How to Measure Bolt Pattern

Many competitive cyclists choose to replace the stock chain rings on their bicycle's cranks in favor of fast-shifting, lightweight, modern variants. It is important to precisely measure the bolt pattern of your bicycle's crank to avoid purchasing the wrong size chain ring for your bike.

Things You'll Need

• Metric tape measure
• Calculator

Instructions

1. Pull the chain off of your bicycle's chain rings and allow it to rest on the bottom bracket.

2. Hold the crank steady and measure from the bolt center of one of the four or five chain ring bolts to the center of the bolt adjacent it. Write down this measurement.

3. If you have a five bolt crank pattern, multiply the distance between the two bolts by 1.7 to find the B.C.D. (or bolt center distance).

4. If you have a four bolt crank pattern, multiply the distance between the two bolts by 1.4 to find the B.C.D.

5. B.C.D. measurements can range from 56mm (Suntour Granny Gear) to 151mm (Campagnolo Standard), so do not be surprised if the measurement is incredibly small or incredibly large. Simply take your measurement to your local bicycle shop, and they should be able to help you find the chain rings you need.

References

• Bicycle Chainrings