a nasty surprise for someone....?

[Brucey]

Is what I was wondering about a few days ago as I rode home.

I usually keep my eyes peeled for bits of rubbish in the road, because they might go through my tyres. Near the top of a rise on my way home, I saw something lying in the road and of course steered well clear of it. However I glanced at it as I went past and for a few moments it didn't register and then I didn't believe that I'd seen what I thought I'd seen. So after a few more yards curiosity got the better of me and I had to go back and have a better look, didn't I....?....

Sure enough the thing I'd seen was exactly what I thought it was; a slightly used bicycle disc brake pad. And not far away I found another one;

They travel in pairs; I find these work best if they are actually attached to my bike....

I don't remember seeing a dead body at the bottom of the hill so I would suppose that the rider didn't have a really nasty accident, but at least one of their brakes wouldn't have worked at all once the pads fell out.

The pad is of a common sort that is fitted to brake calipers that have either screw-in pins or split pins in them. I suppose that if the pin falls out or is absent from the start, then the pad spring may hold the pads in for a while; the pads were each about 0.2mm worn, so they had been used for a little while before they fell out.

I would suppose that the pads were fitted by someone that didn't know what they were doing (the disclaimer about home maintenance on most brake instructions suddenly seems more relevant now...) but it is also possible that someone tampered with the brakes I suppose. For me, SOP is to pull on the brake levers before I head off; I do this without even thinking about it now and it means that if my bike has taken a knock whilst it has been parked, and this has somehow affected the brakes, I will probably notice . However if the pad pins were missing from a disc brake, the brakes would feel quite normal at the lever, right up until the moment the pads fell out....

cheers

[Woodtourer]

Brake pads are overrated anyway!!

[fastpedaller]

I'm not familiar with disc brakes, but would there be enough travel (either in cable/lever movement or in hydraulics before seals were breached) for the pistons to contact the disc and provide some braking? certainly not ideal, but maybe a life-saver.

[Cyril Haearn]

One earnestly hopes the machine had a second hand-brake
And a back-pedal brake of course

[garygkn]

Perhaps they were being carried and the bicycle had working brakes but these fell to the ground from a loose pocket or pannier?

I'm a trendy consumer. Just look at my Moto G (4) using hovercraft full of eels.

[Marcus Aurelius]

Disc brakes are a nightmare. I avoid them whenever possible.

[Brucey]

I'm not familiar with disc brakes, but would there be enough travel (either in cable/lever movement or in hydraulics before seals were breached) for the pistons to contact the disc and provide some braking? certainly not ideal, but maybe a life-saver.

When you pull the brake lever once, normally there is about 1mm of piston movement. Not enough bearing in mind you need at least another eight mm once the pads are missing.

With an 'open' hydraulic system it will 'self adjust' about 0.5 to 1mm per lever stroke. So potentially if you pulled the lever between 8 and 16 times a hydraulic system might make up for the ~8mm of lost pads and bring the pistons into contact with the disc. However this would involve the pistons going further than normal; about 3.2mm (the thickness of two backings) plus some remaining friction material (manufacturer's recommendation is ~0.8mm each pad remaining when you change pads) i.e. about another 1.6mm, or a total of ~4.8mm further than normal. I would suppose that the brakes are safe if just the backings remain but that is still 3.2mm further than 'normal'. I think one or both pistons will probably go past the seals in the caliper body (resulting in an oily mess and no brake pressure), even if you managed to pump them out quickly/far enough to be useful.

cheers

[Brucey]

Perhaps they were being carried and the bicycle had working brakes but these fell to the ground from a loose pocket or pannier

Possibly, but used pads, hardly worn? Seems somewhat unlikely to me.

cheers

[thelawnet]

meh.

I went to the pub today.

there was a bike parked outside.

it had a rear (v) brake with no attached cable, noodle or pads

brakes are overrated

[Brucey]

I see bikes with defective V brakes all the time, sticking out like weird ears. In fact I look out for these because I know that an oncoming rider with brakes like that probably won't be able to stop.

Thing is, this can't be a surprise to them when the brake doesn't work; the rider can see that there is something wrong with the brake and indeed they probably unlatched it when the wheel wouldn't go through without rubbing.

cheers

[amediasatex]

The real question is:

Did they lose both pads from one brake, or one pad each from both brakes? Enquiring minds need to know...

Had a hairy situation on an audax before xmas, one of my friends has had a few issues with her brakes over the last year or so (TRP cable/hydro hybrids) so was used to having slightly iffy brakes and ignoring warning signs But on this ride both brakes failed simultaneously while we were about 15miles from the finish, she managed to just about come to a rolling stop and after a bit of poking we realised that the rear pads had worn down to the backing and the rear wheel was now free running as there wasn't enough travel left in the pistons to get the backing plates to make any more contact. The front was a combination of very worn pads and a pad wear/piston adjuster that kept screwing itself out under hard braking.

We managed to ride the last 15 miles back with me being her brakes by grabbing hold of the back of her jacket with one hand and braking with the other! A few dodgy moments on some steep lanes got us both a bit sweaty but we made it home ok in the end.

[foxyrider]

Brake pads are overrated anyway!!

I had total failure of my disk brakes on Saturday, fun it was not! However, even with the pads shredded they are still in situ,

I managed to get just enough contact for some slow speed control, by carefully choosing my route home and keeping the speed well down I avoided needing any real braking for 60km.

I hate disc brakes!

[LittleGreyCat]

Hmmmm............

My new Spa Wayfarer Disc tourer (have I mentioned it before?) also has fittings for cantilever brakes on the frame should someone want to swap away from discs. Or need to rig emergency brakes should the discs fail when on tour.

Leaving aside the issue of suitable rims, and recalling the discussion of secondary brakes on a tandem, and also the discussion about overheating brakes on heavily laden bikes down long steep hills how sensible would it be to install cantis as backup brakes?

[amediasatex]

Hmmmm............

My new Spa Wayfarer Disc tourer (have I mentioned it before?) also has fittings for cantilever brakes on the frame should someone want to swap away from discs. Or need to rig emergency brakes should the discs fail when on tour.

Leaving aside the issue of suitable rims, and recalling the discussion of secondary brakes on a tandem, and also the discussion about overheating brakes on heavily laden bikes down long steep hills how sensible would it be to install cantis as backup brakes?

It would be an over-reaction IMO. Just keep on top of the brakes you have, keep them in good order and check the pads and operation regularly (as you should with any brake system). You only need backup brakes if your primary brakes fail, so put the effort into making sure they don't, otherwise where do you draw the line, you might need backup backup brakes if they were to fail

[Brucey]

The real question is:

Did they lose both pads from one brake, or one pad each from both brakes? Enquiring minds need to know...

we'll never know for certain, but I would note that

a) the pads were lying closer together in the road than one bike length and
b) once one pad can escape there is nothing to stop the other one in that caliper, if they are normally retained by a pin or screw.

Had a hairy situation on an audax before xmas, one of my friends has had a few issues with her brakes over the last year or so (TRP cable/hydro hybrids) so was used to having slightly iffy brakes and ignoring warning signs But on this ride both brakes failed simultaneously while we were about 15miles from the finish, she managed to just about come to a rolling stop and after a bit of poking we realised that the rear pads had worn down to the backing and the rear wheel was now free running as there wasn't enough travel left in the pistons to get the backing plates to make any more contact. The front was a combination of very worn pads and a pad wear/piston adjuster that kept screwing itself out under hard braking.

We managed to ride the last 15 miles back with me being her brakes by grabbing hold of the back of her jacket with one hand and braking with the other! A few dodgy moments on some steep lanes got us both a bit sweaty but we made it home ok in the end.

TRP HyRd brakes have been through two iterations; the first ones (which may have been recalled, do check) have a smaller reservoir than the later ones. [also the first ones came with instructions that didn't labour the point that one of the screws that looked like an adjuster wasn't one, and that the normal bite point of the brake was midway through the stroke, not at the top of the stroke.] Presumably they made the reservoir change because the system could too easily run short on fluid, eg when the pads were worn. However I have not actually seen this; what I have seen is that folk have fiddled with the pushrod screw and this has removed the self-adjustment facility; the brakes can temporarily feel wonderful, with a bite point at the top of the stroke, but as the pads wear you will soon have no brake at all. I am pretty sure that about 9/10 complaints about HyRd brakes have this problem (and/or a cable adjustment problem which can also cause the same thing) at their heart.

Hydraulic systems should carry on working -albeit noisily- when the linings are worn right off and there is nothing but backing left.

One common feature with all 'open' hydraulic systems (cable/hydro or full hydro) is that -when they are working normally and have not been fiddled with contrary to the manufacturer's instructions- the brakes self-adjust, so the pads can wear without the rider knowing anything about it. Since wear rates can be x10 faster in wet/muddy conditions (esp with resin/semi-metallic pads) I advise riders to check their pads every ride, so they are not caught out.

BTW my objective -past showing that even the very unlikely can happen perhaps- in posting this was not to have a go at disc brakes per se, it was more to point out that (potentially every time you throw your leg over a bike) you can't take anything for granted; new bikes come covered in stickers warning the rider that riding along with the QRs loose is 'extremely hazardous' and that you should read the manual. I guess it is good if systems have a backup or at least a 'graceful failure mode'.

A fundamental question is raised though; whether it is a good idea to have systems on bikes which are both safety critical and non-user serviceable, especially if they don't have a graceful failure mode.

cheers