Slotted vs Plain Discs

[gramicci101]

Originally Posted by 2point0

I suppose it could be argued that since slotted rotors have more surface area, they make a marginally better heatsink. But really, it just looks neat.

It depends on where the heat is being applied and where it needs to go. If you look at a CPU heatsink, the CPU mating surface is machined flat and is coated with special heat-transferring goo. That's because the chip itself is generating the heat, so you want as much surface area as possible in contact with it to transfer heat away as efficiently as possible. The other side of the heatsink is vaned, or has heat pipes, or god knows what else. This is where the heat from the CPU spreads out across the much greater surface area so it can transfer heat to the air. Air not being as efficient at transferring heat as aluminum is, the heatsink needs all the vanes and fans and neon lights to work most effectively.

With your brakes, heat is being generated by friction between the pad and the rotor. In effect, the pad is the heat source. You want as much rotor surface area as possible in contact with the pad, which means no slots or holes. Otherwise you have spots on the face of the pad that could be transferring heat to the rotor, but aren't, because there's a slot there. The heat travels from the surface of the rotor inwards, along the vanes inside the rotor. Air comes from inside the wheel well or from nifty brake ducts, enters the center of the rotor from the back, and flows outward along the vanes to transfer heat from the rotor and get it out of the brake system. Good rotors' vanes will be designed to pull as much air through as possible, to transfer as much heat as possible. This is why companies will use their curved vane solutions as selling points for their rotors. Or like DBA's 5000 series, have an odd but strangely symmetrical interior vane construction, greatly increasing the vanes' surface area while not diminishing airflow.

Sometimes there's just too much heat for the air to dissipate effectively, and you get heat soaked rotors, which gives you heat soaked pads because their heaksink is no longer effective. This gives you boiled brake fluid, which quickly introduces you to a reason why you should have upgraded your brakes, otherwise known as the wall. This is bad.

[major quicknap]

Originally Posted by mikepaul21

not questioning your reply (I just learnt everything you just stated) but why do so many exotic car companies that are always competing for the best track performance use drilled and slotted rotors on their vehicles.

I am suggesting that most "exotics" never see a track. The drilled discs are just for looks/marketing.

[major quicknap]

Originally Posted by wparsons

and are fine with the potential downsides.

Besides the wavy wear (which is not an issue) being seen with AP Racing J-hook rotors what are downsides of slotted discs?

[Poodles]

Originally Posted by major quicknap

I am suggesting that most "exotics" never see a track. The drilled discs are just for looks/marketing.

BINGO!


It's marketing, plain and simple.


F1 cars don't run drilled/slotted. Ditto for Le Mans (from what I've seen). From what I've seen, NASCAR uses either slots or plain disks, but never crossdrilled.


Also, never seen cast in holes in rotors. Even on carbon ceramic rotors, they're drilled. If they were cast (or better yet, forged in) they wouldn't have the cracking issues. Crossdrilled is a massive brake failure waiting to happen IMHO...

[wparsons]

Originally Posted by major quicknap

Besides the wavy wear (which is not an issue) being seen with AP Racing J-hook rotors what are downsides of slotted discs?

Increased pad wear, potential uneven wear.

[Andrew025]

Instead of asking "blanks vs slotted/drilled", ask yourself why you think you need to upgrade/change your rotors.
What are you trying to achieve?


All I know is, I'm buying some spatulas now.

[troek]

the r32 gt-r has that spatual mod as an option, combined with a duct directing air ait it, it is supposed to be quite effective. my friend did something very similar with some sheet metal on his r33 which he tracked regularly at fuji, and said he never had a heat issue again.

[major quicknap]

Originally Posted by Andrew025

Instead of asking "blanks vs slotted/drilled", ask yourself why you think you need to upgrade/change your rotors.
What are you trying to achieve?

J-hooks came with the Essex Sprint kit. I am wondering if there any benefit to going plain discs.

[dradernh]

Originally Posted by major quicknap

J-hooks came with the Essex Sprint kit. I am wondering if there any benefit to going plain discs.

IIRC, they're cheaper. And, they're likely to work just as well for you.

[Black Tire]

Originally Posted by major quicknap

I'm wondering if the use of slots in discs is an anachronism from when materials weren't as advanced as now.

Ding, Ding, Ding. I think this is the case. [Note: all these comments refer to track use; I don't think it makes a whole lot of difference on the street.] I used to run slotted rotors years ago. They definitely helped with pads that were off-gassing. The newer compounds that I have been using don't seem to need them at all. Slotted rotors generally wear the pads faster. I have not seen a reduction in bite with the plain rotors and modern track pads.

Why slots?
• Some nice kits come with them –*like the Essex Sprint Kit (yes I know they're J-Hooks, but same thing essentially).
• They do still have the benefit of clearing some of the water in the rain. This improves the initial bite of the pads as the water on the rotors can clear faster.
• The slots are a super easy way to gauge if it is time to replace your rotors. If any of the slots are gone, the rotors are junk.

[OrbitalEllipses]

Plain face rotors will work for 99% of applications and as the poster above explains, are a holdover from a bygone era.

That said, I do run J hooks. Bling bling!

[gramicci101]

Originally Posted by OrbitalEllipses

That said, I do run J hooks. Bling bling!

I think the center lug wheel and massive caliper in your profile pic are bling enough already.




Yes, I know what that's from.

[OrbitalEllipses]

Originally Posted by gramicci101

I think the center lug wheel and massive caliper in your profile pic are bling enough already.




Yes, I know what that's from.

Thank you for that valuable insight. Glad you can read P O R S C H E sideways too.

[JRitt]

Hi Guys,
Here is something I wrote for our blog a while back:
Drilled vs. Plain vs. Slotted brake discs

I think that summarizes it pretty well.