Brake Rotor Question

[bmgmd]

While inspecting the pad thickness, I noticed that the front cross-drilled rotors have concentric grooves.

I will need to change pads, but is there a concern with the rotors? It is above the minimum thickness in the grooves.

I know that I should turn the rotors, but it would seem that the process would decrease the thickness of the rotor.

Any advice is appreciated.

Thanks,

Brian

[Gogar]

Yes, you should have them machined so there's no grooves. If that takes them below the minimum thickness then you need new rotors. But rotors are cheap, so don't worry about it. That's just the way it is.

[rfn026]

The brake rotor is really a huge heat sink. It purpose is to abosrb the heat of braking - and then disperse this heat to the atmosphere. Remember that braking is all about energy conversion.

If you machine the brake rotor is reduces the amount of heat the rotor can absorb. Basically it now has less mass. I'm not a big fan of machining brake rotors for just this reason.

Richard Newton
Porsche Brakes

[RexNoctu]

Leaving the grooves will eat your new pads causing them to wear out quicker. How deep are the grooves? Any idea what caused them?
If they are shallow then it comes down to either turn them or plan on checking / replacing your pads more often. If they are deep find out what caused them fix it and get them turned / replaced.
That would be my recommendation anyway.

[RWebb]

also: are they rounded or sharp edged (bad)

use finger nail / touch to assess

[djpateman]

I'm assuming the groove you speak of are wear patterns. These must be removed by machining.
If you use new pads with worn rotors, you will only have a small fraction of the braking performance you would have with machined rotors; the pads would only touch the high points on the rotor. Unless the grooves are really shallow, and the rotors will machine down to above minimum thickness, it is not worth doing so; there are two minimum thicknesses: minimum machine to thickness and minimum service thickness.

[RWebb]

I thought the pads would just wear down to match a shallow, rounded groove pattern?

i.e. only sharp or deep grooves req'd new rotors...

[Flieger]

Originally Posted by RWebb

I thought the pads would just wear down to match a shallow, rounded groove pattern?

i.e. only sharp or deep grooves req'd new rotors...

This works for me, although there is more squealing.

[djpateman]

Originally Posted by RWebb

I thought the pads would just wear down to match a shallow, rounded groove pattern? i.e. only sharp or deep grooves req'd new rotors...

They will, given enough time. In the meantime do you still want to be able to stop effectively? More than that, the rotors are often warped, glazed or work hardened, and the machining gets rid of those problems as well.

Rule of thumb: if it is time to replace the pads, then it is time to resurface or replace the rotors.

[bmgmd]

How deep are the grooves? Any idea what caused them?

probably less than 1mm. I don't know what caused them, that's why I posted the topic.

are they rounded or sharp edged (bad)

they are smooth and rounded. More wavy than anything else.

I thought the pads would just wear down to match a shallow, rounded groove pattern?

my thoughts also.