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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

Big Fat Dummy bike in Thorfrost White color, side view
Big Fat Dummy parked, rear view of white deck
Big Fat Dummy Fork detail
Person with Big Fat Dummy using ice auger preparing to Ice fish on frozen lake on sunny day
Person riding Big Fat Dummy on Frozen Lake with gear bags on back

Specifications

Big Dummy Fat Geometry
units:

Select a few bike sizes to compare.

SIZE SM MD LG
Reach 16.1 408 17.0 432 17.6 448
Stack 22.8 578 23.5 597 24.6 625
Head Tube Angle 69.0° 69.0° 69.0°
Head Tube Length 3.9 100 4.7 120 5.9 150
Seat Tube Length 14.0 356 17.0 432 20.0 508
BB Drop 2.2 55 2.2 55 2.2 55
Wheelbase 60.3 1532 61.5 1563 62.6 1590
Chainstay Length 34.4 875 34.4 875 34.4 875
Top Tube Length, Actual 23 584 23.5 598 24.3 617.3
Top Tube Length, Effective 23.2 590 24.4 620 25.4 645
Seat Tube Angle 72.5° 72.5° 72.5°
Standover Height 29.4 746 31.2 792 33.1 841
Stem Length 2.4 60 2.8 70 3.1 80
Stem Angle 7° 7° 7°
Handlebar Width 29.5 750 31.5 800 31.5 800
Crank Length 6.7 170 6.9 175 6.9 175
Fork Length 18.4 468 18.4 468 18.4 468
Fork Rake 1.9 47 1.9 47 1.9 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 Construction

4130 Chromoly, Natch tubing, double-butted main triangle, trumpet flaired tubes, TIG welded

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)

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)

55mm offset adapter (included)

Max Chainring (CL)[3]

No frame limitations

Bottom Bracket

100mm threaded (1.37" x 24TPI)

Tire Clearance Frame [1]/[2]

26 x 5.25" 

29 x 3.0"

Tire Clearance Fork [1]

26 x 5.25" 

29 x 3.0"

Rigid Fork Spec

468 x 47mm

Max Suspension Fork Length [4]

511 x 51mm (Fatbike 100mm)

Bottle Mounts Frame

2 Three-Pack (S)

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

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) 

Support

Frame Warranty

LIMITED WARRANTY

This Surly product is warranted against defects in materials and workmanship for three years from the date of retail purchase of the product, subject to the limitations detailed below. Save your dated receipt for proof of purchase.

This warranty does NOT cover the following:

  • Damage due to improper assembly or follow-up maintenance or lack of skill, competence or experience of the user or assembler
  • Products that have been modified, neglected, used in competition or for commercial purposes, misused or abused, involved in accidents or anything other than normal use
  • Installation of components, parts or accessories not originally intended for or compatible with bicycle as sold
  • Damage or deterioration to the paint, surface finish, aesthetics or appearance of the product
  • Normal wear and tear
  • Labor required to remove and/or refit and re-adjust the product within the bicycle assembly

This limited warranty is expressly limited to the repair or replacement of a defective product, at the option of Surly, and is the sole remedy of the warranty. This limited warranty applies only to the original purchaser of the Surly product and is not transferrable. This warranty applies only to products purchased through an authorized dealer or distributor. In no event shall Surly be liable for any loss, inconvenience or damage, whether direct, incidental, consequential, or otherwise resulting from breach of any express or implied warranty or condition, of merchantability, fitness for a particular purpose, or otherwise with respect to our products except as set forth herein.

This limited warranty gives the consumer specific legal rights, and those rights and other rights may vary from place to place. This limited warranty does not affect your statutory rights.

TO THE EXTENT NOT PROHIBITED BY LAW, THESE WARRANTIES ARE EXCLUSIVE AND THERE ARE NO OTHER EXPRESS OR IMPLIED WARRANTIES OR CONDITIONS INCLUDING WARRANTIES OR CONDITIONS OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.