Even though they’re made of steel, brake rotors wear out.  The big question is when do you need to replace them?  Well in order to do that you have to determine how thick the rotor is, because when a rotor is worn out, it’s simply thinner than it was when it was new.

This can get to be really cumbersome. What you have to do is check the VIN-number and record the production date that’s on the back edge of the drivers door. Then measure the diameter of the rotor and take all of that information and go to a rotor specification book. Now these things are truly cumbersome because you’ve got, in many cases, hundreds of pages, you’ve got line after line of very fine print with all kinds of numbers, and if you happen to read up a line or down a line, you may condemn a good rotor or you may say that a bad one is good, so you’ve got to be real careful with this. 

But what you do is take the rotor and a brake rotor micrometer, such as this one, and you put it down over the rotor like that, take it off, and you can see on the digital read-out what the thickness of the rotor is.  You compare that to what the specification was in the book, and it’s either good or it’s bad.  But through all of these steps and all of these measurements and everything, there are a lot of ways to make mistakes. 

Now here’s something that does away with all of those mistakes. This is a new ATE rotor and it’s grooved (well, grooved is not new), and it helps rotors perform better because it helps dissipate the gases that form between the brake pads and the brake rotors.  But this one is different: that groove is also a wear indicator.  In other words, when the groove is worn away in any part of the rotor - you can no longer see the groove - that rotor is shot, and it’s time to replace it.  Takes all the guess work out of determining when to replace the rotors, and I think it’s pretty clever. 


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