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
Select a few bike sizes to compare.
|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|
|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|
- 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
- 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
- Steerer Tube
- Crown Race
- Stock Headset Upper (S.H.I.S.)
- Stock Headset Lower (S.H.I.S.)
- Seat Collar
- Front Derailleur (Clamp)
High direct mount top-pull (Ø34.9mm)
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"
29 x 3.0"
- Tire Clearance Fork 
26 x 5.25"
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)
2 Standard + 2 Three-Pack (M - L)
- Bottle Mounts Fork
- Rack Mounts Frame
Yes (Surly Dummy Rails)
- Rack Mounts Fork
Yes (upper, lower, and mid-blade threaded)
- Fender Mounts Frame
- Fender Mounts Fork
- Other Features
Internal dropper post routing compatible
 Different tire and rim combinations will result in different clearances.
 Depending on drivetrain configuration, tire clearance may be limited by the chain and not frame.
 Listed chainring clearance is worst case scenario. Clearances vary widely depending on components and configurations.
 Suspension fork length listed at full extension (not at sag)
- Surly Bike Sizing Chart
[pdf] - 308KB
- Big Fat Dummy Framesheet
[pdf] - 1.5MB
- Big Fat Dummy Fork Instructions (Wednesday Fork)
[pdf] - 6.9MB
- Dummy Rail Collar Instructions
[pdf] - 555KB
- Dummy Deck Instructions
[pdf] - 695KB
- Dummy Rail Instructions
[pdf] - 672KB
- Big Dummy/Big Fat Dummy Frame Insert Instructions
[pdf] - 122KB
- Dummy Bag Instructions
[pdf] - 2.4MB
- Universal Thru-Axle Instructions
[pdf] - 269KB
- Wheel, Rim & Tire Instructions
[pdf] - 279KB
- Bicycle Owner’s Manual (English)
[pdf] - 1.2MB
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.