What causes scored discs

[obi_waynne]

What causes scored discs? Surely the pad and disc surface are flat so when they are pressed together they should wear at the same rate?

Is this down to cheap pads, defective discs or could rust build up and wear and tear and heat build up cause discs to become scored?

 

[RobBentley]

I'm going to go with it being to do with the pad compound. The stock Audirembo pads always score the disc. They did on the RS6 and they did on the RS4. Oddly though the AP racing discs with Ferodo DS2500 pads i've got on the 6 now, don't seem to suffer the same fate.

 

[old-git]

I don't think that discs are made of as good a material as they were made from 20 years ago. The remova of asbestos may also have a bearing on it.

 

[HDi fun]

I don't think that discs are made of as good a material as they were made from 20 years ago. The remova of asbestos may also have a bearing on it.

Disc scoring is unavoidable regardless of pad formulation or disc materials. Discs have always shown circumferential scoring, long before asbestos was removed from the pad material.

There are two types of friction: adhesive and abrasive.

Adhesive friction is the one we rely upon 99.9% of the time in road applications. It depends upon a thin layer of pad material being (EVENLY) transferred to the rotors during normal usage. This is why we are now advised to bed in new rotors and pads fairly aggressively. After a short period of gentle braking (10 miles or so) it's best to burnish the pad/disc interface with a series of hard braking operations. THe key word here is EVEN transfer of pad material. So, do not come to a halt, but perform a series of 60mph to 20mph brake applications. It's quite reasonable to see some smoke after the 5th-6th application.

All rotors will show circumferential scoring.

 

[old-git]

Don't agree. Back in the 70s, when working in car spares (part time) we sold very few discs. Four reasons:

1. Discs tended to get scored only when people didn't change the pads early enough so wore them down to the metal.
2. If lightly scored they would get the discs skimmed rather than replace them.
3. Modern pads are (generally) harder and require more force compared to the old asbestos pads, which adds to both pad and disc wear.
4. Modern cars are heavier requiring more braking force, adding to wear.

PS. We never bothered with any sort of bedding in, just change the pads and off we went - No problem.

 

[HDi fun]

I think the heavier cars thing is contributing a bit here. Modern pads probably are more aggressive, most contain metallic components, which asbestos pads did not contain.

I do remember the old style pads being absolutely useless when waterlogged.