bobzmyunkle
Über Member
Does anyone know what thickness a Shimano icetech rotor is when worn through to the inner alloy?
Failed Disc
- Thread starter Marchrider
- Start date
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OP
OP
Marchrider
Über Member
apparently 3 layers all of 0.6mm
outer face of Stainless and an inner core of 0.6mm aluminium to take the heat away
I presume the aluminium inner is to compensate for the poor heat conductivity of the stainless steel - I would guess a far better disc would be 100% ductile cast iron, but they wouldn't look as nice and shiny, and could soon look a little rusty.
aesthetics wins against efficiency for marketing ?
bobzmyunkle
Über Member
So not necessarily a good idea to wait until the outer layer wears through before replacement.
Profpointy
Legendary Member
Double upvote for that image !
Unfortunately "nonsense" is not an argument.
Reynard
Guru
- Location
- Cambridgeshire, UK
I break things, not make things, but yes, you would expect a reasonable Factor of Safety (FoS) to have been applied. At the Product Design Specification stage (PDS), the exact numbers for that particular geometry will have been worked out. The usual assumption at the PDS stage is that the end user of a product (not necessarily bicycle brake disks) will eschew maintenance and try and do daft things, and so a certain amount of "idiot-proofing" is built in.
Basically, the FoS is based on the load applied to a component, and how much stronger you want it to be than the maximum allowable load. However, as the component wears, the FoS reduces, simply because the maximum load it can take without failure also reduces. Modulus remains the same, but you've simply got less material taking that same load every time, which makes it more likely to deform and fail. And as you can see from the photo in the very first post, the braking surface has sheared off the support arms where they meet, as the force applied under braking was greater than what the worn disk could take.
That's simply been worn well past the time to change it.
Now I only have one bike with discs (mechanical, not hydraulic), and I don't do a particularly vast mileage, but I suspect that this failure is more likely to be down to persistent fouling or grinding away of material rather than purely high mileage. Expected mileage / lifespan / durability for average or typical use will have been covered at the PDS stage, and the spec should be more than adequate. Of course, the discs are consumables even if they are a component that lasts a reasonably long time, but just like with a car, any mud or grit caught in the calipers will act as a grinding paste, promoting excessive and premature wear. The other possibility is using pads that are too abrasive. Either way, the net result is the same.
Tom B
Guru
- Location
- Lancashire
In the interests of experiment I have worn disks down past what they should.
Mine was a boring plain single metal type from Theo and Noah or Noah and Theo
Mine failed on one of the arms there was a noticeable noise from the brake which prompted closer inspection and immediate replacement before this happened. But then I am the sort of person who does investigate noises to understand them, even if I do leave them sometimes - broken spoke from a month ago being one.
That reminds me.... I need to change my front pads.
Mine was a boring plain single metal type from Theo and Noah or Noah and Theo
Mine failed on one of the arms there was a noticeable noise from the brake which prompted closer inspection and immediate replacement before this happened. But then I am the sort of person who does investigate noises to understand them, even if I do leave them sometimes - broken spoke from a month ago being one.
That reminds me.... I need to change my front pads.
Ming the Merciless
There is no mercy
- Location
- Inside my skull
Measured my front one yesterday whilst I was replacing tyre. Currently 1.9mm thick , so should be good awhile.
