Failed Disc

[Marchrider]

my brother just sent me a picture of his front disc he was going slow and didn't come off, but jeez, that is scary

 

[richardfm]

How thin is it?

 

[Marchrider]

How thin is it?

he is going to measure it - I don't think he ever does much in the way of maintenance and he does huge mileage

what would be a typical 'time to replace' thickness ? it's looking about 1mm on that image

 

[FishFright]

my brother just sent me a picture of his front disc he was going slow and didn't come off, but jeez, that is scary

View attachment 762889

It looks like the caliper was set incorrectly so the pads wore the bit where it snapped,

 

[sevenfourate]

Very worn. Or very cheap ?

 

[Ming the Merciless]

They last quite a few miles, but do need replacing once they get below a certain thickness. Same as rims need replacing for rim brake bikes.

 

[Marchrider]

It looks like the caliper was set incorrectly so the pads wore the bit where it snapped,

it does doesnt it, and that would def cause a failure

 

[roubaixtuesday]

They often have minimum thickness stamped on them.

Even with an Iwanson gauge, I find them very hard to measure though.

 

[roubaixtuesday]

It looks like the caliper was set incorrectly so the pads wore the bit where it snapped,

You mean it's wearing the arms rather than the disc?

 

[Regular.Cyclist]

Buy him one of these and have him carry out regular checks on remaining thickness.

 

[FishFright]

You mean it's wearing the arms rather than the disc?

Yes , that's the one.

 

[roubaixtuesday]

Yes , that's the one.

Not sure how it's possible to set pads wrong in that dimension? If it is, it's a mistake I'm yet to make, and I'm pretty good at getting them in quickly!

 

[Ming the Merciless]

he is going to measure it - I don't think he ever does much in the way of maintenance and he does huge mileage

what would be a typical 'time to replace' thickness ? it's looking about 1mm on that image

Shimano recommends replacing when rotor brake surface is down to 1.5mm thick.

 

[Marchrider]

do these discs come in different diameters ? could the wrong on have been fitted ?
(I know nothing about these discs, my bikes are on rims)

Buy him one of these and have him carry out regular checks on remaining thickness.

View attachment 762891

I have one of these for checking my rims

 

[Alex321]

do these discs come in different diameters ? could the wrong on have been fitted ?
(I know nothing about these discs, my bikes are on rims)

They do. Most commonly 140 or 160mm for road bikes, often larger for mountain bikes.

If you fit the wrong size, it either won't go into the caliper at all, or you may need to change the caliper bolts. It may be possible to fit a larger one without adjusting the calipers and have them catching the wrong place.

But the noise & vibration if the pads aren't pulling against the correct surface would be intolerable, would have thought, so that sounds unlikely.