[LLB-M2]

Hi,

I checked the manual and it says full size is 30mm and minimum is 28,4mm.
The discs of my bought M2 have a rest of 29.1mm and the stock pads looks very good.. The most wear is of the (more) expensive disc than the pads

What do you think, how long will it last, while moderate driving? Next sommer i will have a trackday and think about 20 rounds Nordschleife. Can be a disc killer?!
How often do you check the thickness?

[WagonR]

The minimum thickness is not a measure of when you need to replace the rotor. The minimum thickness is a measure of how much thickness is needed on the rotor to retain it when you replacing the pads. Extrapolating from new measure (30.0mm) to the minimum thickness to not replace measure (28.4mm) you could extrapolate that 1.6mm is how much can be used for two sets of pads, so 3.2mm total, or down to 26.8mm or replacement thickness. I'm sure there are margins of safety built into BMW's number, but also, reasons to not go that thin if your running on the track.

That said, the 28.4mm on the rotor does not mean replace at this thickness, so no, you don't have to.

[LLB-M2]

Originally Posted by WagonR

The minimum thickness is not a measure of when you need to replace the rotor. The minimum thickness is a measure of how much thickness is needed on the rotor to retain it when you replacing the pads. Extrapolating from new measure (30.0mm) to the minimum thickness to not replace measure (28.4mm) you could extrapolate that 1.6mm is how much can be used for two sets of pads, so 3.2mm total, or down to 26.8mm or replacement thickness. I'm sure there are margins of safety built into BMW's number, but also, reasons to not go that thin if your running on the track.

That said, the 28.4mm on the rotor does not mean replace at this thickness, so no, you don't have to.

I really thought it has to be replaced when it reaches minimum thickness. Big thanks to you, saved 1k of my bucks.

[///MPhatic]

Originally Posted by WagonR

The minimum thickness is not a measure of when you need to replace the rotor. The minimum thickness is a measure of how much thickness is needed on the rotor to retain it when you replacing the pads.

I don't think this is correct.

It's my understanding that the minimum thickness is for rotor replacement (1.6mm of wear) regardless of how many sets of pads, as that completely depends on how the car is driven, and what pads are used.

[WagonR]

Interesting. In the instructions in TIS, on replacing pads, here's the step on measuring rotor thickness:



I guess in mind it would be crazy if you were 0.1mm over the min thickness to install pads, unless there was more than 0.1mm of ware left on the disc. (i.e. some life was built in for use past the minimum thickness with new pads).

But, now that I click through the "minimum brake disc thickness" link above, I'm not sure about my understanding. Here's the link:



On one hand, it says you can install new pads if it's above the min thickness, but on the other it does say to replace if it's reached the min thickness. Does that mean replace at any time, or just you must replace during a pad change if at/below the min thickness?

LLB-M2 and ///MPhatic sorry if I've caused confusion or gave bad information.

[///MPhatic]

Originally Posted by WagonR

On one hand, it says you can install new pads if it's above the min thickness...

To me this is more like a note for the tech basically saying that if the rotor is under the minimum thickness he needs to ask the SA to recommend to the customer to buy new rotors, but if it's over the minimum thickness then the pads are installed and the SA merely advises the customer how close it is.

Originally Posted by WagonR

but on the other it does say to replace if it's reached the min thickness. Does that mean replace at any time, or just you must replace during a pad change if at/below the min thickness?

I'd say that means replace at any time, regardless of where the pads are, but I can't say for certain because I'm not a BMW tech.

[LLB-M2]

This caused really confusion. I have the same program in german language and the meaning on both shwon pages are the same.
Only add new pads when the disc is thicker than the minimum.
And minimum size is 28.4mm

And 1.6mm (0.8mm each side of the disc) is nothing. The Original normal pads of my blue brake have a rest of around 7-8mm (without steel). And my discs only 0.6mm to end of lifetime. So, there would never be a pad replacement.

[FaRKle!]

The key thing to look at on the TIS page is, "Applies only to M vehicles and perforated ventilated brake discs." The information below that line is what you should follow.

[WagonR]

Originally Posted by LLB-M2

This caused really confusion. I have the same program in german language and the meaning on both shwon pages are the same.
Only add new pads when the disc is thicker than the minimum.
And minimum size is 28.4mm

And 1.6mm (0.8mm each side of the disc) is nothing. The Original normal pads of my blue brake have a rest of around 7-8mm (without steel). And my discs only 0.6mm to end of lifetime. So, there would never be a pad replacement.

I'm sorry for causing confusion. I had my understanding confirmed by a tech when I needed to replace the pads on another BMW, and reading the TIS info seemed to confirm a minimum thickness at pad replacement meant it was okay, but it seems like I was wrong.

On the rotor life of 0.8mm per side...yeah, that seems crazy to me. Basically 5% wear and replace. Obviously the disk isn't solid, so it's not actually 5%, but still, effectively it is.

[WagonR]

Originally Posted by FaRKle!

The key thing to look at on the TIS page is, "Applies only to M vehicles and perforated ventilated brake discs." The information below that line is what you should follow.

I think all that say is for M vehicles use -1.6mm, don't use -2.4mm. Either way, the point is the same. The consensus seems to be replace the rotor whenever measured at the min-thickness, not that you can install news pads if the rotor is above the minimum thickness and not address again until the next pad change.

[CTSean]

Originally Posted by WagonR

On one hand, it says you can install new pads if it's above the min thickness, but on the other it does say to replace if it's reached the min thickness. Does that mean replace at any time, or just you must replace during a pad change if at/below the min thickness?

It's 2 completely independent directions.

When replacing pads, the rotor doesn't have to be replaced if it's above minimum thickness.

If the rotor is at or below minimum thickness, it has to be replaced, without regard to the status of the pads.

[LLB-M2]

Ok, i will drive them till minimum thickness. Then replace them and buy new rotors and sport pads.