[PininMargherita]

Originally Posted by Skyhigh

The above makes no sense - then the unused diametrical space on the rotors must be min 3 cm..... that's is A LOT:



I don't have that much area without contact on my M Sport brakes.

Yeah it’s noticeable imo. I’ll try and take a pic with good lighting.

[Skyhigh]

You are missing the point of the explanation already given. Pads may be the same, but they are not put on a larger area, only on an area which is radially further away from the axle due to the larger rotors.

[PininMargherita]

Originally Posted by Skyhigh

You are missing the point of the explanation already given. Pads may be the same, but they are not put on a larger area, only on an area which is radially further away from the axle due to the larger rotors.

Orange = 370
Blue = 340

[Skyhigh]

I honestly don‘t understand what you are trying to say! On your photo the unused area on the rotor has a radius of 1, max 2mm. Perfectly normal. Not even remotely close to 30mm (370-340)!

[PininMargherita]

Originally Posted by Skyhigh

I honestly don‘t understand what you are trying to say! On your photo the unused area on the rotor has a radius of 1, max 2mm. Perfectly normal. Not even remotely close to 30mm (370-340)!

Nah the unused area is the outside of the rotor - you can see the unused rotor in the pic on the outside edge. The brake pad sits low towards the center of the rotor.

[PininMargherita]

Originally Posted by Skyhigh

I honestly don‘t understand what you are trying to say! On your photo the unused area on the rotor has a radius of 1, max 2mm. Perfectly normal. Not even remotely close to 30mm (370-340)!

See this thread too:
https://f80.bimmerpost.com/forums/sh....php?t=2107197

You can see how the pad sits against the bottom of the rotor but the outside edge of the rotor is unused.

[SD Convert]

Originally Posted by PininMargherita

I own two cars one with 340 and the other with 370mm calipers. They use the same pads.

You also wrote:

• because they're the same pads, the contact area is the same - This is correct but has nothing to do with the "issue" you're describing.
• This leaves the 370mm rotors with some unused rotor material around the edges - This is not correct. The fact that the caliper for the 370mm rotors has longer mounting ears negates this. Also, these rotors are not the rotors that came with the calipers. Once you move to 3rd-party (aftermarket) rotors, you take a chance that the sizing will be a bit off. Different brands have different chances of this.

Of course they use the same pads. That's the way BMW/Brembo designed them. It keeps inventory costs down. The same front pads are used on 340, 370 and 380mm rotors. The same rear pads are used on 345 and 370mm rotors. In all cases, the pads are more or less centered on the rotor surface (within a few MM).

In what way is this a problem?

Originally Posted by PininMargherita

See this thread too:
https://f80.bimmerpost.com/forums/sh....php?t=2107197

You can see how the pad sits against the bottom of the rotor but the outside edge of the rotor is unused.

That's an M3 with a few (1-3) MM unused in the center (the part where the factory crosshatch is still visible - not the outside). Different rotor, different placement, different symptom. This is not what you're trying to describe.

Originally Posted by PininMargherita

Orange = 370
Blue = 340

I see under 3mm (under 1/8") of possibly unused rotor on the outer edge of the 370mm rotor.

Originally Posted by PininMargherita

Nah the unused area is the outside of the rotor - you can see the unused rotor in the pic on the outside edge. The brake pad sits low towards the center of the rotor.

The amount of space that the pad is in from the edge is trivial.

[Skyhigh]

I am glad I am not the only one who does not understand what he is trying to say….
He even posted evidence (photos) contradicting his own statements but still claims the same. I for one am lost… 🫣

[PininMargherita]

Originally Posted by SD Convert

You also wrote:

• because they're the same pads, the contact area is the same - This is correct but has nothing to do with the "issue" you're describing.
• This leaves the 370mm rotors with some unused rotor material around the edges - This is not correct. The fact that the caliper for the 370mm rotors has longer mounting ears negates this. Also, these rotors are not the rotors that came with the calipers. Once you move to 3rd-party (aftermarket) rotors, you take a chance that the sizing will be a bit off. Different brands have different chances of this.

Of course they use the same pads. That's the way BMW/Brembo designed them. It keeps inventory costs down. The same front pads are used on 340, 370 and 380mm rotors. The same rear pads are used on 345 and 370mm rotors. In all cases, the pads are more or less centered on the rotor surface (within a few MM).

In what way is this a problem?



That's an M3 with a few (1-3) MM unused in the center (the part where the factory crosshatch is still visible - not the outside). Different rotor, different placement, different symptom. This is not what you're trying to describe.



I see under 3mm (under 1/8") of possibly unused rotor on the outer edge of the 370mm rotor.



The amount of space that the pad is in from the edge is trivial.

> Different rotor, different placement

Not true. Caliper dictates pad placement.

[Onizukachan]

Originally Posted by PininMargherita

The brake pads are the same between the 340mm and the 370mm, so their contact patch is the same. This leaves the 370mm rotors with some unused rotor material around the edges.

This is correct. Same calipers except the 370/380 version has ~15mm longer ears compared to the 340. Or you could say the 340 has shorter ears since I suspect the 370/380 was designed first.
Same pad though because same caliper body

[SD Convert]

Originally Posted by PininMargherita

> Different rotor, different placement

Not true. Caliper dictates pad placement.

Once again, you missed the point. This 3-item list was only related to how poor your "example" was, specifically, they were comparisons of your "example" to the problem you're attempting to describe.

To clarify, the example you provided in the link (https://f80.bimmerpost.com/forums/sh....php?t=2107197) used a different rotor than you have (380mm OEM vs. 370mm aftermarket - the orange calipers come with dimpled rotors) AND has a different placement of the pads WRT the rotor (I made no mention as to why the placement was different) AND exhibits a different symptom then you're claiming (unused space on the inner edge of the rotor vs. outer edge).

In your "example", the radial position of the pads on the rotor is determined by the caliper, the hub (the M3/M4 hub moves the caliper mounting holes out 5mm to allow for a 380mm rotor) and use of OEM rotors. It should be noted that aftermarket rotors can have an outer diameter that's a few mm larger than the OEM rotors, therefore making the rotors also relevant when discussing pad placement relative to rotor surface.

Overall, the "example" you provided is not really an example of anything related to this thread except your lack of attention to detail.