is there such a thing as rim brake fade?

General cycling advice ( NOT technical ! )
A1anP
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is there such a thing as rim brake fade?

Postby A1anP » 3 Aug 2016, 1:49pm

Because I think I'm getting it. All my searches on brake fade seem to turn up disk brake fade.

What's happening, on a road bike with standard caliper brakes, is that when coming down a steep hill, the brakes work fine to start with, then after a wee while a gritty noise sometimes starts and the brakes stop working so well. That can make me feel quite uneasy and not at all certain that I will make it round the next corner.

I'm not certain what causes it, but clearing the gunk from the slits in the brake pads usually seems to stop it for a while. But by the end of a ride on wet / dirty roads, it can be happening again.

Any idea how I can reduce / stop this effect? Could it be the pads (I'm using Discobrakes pads) or how they're set up?

Thanks for looking,
Alan
Going upwards at 45 degrees...

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Si
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Re: is there such a thing as rim brake fade?

Postby Si » 3 Aug 2016, 5:24pm

I've had rim brake pads go hard and shiny and offer a reduced quality of braking. However, this seems to be a one way process (until you start pruning) unlike disc brakes.

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bigjim
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Re: is there such a thing as rim brake fade?

Postby bigjim » 3 Aug 2016, 5:48pm

Yes I'm sure they overheat and fade, some worse than others. I try to release them and re-apply on steep dodgy hills in order to let them cool. It's best of course to let the bike fly and use that speed for the uphill part. That scraping noise is usually, in my case the bits of aluminum the blocks pick up off the rims. I regularly dig the Ali out of my blocks and put them back in order to save my rims.

fastpedaller
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Re: is there such a thing as rim brake fade?

Postby fastpedaller » 3 Aug 2016, 5:53pm

Many years ago a clubmate and I descended the snake pass at over 60mph - I had the cheaper "coolstop" pads which performed ok, but his more expensive Shimano ones ended up as a load of goo! That was REAL brake fade :shock: clearly not high-temp resistant :lol:

A1anP
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Re: is there such a thing as rim brake fade?

Postby A1anP » 3 Aug 2016, 6:26pm

Thanks for the replies. Good to know that others have seen similar.

bigjim wrote:I try to release them and re-apply on steep dodgy hills in order to let them cool.


I do the same when things go gritty. It's the last resort, other than looking for a soft landing somewhere...

My best guess at what's going on is that there's a build-up of crud in the slits in the pads, which gets released when they get hot. The "toe-in" helps to trap the loose grit as well (maybe??). So I should treat it as a warning to give the pads and rims a good clean out.

I have contemplated going over to disk brakes but that brings a whole new load of potential problems, and I've had disk brake fade on my mountain bike as well.

Cheers,
Alan

p.s. I wasn't able to spot any bits of metal in the pads
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Si
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Re: is there such a thing as rim brake fade?

Postby Si » 3 Aug 2016, 6:32pm

oh yeah, there is certainly the possibility dramatic tyre-fade, followed by dramatic skin-fade with rim brakes :lol:

Brucey
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Re: is there such a thing as rim brake fade?

Postby Brucey » 3 Aug 2016, 10:25pm

you can get noises if there is crud trapped in the brake blocks but the most common thing is that the brake block gets too hot on a long descent and starts to soften and wear at an accelerated rate.

If you alternate between brakes, changing when the one brake starts to get noisy, you will be able to moderate your speed on long descents without overheating the brake blocks, which will then last longer. The brake not in use has a fair chance to cool down.

The length of time between alternations (as indicated by brake noise) ought to be at least ten seconds. If the time period goes to just a few seconds, it is time to let the bike run or to stop the bike and let the brakes cool off.

If you drag both brakes and don't give them a chance to cool off you will wear the brake blocks very quickly for sure. You will likely also wear the rims faster. But most importantly you run an increased risk of the tyres blowing off the rims, or an inner tube failing.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Grandad
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Re: is there such a thing as rim brake fade?

Postby Grandad » 4 Aug 2016, 12:06am

Riding a traditional trike down a long hill on a cold winters day I used the brakes alternately. However as both were on the front wheel I suspected that the rim might heat up. Stopping at the bottom and taking my glove off I felt it to check - removed painful finger very quickly :shock:

ambodach
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Re: is there such a thing as rim brake fade?

Postby ambodach » 4 Aug 2016, 8:21am

Coming down the hill from Glenelg direction ( can' t remember the name of the pass) with a touring load my front brakes started to smoke they were so hot. On another occasion coming south over the hill to Drumnadrochit the heat melted the adhesive holding the patches. Not quite a visit from the fairy but close.

A1anP
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Re: is there such a thing as rim brake fade?

Postby A1anP » 4 Aug 2016, 8:31am

Thanks Brucey, I think I might be getting the picture... braking for too long, or too hard, is softening the blocks, leading to the gritty noise and loss of braking power. The alternating between front and back brakes is a great idea, will try to remember it next time.

It's a bit disappointing that it happened yesterday on a descent that's just 0.1 mile long, although I reckon it maxes at over 10% (despite not having a chevron on the map). It is only trying to stop quickly on steep descents where I've had the problem. Could be as little as 5-10 seconds of braking. When I was in Majorca earlier in the year, I was using a hire bike and it coped fine with much more serious descents than I normally put my bike through at home.

Interestingly I didn't have any problems prior to changing the wheelset on my Triban 3 from the stock wheels to Shimano R501s. I felt the braking was noticeably better after doing that, but perhaps that comes at the expense of generating more heat. Maybe I should be looking for more heat resistant brake blocks...?

Cheers,
Alan
Going upwards at 45 degrees...

A1anP
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Re: is there such a thing as rim brake fade?

Postby A1anP » 4 Aug 2016, 9:03am

ambodach wrote:On another occasion coming south over the hill to Drumnadrochit the heat melted the adhesive holding the patches. Not quite a visit from the fairy but close.


That's scary! There's no way I would risk coming down that hill on my road bike the way it is. I rode up it earlier in the year, which is hard but much less hazardous to health. The Foxhole descent on the north side is a straight freewheel, no problems :D
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Keith Bennett
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Re: is there such a thing as rim brake fade?

Postby Keith Bennett » 4 Aug 2016, 9:15am

The explanation by Brucey brings back to me a science lesson in school (1940s) By applying heat continuously to a solid (brake block or pads) will eventually change from a solid to a liquid hence the softening and loss of friction eventually this liquid ,when hot enough will change to a gas, a problem with early hydraulic motor vehicle systems when the non compressible brake fluid changed to a compressible gas.

Eammno
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Re: is there such a thing as rim brake fade?

Postby Eammno » 4 Aug 2016, 10:42am

I've experienced this, and as others have said I found it was flakes of aluminium and grit embedded in the brake block. I too initially thought I had brake fade, but when the brakes started going rough and gritty very soon after application on very slight inclines, at slow speed I decided brake fade was not the answer.
So I tried digging out the embedded crud, and sanding the blocks to expose a fresh layer of brake material, but didn't really fix them it till I replaced the blocks which was a braking revelation!
I wonder if the brake blocks change after being overheated on a long descent which allows aluminium to be picked up

A1anP
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Re: is there such a thing as rim brake fade?

Postby A1anP » 4 Aug 2016, 1:56pm

I cleaned up the brake pads and rims and tried the same spot again today. Reached the steep section doing 30mph then did 12 seconds of hard braking to reach the corner safely... no problems. Then dragged the brake for 30 seconds at the next bit of downhill just for the hell of it. Just a bit of rim heating, barely warm really.

Who knows what it all means, but at least it gives me some confidence back :)
Going upwards at 45 degrees...