Slotted rotors

[The Art Doctor]

Are drilled vs cast in holes still a thing?  I remember years ago Porsche saying drilled holes will crack while cast in holes will not.  Then they switched to carbon rotors as a $10,000.00 factory optional upgrade.....

[GTRS Fiero]

Interesting.  I've never had that happen on a street car.  I've seen racecars have cracked rotors, but not often.

When people say "drilled" I've always assumed that's what they meant.  Silly me.  Since I just bought mine with holes in them, I dunno.

[Fierofool]

I think cast would be better  because the metal is evenly stressed.   They are called cross-drilled maybe because that's how they appear.  I cant think of another word that could describe it.

[The Art Doctor]

Here is a pick stolen from Google.  Lots of images like this if you search "cracked drilled rotors"

[GTRS Fiero]

Hmmm.  In my mind, I had pictured the cracks being at a radius to the center.

[Fierofool]

I suspect those are aftermarket drilled holes.  The disks I have, have chamfered holes, and the chamfer is rough as if cast, not countersunk with a larger drill bit. 

[GTRS Fiero]

Mine do not have countersunk holes.

[The Art Doctor]

You can't countersink the inside of the hole in the vented area.  From what I know most of the cracking is due to heat in spirited driving/racing.  Seems like weekend warriors have most issues as they do not change rotors every race like many racers do.  I've never had drilled or slotted on anything.  Lots of opinions out there on this subject.

[Fierofool]

These disks aren't vented.  They're for the early years. 

[GTRS Fiero]

Mine came with drilled or slotted rotors.  I don't specifically recall, anymore.  I figured there was a reason, so that's what I used to replace them, sortof.  What I got was what I got, not necessarily what I asked for.

[scottb]

The picture from above looks like someone did those by hand, the layout is not consistent. The cracks are typical of what I saw on the racecar.

In my opinion you need to take in to account the surface area that the holes remove. It may not seem like much but it does add up. The less surface area on the rotors is less area the pads have to grip.

I still don't think it is worth it on a street car.

[TopNotch]

Drilled or not, the rotor in that picture was used well beyond it's useful life. No wonder the holes cracked. It should have been replaced long before the grooves got that deep.