 875 875 875
Top Tube Length, Actual 584 598 617.3
Top Tube Length, Effective 590 620 645
Seat Tube Angle 72.5° 72.5° 72.5°
Standover Height 746 792 841
Stem Length 60 70 80
Stem Angle 7° 7° 7°
Handlebar Width 750 800 800
Crank Length 170 175 175
Fork Length 468 468 468
Fork Rake 47 47 47

NOTE: The Big Fat Dummy is only available in three sizes, which is a departure from our normal way. Here’s the thing, its sizing and fit is a little different than other bikes. By using shorter seat tubes with a longer seatpost, two people of different heights can ride the same size frame. We found it works pretty well – hell the Large size even fits Sov. And nothing fits Sov.

Frame Specs

  • Frame Construction: 4130 Chromoly, Natch tubing, double-butted main triangle, trumpet flaired tubes, TIG welded, ED coated
  • Fork Construction: 4130 Chromoly, Natch tubing, double-butted tapered fork blades, TIG welded, ED coated
  • Rear Dropout Configuration: Vertical
  • Rear Hub Spacing: 12 x 197mm (Surly axle included)
  • Rear Hub Spacing: 10 x 190mm with Surly 10/12 Adapter Washers (not included)
  • Front Hub Spacing: 15 x 150mm (Surly axle included)
  • Rear Brake: Disc - 51mm I.S. (203mm max rotor)
  • Front Brake: Disc - 51mm I.S. (203mm max rotor)
  • Head Tube: Ø44mm
  • Steerer Tube: Ø28.6mm (1-1/8")
  • Crown Race: Ø30mm (1-1/8")
  • Stock Headset Upper (S.H.I.S.): ZS44/28.6
  • Stock Headset Lower (S.H.I.S.): EC44/30
  • Seat Collar: Ø33.1mm
  • Seatpost: Ø30.9mm
  • Front Derailleur (Clamp): High direct mount top-pull (Ø34.9mm)
  • Front Derailleur: 55mm offset adapter (included)
  • Max Chainring (CL): No frame limitations
  • Bottom Bracket: 100mm threaded (1.37" x 24TPI)
  • Tire Clearance Frame: 26 x 5.25"
  • Tire Clearance Frame: 29 x 3.0"
  • Tire Clearance Fork: 26 x 5.25"
  • Tire Clearance Fork: 29 x 3.0"
  • Rigid Fork Spec: 468 x 47mm
  • Max Suspension Fork Length: 511 x 51mm (Fatbike 100mm)
  • Bottle Mounts Frame: 2 Three-Pack (S)
  • Bottle Mounts Frame: 2 Standard + 2 Three-Pack (M - L)
  • Bottle Mounts Fork: 2 Three-Pack
  • Rack Mounts Frame: Yes (Surly Dummy Rails)
  • Rack Mounts Fork: Yes (upper, lower, and mid-blade threaded)
  • Fender Mounts Frame: N/A
  • Fender Mounts Fork: N/A
  • Other Features: Kickstand plate
  • Other Features: Internal dropper post routing compatible

[1] Different tire and rim combinations will result in different clearances.
[2] Depending on drivetrain configuration, tire clearance may be limited by the chain and not frame.
[3] Listed chainring clearance is worst case scenario. Clearances vary widely depending on components and configurations.
[4] Suspension fork length listed at full extension (not at sag)

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