Rotor wear

[Sander23]

Today I was checking my break pads.
Both front and rear still have 2 mm left but my rotors seems to have wear more then my break pads.
It has only 1.6mm left (shimano 4pot brakes). I can clearly see the edge on the rotors
I'm still on my original rotors and brake pads after 5500km. And that's 1 season of winter included.

Brakes are xt 4 pots, pads are original shimano resin and rotors are sm rt64

 

[RustyIron]

Yes, rotors wear. The minimum thickness might be printed on your rotors, if you look closely. Often the rotor will acquire grooves or a curved wear pattern that will necessitate change before the minimum thickness is reached. How is the performance of the brakes?

 

[irie]

Part # 3: Shimano Brake System Service

After submitting Part # 1 and Part # 2 of the tech series on Shimano brakes, I realized I had not included anything on checking your Shimano brake rotor for minimum thickness or signs of uneven rotor wear. You can review Part # 1 and Part # 2 in the series here...

www.emtbforums.com

Written on the rotor, probably 1.5mm

 

[cozzy]

Yes I get through a set a year usually, plus quantities of pads. Maybe I brake too much
Just bought trp which are 2.3mm thick to allow a little leeway. I do think 1.8mm is too thin these days.
Worth buying one of them measuring caliper tools to keep an eye on them. Mine was a middle of Lidl special.

 

[steve_sordy]

Yes I get through a set a year usually, plus quantities of pads. Maybe I brake too much
Just bought trp which are 2.3mm thick to allow a little leeway. I do think 1.8mm is too thin these days.
Worth buying one of them measuring caliper tools to keep an eye on them. Mine was a middle of Lidl special.

Get a "G" type calliper, not the "F" type. If there is a lip on the edge of the disc, an F type will be unable to measure the wear area. G type ones avoid the lip.

 

[Montana St Alum]

Get a "G" type calliper, not the "F" type. If there is a lip on the edge of the disc, an F type will be unable to measure the wear area. G type ones avoid the lip.

You're going to have to elaborate on that.

 

[Alexbn921]

I replace my rotors every 4th set of pads. I measure them too, but don't push the limits of wear anymore. Usually rotors don't wear completely evenly and as the wear performance drops off. Of course I'm only getting 300ish miles out of a set of pads and 1200 on a rotor.

 

[Shark58]

Brakes are xt 4 pots, pads are original shimano resin and rotors are sm rt64

Shimano rotors are 1.95 mm thick when new and have a 1.5 mm wear limit.
Magura rotors are 2.2 mm when new and have a 1.8 mm wear limit.

No big difference.

 

[TheSnowShark]

You're going to have to elaborate on that.

You can measure very well with a standard caliper, but you have to add 2 shims of known thickness, for my part I use 2 small neodymium magnets, you will of course have to deduct the thickness of the 2 magnets to get the real value..

 

[Paulquattro]

Shimano rotors are 1.95 mm thick when new and have a 1.5 mm wear limit.
Magura rotors are 2.2 mm when new and have a 1.8 mm wear limit.

No big difference.

Only that if your running Magura rotors with shimano callipers you can run the rotors down to 1.5mm as its the calliper that's the deciding factor in the max disc wear

 

[Montana St Alum]

You can measure very well with a standard caliper, but you have to add 2 shims of known thickness, for my part I use 2 small neodymium magnets, you will of course have to deduct the thickness of the 2 magnets to get the real value..

I've never heard of "G" type Vs. "F" type rotors. My magnet is mounted on the rotor, but can be transferred between rotors as the magnet mount is just held in place by the centerlock.

What is a "G" type, what is an "F" type and is there a place in the product description that identifies these as such? I've just never heard of this distinction, is all.

 

[Stihldog]

Regardless of which measuring tool you use (G or F type calliper) , do an initial measurement for your tool and for personal reference. A slight angle deviation of whichever tool you use can make a difference.

I start off with a clean finger-thumb-pinch-n-drag method over the rotor wear surface. Any ridge over the thickness of your finger nail …then I measure.

G-type.

F type.


Look at your own hand to see the cave-man type.

 

[TheSnowShark]

I've never heard of "G" type Vs. "F" type rotors. My magnet is mounted on the rotor, but can be transferred between rotors as the magnet mount is just held in place by the centerlock.

What is a "G" type, what is an "F" type and is there a place in the product description that identifies these as such? I've just never heard of this distinction, is all.

This is simply to measure the thickness of the brake disc in the center, avoiding the outer edge

 

[Sander23]

I have measured it with my digital caliper, it switches between 1.5 and 1.6. Performance isn't what it was as they were new.

I allways thought pads wear before rotors but my pads seems to have like 50% left after 5500km and they are still the first pads the bike came with.
So it seemed strange that my rotors are allmost at its limit.

 

[Sander23]

Also my bike has centerlock and a build in magnet.
Can I use a centerlock to 6 bolt adapted with a magnet?

 

[Sander23]

Only that if your running Magura rotors with shimano callipers you can run the rotors down to 1.5mm as its the calliper that's the deciding factor in the max disc wear

That's some usefull information

 

[Montana St Alum]

Regardless of which measuring tool you use (G or F type calliper) , do an initial measurement for your tool and for personal reference. A slight angle deviation of whichever tool you use can make a difference.

I start off with a clean finger-thumb-pinch-n-drag method over the rotor wear surface. Any ridge over the thickness of your finger nail …then I measure.

G-type.
View attachment 128958
F type.

View attachment 128957
Look at your own hand to see the cave-man type.

Ah, thanks. I thought this was in reference to the brake caliper being of a "type".

 

[Stihldog]

Ah, thanks. I thought this was in reference to the brake caliper being of a "type".

No problem. Depending on the type of hub you have, bolt-on or center-lock, that will determine the type of rotor you will use. An adapter is needed if you use a bolt-on rotor to a center-lock hub.

And then there’s different diameter's and thickness of rotors which will likely match the type of brake or style of bike.

Efficient heat dissipation rotors are more expensive but are similar to “flat” rotors.
Welcome to the science of braking.

 

[Mikerb]

I have measured it with my digital caliper, it switches between 1.5 and 1.6. Performance isn't what it was as they were new.

I allways thought pads wear before rotors but my pads seems to have like 50% left after 5500km and they are still the first pads the bike came with.
So it seemed strange that my rotors are allmost at its limit.

thats sounds like a pad/rotor mismatch!! I would reckon most get through a set of pads in 400/500 miles..........and most mtbers would be using sintered rather than resin pads. If your pad to rotor friction is a ctually wearing the rotor rather than the pad, your braking must be pretty poor?...........and those rotors must be pretty poor as well.

 

[Shark58]

Only that if your running Magura rotors with shimano callipers you can run the rotors down to 1.5mm as its the calliper that's the deciding factor in the max disc wear

First time I read that. Do you have a source?

Also, if you put a significantly thicker rotor into your calliper, you will have to remove oil from the system or risk damage to it. This in turn will limit the usable thickness.

 

[Sander23]

thats sounds like a pad/rotor mismatch!! I would reckon most get through a set of pads in 400/500 miles..........and most mtbers would be using sintered rather than resin pads. If your pad to rotor friction is a ctually wearing the rotor rather than the pad, your braking must be pretty poor?...........and those rotors must be pretty poor as well.

Well they where pretty powerfull when I got the bike, and I came frame basic magura mt4 brakes.

Lately the breaking performance is not as good as it should be specially when its wet.

 

[steve_sordy]

Some rotors fitted to new bikes will say on the disc, resin pads only. If you fit harder pads they will wear out the rotor too quickly.

Ref the G type vs F type: Thanks to @Stihldog for providing the answer so clearly, he has saved me the job.

 

[Montana St Alum]

No problem. Depending on the type of hub you have, bolt-on or center-lock, that will determine the type of rotor you will use. An adapter is needed if you use a bolt-on rotor to a center-lock hub.

And then there’s different diameter's and thickness of rotors which will likely match the type of brake or style of bike.

Efficient heat dissipation rotors are more expensive but are similar to “flat” rotors.
Welcome to the science of braking.

Yeah, I have 160mm, 180mm 200mm and 203. One 180mm and the 200mm are centerlock HS2 and are really nice rotors. The only rotors I've had problems with are Ice Tech - mostly on my son's bike as he tends to warp those. They're really built for light weight. The rotors on my Elite 3 are of various levels and yes, you have to be aware (as Steve mentioned) the restriction on very low end ones. I have 3 wheelsets with centerlock and 4 with 6 bolt.

A variety of brakes as well.
When I got the Elite, it had M420s on it. I swapped some XT levers/masters from an old set of 2 piston XT's on there. Dang f that hasn't been the best set of brakes I've used so far. I was cleaning out the work space and came up with 2 more XT levers and 2 M420s! Guess I'll be doing some brake work. It actually pays to clean out stuff every once in a while! Then there are the Miles, Shimano, SRAM and MTX - resin, sintered, semi-metallic and ceramic. I'm not really sure how I've ended up with so much sh*t.

 

[Sander23]

I found 2 brands of rotors that I'm interested in.

Shimano RT-MT800 ice tech but they are pretty expensive because I need one with build in magnet.

Galfer DB034W has a hole where I can switch rotors and can swap magnet over.
Only need a adapter cl to 6bolt


Shimano is 1.75mm thick
Galfer is 2.0mm thick.

Wich one will give better performance and longevity?

 

[Paulquattro]

First time I read that. Do you have a source?

Also, if you put a significantly thicker rotor into your calliper, you will have to remove oil from the system or risk damage to it. This in turn will limit the usable thickness.

Hi
Yes me
There is loads of reserve oil in a reservoir for the slight increase in thickness
They limit the wear because of the calliper pistons not the reservoir /master cylinder
They play safe with a minimum wear so as if you use all the lining and the rotor was at minimum thickness you would still have enough not to pop the pistons out ignoring the min thickness and wearing the rotor thinner than recommended just increases the risk of pistons popping out when the pads are worn
So putting a thicker rotor on and wearing the rotor to the calliper oem specs wont do any harm and you get a bit more out of your discs

 

[Bones]

I fitted the TRP rotors to my bike and there's not much clearance left on the xt caliper if it ever warps. I also have to admit that I let the old rotors get down to 1mm before changing them .
BTW you can use ordinary measuring calipers on the discs as there is a recess that clears the lip.

 

[Sander23]

I fitted the TRP rotors to my bike and there's not much clearance left on the xt caliper if it ever warps. I also have to admit that I let the old rotors get down to 1mm before changing them .
BTW you can use ordinary measuring calipers on the discs as there is a recess that clears the lip.
View attachment 128993

How tick are those discs new?

 

[Bones]

2.3 mm

 

[Shark58]

if you use all the lining and the rotor was at minimum thickness you would still have enough not to pop the pistons out ignoring the min thickness and wearing the rotor thinner than recommended

My main concern is not popping the pistons out, but having a catastrophic failure of the rotor worn to thin under heavy breaking. For me it’s not worth the small saving.

 

[Paulquattro]

My main concern is not popping the pistons out, but having a catastrophic failure of the rotor worn to thin under heavy breaking. For me it’s not worth the small saving.

View attachment 129022

And to quote your original concern

"Also, if you put a significantly thicker rotor into your calliper, you will have to remove oil from the system or risk damage to it. This in turn will limit the usable thickness."

This was not about a worn rotor surface it was a calliper concern

But by your reckoning you are saying the thicker discs are made of weaker material and you couldn't wear out a magura rotor for example to the same thickness as a shimano rotor without it failing when the magura rotor starts off thicker .