a nasty surprise for someone....?

[reohn2]

Lack of maintenance never did any type of brake any good

[rmurphy195]

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.

Unlikely - discs are often full of holes, and while the pads may run on them without snagging the pistons would be smaller and would probably jam!

[thelawnet]

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.

Usually one of these two systems:


or



If the pads (which look like B01s?) had been recently replaced, then it's possible that the split pin was inserted but then not bent.

After inserting the pads into the caliper the pin secures the pads & spring to the caliper.

However, the pin needs to be bent using a pair of pliers



Perhaps this was not done, and the pin fell out.

(once the pin has been bent once, the pin will never really be straight again, so if the same pin is been reused after removing pads for inspection or whatever, it's quite unlikely to work its way out, but on a new pin & pads it seems to be quite plausible)

The screw & clip systems are threaded & secured with 2NM of force or so, the snap ring is a failsafe, but perhaps in some scenario if the snap ring was missing, the screw could fail.

[thelawnet]

Lack of maintenance never did any type of brake any good

the issue with disc brakes is that you can wear through the pads and trash discs and/or calipers.







Caliper brakes are a bit more straightforward to renew in that respect.

[Syd]

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.

Usually one of these two systems:


or



If the pads (which look like B01s?) had been recently replaced, then it's possible that the split pin was inserted but then not bent.

After inserting the pads into the caliper the pin secures the pads & spring to the caliper.

However, the pin needs to be bent using a pair of pliers



Perhaps this was not done, and the pin fell out.

(once the pin has been bent once, the pin will never really be straight again, so if the same pin is been reused after removing pads for inspection or whatever, it's quite unlikely to work its way out, but on a new pin & pads it seems to be quite plausible)

The screw & clip systems are threaded & secured with 2NM of force or so, the snap ring is a failsafe, but perhaps in some scenario if the snap ring was missing, the screw could fail.

Both those systems, used correctly, are superior to the pad retaining clip used on BB7 for example.



These can be a pain to get the pads locked in during installation and can misshape over time, resulting in them coming adrift.

The pads in the OP do seem to make use on some pin system though so very likely an error or omission somewhere along the line.

[Brucey]

….the issue with disc brakes is that you can wear through the pads and trash discs and/or calipers.



Caliper brakes are a bit more straightforward to renew in that respect.

This sort of thing is more or less inevitable when you have self-adjusting brakes; the pads wear away and there is no sign. It takes a special case to wear through the pad backing though.... By contrast if the lever comes back to the handlebar, most people will work out that something is wrong even if they don't know what it is exactly.

The upshot of this sort of thing with (say) car brakes is that they are fitted with pad wear sensors, hydraulic fluid level sensors and goodness knows what else. These systems go wrong themselves and cause at least as many false warnings as real ones; when a real warning occurs there is no guarantee that anyone will take any notice of it.

Which all goes to show that attempts to make a system truly idiot-proof can merely result in the generation of a new improved form of idiot, I suppose.....

cheers

[Brucey]

BTW it has been mentioned to me that 'split pins don't seem very strong' in relation to bicycle brakes. This seems to be true, they are not particularly strong in absolute terms.

However I was recently working on some AP-Lockheed brakes which normally have to stop ~2.5 tonnes and occasionally have to stop at least double that. These brakes also use split pins to retain the pads. There are two of them but they have a long span (about 60mm between the supports) and for the front brakes the pins are 3/16" (less than 5mm) and for the rear they are 5/32" ( about 4mm). You can bend them in half using your fingers if you try, they are not very strong.

AP-Lockheed make brakes for racing cars, trucks, cars you name it that are designed the same way and they are not alone in doing so. The reason these 'not very strong' pins work is that the main brake forces are reacted against the caliper body by the pad backing; the pins see no real load in service. Mostly it seems to work very well. However there are certain fault conditions and design variants which are not 100% immune to problems; in some brakes the backings have curved end faces. If the disc itself ends up with a more worn or rusty 'track' on it, there can be a substantial force twisting the pad in the caliper body (about an axis parallel to the axle itself). Normally the backing can't twist far before it binds in the caliper body but with curved ends to the pad backing, potentially this movement can load up the split pins. Similarly if the caliper was badly mounted, so that the tangential forces on the pad are not reacted against an orthogonal face inside the caliper, there could be a net force on the pad which is trying to force it out of the caliper.

In bicycle brakes the same logic applies, but the split pins -feeble looking as they are- are very much larger than they would be if the brakes were 'scale models' of larger brakes. IIRC the split pins used in bicycle brakes are ~2.5mm diameter, even though the brakes are less than 1/5 th the size. Normally the main brake forces are reacted into the caliper body by the pad backings, but if the brakes are badly installed (with the disc not in the middle of the caliper body slot) and/or the pads get very worn, of the caliper is installed so that it isn't properly tangential to the dsic, then the pads can start to 'escape' from the caliper body. When this happens the retaining pins get loaded up and it is anyone's guess whether the pads will stay put or not.


a fitting kit for a car brake; note the cross-drilled (solid) pins and 'R' clips

The use of solid pins is to be preferred over split pins if you are worried about their strength (a solid pin of a given diameter is many times stronger than a split pin that goes in the same hole); however solid pins need a secure retaining system of some kind. Large pins are usually cross-drilled and fitted with lockwire and/or an R clip that is designed not to foul on anything. In bicycle brakes the pin is usually threaded and has a different type of R clip fitted in a groove in the far end of the pin as a secondary retainer. This is usually enough to retain a loose pin but it isn't 100% secure; if you try to uscrew the pin with any real effort the R clip often just pops off. If you just wipe the caliper body with a rag you can catch the ends of a poorly fitted R clip and it can pop off that way too.

Note also that any pad springs in car brakes are simply there to stop the pads from rattling. If they are rusty, broken or missing altogether it is rarely a catastrophic fault. However in many bicycle brakes they are part of the primary pad retention system; given that they are often the first things to wear through if the pads are abnormally worn, you can potentially lose worn pads from certain brakes when the springs are damaged.

For example BB5 brakes (and many clones) use a spring to retain the pads; if the caliper is not set over the centre of the disc and the pads are worn, the spring can fail (it is within the emaining thickness of the friction material) and a pad can be lost.

cheers

[LollyKat]

Just a few weeks ago I spotted a couple of disc brake shoes/pads lying in the road. They were very much larger than bicycle ones, though, so presumably from a car or motorbike.

[durhambiker]

Brake pads are overrated anyway!!

So is a broken leg

[durhambiker]

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

tell me more

[Marcus Aurelius]

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

tell me more

On a road bike, I really don’t like them, or having them around in the group. On a mountain bike, I wouldn’t be without them. A prime example of what happens when you get a mixed bunch of riders, with mixed abilities, and a mixture of rim and disc brakes, happened on a BC Guided ride I was assisting on, the other week. One of the riders with disc brakes, braked hard, with no warning. One of the other ride leaders, with rim brakes couldn’t stop as quickly, and went straight into the back of the disc braked rider, resulting in a rider with an unrideable bike ( who had to employ a spousal evacuation) and a ride leader with a suspected broken rib or two. Fortunately, it wasn’t my ride, and I didn’t have the hassle of the accident report, and everything else that goes with it. Mountain bikes are generally much heavier than road bikes, normally used in conditions which necessitate having better braking performance, and not usually used in large groups, on roads.

[thelawnet]

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

tell me more

On a road bike, I really don’t like them, or having them around in the group. On a mountain bike, I wouldn’t be without them. A prime example of what happens when you get a mixed bunch of riders, with mixed abilities, and a mixture of rim and disc brakes, happened on a BC Guided ride I was assisting on, the other week. One of the riders with disc brakes, braked hard, with no warning. One of the other ride leaders, with rim brakes couldn’t stop as quickly, and went straight into the back of the disc braked rider, resulting in a rider with an unrideable bike ( who had to employ a spousal evacuation) and a ride leader with a suspected broken rib or two. Fortunately, it wasn’t my ride, and I didn’t have the hassle of the accident report, and everything else that goes with it. Mountain bikes are generally much heavier than road bikes, normally used in conditions which necessitate having better braking performance, and not usually used in large groups, on roads.

I don't see that there is a significant weight difference between a MTB & a road bike when you take into account the rider.

Some things I have noticed:

I recently replaced the v-brakes on my wife's hybrid with new Shimano T4000s (levers & brakes) - she finds the front brake to be terrifyingly powerful

My daughter + bike weighs certainly less than half what I weigh and likewise finds her v brakes to be very powerful

I have 160mm/160mm hydraulic discs, and 180mm/160mm hydraulic discs - the 160mm/160mm are not powerful enough on the hairiest moments (total weight 100kg+)

I have also been told by an Indonesian friend of someone grabbing his hydraulic brakes & going over the bars & getting injured, however they quite likely much lighter than I.

At any rate Shimano seem to think their v-brakes are too powerful and make a device to make them less effective.

https://bike.shimano.com/en-EU/technolo ... -unit.html

[pliptrot]

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

Surely better if new?

I'm a trendy consumer. Just look at my SM-G900F using hovercraft full of eels.

[Marcus Aurelius]

tell me more

On a road bike, I really don’t like them, or having them around in the group. On a mountain bike, I wouldn’t be without them. A prime example of what happens when you get a mixed bunch of riders, with mixed abilities, and a mixture of rim and disc brakes, happened on a BC Guided ride I was assisting on, the other week. One of the riders with disc brakes, braked hard, with no warning. One of the other ride leaders, with rim brakes couldn’t stop as quickly, and went straight into the back of the disc braked rider, resulting in a rider with an unrideable bike ( who had to employ a spousal evacuation) and a ride leader with a suspected broken rib or two. Fortunately, it wasn’t my ride, and I didn’t have the hassle of the accident report, and everything else that goes with it. Mountain bikes are generally much heavier than road bikes, normally used in conditions which necessitate having better braking performance, and not usually used in large groups, on roads.

I don't see that there is a significant weight difference between a MTB & a road bike when you take into account the rider.

Some things I have noticed:

I recently replaced the v-brakes on my wife's hybrid with new Shimano T4000s (levers & brakes) - she finds the front brake to be terrifyingly powerful

My daughter + bike weighs certainly less than half what I weigh and likewise finds her v brakes to be very powerful

I have 160mm/160mm hydraulic discs, and 180mm/160mm hydraulic discs - the 160mm/160mm are not powerful enough on the hairiest moments (total weight 100kg+)

I have also been told by an Indonesian friend of someone grabbing his hydraulic brakes & going over the bars & getting injured, however they quite likely much lighter than I.

At any rate Shimano seem to think their v-brakes are too powerful and make a device to make them less effective.

https://bike.shimano.com/en-EU/technolo ... -unit.html

In the wet, the differences in braking performance become a big issue. A mixture of Disc brakes and rim brakes, in the circumstances I described, is a very bad cocktail, there’s not such a critical disparity when it’s not wet, but there’s still a disparity.

[Brucey]

with any close-running group of cyclists the biggest danger is them running into one another. With inexperienced riders this is always a major risk. Having brakes that work differently to one another just multiplies the risk further; one of the reasons why pros are (by and large) not at all keen on disc brakes is that there are quite enough accidents in the peloton anyway, and having some folk riding on brakes that (at times) work differently to others just adds to the problems that are already there. When a prang does occur the discs can work like bacon slicers.

I can't think of anything worse than a group of inexperienced cyclists trying to ride close to one another with a mixture of brakes/abilities.

BITD if there was a fast group and there were more than two riders who were considered inexperienced, a second group would be formed so that they could get some training without risking others. If one or two inexperienced riders were to ride with the main group they would be consigned to the back (where at least they wouldn't bring others down) for quite a few rides until they had learned how to ride a wheel properly.

Both good policies.

Dealing with a group of inexperienced riders is like herding cats; nightmare.

If I had my way I would have inexperienced riders do several hundred miles on the track, on a track bike, in a tight group, so that they learned how to ride a wheel properly, before they ever try and ride in a close group on the road. In the event of an accident you are not stuck in the middle of nowhere.

cheers