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Bikes. Parts. Chaos.

The Big Fat Dummy is a long tail cargo bike that took a few too many doses of growth hormones. At first glance, you might say that we just put bigger tires on a Big Dummy. But if you said that, you’d actually be very wrong so just… don’t. Think of Big Fat Dummy as more of a second or third cousin to Big Dummy rather than a brother. They share some of the same DNA and look sort of similar, but they’re two very different bikes and really only interact when they both reach for the potato salad spoon at that family reunion that no one really wants to be at anyway.

Now that that’s out of the way, let’s get down to the nitty gritty of what makes this hulking beast of a bike tick. Our goal with designing a cargo bike around fat tires was to create the most stable, stiff, and traction-laden ride possible while hauling a ton of stuff. Big Fat Dummy has a longer toptube and slacker headtube than its more svelt cousin giving it a nice, predictable, and stable ride. We also used thinner, lighter tubing to construct its cargo area so while it’s an overall burlier bike, there’s not much difference in weight.

Big Fat Dummy accepts either 10mm or 12mm axles in the rear with a spacing of 190/197mm. That big ‘ol spacing equates to one thing: tire clearance for days. Big Fat Dummy maxes out at a massive 26 x 5.25” tire.* While that large of a tire provides the most traction and stability a bike can possibly offer, it’s also a lot of rubber to push and might not be for everybody. Luckily, Big Fat Dummy is also a blast to ride with 3” tires too. It uses the same 100mm suspension-corrected fork as the Wednesday, meaning if you want to add a little squishy squishy to your ride, you can throw a Bluto on and let ‘er rip.

If you intend to carry a passenger on your Big Fat Dummy, Surly requires use of our Dummy Rail Collars. These provide a secondary retention system for the rack, as well as stiffen the rack system. In addition, a stoker handlebar set up, found on tandem bicycles, is recommended as well. Make sure to check with seat post manufacturer for stoker handlebar compatibility. All Big Fat Dummy framesets and bikes ship with a Dummy deck, rails, bags, and the aforementioned Dummy Rail Collars so you can immediately start hauling cargo — human or otherwise.

Big Fat Dummy is ready and willing to carry all sorts of shit — literally. It’s already in use on an organic farm in Ecuador so it’s likely that it’s hauled some form of manure by now.

*Using a 26 x 5.25” tire will cause some drivetrain limitations. For all the nuts and bolts of compatibility read Andy’s blog on the subject.


Big Dummy Fat Geometry

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
Stem Angle
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.


Surly 4130 CroMoly steel. Main triangle double-butted. TIG-welded cargo specific engineered for stiffness and durability.

Rear Dropouts


Vertical, 197 x 12mm spaced

Cromwell Green:

Vertical, 197 x 12mm spaced, Surly thru axle included

Brake Compatibility

51mm disc mounts


Upper and lower tripple bottlecage mounts on downtube, Double waterbottle bosses on seatube (not included on the small), Surly Trip Guides for continuous brake/shift housing or brake hydraulic line (toptube and seatsaty routing), Internal dropper post routing

Seatpost Diameter


Seatpost Clamp Diameter

33.1mm (Surly stainless included)

Headset/Steerer Tube



Cromwell Green:

ZS44/28.6 upper, EC44/30 lower

Front Derailleur Clamp Diameter

34.9mm, direct mount

Bottom Bracket Shell

100mm wide, threaded English (1.37" x 24t)

Chainring Clearance

No frame limitations. Use whatever you want.

Tire Clearance

26 x 5.25", individual tire and rim combos affect tire clearance


Surly Wednesday, Tapered straight blade 4130 CroMoly. 468mm axle to crown, 47mm offset. 51mm I.S. front standard disc mount, 150mm x 15mm thru-axle dropouts (axle included), 100mm suspension fork compatible.

Thru Axle

HU0139 Surly 15x150 Front Thru Axle
HU0136 Surly 12x197 Rear Thru Axle


Bliolet and Cromwell Green


Frame 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.