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Signs if your bike disc brake rotors need replacement or pads explained

When it comes to wear and tear disc brakes are one one of the things that are constantly under stress and they wear and tear faster than any component on a bike whether it is a road bike a mountain bike or any other cycle disc brakes are the things that need replacements the most after the chain of course because chains are under even more stress than disc brakes.

But our topic today is disc brakes and how can you tell if your disc brake rotors need replacement or maybe your pads?

It’s very easy to sometimes misjudge what could be wrong with your bike and a very short answer to performing checks on your rotors, this is a list of checks that you should always perform on your rotors rather than making a wrong assumption

  1. cracked rotor
  2. grooves on rotor
  3. the thickness of the rotor

These are the most common things that usually happen the list can go on but those would be the factors that are visible like a bent rotor and other things but I didn’t mention them because if rotors are bent to some extent they can be trued and that’s another topic altogether.

Cracked rotors :

A cracked rotor is the worst thing that you should immediately change on your bike and does not ride it before that because it may hold for some time but eventually the rotor will fail and bend a damaged rotor with a small or a big crack is dangerous and you should get it to replace as soon as possible.

Grooves on the rotor :

Grooves on the rotor appear usually when you are not using appropriate pads for example if a disc rotor was specified to be used with resins pads only and you put metallic pads on them it’s sure to get grooves on there and that in turn start to affect the pads and if you keep on the same metallic pads on them they will start to chew the rotor it will eventually either bend or deform

But in this case, whether you keep it on the bike or the rotor will need a replacement or it will soon fail and deform and you had not wanted to be on that bike at that time

The biggest indicator of groves on the rotor is that it will make loud noises of metal bending under stress or metal scraping.

The thickness of the rotors :

there are very few extreme cases like a bent or cracked rotor or grooved rotor mostly the rotors become thinner and the braking performance drops over time and you can feel it as well but to check the rotor thickness making a guess based on visualizing is not a good idea there are alot of methods to check the thickness of the rotors and using a caliper is the most easier method and they are readily available everywhere as well

The can be used to take exact measurements over 0.05mm which is really great, but when you are trying to measure the thickness of your rotors with a vernier caliper the most important point to keep in mind is to not measure it from its outer diameter instead use some balls or something solid to stick on its arms and notice the reading beforehand and afterward and subtract them to get the accurate reading

the readings that you should always take from the rotor should be where the pads are always in most contact, the outer edges of the rotors will always remain either the same thickness or will wear very little.

Are all brand rotors the same thickness :

All brand rotors are not the same thickness and you might see different thicknesses in different size rotors as well for example usually Shimano rotors are 1.8 mm thick or 2 mm thick for 160 mm rotor but the thickness may vary if the rotor size changes for example if you take the Shimano rotor which is 203 or 220 mm then there can be a difference of thickness

So can be the difference on other brands as well like Magura and SRAM so thickness may very well vary between 1 brand only and in different brands as well it may be standardized according to one brand or it may not be standardized there are both possibilities present.

Now the question arises how would you measure if the rotor has worn down too much or it has become too thin there is a chance that it may wrap or break sometimes so for those problems there are easier methods to know that.

what’s the minimum thickness to consider changing rotors :

There are lots of ways to know how thin is too thin for a rotor thickness to be used actively or to consider replacement here are some of it

  • Minimum thickness is always mentioned on the brake manuals you can easily compare your from there
  • Minimum thickness is usually also mentioned right on the rotor
  • minimum thickness can also be known on the buyer page of the manufacturer (Shimano, SRAM, Magura, etc)

These are the most easiest and authentic ways to check for the exact minimum thickness if you may notice on your rotors you should consider changing them as soon as possible

Other than that the basic standard for changing rotors is discussed in a different form on the internet as well for example

If your brakes were 1.8 mm thick then the minimum thickness you should consider would be 1.5 mm similarly if the thickness of your rotor was 2mm then the minimum thickness to consider changing rotors would be 1.8 mm and so on and so forth to understand things in very simple terms

when rotor thickness decreases from its original thickness no matter what it is (1.8mm or 2mm or 1.5 mm) when it decreases 2mm- 3mm you should consider changing them this standard or pattern is noticed with all brands and all sizes, you could take it as a standard across all brands

Moving on to the pads and then I dont think comparison will be needed but I will do it anyway so that you have a very clear understanding of things.

How to know when to Replace pads :

As I have generalized the rotor thickness above as well as the pads thickness or to phrase it how would you know when you need to replace your disc brake pads

The formula is simple as it is with the thickness of the rotors when the pads become 2mm – 3mm thicker than its time to change them usually you will be left with 1 mm or 2 mm thickness but with different brands offering different thicknesses the 1mm left formula doesn’t always work 2-3mm reduction in pad material is a better evaluation 

Of course pads, the material can vary as well but other than organic/resin pads you should worry more about the rotor than pads because those pads take a very long time to wear down while organic pads wear faster.

As far as metallic or semi-metallic pads are concerned you should use them if the manufacturer has specified them to be used on your rotors if not then you should avoid using them except if the conditions are extreme like you are biking in rain for some reason then organic pads will obviously not be a very good choice you have to use semi-metallic or metallic pads but going overboard with them will just damage your rotors or you could always buy rotors that are compatible with them that would be much better.