Surly's MWOD chainrings convert your Mr. Whirly crankset into an offset mountain double crank. In simple terms, they allow your fat bike to run an extra wide rear tire and rim combo (for example, 4.7-inch tires on 100mm rims or 82mm rims on your Pugsley) while avoiding chain-on-tire rub. This outer chainring bolts directly to the inner ring with four chainring bolts.
To choose the correct chainring, 1) determine the number of teeth (they're usually marked, or simply count them), 2) determine how many bolt holes there are (usually 4 or 5), and 3) determine the Bolt Circle Diameter (BCD; see diagram).
Common BCDs include:
130mm (Shimano Road)
135mm (Campagnolo Road)
110mm (Compact Road)
104mm, 94mm, and 64mm (Mountain)
Finding the number of teeth and bolts holes is easy. If you don't know your chainring's BCD, measuring it is tricky. So, instead, measure the exact distance (center to center) between 2 adjacent bolt holes. Then find that number on the correct chart below to determine the BCD for your chainring.
|BCD Chart for 5-bolt Chainrings|
|Bolt to Bolt (measure center to center)||Bolt Circle Diameter (BCD)|
|BCD Chart for 4-bolt Chainring|
|Bolt to Bolt (measure center to center)
||Bolt Circle Diameter (BCD)|
If you have any questions concerning chainring compatibility, please contact us.