Brake disks debate - Drilled or flat?

What’s the thinking on drilled or flat(/slightly grooved) brake disks?

Other than looking snazzy, I believe the theory on drilled disks is increased cooling. However, drilling reduces the braking surface area and I know there are claims it creates greater heat peaks (even if they cool slightly quicker) and therefore reduces the life of pads (that are touching the disks during these peaks).

What are your thoughts? Have I got this all wrong?


Uldis will be along in a minute…

but i think the holes are there to aid escape of gasses not to aid cooling that’s what the vents up the centre are for.

the danger with holes is that they provide a stress point and are more prone to cracking, although the holes might stabilise the temperature distribution as well and this might help stop warping… but as Uldis will say in a moment, warping isn’t usually what happens - even when people think they have warped discs its normally chemical deposition at the surface of the disc.

all of that is how i understand it.

Grooved (lightly).
Solid will perform better but has no water clearing capabilities and needs good know pads (yes, Pagids are tops).
You only need an escape route for gas release at high temps. Also, they will help scrape any shite off the pads (or water).

Drilled disks cool better, BUT
-they have less friction area than a solid one (Porsche keeps using them as the friction area has been designed like this, and those cars have no ducting, relying on turbulent air movement for cooling only)
-all the holes wear out a pad quicker (and they get filled if a bad pad is used)
-holes have a surrounding stress area, and due to the continuous heat cycles, tend to develop cracks. Some people say they have to be cast in instead of drilled but I don’t see why.
-if the hole is countersunk to avoid the 90 deg angle (like Brembo does) you have even less friction area.

And all this is true on the road, with brakes with no ducting.
Race cars have ducting and the air needs to be directed through the vanes, part of it will escape on a drilled disk through the sides (which come to think of it wouldn’t be a bad thing, but there must be a reason why they don’t do it in racing)

In essence, grooved is Ok for our use. Besides, it will last longer.

Don’t the grooves allow the gases to escape?


yes IDG and also water…

Beat me to it Mike.

On the theme of “warping”, yes, it’s not that the disks really warp. Yes, it happens, but most of the times it’s the uneven depositions we feel.
Anyway, drilled disks still “warp”