Trust Surly to come up with a reasonable solution to a bizarre problem. The Surly MWOD chainring set moves a bike's chainline away from the spinning tire allowing for the use of super wide tires on extra wide rims. The genius part is that it doesn't increase the Q factor (a.k.a. width of the bottom bracket) and keeps the low gears necessary for pedaling bikes with monster tires. The chainring set bolts directly to Mr. Whirly cranks and is available in two sizes.
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.