Failed Disc

[Dogtrousers]

A few years ago I invented, or rather discovered, an amazing type of brake called the pothole brake.

There are still some details that need sorting out before I go to market with it. The airborne rider side effect needs reducing. But it's a tremendous stopper.

 

[brommieinkorea]

No - it was a 180 mm disc in a caliper fitted for a 160mm disc

the image seems to fit very well with what he is saying - it looks like the pad has missed the last 10mm of the disc and caught the last 10mm of the legs that hold the disc - seems very plausible with what he is saying
and to back that up the spec for the bike says it should be 160mm disc, and the one the bike shop fitted is 180 mm - no rat to smell

as for measuring - of course you can measure the disc with digital (or or vernier) calipers, just stick a washer or similar to each side of the shiny bit and bridge the edge. And with all those snapped off bits you probably don't even have to do that

and he may of even used a micrometer (and you get vernier gauges on micrometers), all that stuff will be in his workplace - He just has little to no interest in the mechanical workings of a push bike and gets the bike shop to most of it, And I would have full confidence in measuring something like that to 0.1 of mm

A 180mm disc would not fit to a caliper set up for 160/165. A caliper set for 180mm with a 160mm disc wouldn't make contact. So, the disc was not the wrong size (there couldn't be any wear if it was). The braking surface of the disc is clearly worn to less than 50% of new. New discs are 2mm thick. A micrometer and a vernier caliper are two totally different things, my guess is the owner of this bike would mistake a micrometer for a c-clamp and therefore it is a moot point.

 

[Marchrider]

A 180mm disc would not fit to a caliper set up for 160/165. A caliper set for 180mm with a 160mm disc wouldn't make contact. So, the disc was not the wrong size (there couldn't be any wear if it was). The braking surface of the disc is clearly worn to less than 50% of new. New discs are 2mm thick. A micrometer and a vernier caliper are two totally different things, my guess is the owner of this bike would mistake a micrometer for a c-clamp and therefore it is a moot point.

don't think you have made a very good job of reading the thread, you have clearly missed a chunk of it

brother was using a digital caliper, and he would know how to use them and he was getting measurements ranging from 1.1 to 1.3mm (which would be greater than 50%) esp if the were starting at 1.8mm, such as the shimano ones he bought

 

[fossyant]

I think you might have some brake dust (from your rim brakes) in your eyes.

That will be you 'bent' riders all the way down there.

 

[brommieinkorea]

"he would know how to use them" apparently not, a caliper is a wildly inaccurate tool for measuring something flat like a disc, so wrong tool. Of course that could be why he got measurement so wildly out and innaccurate....
Oh FWIW discs are fairly standard acctoss manufacturers with 140,160,165,180 and 203mm being more or less 'normal'.

 

[Marchrider]

"he would know how to use them" apparently not, a caliper is a wildly inaccurate tool for measuring something flat like a disc, so wrong tool. Of course that could be why he got measurement so wildly out and innaccurate....
Oh FWIW discs are fairly standard acctoss manufacturers with 140,160,165,180 and 203mm being more or less 'normal'.

why would it be wildly inaccurate ? very easy to measure something like that with flat calipers, esp if you are only looking for 0.1mm of accuracy.
I wouldn't have bothered with my micrometer to measure that either, no point trying to get it to within 5 microns when looking for a ball park figure

utterly bizarre that folk can look at some crappy image on the internet then state the given measurements must be entirely wrong cause they think it is 0.3mm, 0.5mm and now you're saying its below 1mm - jesus

 

[brommieinkorea]

why would it be wildly inaccurate ? very easy to measure something like that with flat calipers, esp if you are only looking for 0.1mm of accuracy.
I wouldn't have bothered with my micrometer to measure that either, no point trying to get it to within 5 microns when looking for a ball park figure

utterly bizarre that folk can look at some crappy image on the internet then state the given measurements must be entirely wrong cause they think it is 0.3mm, 0.5mm and now you're saying its below 1mm - jesus

Within .1mm is highly inaccurate.

 

[C R]

Within .1mm is highly inaccurate.

Depends for what purpose.

 

[silva]

For the record, this subdiscussion is about 0.1 not 1 mm, right?
In that case, I'd call 0.1 mm rather wildly accurate than inaccurate.

 

[rualexander]

For the record, this subdiscussion is about 0.1 not 1 mm, right?
In that case, I'd call 0.1 mm rather wildly accurate than inaccurate.

In the context of a disc with a minimum recommended thickness of 1.5mm then 0.1mm is 6.67%, which is a pretty significant amount.

 

[Ming the Merciless]

Within .1mm is highly inaccurate.

How far did you ride? I rode 43 km, 950 metres, 30 centimetre's, 20.3mm.

Why so wildly inaccurate, how far did you really ride, and be accurate this time.

 

[wafter]

don't think you have made a very good job of reading the thread, you have clearly missed a chunk of it

Evidently the irony of that statement is as lost on you as the bulk of guidance and suggestions contributed by other members..

 

[Dadam]

"he would know how to use them" apparently not, a caliper is a wildly inaccurate tool for measuring something flat like a disc, so wrong tool. Of course that could be why he got measurement so wildly out and innaccurate....
Oh FWIW discs are fairly standard acctoss manufacturers with 140,160,165,180 and 203mm being more or less 'normal'.

What cobblers!

Min recommended thickness (according to google is 1.5mm). So if your degree of accuracy is 0.1mm (+/- 0.05mm) and your disc measures 1.7mm you're ok. 1.6 probably ok for a while but best to replace.

Nobody needs a flipping micrometer for that, are you having a laugh? I guess the point you're making is that the worn area is dished and the lip will stand proud so if you clamp the jaws on the lip you're not reading it right, but it's a piece of piss to compensate for that. For starters there's a relieved area at the base of the jaws. Secondly you just measure the thickness of something known and consistent like a couple of shims or washers then hold them in place in the caliper jaws. Subtract thickness of washers and there you are. Entirely good enough to tell if they're too worn.

 

[Dadam]

As I think was said upthread, the primary failure mode is it's worn too damn thin, but also looks to me like the disc being 180 instead of 160 has exacerbated things by wearing the support legs.

Just had a look at my bikes. I have 7 bikes 🫢 and 6 of those have hydro discs. The braking surface of the 160mm Shimano and Tektro looks to be about 15mm wide and that of the 180mm Shimano on the e-MTB is about 17.5mm wide. The swept area on most of them seems to be all the way from the rim to a few mm outside the support leg area, which would seem sensible. But if you put a 180mm disc on the bikes that take 160, and adjusted the caliper as best you could, I could see it doing exactly what's shown in the picture, i.e. fitting "more or less", and the brakes functioning, but the braking area shifted down 5-7mm to overlap the legs. Wearing those legs made it fail earlier but it would have failed soon at that thickness regardless.

 

[Psamathe]

and I have never suffered any squeal, and any initial post-purchase brake rub that I haven't managed to dial out.

I have mechanical disks (BB7s) and love them. Only minor thing is squeal when they get wet which is only on camping tour (as they are outside overnight) and dew gets them fairly wet then leaving campsite invariably early in morning cycling through silent deserted village/town spent night at making noise braking at every junction. They dry out after a few miles but by them in open countryside so noise wouldn't disturb anybody anyway.

Ian