As a huge step up from other braking systems, the effectiveness of a disc brake system heavily relies on its core component, the rotor. It is a thin circular disc with a diameter measured as its size. Its motion corresponds to the motion of the wheel and that’s why the disc braking system focuses on stopping the rotor as it will, in turn, stop the wheel.
However, like all other things, the rotor will decay over time, and eventually, it is needed to be replaced. To do that, you need to find the size of the rotor i.e. the diameter, which is generally measured in millimeters. This guide will walk you through the most advanced and accurate method of finding the diameter of your rotor.
Contents
What does Measuring the Rotor Size Mean?
Although many of you might claim to know what is meant by the rotor size, many of you surely don’t know exactly what it means. To be precise, it is the distance of two points on the edge of the rotor which faces each other and has the center between them.
Required Tools for the Measurement
You could think of using a vernier caliper, but you won’t be able to find the exact edges you are looking for. Besides, they are not long enough to measure the largest of the rotors. For the method we’ll show you, you are going to need the followings:
- A medium/large square ruler
- A medium/large speed square
- 3 or 4 plastic table clamps (optional)
How to Measure Rotor Size | the Process
After you’ve gathered the necessary instruments and you’ve taken the rotor out from the braking system, we can now move on to measuring its diameter. We will guide you throughout the process step by step. Each step will be explained as comprehensively as possible just to make it easier for you to follow.
Placement of the Square Ruler
Choose a large table with an even surface that can fit your square ruler and speed square. Then, place the square ruler on one end of the table. If you have clamps, put two clamps on both arms and fix it on the table. If you don’t have any clamps just set the square ruler along the edge of the table without dropping it.
Placing the Speed Square
Put the speed square on the larger arm of the square ruler at a right angle, aligning with the square ruler. You should be able to drag the speed square back and forth while sticking it to the larger arm. The smaller arm of the square ruler should be parallel to the edge of the speed square which it faces.
Setting the Rotor for Measurements
Keep the speed square far from the bottom of the square ruler. Then, take the rotor and put it inside of the square ruler. Make sure that the rotor touches both arms of the square ruler. Apply a little bit of pressure to corner the rotor inside the square ruler.
While holding the rotor with one hand, use your other hand to slide the speed square down towards the rotor. If you did it right, the speed square should touch the rotor without losing the parallel configuration of before. At this position, the rotor should touch the two instruments at only 3 points.
Getting the Measurement
Once you’ve established a firm grip of the speed square, you can remove or keep the rotor there. The diameter of the rotor is the distance between the parallel edges of the smaller arm of the square ruler and the base of the speed ruler. You can read the value from the scale on the larger arm of the square set and know the size of your rotor.
Conclusion
Although this is an unorthodox method, the results obtained using this method are very precise. This process of finding the diameter reduces the possibility of human errors. You are essentially finding the opposite edges that run through the circle and measuring the distance between them.
Some disc rotors do not have a complete circular edge. They have different designs one of which includes alternating little gaps at the edge. Also, you can measure the diameter of any sized rotor in this one. Just make sure that your tools are big enough to fit the circular object.
Also read-How to Measure Rotor Thickness?
What is the rotor size on a 1987 Chevy Caprice rear brakes