new disc brake pads vs new rotors...

[eddief]

in other words if you install new pads and new rotors and the pads hold up really well, how many pads changes do you do before the rotors wear out and needing to be changed. maybe too random to know?

[tellyho]

Honestly, I've never changed rotors. Bike I've owned longest with discs was 10 years or so, but MTB mileage, so not as much. But probably more braking per mile.

[Likes2ridefar]

Only change rotors when they are worn thin or damaged. So, very rarely. I never keep a bike long enough to think about changing the rotor due to wear.

[Nomadmax]

Measuring calipers or a micrometer tell me when to replace rotors.

[KonaSS]

I thought I remembered hearing a rule of thumb on an Escape Collective podcast about changing rotors after 3 sets of pads. But clearly that is just a guideline.

Best tool to have is a caliper and you can check the thickness of both your pads and your rotors.

[catchourbreath]

Rotors wear, many have a minimum thickness marked on them usually around 2.5mm(make sure to measure the middle not the edge). Also if you switch pad material you sometimes need to switch Rotors, such as Metallic to resin or if a rotor is stamped "resin only" etc.

[herb5998]

Use a micrometer to check your rotor thickness, be sure to measure in an area with wear (another reason a micrometer is better than vernier calipers for this).

Shimano min thickness is 1.5mm, Campagnolo is 1.65.

There are also min thicknesses for pad material, again a micrometer is a good tool to verify this.

As others have said, generally pads will need replacing before discs, but that can vary based on the manufacturer and type of pad material

[catchourbreath]

Whoops I meant 1.5mm. Calipers work fine if you measure the middle of the rotor, usually 160mm and below the jaws can clear far enough in. Anything bigger and you'd likely need the micrometer.