Rotor wear

[Shark58]

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 .

My first comment has never been my main concern. It was an answer to your comment about the calliper defining possible minimum rotor thickness.

By my reckoning the thicker rotors are based on a different rotor design not weaker material.

 

[Paulquattro]

By my reckoning the thicker rotors are based on a different rotor design not weaker material.

So why would you worry about wearing the thicker disc down a bit more ,
when the thinner disc can be worn down officially to a thinner end than the thicker disc all materials being equal
Both discs will be worn the same amount at end of life just you will have had more life out of the thicker disc
Its as simple as that

 

[Shark58]

why would you worry about wearing the thicker disc down a bit more ,

Because only the rotor surface is tempered. The further the disk is worn the softer the material.

When the manufacturer laser etches a wear limit onto the rotor and not the calliper I tend to believe there is a reason for this and I feel it’s prudent to observe that limit.

The good thing is, we can all do as we like. You wear the rotor razor thin and I change it out at the wear limit. We are both happy.

 

[Paulquattro]

Because only the rotor surface is tempered. The further the disk is worn the softer the material.

When the manufacturer laser etches a wear limit onto the rotor and not the calliper I tend to believe there is a reason for this and I feel it’s prudent to observe that limit.

The good thing is, we can all do as we like. You wear the rotor razor thin and I change it out at the wear limit. We are both happy.

Its hardly razor thin at shimanos minimum limit now is it

The rotor is hardened as a whole not just the surface
I think one is picking now.

 

[Shark58]

The rotor is hardened as a whole not just the surface

You should read up on what actually happens during the tempering process. Nobody wants the same hardness in the core of a brake disk as on the outside.

 

[Paulquattro]

You should read up on what actually happens during the tempering process. Nobody wants the same hardness in the core of a brake disk as on the outside.

Really show me the correspondence to back up your finding relating too MTB rotors and there hardening process

And one more thing ,
Your so convinced its a thin layer of hardening what do you think happens to a disc in use when heat cycled
You think it might harden with use ??

 

[Shark58]

And one more thing ,

Grasping at straws - I‘m out.

 

[ThierryGTLTS]

My first comment has never been my main concern. It was an answer to your comment about the calliper defining possible minimum rotor thickness.

By my reckoning the thicker rotors are based on a different rotor design not weaker material.

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.

I always use the rotors more than the pads!
And it's the manufacturer configuration, Shimano with resin pads.
But hopefully they last enough (more than 5000km).

Have a Nice Day
Thierry

 

[Paulquattro]

Grasping at straws - I‘m out.

People who have no educated answers normally say that ,
Just because you couldn't come up with any literature to back up your comments or answer any of my points.
Why is that ?

 

[Mikerb]

I thought the reason for using resin pads was that they heat up quicker and therefore deliver good performance for less heavy use of the brakes. The downside being they stop working as well if heavilly used ( ie stopping a heavy bike/ downhill riding).....or used in wet muddy gritty conditions. They seem usually to be specced in combination with "resin only" markings on the rotors, and that combination seems most common on hybrid bikes and hardtails as opposed to most emtbs for enduro or even trail use.

So is it the case that the resin pad/resin only rotor combination is less than ideal for EMTB use especially in mixed trail conditions?

e.g. my wifes Cube Access ( same as Cube Reaction hard tail) has that resin pad/resin only rotor combination ( Shimano). Her MTB use is restricted to fireroads and clement weather and I have noticed no discernable wear on pads or rotor after 650 miles.
My SRAM RSC brakes on both my bikes wear out rear pads in a bout 300 miles and front pads in a bout 500 miles but without any discernable rotor wear after over a 1000 miles.

 

[irie]

I thought the reason for using resin pads was that they heat up quicker and therefore deliver good performance for less heavy use of the brakes. The downside being they stop working as well if heavilly used ( ie stopping a heavy bike/ downhill riding).....or used in wet muddy gritty conditions. They seem usually to be specced in combination with "resin only" markings on the rotors, and that combination seems most common on hybrid bikes and hardtails as opposed to most emtbs for enduro or even trail use.

So is it the case that the resin pad/resin only rotor combination is less than ideal for EMTB use especially in mixed trail conditions?

e.g. my wifes Cube Access ( same as Cube Reaction hard tail) has that resin pad/resin only rotor combination ( Shimano). Her MTB use is restricted to fireroads and clement weather and I have noticed no discernable wear on pads or rotor after 650 miles.
My SRAM RSC brakes on both my bikes wear out rear pads in a bout 300 miles and front pads in a bout 500 miles but without any discernable rotor wear after over a 1000 miles.

Which makes and models of mtb rotors have "resin only" marked on them?

 

[Planemo]

Which makes and models of mtb rotors have "resin only" marked on them?

I've deffo seen this on some old Shimano discs I had. Not sure of the model though. And they were teeny 160's IIRC.

 

[steve_sordy]

Which makes and models of mtb rotors have "resin only" marked on them?

I first saw this on a Shimano disc. Too long ago now to remember specs.

 

[Paulquattro]

Which makes and models of mtb rotors have "resin only" marked on them?

The cheap Shimano ones generally
They tend to look more stamped out to get the shape
Unlike the ground faced ones that tend to be Laser cut then gound to thickness and look higher quality.

 

[irie]

The cheap Shimano ones generally
They tend to look more stamped out to get the shape
Unlike the ground faced ones that tend to be Laser cut then gound to thickness and look higher quality.

For the avoidance of doubt specifically which mtb rotors?

 

[Dax]

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.

This is the opposite of my experience with Ice Tech rotors, I’ve used them for DH in the alps and Canada a lot, never warped one. That’s the 6bolt ones without the cooling fins, not tried the Center locks.

 

[Montana St Alum]

For the avoidance of doubt specifically which mtb rotors?

I think Shimano RT-56 are "Resin only". I don't think SRAM makes any. I'd expect there are oddball manufacturers on Amazon that sell them, who come and go.

 

[JP-NZ]

I think Shimano RT-56 are "Resin only". I don't think SRAM makes any. I'd expect there are oddball manufacturers on Amazon that sell them, who come and go.

RT56 are indeed resin only. I just went and snapped a pic of my rear disc on my XTC hardtail. The lower spec discs than this RT46? RT26 etc are all resin only.

RT66, RT76, RT86 etc are all fine with metal and resin

 

[JP-NZ]

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.

You must be doing a tonne of downhill. I'm at 1,300 miles on my Trek Rail and still on original (XTM8120) resin pads and (RT76) rotors.

 

[Montana St Alum]

I have had occurrences where I replaced pads on worn (but not to limits) rotors and they were really noisy. Took off the pads and saw that the inside and outside were a bit glazed from bedding them in. There must have been some wear that resulted in an uneven dished in curve on the rotor surface. Replacing the rotor was the quickest - though not the cheapest cure. I'm like that with chains, too. I've found that shifting can degrade before a chain wear indicator shows it to be at its limit.

 

[2WheelsNot4]

I wouldnt get too hung up by this. Playing right into the hands of the manufacturers claiming 1/2mm off and it needs replacing. bitd ive worn rotors really thin, sometimes down to 1mm, and ive seen thinner.

Rotors for a very long while were about 1.85mm, and its just recently rotors at 2.2/2.3mm are becoming commonplace.

 

[rod9301]

I think rotors should be changed before you get to the minimum thickness.

Less rotor mass means they will get hit a lot sooner. So you will get brake fade.

 

[Binhill1]

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

I had hope ones and got down to 0.50 before someone noticed . Guessing round about 8000 miles just under 4 years . Can't complain about that can I.

 

[Sander23]

I found a really good deal on shimano cl icetech rotors but they have internal lockring and I need external. Can I just bit them and use the external ones I have now or are the rotors also different?

 

[Rod B.]

Which makes and models of mtb rotors have "resin only" marked on them?

Brake pad compatibility on Shimano braking systems can be referenced using Shimano's compatibility charts.

2023-2024 SHIMANO Product Information Web

You will note that some Shimano brake rotors will have an a "*2" suffix attached at the end of the rotor model number. This denotes that the rotor is compatible with resin brakes pads and not metallic.

 

[Rod B.]

I found a really good deal on shimano cl icetech rotors but they have internal lockring and I need external. Can I just bit them and use the external ones I have now or are the rotors also different?

Sander23,

Yes, you can use your external lock ring in place of an internally splined lock ring. Shimano uses two types of rotor lock ring, "External" and "Internal Splined." Which lock ring a person uses is dictated by the axle, hub end caps, and restrictions in amount of space at the hub. If your hub uses an external lock ring, then yes, you can use it on any Shimano center lock hub that you buy.

External Lock Ring

Internally splined Lock Ring

Shimano Ice Tech Rotor on my Rise M20 with Noble TR37 wheels.

Close up of the external lock ring

From reading your posts, I see you are mainly interested in Shimano Ice Tech rotors. As you've noted, the magnet rotors are expensive. Last year I posted a technical article which details how to convert the cheaper Shimano RT-MT800 "Non magnet" rotor and turn it into a RT-EM810 magnet rotor.

The conversion process is quick and easy, but does require a metric thread tap and correct drill size. You will also need to remove the magnet assembly from a worn out RT-EM810 rotor and re-use it on the converted MT800 rotor. Here is the link to the article if you are interested in reading it:

Shimano Brake Center Lock Rotor Hack - Converting a RT-MT800 into a RT-EM810 magnetic rotor

Hello, This tech article will describe how to convert a Shimano "Non-Magnetic" RT-MT800 center lock brake rotor into a "Magnetic" RT-EM810 brake rotor. I hope you find this article useful. If your bike has Shimano brakes, you will have likely noticed there is a shortage of Shimano brake parts...

www.emtbforums.com

 

[Arminius]

RT56 are indeed resin only. I just went and snapped a pic of my rear disc on my XTC hardtail. The lower spec discs than this RT46? RT26 etc are all resin only.

RT66, RT76, RT86 etc are all fine with metal and resin

View attachment 129131

Can you please remove that orange sticker……

 

[Shorty4]

Be very careful running pads and rotors below minimum recommended thicknesses.
I've had to pull several calipers apart on other riders bikes to repair or replace chipped and broken pistons caused by running either pads or rotors below minimum thickness.
The higher end calipers run ceramic pistons and when they come out too far as a result of either too thin pads or rotors or a combination of both they can twist sideways and jam which usually chips the piston and results in a jammed piston and flakes of ceramic inside the caliper. I have stripped the caliper down and cleaned all the broken bits out and then refitted the damaged piston and new pads to enable the bike to be ridden as the pistons usually chip on the back. But the pistons can also crack in half so that usually means it can no longer be used as Shimano don't sell replacement pistons but compatible pistons are availble online and do seem to be ok to use.
Using sintered/metal pads with calipers with resin pistons will also lead to the pistons melting and jamming under etxreme use.
Here in Oz on a hot day with 25kg of EMTB plus a a 100kg rider the disks get to red hot on a long downhill run so it doesn't just apply to competition riders only.

 

[Rocketb]

Great info here learnt a lot. I replace my pads and rotors together twice a year. I’m a heavy rider on a heavy bike riding 3 times more than on a mtb. I believe brakes are the most important aspect on an emtb so no second guessing this component.

 

[irie]

Brake pad compatibility on Shimano braking systems can be referenced using Shimano's compatibility charts.

2023-2024 SHIMANO Product Information Web

You will note that some Shimano brake rotors will have an a "*2" suffix attached at the end of the rotor model number. This denotes that the rotor is compatible with resin brakes pads and not metallic.
View attachment 129305

View attachment 129307

View attachment 129308

View attachment 129309

Thanks for this post. However, which of these rotors are specified on MTB's, or more relevantly since this an eMTB site, on eMTB's?