Bicycle chainrings are one of the most important components on a bike, but it can be difficult to determine the correct size for your bike. It's important to know how to measure the Bolt Circle Diameter (BCD) of your bike's chainrings, as this will determine the size of chainring you need to purchase. Understanding how to measure the BCD of your chainrings will help you ensure that your chainrings are the right size for your bike, and that your chainrings are compatible with your drivetrain.
What is BCD?
BCD is the diameter of an imaginary circle that passes through the center of each bolt hole on the chainring. The BCD of a chainring is typically measured in millimeters, and the BCD for a particular chainring will be the same for all of the chainrings on the bike. The BCD is used to determine the size of chainrings that will be compatible with the drivetrain of a bike.
Tools Needed to Measure BCD
Before you can measure the BCD of your chainrings, you'll need to gather a few tools:
- Tape measure
- Ruler
- Pen or pencil
- Calculator
How to Measure BCD
Once you have the necessary tools, you can begin measuring the BCD of your chainrings. Here's how:
- Start by counting the number of bolt holes on your chainring.
- Using a tape measure, measure the distance between the center of two adjacent bolt holes.
- Divide this measurement by two and record the result.
- Repeat this process for each pair of adjacent bolt holes.
- Once you have the measurements for all of the pairs of bolt holes, add them together and divide the result by the number of pairs.
- The result is the BCD of your chainring.
It's important to remember that the BCD of a chainring is the same for all of the chainrings on the bike, so if you measure one chainring and get an answer, you know that all of the chainrings will have the same BCD.
Example
For example, let's say that you have a chainring with four bolt holes. You measure the distance between each pair of adjacent bolt holes and get the following measurements: 16mm, 17mm, 18mm, and 19mm. When you add these measurements together and divide by four, you get an answer of 17.75mm, which is the BCD of your chainring.
Frequently Asked Questions (FAQs)
What is BCD?
BCD stands for Bolt Circle Diameter, and it is the diameter of an imaginary circle that passes through the center of each bolt hole on the chainring.
What tools do I need to measure BCD?
You will need a tape measure, ruler, pen or pencil, and calculator to measure BCD.
How do I measure BCD?
Start by counting the number of bolt holes on your chainring. Then use a tape measure to measure the distance between the center of two adjacent bolt holes. Divide this measurement by two and record the result. Repeat this process for each pair of adjacent bolt holes. Once you have the measurements for all of the pairs of bolt holes, add them together and divide the result by the number of pairs. The result is the BCD of your chainring.
What is an example of measuring BCD?
If you have a chainring with four bolt holes, and you measure the distance between each pair of adjacent bolt holes and get the following measurements: 16mm, 17mm, 18mm, and 19mm, when you add these measurements together and divide by four, you get an answer of 17.75mm, which is the BCD of your chainring.
What is the importance of measuring BCD?
Measuring the BCD of your chainrings is important because it will determine the size of chainring you need to purchase. Knowing the BCD of your chainrings will also help you ensure that your chainrings are compatible with your drivetrain.
What should I do if my chainring BCD is not compatible with my drivetrain?
If your chainring BCD is not compatible with your drivetrain, you will need to purchase a new chainring that is compatible with your drivetrain.
What happens if I don't measure the BCD of my chainrings?
If you don't measure the BCD of your chainrings, you may end up purchasing the wrong size chainring, which could damage your drivetrain or cause other problems with your bike.
How do I know if my chainrings are compatible with my drivetrain?
The best way to determine if your chainrings are compatible with your drivetrain is to measure the BCD of your chainrings and compare it to the specifications for your drivetrain.
What happens if I buy a chainring that is not compatible with my drivetrain?
If you buy a chainring that is not compatible with your drivetrain, it could damage your drivetrain or cause other problems with your bike.