fooferdoggie 

they are on our tandem with 203mm rotors 4 piston Shimano deore calipers. right now I am trying a basic sram rotor. they are glazing just from going down a 18% grade thats about 1.5 blocks and keeping the speed at 25mph. the tandem is heavy around 400 pounds but this is only 20 or 30 seconds of braking. maybe 3 or 4 times. week. only on the back too. these are MTX ceramic pads. I had al little of this on an ice-tech rotor but that was from longer decents a lot longer. the scratch was from the ice-tech rotor when it was worn. the thing is we have a 5 degree slope we go down every time we ride and if I use the back brake the whole way down it works normally till the next day and I have to repeat it.

Polaris OBark

Lack of heat dissipation fins on the pads and (I am guessing) on the rotors. What is with the huge groove on one of the pads?

fooferdoggie 

well yes but its only 30 or so seconds of hard use. the groove was from a worn rotor that I replaced with the sram. I am debating going back to an ice tech rotor. the front ever does it no matter how hard I brake.

FBinNY 

Simply put, it's too much bike for the braked. Your descent would represent a heavy load with a solo bike. With a random, it's twice as bad.

There are a variety of techniques that can help.

1 try using the "air brakes" more by allowing a slightly higher speed. Since air drag is proportional to the square of speed, going even 5mph faster will increase air drag by over 45%, greatly reducing demand on the brakes.

Also do whatever you can to worsen your aero profile.

2- use effective braking technique by cycling the brakes. Rather than holding 25mph, allow the bike to exceed that, then brake down to 20 or so, then repeat. This improves cooling, and should reduce the glazing.

If technique alone isn't enough, improvise a mister to cool the rotor. Or if all else fails, and descents like this are only occasional, consider making a drogue chute which the stoker can deploy when needed.

fooferdoggie 

this is such a short section but its also has several houses on it and people back out o their driveways right onto the road. like I sad a block or so. going faster is not safe and I would not be able to do an emergency stop if someone pulls out and they have. every 25 may be pushing it with the rough road.
but its so short you would not think the system has enough time to heat up. it is last most 20 or 30 seconds.
here is a pic. not a road you want to fly down. so debating on buying another ice tech rotor. my wife can use the back rim brake.

mpetry912 

This does not look like a descent that could heat rotors or pads badly enough to render them unusable

suggest try softer pads ? and maybe drag the rear brake only ?

I liked the mister idea. or the drag chute

/markp

fooferdoggie 

I know thats the thing we have done worse then this the nI had the ice-tech rotors and finned pads. I dont think I had an issue with the ceramic pads on the ice-tech rotor but cant remember for sure as the ice-tech was on its last legs when I changed over. I guess if I buy the ice tech and still have issues I I will have to go back to the overpriced finned pads. I used to only have issues when I keep the speed at 25 on mile long decents. then I would get black buildup on the rotor and that was a real pain to remove had to sand off. we have not been riding hills but this guy in the last several months and it only takes a few times to cause issues. I will email mtx and ask them too.

Schweinhund

What I know about disk brakes is strictly limited to the industrial equipment and motor vehicles I've built/repaired. Cars, trucks, motorcycles
Glazing is caused by heat. heat is caused by as you know, friction. Certain pad materials can generate more heat.
Ceramic is generally mixed with an organic material, but the higher the ceramic content the longer the bed in, lower is a faster bed in. (higher noise with high ceramic too)
The MTX pads are sold as a fast bed in. so they are softer pads. lower ceramic content.
Your short run is just enough to overheat those pads.
I'd get something semi metallic or metallic and use the crap out of disk brake quiet.
.

Schweinhund

Just to put it out there, ceramic is low dust and low noise and doesn't chew up rotors. That's the why of it.
It ain't the best braking material. IMHO.

zebede

As was suggested above "cycling" the brakes to mitigate heat build up.
The technique from the days of rim brakes was to alternate front and back.
Pulse the back brake hard for a moment and then the front or vice versa.

Iride01 

I always thought the better braking technique for going down steep hills was to slow the bike to a low speed fairly rapidly, then let it accelerate on it's own with out brakes. When the speed gets high, then again slow the bike back down rapidly to a low speed with the brakes.

If you need to get to the bottom faster so you can beat everyone else, then you still have to modulate the braking. On then off to maintain a speed range that you can safely descend at.

Dragging one or both brakes for extended times is never a good thing.

fooferdoggie 

that's what I am thinking its cheaper getting new pads for sure. they would be ok if I went back to the ice tech rotors but its far less to go back to normal metallic pads. t=I will use them in the front as they do fine there and I have pas to go through.

fooferdoggie 

yes on long decents I do but this is too steep and short and I need both brakes to keep at 25 and it takes a fair amount of braking.

GamblerGORD53

My tour bike loaded is 290 lbs. With my front SA XL dyno DRUM brake it's child's play. For the 1st tour and across B.C. the 2nd tour I had an absolute POS rim caliper on the Rohloff.
I was stopping from over 30 mph in the middle of a hill to take pics in the mountains. Overheating is a laughable concept. ZERO drama in any weather.
Now with a cable TRP Spyre and resin pads on the Rohloff it stops instantly.
Before >>



Kicking Horse Pass >>

After I got the disc mount welded in Seattle. The front fork is a tandem from R+E. I put a 3" CF wrap by the clamp for the brace arm.

fooferdoggie 

I just checked how long I brake on that hill and its only 7 to 9 seconds.

FBinNY 

Keep in mind that at 400 pounds. It's still a lot of kinetic energy. It's comparable to why trucks have to stop to cool brakes on long descents where as cars don't.

You might try a 10 second stop midway down, or descend slower so rotors have more time to dissipate heat.

GhostRider62

This is why disc brakes suck

I have the same problem. A week don't go by that I am not fixing them.

I know how to brake and have more than a basic understanding of physics. Of course, I could dynamite those 20% gradients, block off the driveways and side streets.

fooferdoggie 

we have been going down this hill for over 3 years. but only now that we have not been doing any other hills and a new rotor have I had issues. I will replace the pads with shimano pads and see.

maddog34

WHY do you think "The pads are glazing"? cuz' i ain't seeing any "glazing".. all i'm seeing is normal use , and edge chips from screwdriver abuse or impatience when re-installing the wheel.....
Are they squealing? Not braking as well as when freshly resurfaced?
Seriously.. WHY are you complaining of "glazing" when none is evident?
Are you just misusing the term?

And it sounds, from your description of your riding technique, that you constantly drag the rear brake on downhills... Take the advice already given as to brake/release/brake/release, instead of dragging the brake in one long pad overheating session.. and learn to use the front brake more often.

fooferdoggie 

they are glazed and it only takes a bit of sanding to make them look normal. if I dont they dont grab. My mechanic at the shop thinks when I use a smaller hill to bed the pads in it may be causing them to glaze as its too much heat to start with and I may have overheaded the rotor and thats causing issues since they have glazed so many times. I showed the hill its way too steep and short to let the speed go we would hit 35mph or more its on 9 seconds of braking. I have been doing it for years with no problem till now.

maddog34

ok.. you're misusing the term "glazing"... what you've been fighting is NORMAL "Bedding in" of the brakes... fresh pads are GRABBY. "Grabby" isn't consistent braking.

learn to use more front brake... Seriously.
and 35mph is fun to most riders.... about double that speed gets scary.. i love downhills.

brake with BOTH brakes for 3-5 seconds, release for 2-3 seconds, repeat as needed. What you want to achieve is a cooling of the INTERFACE between the pad surface and the Disc surface...this only takes a second or two... you are allowing the PLASMA created when Brakes Operate to dissipate... brakes turn motion into HEAT energy, Period. That SURFACE heat needs a way to dissipate.

Try this old M/C trick.. file tiny Grooves in the Pad surfaces... 1/4", tiny groove, 1/4", next tiny groove, etc...the Grooves will be filed as to route the PLASMA towards the outside of the caliper, at about a 45 deg. angle... ok? and quit just applying the brake all the way down your nemesis hill... report back with the results.

one other thing... pads that were seated to a different disc have LESS Contact with the new disc, period.. what happens to the areas that Do touch? They Get Used Harder... and get.. HOTTER.

a request.. could you post a pic of the DISCS involved? not seeing them here.... and if you simply post the brand/model number, then i look them up, i'll see hundreds of ads for bicycle brakes for the next several months, possibly years...... sigh.

Redbullet

I am new in using disk brakes, so my opinion might not be the best. But I don't think they are glazed because they don't look glossy. They rather look like hardly used and porous, with some materials filling the pores - as expected. Plus a scratch that might come from some dirt on the disk, which should not generate important issues.
I also have issues with front disk brake. While sanding pads (not sure it was needed), I noticed some metallic small parts inside the resin which remained after sanding, but I consider it is by design and not a sign of glazing.

FBinNY 

The low temp wear from everyday moderate braking may mitigate glazing before it becomes problematic. I'm not saying it does, only that it might.

Consider the problem. Glazing will happen when the rotor heats to above a critical temp. In other words, during the last few of those 7-9 seconds.

If you were to pulse the brakes, you could prevent heating to that level, or better balance the glazing/deglazing cycle. Likewise more use of brakes between revisits to this hill will help.

BTW other things that may help include a thicker or heavier rotor, which will be a better heat sink, and stay cooler. Also, check for pads with better hot performance, less likely to "melt" into glaze.

Redbullet

If 7-9 seconds (or less) of hard braking create an issue, then I would say that disk brakes have a critical issue of functionality. I used rim brakes (Al. rims) for a much longer period than 7-9 seconds of hard braking (front) and I never had an issue. But I would rather say that in this post, the pads from the picture show no sign of glazing; just signs of heavy usage.

FBinNY 

Like you, I (greatly) prefer rim brakes on road bikes, and say so whenever asked.

However, preferences aside, the OP is looking for help with what he has, not advice to change.

Also keep in mind that the OP's tandem weights 400#s so it's a very different animal than a solo bike. Just as heavier and/or faster motor vehicles use larger brakes, so should bikes.

My initial post here was that the OP had too much bike for the brakes. I believe that's the key issue, but I also believe that it can be managed, if the OP changes things (both hardware and/or technique) to create more breathing room.