Surly MWOD Chainrings: The “Easy Button” for getting Really FAT

A few years ago the 65mm Large Marge rim with a 3.7” Surly Endomorph tire was the pinnacle of fat. With this tire and rim combo, any bike with a 100mm wide bottom bracket could easily run three chainrings in the front and all nine cogs in the back. Once 80mm, 90mm, and 100mm wide rims hit the market, drivetrain options for fat bikes became less straightforward because of chain-on-tire rub issues.

MWOD Chainrings, Silver Mr. Whirly Crank Arms, and Chris King BB


If someone wants to upgrade to a fatter setup, there are a few drivetrain options:

One solution is to remove two or three of the small cogs on your cassette and turn your nine speed cassette into a six or seven speed cassette. The downside to this is that some rear derailleurs don’t have enough adjustment in their limit screws to accommodate such a drastic outboard setting. Older Shimano rear derailleurs like the Shimano M771 are the exception.

Another solution is to run a single chainring in the front and a nine or ten speed cassette in the rear. This is certainly a clean solution but for climbing hills and/or riding in very soft conditions this setup is not ideal unless you like long walks with your fat bike.

In my opinion, Surly’s MWOD (Mr. Whirly Offset Double) chainrings are the “Easy Button” for running the fattest rear tire & rim combo that will fit in your frame.

MWOD Chainrings

Who needs it?
Anyone who wants to run an extra FAT tire & rim combo

How does it work?
MWOD rings move the granny and middle rings to the middle and outer positions of the crank, effectively increasing tire clearance at the chain by 7mm without increasing your Q-factor and without losing your crawling gear. They are available in 20/33t and 22/36t.

What parts do you need to run MWOD chainrings?

• Shimano compatible outboard bottom bracket
• 100mm Surly Mr. Whirly Spindle
• Surly Mr. Whirly Crank arms - No spider required because the MWOD chainrings bolt directly to the crank arms
• MWOD chainrings
• 3x9 or 3x10 Front Derailleur – Although you are only running two chainrings, you need the extra outward “throw” provided by a 3x front derailleur

NOTE: Surly also sells a complete MWOD Crankset that comes with a bash guard and bottom bracket. I chose to buy the parts separately because I wanted to use a Chris King BB and don’t want a bash guard on my fat bike.

MWOD Crankset


What is the downside?
It is a very clever solution to gaining more chain clearance. The only downside is that you are limited to two chainrings in the front vs. three. Also, you need to be aware of cross-chaining in the big/big combo. I am running a 22/36t MWOD with an 11-34t cassette in the rear and I haven’t missed my standard triple front chainring. I have also been pleasantly surprised with how well the front shifts despite a 14t jump from the small ring to the big ring. I am a fan of running the biggest tire & rim combo possible for the added float and stability it provides. The MWOD has allowed me to run a 4.7” Big Fat Larry tire on a 90mm wide rim in the rear and retain all nine cogs. Greatness!