Brake rotor wear

[winjim]

How worn dare I let my disc brake rotors get before they need replacing?

 

[S-Express]

How are you measuring the wear?

 

[winjim]

How are you measuring the wear?

At the moment, just visually and by running my finger over the surface. A decent vernier caliper will probably be the next tool I buy although I imagine a micrometer would be more suited to this particular task.

 

[lpretro1]

They vary - some have the min depth stamped on the rotor e.g Avid rotors say 1.6mm min - u just need to make sure you measure a flat bit. As a rule of thumb once 'shoulders' start to appear on the rotor it is a sign of getting time to change

 

[Levo-Lon]

Mic for rotor wear measuring as vernier will sit on the high un worn lip and give you a false reading .
some of the shimano rotors have a multi alloy construction , they are potentially dangerous when the hard surface has worn away..but there stamped for checking

 

[winjim]

They vary - some have the min depth stamped on the rotor e.g Avid rotors say 1.6mm min - u just need to make sure you measure a flat bit. As a rule of thumb once 'shoulders' start to appear on the rotor it is a sign of getting time to change

Well there is definitely shouldering, it's very apparent when I run my finger over them. I'll have to go and look if there's anything stamped on them. I think they are Avid rotors, the brake calipers are BB5.

Mic for rotor wear measuring as vernier will sit on the high un worn lip and give you a false reading .
some of the shimano rotors have a multi alloy construction , they are potentially dangerous when the hard surface has worn away..but there stamped for checking

That's what I figured about the vernier. Come to think of it, there might be a micrometer I could borrow, lurking in the bottom of a toolbox at work. I reckon it's probably new rotor time though.

In the meantime I might swap front and rear so the presumably less worn rear rotor is now at the front and the more worn front rotor is now at the less safety critical rear. Does that make sense?

 

[fossyant]

You can swap the rotors but make sure both are the same size.

 

[fossyant]

Personally, I'd renew

 

[ianrauk]

@winjim . How many miles have your rotors done? I'm near 19,000 miles on mine with only little wear.

 

[Yellow Saddle]

Well there is definitely shouldering, it's very apparent when I run my finger over them. I'll have to go and look if there's anything stamped on them. I think they are Avid rotors, the brake calipers are BB5.

That's what I figured about the vernier. Come to think of it, there might be a micrometer I could borrow, lurking in the bottom of a toolbox at work. I reckon it's probably new rotor time though.

In the meantime I might swap front and rear so the presumably less worn rear rotor is now at the front and the more worn front rotor is now at the less safety critical rear. Does that make sense?

Some discs have shoulders from day one. Usually the more expensive ones made from heat-treatable stainless steel. I really would not worry about swapping them for safety sake. I think in all my years of working on bikes I've come across just one genuinely worn-out disc. Usually they are ruined by scoring or bending.

The minimum limit is not so much for safety sake but for making sure that the reservoir doesn't run out of fluid when running worn pads on a worn disc. Even at 1mm there is plenty of strength left.

Let's see a photo of that worrying disc of yours.

An easy way to check is to put a straight edge against the disc and you'll quickly see what's what. If you only have a vernier at hand, you can still measure wear. Just use the plunge meter at the rear of the vernier.

 

[goody]

I replaced mine when the lip on the outer edge made it dificult to get the wheels in and out. Grinding it down got a couple more months out of them but at less than £10 each and thousands of london commuting miles it's not really a heartbreaker to replace and my rims still look like new!

 

[Yellow Saddle]

I replaced mine when the lip on the outer edge made it dificult to get the wheels in and out. Grinding it down got a couple more months out of them but at less than £10 each and thousands of london commuting miles it's not really a heartbreaker to replace and my rims still look like new!

Now there's something I've never seen before. I don't suppose you still have those discs so that I can take some photos for my archive?

 

[goody]

No threw them out in a recent tidy up. It was the first bicycle discs I've worn out but seen it lots on car and m/cycle discs. The discs weren't circular but the wavy type and the lip developed at the outer edge of each of the 'waves'. The pads I used were discobrakes ceramic pro which last for ages maybe at the expense of disc wear. But commuting in London is hard on brakes especially if you stop at red lights!

 

[Yellow Saddle]

No threw them out in a recent tidy up. It was the first bicycle discs I've worn out but seen it lots on car and m/cycle discs. The discs weren't circular but the wavy type and the lip developed at the outer edge of each of the 'waves'. The pads I used were discobrakes ceramic pro which last for ages maybe at the expense of disc wear. But commuting in London is hard on brakes especially if you stop at red lights!

I must say, cruising through the red light district also makes me brake frequently.

 

[winjim]

@winjim . How many miles have your rotors done? I'm near 19,000 miles on mine with only little wear.

It's difficult to put a figure on it as I don't record all my rides but much less than that I should think. The bike was new in 2012 so they've had four years. It does get ridden all year round in all weathers and my commute includes some very steep hills so the brakes do get well used.

Some discs have shoulders from day one. Usually the more expensive ones made from heat-treatable stainless steel. I really would not worry about swapping them for safety sake. I think in all my years of working on bikes I've come across just one genuinely worn-out disc. Usually they are ruined by scoring or bending.

The minimum limit is not so much for safety sake but for making sure that the reservoir doesn't run out of fluid when running worn pads on a worn disc. Even at 1mm there is plenty of strength left.

Let's see a photo of that worrying disc of yours.

An easy way to check is to put a straight edge against the disc and you'll quickly see what's what. If you only have a vernier at hand, you can still measure wear. Just use the plunge meter at the rear of the vernier.

I'm not sure how evident the wear is from those photos. It's very obvious to the touch. There's no minimum thickness stamped on them, just diameter, bolt torque and rotation direction. I can make a proper measurement on Monday, assuming that micrometer is where I think it is.