My brake blocks appear to be eating my rims

[Smurfy]

In my experience, the noise gets worse the more grit is embedded. It's something that correlates well with wet riding, and off road riding (where there is usually puddles and grit abounding)

 

[Yellow Saddle]

1. I'd suggest that the transfer of aluminium to pad under the conditions you describe is very low.
2. What you describe will not lead to the grit on metal sound, which I think is what the OP means when he says his brakes are noisy.
3. Although the high local temperatures result in a small amount of material transfer, 'crystallised rubber' will never result in the same highly damaging abrasion as grit, for the simple reason that only materials significantly harder than aluminium are able to deeply scratch or seriously abrade the rim.
4. Your comparison to extrusion is not a good one, as extrusion requires enormous pressure as well as high temperature.

Low maybe, but enough to embed chunks in the pad. Remove a piece carefully one day and you'll see that it doesn't look like a piece of swarf created by a machine tool or sharp instrument. It is lumpy and crumbly.
The stuff I'm talking about and fish out of black brake pads is definitely aluminium. Further, I never find any other material in there, only alu. Perhaps you think otherwise and then a macro photo of embedded grit as you describe will bring resolution to the issue. So far I only find metal.

I have explained that the alu's temperature rises and therefore something softer than alu at room temperature does gouge it out as described. Examine the scratches on your rim with a magnifying class and compare them to a scratch you put in there with an awl or even rough sandpaper. You will see a difference at the fringes. If you thin the brake pads subsequently buffed the fringes, try doing that by putting a scratch on a rim and them applying the brakes. You will see that it does not change shape like a heat-induced roll-up.

As for the pressure, I think localized pressure at the hard point in question is sufficient to do the job.

 

[Yellow Saddle]

In my experience, the noise gets worse the more grit is embedded. It's something that correlates well with wet riding, and off road riding (where there is usually puddles and grit abounding)

Your explanation for the alu pick-up and noise is grit.

Here's a slight enlargement of the OP's brake pad. Point out the grit that caused the problem.

Here's a snip of the picture I posted earlier of a rim damaged by a brake pad. Have a look at the shape of the grooves. Some are intermittent, others are continuous, but none display a typical scratch. I don't have a better photo unfortunately since all my rims are on Koolstops. Perhaps @Globalti still has his scraped rim in the garage? Perhaps the OP has a nice macro camera and can show us what his rim looks like.

 

[Ihatehills]

@Yellow Saddle I'll try and get some pictures tonight. I think that it must be the blocks as you suggest as both rims are scored and I'm not riding in any different conditions to my old bike.
Why would specialized use unsuitable blocks, this must surely be a common issue. I've now ordered some koolstop blocks to see how they fare, I might take it back to the shop at the weekend to see what they say .

 

[vickster]

Why would specialized use unsuitable blocks, this must surely be a common issue.

Cos they're cheap and they have a huge marketing/sponsorship budget to support?

 

[Kestevan]

Shimano ultegra pads are noisy, dodgy in the wet and chew through rims in about 12 months.
Koolstop Salmon or SwissStop Green cure the problem, stop better in the wet than anything else I've tried and increase the life of the rims.

Halt Gooey and Clarks pads fall somewhere in between.

Personally I find a new rim/wheel more expensive than decent pads, so fit SwissStop to my bikes.

 

[mcshroom]

I go for the red-black-grey Clarks pads which seem to work about as well as the KoolStops I replaced a few changes ago. Bonus is that they're only a Fiver a pair.

OEM brake pads are often awful unfortunately. I did very similar to you with a brand new hybrid a few years ago. Switched the pads out for something softer (Yellow Jagwire ones I think in that case) and suddently the bike braked better, was quieter, and stoped chewing up rims.

 

[wam68]

Have to say the Clark's have been good to me. Very good at stopping, even in the wet and they are dirt cheap at CRC

 

[Yellow Saddle]

@Yellow Saddle I'll try and get some pictures tonight. I think that it must be the blocks as you suggest as both rims are scored and I'm not riding in any different conditions to my old bike.
Why would specialized use unsuitable blocks, this must surely be a common issue. I've now ordered some koolstop blocks to see how they fare, I might take it back to the shop at the weekend to see what they say .

My guess is that your shop will be ignorant of the issue. You may here answers like "grit" or "hard rubber" or simply "that's just how it is." Don't expect too much.

Specialized commits bigger crimes than the unsuitable blocks you have on your bike. A special Specialized invention called Zerts comes to mind, but I can mention many others. To be fair, Specialized simply fits brakes made by SRAM or Shimano or Campagnolo. None of these companies have done enough in my opinion to improve the situation. They're all too proud to license others' patents.

 

[Smurfy]

Low maybe, but enough to embed chunks in the pad. Remove a piece carefully one day and you'll see that it doesn't look like a piece of swarf created by a machine tool or sharp instrument. It is lumpy and crumbly.
The stuff I'm talking about and fish out of black brake pads is definitely aluminium. Further, I never find any other material in there, only alu. Perhaps you think otherwise and then a macro photo of embedded grit as you describe will bring resolution to the issue. So far I only find metal.

I have explained that the alu's temperature rises and therefore something softer than alu at room temperature does gouge it out as described. Examine the scratches on your rim with a magnifying class and compare them to a scratch you put in there with an awl or even rough sandpaper. You will see a difference at the fringes. If you thin the brake pads subsequently buffed the fringes, try doing that by putting a scratch on a rim and them applying the brakes. You will see that it does not change shape like a heat-induced roll-up.

As for the pressure, I think localized pressure at the hard point in question is sufficient to do the job.

Your explanation for the alu pick-up and noise is grit.

Here's a slight enlargement of the OP's brake pad. Point out the grit that caused the problem.

View attachment 101419

Here's a snip of the picture I posted earlier of a rim damaged by a brake pad. Have a look at the shape of the grooves. Some are intermittent, others are continuous, but none display a typical scratch. I don't have a better photo unfortunately since all my rims are on Koolstops. Perhaps @Globalti still has his scraped rim in the garage? Perhaps the OP has a nice macro camera and can show us what his rim looks like.

View attachment 101420

I'm not convinced that a polymeric or rubbery material can transform to something hard enough to damage aluminium. The only transformation that would fit that description is carbon to diamond, but we know that synthetic diamond production requires extremely high pressures and temperatures, or other special conditions.
https://en.wikipedia.org/wiki/Synthetic_diamond

The 'lumpy crumbly' description is perfectly consistent with a piece of grit creating quantities of aluminium powder, which is then loosely compacted together with brake dust. Of course the particle of grit that produced the aluminium powder may be elusive, as it only takes one grit particle to produce quite a lot of aluminium powder, and there is no guarantee that the grit particle will wait patiently for you to inspect the brake pad, rather than dropping out while riding.

 

[Maxime]

Shimano ultegra pads are noisy, dodgy in the wet and chew through rims in about 12 months.
Koolstop Salmon or SwissStop Green cure the problem

I have to agree, I did 4000km on my touring (lot of rainy conditions) bike with a set of swisstop (still plenty of remaining life in the pad) and no rim overwearing trouble for the moment. Best pad ever, but quite expensive !

 

[Yellow Saddle]

I'm not convinced that a polymeric or rubbery material can transform to something hard enough to damage aluminium. The only transformation that would fit that description is carbon to diamond, but we know that synthetic diamond production requires extremely high pressures and temperatures, or other special conditions.
https://en.wikipedia.org/wiki/Synthetic_diamond

The 'lumpy crumbly' description is perfectly consistent with a piece of grit creating quantities of aluminium powder, which is then loosely compacted together with brake dust. Of course the particle of grit that produced the aluminium powder may be elusive, as it only takes one grit particle to produce quite a lot of aluminium powder, and there is no guarantee that the grit particle will wait patiently for you to inspect the brake pad, rather than dropping out while riding.

I want to resurrect this thread but I doubt you are still around.

I've been running an experiment and I'm struggling for an explanation.
The two pads in this picture have been on the same wheel. The one on the one side, the other on the other side.

As you can see, there's a marked difference in aluminium pick-up between the two pads.

Further, there is no evidence of any grit anywhere in the black pad. After taking the photo I removed all the aluminium and prodded all over the pad with no success in finding grit. I am convinced it is not grit that causes the problem but pad chemistry.

I have also ascertained that the flash temperatures at the asperite level during braking is about 600 degrees C.
I understand the mechanism of metal pick-up once some metal is embedded in the pad. That's well understood and can be simplified as gallling. What is not understood is what seeds the galling.
The mystery is why one pad seeds it and the other not.

Any explanations?

 

[Alan O]

II have also ascertained that the flash temperatures at the asperite level during braking is about 600 degrees C.

I've nothing I can contribute that might help answer the question, but I'd just like to note that I'm not at all surprised by that - friction can indeed cause enormous temperature rises on the tiny tiny tiny local scale.

 

[bonsaibilly]

I've nothing I can contribute that might help answer the question, but I'd just like to note that I'm not at all surprised by that - friction can indeed cause enormous temperature rises on the tiny tiny tiny local scale.

Yebbut, the Earth is flat, that's what my teachers told me, so it must be.

BB

 

[Alan O]

Yebbut, the Earth is flat, that's what my teachers told me, so it must be.

BB

Everything is flat, at some scale :-)

(or nothing is flat - I can never remember)