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Adherent and abrasive frictions merely describe two process of friction. There are multivariate other factors at work in the wear of a disc which is a separate thing. You may eliminate the lions share of abrasive friction and still suffer physical disc wear.
TJ, by your own admission you're old and slow. You may be using your brakes alot, but you're braking from a low baseline. Even if they get hot, they're not dealing with very high torque whilst hot, because speeds and thus forces are comparatively low.
Also, slow speeds in pants conditions means theres far less debris thrown up and less grinding paste in the brake system - we all slow down for deep puddles to avoid a massive splash right?
You see this with faster riders all the time in poor conditions - proportionately they're far more caked in clart that us joe ordinarys.
I've spoken before on adherent and abrasive friction being in a constant state of flux throughout a ride at any instantaneous moment.
What is the readiness of the pads to deposit fresh material on the disc- Have the pads cooled since their last use?
How much pad material was laid on the disc during the last braking event (or was it worn off)?
how hard are the pads?
How hard is the disc? Not all steels are the same.
How much braking force is required?
Is the brake contaminated with trail debris?
How much debris is there?
How hard is the debris?
Will the next braking event be long enough to built adequate heat to deposit a layer of material on the disc, or will it wear away the layer on the disc because it doesn't get hot enough?
Ad infinitum.
Its clear to me from my own experience that hard aggressive use wears discs and pads quicker irrespective of conditions. This shouldn't be a surprise.
Back in the 90s we’d often wear out a set of pads in one ride – chalk mud + water = abrasiontastic.
Rims would last a winter. I had a pile of rims with scarily concave sidewalls.
Them were the days! Used to regularly do the same in the peak district.
Oh what fun to blow the entire side of your rim off, ruining both wheel and tyre, due to worn concave rim giving way under tyre pressure, way up high on Jacobs ladder in the snow, when it was getting dark and you still had to ride back to Macclesfield.
Its clear to me from my own experience that hard aggressive use wears discs and pads quicker irrespective of conditions. This shouldn’t be a surprise.
of course - but the materials science is clear - its when you get into just abrasive friction zone you get this wear out in a few miles issue which is not the same as greater wear due to hard useage
From previous discussions on her there are some fast riders who do not get the ultra rapid pad wear, there are slow riders who do
Grit on the disc surface is only there for one turn of the wheel. Its cleared by the drilling in the disc
As above - its not just about speed and conditions - there are many other factors. I have linked to some of the materials science in an earlier post. Its when all the factors line up to mean you are in the abrasive friction zone only then the pads wear out in a few miles
Ive tried to explain it. I have linked to articles that explain it, I have read widely around the topic because I was puzzled and that the conclusion I came to based on a lot of good materials science
Its complex and multifactorial. its not just fast rider in poor conditions = rapid wear.
Disc brakes and how they work is one of the most poorly understood things on bikes.
he benefits of adherent friction
Once the brake pad material is sufficiently transferred to the surface of the rotor, it creates what we call sticky brakes. The material transferred acts as a sort of adhesive that literally sticks to the brake pad as it’s being compressed against the rotor. What this does is create a barrier between the pads and the rotors so that the rotor is not being ground down to a powder by the brake pads. What this benefit really means is that your brakes will last significantly longer. Since the rotor is not being ground down the rotors almost don’t wear, which means they will last a very long time without being damaged. There is no brake dust. Again, because there is no wear, there is no brake dust. Your pads will last 10-20 times longer. Adherent friction is not nearly as a destructive of a force so the brake pads are not being worn down as fast.
From the link on the previous page
I am merely trying to explain why some folk get the rapid pad wear and some do not
Some fast riders get it, some do not. some slow riders get it, some do not. two folk on the same trail at the same speeds one might get the ultra rapid wear from being in the abrasive friction zone and one might not
too many folk just want to shout me down rather than listen to the argument.
I'm out
there are other factors than simply speed ad conditions. when allthese factors line up you get this ultra ra[pid wear
Its clear to me from my own experience that hard aggressive use wears discs and pads quicker irrespective of conditions. This shouldn’t be a surprise.
You mean like they are being asked to do much more work than people going for a bumble.
Of course - its obvious that would be so. You will get more wear
However that does not explain this ultra rapid wear. that is explained buy the abrasive friction issue as above
As above - some fast rider do not get the rapid wear some slow riders do
I'm sure we've discussed this before and it's down to you running relatively small rotors as I do the same on winter bikes? It was down to running ostensibly rubbish brakes that ran hot that keeps the system bedded in rather than wearing out. Running 160/160 brakes in crappy conditions resulted in less pad wear than bigger brakes.
It's a massive compromise though, I'm happy to accept slightly crap braking on familiar trails on a mid week nightride where I'm just enjoying being out and about, or on the gravel bike where I want to be able to ride hundreds of miles in filth.
I'm not happy with that compromise on a bike I want to ride flat out downhill because it's not really very fun as there's not enough power.
Grit on the disc surface is only there for one turn of the wheel. Its cleared by the drilling in the disc
Is it? There's usually grit on the surface of the pads too, a bit more moisture and that grit deposited in the drillings can wash back on to the surface/pad face, once it's in there it take more than one revolution only the rotor to clear.
I Went for a moderately mucky ride yesterday, hosed the bike off after but still hadn't washed all the grit out of the rear brake, that could still be heard grinding away betwixt pads and rotor. In Berkshire as mentioned before, so there's a nice mixture of chalky mud holding various types of grit and puddles don't drain away in April, I've had pads go within a handful of wet rides round here without a particularly urgent pace on my part.
It's inevitable that you'll add some sort of extra abrasive materials to the braking surfaces, it just depends where and when you ride as to what the characteristics of that material is and how it affects pads/rotors...
As above – some fast rider do not get the rapid wear some slow riders do
This is the bit I don't really agree with.
I think theres a commonality of factors that produces broad bands of comparably similar wear for a given case use. Its then modified by particular equipment choice and braking style.
It is a bit weird that you acknowledge multivariate factors as inputs, agree that it's complicated and poorly understood but then bang the adhesive/abrasive friction drum quite loudly as the only factor.
Ta Tinas - thats the theory - brakes that run hotter are less likely to get into the abrasive friction area due to depositing the boundary layer more quickly. Being slower means dragging the brakes more meaning they get hotter. smaller discs run hotter
disc brakes need the heat to work properly Hundreds of degrees C
thats one of the factors
It is a bit weird that you acknowledge multivariate factors as inputs, agree that it’s complicated and poorly understood but then bang the adhesive/abrasive friction drum quite loudly as the only factor.
Its when you get into the abrasive friction zone you get the ultra rapid wear. Multiple factors govern at what point you tip into the ultra rapid wear. Fast riders are more prone to this as they use the brakes less meaning the brakes run cooler, bigger discs mean they run cooler
there is a difference between more wear because of more energy in the braking system and the ultra rapid wear from going into abrasive friction
Abrasive friction wears out brakes much more quickly than adherent.
As above – some fast rider do not get the rapid wear some slow riders do
This is the bit I don’t really agree with.
thats just what I have gathered frommany discussions of this on here. Nowt hard to back it up other than what folk have said on here
Edit: and also from what I saw at the puffer. Some fast riders got the ultra rapid wear, some did not. Some slow riders did, some did not
I have never had any noticeable wear on discs and never replaced one
Same. I've wondered if they're thinning and becoming weaker, though I've never measured them so can't tell. Certainly not noticed any real wear on the braking surface. Live in a hilly area so they get used hard and do thousands of miles on and off road. Always use sintered pads.
tjagain
I’m out
yeah I know. Stoopid me 🙂
Grit on the disc surface is only there for one turn of the wheel. Its cleared by the drilling in the disc
Thats a massive a hugely inaccurate statement for starters (or stoppers?)
Grit stays on mine for long periods of time, you can hear it as you brake.
Clean away but unless you have changed both components you have not eliminated the contamination merely reduced it.
Quite, but these aren't my first set of discs and not only have MTB brakes not squealed anywhere near as much but they've always responded to the cleaning I've done. Something is different here, probably the amount of heat in the short term and the number of miles on a set of cheap discs.
Grit on the disc surface is only there for one turn of the wheel. Its cleared by the drilling in the disc
Yeah no. It hides somewhere, presumably in the holes, and it stays for a while as anyone with ears will testify.
I am merely trying to explain why some folk get the rapid pad wear and some do not
I appreciate that but we don't think you're right.
the materials science is clear – its when you get into just abrasive friction zone you get this wear out in a few miles issue
It's not the abrasive friction between pad and disc. It's the abrasion caused by the grit which is being held there by all the water in the caliper and in the holes.
I have never had any noticeable wear on discs and never replaced one
How do you know? The tolerance on a new disc vs what the manufacturer say is worn one is c. 0.25mm.
You wouldn't even know unless you were measuring.
Paid ~£40 per 160mm rotor for https://www.merlincycles.com/shimano-xt-mt800-ice-tec-centrelock-rotor-180696.html recently for these to fit to my yet to be setup VEL 50 RL wheelset, because they were a bit cheaper than the https://www.chainreactioncycles.com/shimano-ultegra-rt800-ice-tech-freeza-rotor/rp-prod161380 I've had on another wheelset for four years, plus appparently the MTB version has stronger arms to the rotor and is often used by roadie pros (even though the extended road fins look cool IMO)...
Just looked as result of this thread and they are now ~£28 each, bargaintastic.
The new ones I just bought say Ultegra/GRX/Deore XT on the box...
This thread has inspired me to get round to sorting my brakes out.
Got 2x180mm SLX - RT66 rotors from Wiggle for a tenner each (last ones apparently - though CR may have some at that price) Less than half the price elsewhere