Is there any harm done when brake pads/blocks get mashed up in the wet?

[Accy cyclist]

I nipped out on my bike to the local supermarket last night(it was pouring down), It's only a mile there and back. I know pads break down more in the wet, so i expected a fair bit of the black stuff on the rims and forks. I left the bike to drip dry. On checking on it, i was surprised to see the size of pool of black water. My question is, if i leave the black stuff to dry on does it do any harm? I know i've been riding for years and should know about these things,but i've often wondered about it.

 

[ColinJ]

Well, let me put it to you THIS WAY ....!

 

[ColinJ]

Hmm ... for some reason the Google maps link doesn't work now. Anyway, it was VERY scary and I'm sure that you get the message!

 

[tallliman]

@ColinJ, that sounds horrid!

 

[BorderReiver]

Well, if you let the black stuff get on a carbon frame it will dissolve the resin so the frame will fail catastrophically and kill you. That is if it hasn't already dissolved in the rain.
Seriously, though, no it doesn't do any harm. It is a mixture of bits of brake pad and bits of aluminium from the rim. It may contain some oil and "stuff" from the road surface that won't help your braking next time out (and will wear your pads a bit quicker) but it should come off pretty quickly when you use the brakes next. It will make a horrible grinding noise while it does though- that is the sound of your pads and rims being worn away.
Better to clean it off if you can, if not it isn't something to lose sleep over.

 

[Yellow Saddle]

I nipped out on my bike to the local supermarket last night(it was pouring down), It's only a mile there and back. I know pads break down more in the wet, so i expected a fair bit of the black stuff on the rims and forks. I left the bike to drip dry. On checking on it, i was surprised to see the size of pool of black water. My question is, if i leave the black stuff to dry on does it do any harm? I know i've been riding for years and should know about these things,but i've often wondered about it.

It is pure aluminium molecules without any rubber in it.
Metals are interesting at the molecular level in that they don't display the same properties as when they're in bulk. They don't display the same colour, for a start, but they also have some other interesting properties in that state.
When it dries, all you have is aluminium powder. So, no harm done by them.
The rubber also breaks down under those conditions but in bigger chunks and it doesn't colour the water. This can be seen when using say red brake blocks and the water still remains black without a tinge of red.

 

[ColinJ]

@ColinJ, that sounds horrid!

It WAS!

This is what 5 previously WHITE baby wipes looked like after cleaning the rims another time when braking had started to get a bit iffy on a wet ride.

Rim brakes always take a bit longer to bite in the wet. I'm not talking about 'iffy' like that - I am experienced enough to apply the brakes a few seconds before I need to in the rain to get the water off the rims. What I am talking about is so little friction that the brakes barely work. Like braking on old stainless steel rims used to be in the rain.

 

[Will Spin]

It is pure aluminium molecules without any rubber in it.
Metals are interesting at the molecular level in that they don't display the same properties as when they're in bulk. They don't display the same colour, for a start, but they also have some other interesting properties in that state.
When it dries, all you have is aluminium powder. So, no harm done by them.
The rubber also breaks down under those conditions but in bigger chunks and it doesn't colour the water. This can be seen when using say red brake blocks and the water still remains black without a tinge of red.

Actually, that aluminium powder is your rims wearing away. I have bitter experience of hills, plenty of wet weather and a fine flint paste that can wear out an aluminium rim within 2,000 miles!

 

[Globalti]

Clean that black stuff off the rims and clean the brake pads by pulling a fluffy towel or micro-fibre cloth behind them. In wet weather I brake mostly on the front so as to save the rear rim, which gets much dirtier and so wears faster.

 

[Yellow Saddle]

Actually, that aluminium powder is your rims wearing away. I have bitter experience of hills, plenty of wet weather and a fine flint paste that can wear out an aluminium rim within 2,000 miles!

Yes, we know the aluminium powder is from the rim. But wear rate is a function of braking distance in the wet, not traveling distance.

 

[fossyant]

I always washed the crap off the rims, even on the daily commuter each day. As said before, it's the aluminium rim wearing away. Same black goo using red pads.

 

[confusedcyclist]

The thought had never occurred that the black crud might actually be partially aluminium, I figured it was road grime. You learn something new...

 

[Globalti]

It's the same black that you get if you polish aluminium. As Yellow Saddle will tell you aluminium is a soft metal so it's a good choice for bicycle rims that are also giant disc brakes.

 

[wisdom]

Seems normal to me.If mine are particularly bad I rinse them off with the hose when I get home.I commute every day whatever the weather so it seems normal to me.

 

[RoubaixCube]

I heard some older shimano break pads used to 'melt' like icecream in the rain. I experienced the same thing with the pads on the tektro brakes on my Triban before i decided to switch them out for coolstops