Rear brake rotor feels wavy

[Player07]

If you run your finger where the brake pad makes contact you can feel “waves” for lack of better word. Would it be okay to leave it as it is or should I replace it ?

[Triple Jim]

Are these concentric rings? Maybe post a photo. If concentric rings, and not extreme, and the disk is otherwise OK and within the thickness spec, there shouldn't be a problem using it.

If the rear disk is worn noticeably more than the front one, it probably means a previous rider used the rear brake too much.

[NinjaBraap]

Check to make sure there's still actual "Pad" thickness on the pads, that way you know if it's just metal on metal. If there is still pad left, make sure your within spec on the pads. Then take a caliper and measure the thickness of the disc and compare to the service manual spec. If any of the groves are visibly deep, replace the rotor anyway. If it's just starting to wear groves and is really only felt, you caught it in time and just make sure your pads are good. Also, check to make sure your brakes aren't sticking, and are compressing the pads and coming loose normally. If not clean your calipers, flush and bleed your brakes and check again. If it still sticks you'll have to rebuild the caliper. Now if by "waves" you mean the rotor seems to move side to side as you spin it, either your wheel is misaligned (rear only), or you've got a warped rotor. If it's warped, again check the brake pads for uneven wear. You can do that by comparing both pads side by side, and you'll see one or both worn at an angle, or in extreme cases a visible grove in one or both pads. In this case replace the rotor and pads, flush and bleed the brakes.

[Player07]

The rotor itself is straight. It’s just where the pad makes contact.

[NinjaBraap]

Yep check to make sure you have pads at all, and if so that they're in spec. Measure your rotor thickness for spec, and replace pads and/or rotor if necessary. Be sure to flush and bleed brakes when you do, especially if your fluid is dark.

[Player07]

So if everything is in spec and even if the rotors don’t feel “smooth” then it should be fine leaving it like it is ?

[NinjaBraap]

Yeah, but it could wear your pads irregularly then, meaning it'll need replaced more often. Honestly I'd just buy an aftermarket set of rotors for $100 and new pads, flush the entire system and never worry about it again.

[Triple Jim]

It's hard to tell how deep the gouges are in the photos. It looks like what happens when you keep using brake pads until the steel base plate is doing the stopping. Unless the gouges are deep, I'd put in new pads and keep an eye on their wear until the disk smooths a bit.

If the disk is thinner than the wear limit, the conservative approach would be to replace it.

[DannoXYZ]

Did you check how much material was left on brake pads?