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Kick Start My Heart
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Discussion Starter · #1 · (Edited)
I am not sure if I have some misunderstanding of metallic pads – or some other problem.
I overheated and glazed the rotors and not really sure why.
My understanding is that resin pads make less noise, have quicker bite, are easier on rotors, but overheat sooner.
Metallic pads make more noise, wear rotors faster, but have a higher temperature load making then ideal for gravity.
I have run resin pads in the past on my DH bike with my current brake/rotor combo with no issues, but switched to metallic as this year my skillset is up and I wanted to stay ahead of the curve and prevent brake fade before it could occur.
Instead, while I didn’t have brake fade, I had rotor heating and glazing – minor on the front, massive on the rear – noisy as a mofo.

Background:
The Bike: 2006 Specialized Big Hit - 42# of aluminum and steel – 203mm Shimano rotor frt/180mm Shimano rotor rear
SLX brakes, fresh bleed (every year), cleaned rotors with brake clean and iso prior to a proper bed-in.
Pads – finned Shimano – F02A resin – J04C metal – pads are from a reputable LBS.
The Rider: 240# of 6’1” Blue/Blackish trail rider + gear.
The Mountains: Angel Fire, Trestle and Keystone.

This was my first day on the metallics on opening day Angelfire, the day was muddy up high, Hero down lower.
2000’ or so top to bottom- maybe 5 miles of ground distance.
Brakes started early in the day impressive.
Later in the day, they would pick up noise on the last ¼ or so of a run.
Toward the end of the day, noisy for the last ¾, but no fade noted. (Yay!) – maybe even chatter in the last 10%.
Now just noisy all of the time in the rear, a little in the front.

So:
What happened here?
The only change was material, and rider skill/speed.
Is this a normal thing with metallic, and a product of circumstance? – my frustration is that I DIDN’T make MAJOR changes!
I could invest a ton of money and go with 4 pot Saints, blah, blah, blah, but am looking to work with what I have and I don’t see the levers/calipers as the issue.
Would a simple upgrade to a 203 rear be enough to take the additional load?
I could go full IceTech 203’s – if I need to make the investment.

Looking for some thoughts before the next trip out.

Comparison between normal rotor and my rear rotor - the color is darker in real life:
 

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EAT MORE GRIME
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rotor looks like pad is overlapping the edge.
missing a good percentage braking force
reshim and center calipers would be my step one if there is any pad overlap
 

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I know what you mean when you are saying that "nothing has changed" other than rider skill/speed. However... that is likely contributing more than you may think. Higher speeds, probably more runs, and likely steeper grades (harder trails) are all probably contributing to the heat related problems.

Sintered pads don't necessarily mean the brakes don't heat up... it just that they resist the high heat better. As you say, the brakes started making noise, but didn't really fade, which is kind of proof of that. The fact that now the rotors are discolored (and you were getting lots of noise) means they were getting hotter than they were before with resin pads. AT least they were still working though :).

Increasing to 203mm rotors in the rear would for sure help. There is a direct relationship between rotor size, and braking power/heat management. So if you're overheating the brakes, that is really the first step, assuming your bike can fit larger rotors.

I realize you say that you don't want to invest in different calipers/levers. But if you continue to have problems you may want to consider stepping up to a stronger 4 pot brake.

And the brakes don't have to be as expensive as Saints, you could go with the Zee's (basically the budget saint, uses cotter pins instead of a screw to hold in the pads, etc, but costs ~$130ish per brake), or MT520's (budget version of 4 piston XT's, about $95 per brake online) if you want to stay with Shimano, and both of those options would be more suitable to long hard descents.

Good luck finding something that works for you :).
 

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Drinkin' the 29er KoolAid
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Some of the lower end Shimano rotors are spec'd for resin pads only. Not sure what ones you have, but take a look to make sure they don't have "resin pads only" label etched on them.
 

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Keep on Rockin...
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rotor looks like pad is overlapping the edge.
missing a good percentage braking force
reshim and center calipers would be my step one if there is any pad overlap
Yep.

And for goodness sakes, get a 203 rear rotor !!!

I'm a lot lighter than you and found a 180 out back to be completely insufficient for real DH riding.
 

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Years ago I was glazing my rear rotor and presented this issue to a number of folks. General consensus was improper use of my brakes - too little front way too much rear.
 

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Years ago I was glazing my rear rotor and presented this issue to a number of folks. General consensus was improper use of my brakes - too little front way too much rear.
The problem is when it's steep down the entire mtn, you'll be on the rear brake a greater amount of time than the front. Yeah, the front tire can exert more braking force but you need to let off the front brake when you're turning. The idea that you should stay off the brakes most of the time, brake hard with the front brake before the turns, then let off the brakes again sounds great but often not realistic. Like I said before, at my local bike park discolored rotors are normal. It doesn't necessarily indicate improper brake use (unless maybe you're the only one getting brown rotors on that trail).

Amaury Pierron's rear rotor
Bicycle tire Wheel Bicycle wheel rim Bicycle part Spoke
 

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Some of the lower end Shimano rotors are spec'd for resin pads only. Not sure what ones you have, but take a look to make sure they don't have "resin pads only" label etched on them.
^This. OP - Your rotor is an RT56 made only for resin pads, I can see the wording on the rotor in your pic. You need to get a new rotor and going to a 203 would not hurt.
 

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I'm not a DHr but felt a difference in braking when switching the entry level rotor (OPs post above) with SLX or better. As already mentioned, that rotor wasn't meant for the pads you're running.
 

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The problem is when it's steep down the entire mtn, you'll be on the rear brake a greater amount of time than the front. Yeah, the front tire can exert more braking force but you need to let off the front brake when you're turning. The idea that you should stay off the brakes most of the time, brake hard with the front brake before the turns, then let off the brakes again sounds great but often not realistic. Like I said before, at my local bike park discolored rotors are normal. It doesn't necessarily indicate improper brake use (unless maybe you're the only one getting brown rotors on that trail).

Amaury Pierron's rear rotor
View attachment 1254115
I totally agree about the discoloration of rotors. Just discoloration itself isn't something to necessarily be alarmed about. Although, it turns out those were resin only rotors, so it seems we found the problem.

I do disagree about braking more with the rear (and I guess, also where you say only front braking as well). Even braking is the goal(both front and rear at the same time) almost all the time (unless you are wanting to do something brake specific,like an endo, or a skid, etc). Even mid super steep turn, you do "most" of the braking with both brakes before the turn starts, then you feather both of them (like you imply, you don't want to break traction, especially on the front when turning) until you pass the apex of the turn, then let off.

And you don't want to drag the brakes to maintain speed on the straighter sections either, as that causes things to overheat quickly. Instead, cycling the brakes in shorter bursts (of time, not necessarily power) gives the brakes time to dump the heat. The same principle applies to car brakes on steep mountain passes. It does mean that your speed in the straights is a bit variable though, as it "pulses" with your brake timing.

Not neccesarily saying you, or the OP are "braking wrong" (I've never seen either of you ride, so how would I know, and even then, I'm no pro, or coach), but just saying I disagree that you'll be on the rear brake any meaningfully greater percentage of the time.

Glad to see that it looks like the problem was the rotors though, that seems ilke it should be an easy enough fix, with an understandable root cause. I could see the words "only" on the rotors in the photo, but couldn't make out the word before it, and unlike some of the more eagle eyed memebers, I don't know rotor models well enough to spot them like that. But nice work on catching that folks :).
 

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I do disagree about braking more with the rear (and I guess, also where you say only front braking as well). Even braking is the goal(both front and rear at the same time) almost all the time (unless you are wanting to do something brake specific,like an endo, or a skid, etc). Even mid super steep turn, you do "most" of the braking with both brakes before the turn starts, then you feather both of them (like you imply, you don't want to break traction, especially on the front when turning) until you pass the apex of the turn, then let off.
You need more traction on the front wheel dedicated to changing direction. Braking uses up some or all of that traction. Real trails typically don't follow a simple straight away, turn, straight away type layout that we think of when explaining how to brake. Often you're winding back and forth and there's not a straight section before the next turn and you need to free up the front wheel to maneuver. Also, a little over rotation from the back sliding is much safer than the front sliding. When riding DH I use my front brake a ton. I'll regularly break traction reaching the braking limit of the front tire but I still have the rear brake applied longer than the front over the course of a run.

From Mastering Mountain Bike Skills...
Drag the rear brake. If you're braking to prevent acceleration (rather than to decelerate), try dragging your rear brake. This is super handy in steep downhill turns.
 

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You need more traction on the front wheel dedicated to changing direction. Braking uses up some or all of that traction. Real trails typically don't follow a simple straight away, turn, straight away type layout that think of when explaining how to brake. Often you're winding back and forth and there's not a straight section before the next turn and you need to free up the front wheel to maneuver. Also, a little over rotation from the back sliding is much safer than the front sliding. When riding DH I use my front brake a ton. I'll regularly break traction reaching the braking limit of the front tire but I still have the rear brake applied longer than the front over the course of a run.

From Mastering Mountain Bike Skills...
I actually think we're pretty close to agreement, I just wasn't super clear, my bad. I totally understand that traction can only go to "100%", and it can only be do so much of either braking, or turning at once. And breaking the rear tire loose is way safer than the front, as over-rotating/sliding out the rear is a heck of a lot safer than washing out the front. No arguments there, and if I'm in a position like that, I'll choose to brake more with the tire that won't make me crash, and leave my steering to the one that does that best :).

The dragging rear brake paragraph of my post (which you didn't quote, but looks like you were somewhat responding to?) wasn't really focused on turns (although, I didn't specify, so I could see how it could cause confusion). As you said, there are legitimate reasons/situations to be on one brake harder than the other, particularly mid turn.

What I was trying to imply by that statement, was that I see a lot of people (usually newer riders), dragging the rear brake to control speed on straight portions of trail. That is the action that I was trying to describe as being "less good" and would very easily overheat a brake, and what I was trying to say "pulsing/cycling" both brakes should replace. Sorry for the confusion :/.

For what its worth, I did call out that for my riding, I don't feel that the front and rear brake time differs in any "meaningful way" (like 30% front, 70% rear). Typically in the wandering turns you're describing, I'm still on the front some, even if its very lightly. I understand I'm not everyone though, and that all trails are different.

Cheers :).

And, sorry for being off topic.

I hope the OP grabs a 203 rotor for the back, as that will "likely" solve everything (as long as its sintered pad compatible), particularly if their front rotor of the same size didn't have any problems on the same trip.
 

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Kick Start My Heart
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Discussion Starter · #17 · (Edited)
I guess in the past I had just put everything together and all worked and that was good enough.
Running harder and faster this year has taxed this combo.
While fade never occurred, heat was there, and more than ever.
I wasn't worried so much about the discoloration as the shrieking that became more consistent the hotter they got, to now even when cool.

I have a 203 RT66 coming in with adapter.
With more swept area, this should give more leverage at the back, and that will help braking efficiency.
The RT66 is a good for metal, so I am good there.
I will spend some time confirming the setup to be sure caliper is square to the braking surface.
I guess I didn't really have anything 'wrong' so much as I could have set this up better.
The difference between 'stock' and 'tuned'
I learned a lot - Thank You!
Edit: the front is set up crappy as well:

 

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Someone spotted the resin only rotor. They discolor like that with metal pads, and its not from overheating.

I did the exact same thing. Switching rotors, same size but rated for the metallic pads, fixes the issue.

Its not heat, not technique, not anything but incompatible rotor and pad. SLX rotors are dirt cheap and possibly better/quieter than xt!
 

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Kick Start My Heart
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Discussion Starter · #19 ·
I installed a 203 on the rear of the bike, and checked the line up. Sho' 'nuff, brakes run on the top edge of the rotor. Milled the adapter down about 1.5mm, and the track seems to be centered.
Don't do half a job, so I checked the front. Pads have a edge. Kind of a hot mess up there.
The Boxxer runs an Avid adapter. I milled about 1.5 - 2mm from that.
Should be good.
A chest cold has been kicking my butt, but maybe next week I can get it out.


Sent from my XT1635-01 using Tapatalk
 

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Your original rotors are made from cheese, only suitable for resin pads. Will say "Resin Pad Only" on the rotor. Get a proper rotor and you'll be fine.
 
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