Hello, after some time on a long descent my front disc brake started producing squealing/howling sound and vibrated when I engaged it. Braking power also got reduced, so I had to brake well in advance and shift more weight on rear wheel and engage rear brake more.

The issue disappeared after some time but returned again on another descent. Front brake pads were changed a week ago, so I doubt that they're already worn out. At home, I noticed brown marks on front rotor (see pic) and I suspect it was overheating. The temp was around 26-28c today. This is first time I am seeing this, can someone let me know of the following:

- Is this expected/common on long/steep descents?
- How to remedy this (apart from using more rear brake)? I read that you should let the rotors cool off, perhaps there are some braking techniques to counter this?
- Can this cause brake failure and possibly an accident?
- Can I keep riding with this rotor or should I replace it? It's not warped and works just fine.

https://imgur.com/a/mPFlQJB - footage with the sound

Pads just changed, did you ever encounter this previously?

The brownish part and even the braking surface of the disc does look like something I'd expect from overheating.

Are you keeping the brakes on constantly while going down hill? You should in most cases be using them to slow up then release them and allow them to cool until you get to a speed that makes your butt clinch the saddle tightly. Then brake, rinse and repeat till you are at the bottom of the slope.

No, this is the first time I am having this.

Yes, that's exactly what I do - shaving off speed before the corner to hit the apex and then release and roll (sometimes, I am late then brake in the corner).

the rotor looks glazed. Typically a rotor is "cut" (automotive word) or replaced.

What you might be able to do is to use a medium grit emery cloth & evenly resurface both sides of the rotor. Follow it up with some denatured alcohol to clean off any left over debris on the rotor. The pads may need attention as well. Best to remove the wheel from the bicycle, unless you have good attention to detail & a service stand.

How much do you weigh? Is it possible the rotor is worn thin? Same pad as before? What is the diameter of the rotor?

Use both brakes when descending.

I’m thinking some grease or oil may have contaminated the pads and rotor. When it happened to me my rotor overheated and looked just like that. I’d clean the rotor, whole caliper and pads with isopropyl alcohol then sand the pads. Since it’s the second set of pads they may not be too heavily contaminated.

that’s an IceTech (Freeza ?) rotor with finned pads - typically a good combo to dissipate heat

agree with above post - contamination (grease, oil, etc) could have contributed to this

were the pads bedded in properly before heavy use ?

correct pads used ? this caliper / rotor combo uses ‘narrow track’ pads - as opposed to ‘wide track’ pads ... ( glancing at the picture I’m unable to determine if the pad is contacting the area beyond the brake track )

when you remove the pads - also check the calipers for oil, fluid leaking, etc - especially the area around the pistons ... clean this area with iso alcohol or similar ... might need to use a Q tip or similar

is that a Domane? If it is & uses BR-06's, you may want to try a more robust rotor... 2.3mm IIRC is the thickest for 160mm, & try a metal pad. It'll have less chances at fade & glaze, the off set will be that they will have a different yet reassuring feel & be slightly louder when cold.

This was my thought. Did you clean the rotors with alcohol before replacing pads? If not, you may have contaminated the new pads and glazed them.

Ok, based on comments I believe the rotor is contaminated, I will have to clean them. I also didn't bed the front brake after the pads were changed which could contribute to the issue.

The rotor is 160mm Shimano Ultegra R8000 and the bike is Giant TCR.

A good wipe with isopropyl alcohol should do the trick.

I didn't bed in my brakes. They eventually bed in just with your normal riding. At least mine did. Took about 300 miles before they started stopping better than the rim brakes of my previous bikes. Over 5000 miles later I still haven't worn the pads down enough to replace. Mine are Ultegra BR-R8070 disc brakes with a rotor that looks similar to yours.

If you do try to bed in your brakes, next time you change the pads or rotor, then be certain you don't come to a full stop while you are braking hard to bed them in. Bed them in where you don't have to stop so you can let off the brakes and let them cool while moving.

Thanks for advice, I wonder where I would be able to bed them in since I live in netherlands and here we don't have any hills lol

You don't need hills.

Wondering if the pads were bedded. If your frame can handle it, maybe a larger rotor, and also metal pads will help with keeping disc brakes cooler. Metal pads won't have as good an initial bite as organic, pads, but as they get a little bit of heat in them, they are fine.

they can overheat when they get thinner. this guy is at 1.53 so almost gone but it is overheating and it cracked.

Yup. That is why rotors are stamped with their minimum thickness -- the thickness at which they should be replaced. When they're too thin, they are less effective at disappating heat.

yep though this has about .2mm left it is toast the crack is the real issue.

Which suggests that, for you (riding style, terrain, etc), perhaps replacing them before hitting min thickness is the safer route.

Cleaning rotors is easy. Cleaning pads...not so much. Pads that are contaminated have one solution in my experience. This is what I do- I soak the pads with a few drops of 91% isopropyl alcohol and set them on fire. It burns off any oils on the surface. Let them cool off (I got a shock since I skipped this step since I did not see any more flames) and then sand them with very fine sandpaper for 10-20 seconds. Then blow off the residue and reinstall them. That has always fixed the issue if the pads have also picked up oil or whatever.

A propane torch also works pretty well for cleaning pads.

Wow. Makes my method seem not worth my time. I spray the pads down in rubbing alcohol and then give them a good rubbing/cleaning with a shop towel. Rotors though, easy enough. Again, rubbing alcohol and a wipe down with a micro fiber cloth.