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Disc rotor overheating?

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Road Cycling It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle. -- Ernest Hemingway

Disc rotor overheating?

Old 03-31-23, 01:26 PM
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alxsmlv
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Disc rotor overheating?

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

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Old 03-31-23, 01:44 PM
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Pads just changed, did you ever encounter this previously?
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Old 03-31-23, 03:07 PM
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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.
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Old 03-31-23, 03:30 PM
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Originally Posted by shelbyfv View Post
Pads just changed, did you ever encounter this previously?
No, this is the first time I am having this.

Originally Posted by Iride01 View Post
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.
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).
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Old 03-31-23, 04:18 PM
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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.
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Old 03-31-23, 05:06 PM
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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.
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Old 03-31-23, 05:22 PM
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Im 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. Id clean the rotor, whole caliper and pads with isopropyl alcohol then sand the pads. Since its the second set of pads they may not be too heavily contaminated.
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Old 03-31-23, 07:09 PM
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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

Last edited by t2p; 03-31-23 at 07:28 PM.
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Old 04-01-23, 12:52 AM
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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.
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Old 04-01-23, 08:55 AM
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Originally Posted by Ghazmh View Post
Im thinking some grease or oil may have contaminated the pads and rotor.
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.
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Old 04-01-23, 09:18 AM
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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.
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Old 04-01-23, 09:47 AM
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Originally Posted by alxsmlv View Post
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.
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Old 04-01-23, 01:27 PM
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Originally Posted by alxsmlv View Post
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.
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.
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Old 04-01-23, 03:17 PM
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Originally Posted by Iride01 View Post
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
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Old 04-01-23, 04:48 PM
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You don't need hills.

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Old 04-03-23, 02:13 PM
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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.
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Old 04-04-23, 11:09 AM
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they can overheat when they get thinner. this guy is at 1.53 so almost gone but it is overheating and it cracked.
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Old 04-04-23, 11:26 AM
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Originally Posted by fooferdoggie View Post
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.
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Old 04-04-23, 11:29 AM
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Originally Posted by Koyote View Post
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.
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Old 04-04-23, 11:31 AM
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Originally Posted by fooferdoggie View Post
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.
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Old 04-04-23, 12:44 PM
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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.
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Old 04-04-23, 10:45 PM
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A propane torch also works pretty well for cleaning pads.
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Old 04-05-23, 08:01 PM
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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.
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