Massive brake fade

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MichaelB
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Re: Massive brake fade

Postby MichaelB » Tue Oct 17, 2017 1:25 pm

Que ?

Don't quite get what you are aiming at ?

eeksll
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Re: Massive brake fade

Postby eeksll » Tue Oct 17, 2017 2:05 pm

MichaelB wrote:Que ?

Don't quite get what you are aiming at ?


rim brake tracks are better at shedding heat than disc brakes?

CKinnard wrote:I suppose the other safety factors apart from brake fade is rim heat punctures, and tire roll offs.


yeah, whats the first point of failure? blown off tyre due to heat or brake fade due to heat.

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MichaelB
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Re: Massive brake fade

Postby MichaelB » Tue Oct 17, 2017 3:35 pm

eeksll wrote:
MichaelB wrote:Que ?

Don't quite get what you are aiming at ?


rim brake tracks are better at shedding heat than disc brakes?



But are they really ? many people quote/mention this opinion based on the fact that there is more surface area (I think) and therefore this means it has greater heat rejection capacity.

But in reality, this is only part of the story.

There are other factors such as coefficient of friction (between pad & rim/disc), braking load, existing thermal capacity, current temp, braking forces, external temp, etc etc

I don't have any proof, but would happily wager that for all given circumstances, disc brakes will outperform rubber pads on a rim (be it alloy or carbon matrix).

They (rim brakes & rubber pads) may perform well enough for many, and that's fine. For those that choose it. :D

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Thoglette
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Re: Massive brake fade

Postby Thoglette » Tue Oct 17, 2017 4:07 pm

MichaelB wrote:I don't have any proof, but would happily wager that for all given circumstances, disc brakes will outperform rubber pads on a rim (be it alloy or carbon matrix).


Fancy putting your house vs my house on that one? I've been following this one for a long while and I'd wager I can rig a lab demo that results in a set of disks failing first. I reckon I could even do it using the same braking technique.

Hint: there's been plenty of disc failures reported in the press over the last decade and more than a few claimed "I used the brakes just like I would rim brakes".

All one needs to do is find ONE combination of situations where the rim brakes aren't gaining temperature and the discs are. Think a long, gentle decent on a cool day dragging the brakes....
Stop handing them the stick! - Dave Moulton
"People are worthy of respect, ideas are not." Peter Ellerton, UQ

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MichaelB
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Re: Massive brake fade

Postby MichaelB » Tue Oct 17, 2017 4:25 pm

Anyone can make a component fail, that proves nothing. What I am talking about, is that for the same braking type, lever force, deceleration, rain etc, discs would win.

The reality, is rubber blocks on a rim are old hat (and yes they have improved hugely over the 100+ years they have been around), and discs are better. Which is why they are used just about everywhere.

As I said, for many, rim brakes on a bike work well enough, and that's good for those that are happy with that. I'm not, and hence I'm on discs.

Don't have a house to wager, but I'll toss in a carton of good beer. :-)

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Thoglette
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Re: Massive brake fade

Postby Thoglette » Tue Oct 17, 2017 4:35 pm

MichaelB wrote:Anyone can make a component fail, that proves nothing. What I am talking about, is that for the same braking type, lever force, deceleration, rain etc, discs would win.

As you said, you have no proof. Beyond "rubber blocks are old hat".

Meanwhile, out in the real world there are situations that resulted in total failure of disc systems. My favourite example (as it has a fairly balanced discussion of the underlying causes) is this one from Bike Rumour in 2012.

I'll also add that I spent the best part of a decade messing with modified-production race cars. At the time teams were running different brake systems (not just different pads and ducting) for different circuits and race durations.

I've seen discs fail completely in a single lap: there is nothing magical about them. They need to be engineered to suit the need.

I repeat: I'm certain that I could rig a situation where I can get rim brakes to survive while the disc fails. That was the challenge you set.
Stop handing them the stick! - Dave Moulton
"People are worthy of respect, ideas are not." Peter Ellerton, UQ

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MichaelB
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Re: Massive brake fade

Postby MichaelB » Tue Oct 17, 2017 7:45 pm

I too have raced, have an engineering background (automotive, aerospace, defence and general manufacturing), so lets agree that you can make a scenario where either would fail and one would survive, but is that realistic ?

Yes, things can fail, so can rims & rubber pads. Contamination will affect both. Misuse and improper component selection will also cause failure (the Bike Rumor article was a classic case of REALLY wrong parts selected - different discs would have yielded a much different result) but that also proves nothing. The space shuttle crashed, does that mean the old style rocket is better ? Um, nope.

What is realistic is the relative performance for each test, the repeatability of the braking capability, the change in pad/friction surface over time and temperature ranges, weather conditions, braking types.

If you can prove me wrong and show me (other than bicycles, where weight and tradition rule strongly), in a performance application where rubber blocks are used over discs, I'll submit and go he.

Each system has it's place and followers (like pedal straps, downtube shifters and cotton bar tape), and I'm fine with that.

Meh, you stick with your rim brakes that work pretty damn well, and I'll stick with my discs that work that little bit better all round, and much better in the wet.
Peace 8)

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Re: Massive brake fade

Postby ball bearing » Tue Oct 17, 2017 8:40 pm

Rim brakes involve much higher contact speed with pads due to the greater circumference. It seems reasonable that this generates higher temperatures than disc brakes. My guess is that rims dissipate heat more efficiently than discs. My road discs have cooling fins which seem to keep the heat from building up - note to self - maybe I should replace my mtb discs with the finned variety.

Botton line - both systems work pretty well, but I do perfer discs.

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MichaelB
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Re: Massive brake fade

Postby MichaelB » Tue Oct 17, 2017 8:44 pm

Actually, Thoglette, I'd be REALLY interested in test scenarios where a rim brake (treated the same) would actually outperform the rim brake.

Thought about it a bit more and am interested to see what the scenario(s) would be. :-)

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CKinnard
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Re: Massive brake fade

Postby CKinnard » Tue Oct 17, 2017 9:31 pm

BTW, my original musing wasn't rims vs discs....but alloy vs carbon rims when using rim brakes.

Some have said carbon rims have improved significantly in the last few years.
I still think if I was going to ride in the Alps, I'd prefer alloy over carbon rims with rim or disc brakes.
My main reason being I don't know anyone who is riding 10 year old carbon rims, but I know heaps of ppl riding 10+ year old alloy rims, including me. But also because I think getting heat away from rim brake pads is a priority.

eeksll
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Re: Massive brake fade

Postby eeksll » Wed Oct 18, 2017 12:51 pm

CKinnard wrote:BTW, my original musing wasn't rims vs discs....but alloy vs carbon rims when using rim brakes.


I was just giving the pot a bit of a stir :twisted:

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