Slotted vs Plain Discs
 

From what I have read on the infonet the reason for slots have been the same since forever. After reading through this thread http://www.ft86club.com/forums/showthread.php?t=62847 I'm wondering if the use of slots in discs is an anachronism from when materials weren't as advanced as now or if the slots still have a benefit on discs that see a hard time.

IMO, 99% of people are better off with plain solid rotors and the few that could actually benefit from slotted or hooked rotors know why and are fine with the potential downsides.

I see many posts similar responses equating to "if you have to ask you probably don't need it". That's cool and maybe true, but maybe explain why we don't need it?

Please elevate our knowledge to the 1%, even if our skill is in the 99%.

I've read an article where they tested plain vs slotted vs slotted and drilled and the plain face rotors performed the best and the slotted and drilled performed the worst. IIRC the rotors that were just slotted performed about the same as the plain faced ones with no added benefits.

I'll admit I like running slotted rotors because they look cool and are a lot less prone to cracking than slotted & drilled are

Slotted and drilled rotors were originally created back in ye olden times when brake pads would create significant amounts of gas as they heated up. It was known as off-gassing, and had the potential to trap pockets of gas between the pad and the rotor, effectively neutralizing your braking ability and making for a much more eventful drive. The slots or holes were cut as a way for the gasses to escape, which allowed you to smoothly brake to a stop with a confident smile on your face instead of careening wildly into your girlfriend's parents. New pads don't have the same off-gassing problem, so that need for slots or holes has been removed.

People will say the slots or holes will allow heat to escape, but they're wrong. A rotor is a massive heatsink, and by removing rotor material you're removing material available to absorb heat. Heat escapes through the rotor's interior vanes as air from your brake ducts flows across them. You have installed brake ducts, right?

Track junkies have noticed that slotted rotors will give more bite to the pads, because you've got that nice sharp machined edge of the slot digging into the pad, instead of the flat shiny surface of a blank rotor. I can't comment on that, because I'm just not that cool.

Drilled rotors (or cast with holes, for you pretentious types) are there because they look cool. Or so the driver of the '95 Honda Civic thinks. Drilled or cast holes provide a convenient location for cracks to start, as they create a stress point on an otherwise serviceable rotor. I've never heard of anyone sticking a stainless steel pin into the drilled holes as a prank, and most certainly have never done so myself. Ever. Because that would be wrong.

This thread is vomit inducing.

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 would be really interesting to see how the added surface area balances with the removal of mass with regards to thermal capacity.

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.

Yeah, I can't believe it would be vastly different, but I also wonder how the air gaps within the slots affects heat transfer.

Now most of them use carbon- ceramic or carbon-carbon brakes.

I honestly don't know. I know a lot of them use carbon ceramic brakes (Z06, Porsche GT3, Ferrari F430 Challenge, etc...) so that may have something to do with it. Interestingly, the Porsche GT3 Cup uses steel rotors cast with holes, not drilled. Here are two pictures of GT3 Cup rotors starting to crack at the holes: 1, 2. I did find that holes help a little with bite and a little with cooling at the extreme top end of the temperature range, but that's a heavy track usage thing. And race cars' rotors will be replaced long before cracking becomes an issue.

I know GT-R owners have problems with their rotors cracking at the holes too. This thread has some pics of pretty sketchy rotor cracks originating at the rotors' holes. It also has pics of the elusive "spatula" brake cooling mod, which I found interesting. Remember kids: if it's stupid but it works, it might still be stupid. But hey, it works! :D

Dude, that is epic. Good to know even GT-R and Lambo owners know how to ghetto rig. Haha

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.

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

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

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...

Increased pad wear, potential uneven wear.

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.

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.

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.

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.

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!

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.

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.

Would you mind expounding upon us the pros and cons of external vs internal fluid crossover tubes?

Slotted vs Plain Discs
 

Formula 1 use plain disk http://www.formula1.com/inside_f1/un...port/5284.html

I know they are in fibre composite but anyway...

Sure.

External crossover tubes / pipes

Pros

• Easier to bleed- air bubbles don't get trapped as easily inside the external pipes
• Caliper can be easily swapped to leading or trailing (switch the pipe with the bleed screws).
• Caliper is less expensive to manufacture and machine with external tubes
• Easy to repair if damaged- remove the pipe and replace it
• If debris gets inside, it's easy to remove- take the tube off and clean or replace

Cons

• More parts (and part numbers) add to the complexity of the caliper...basically more bits and pieces to be broken and replaced
• Since it is exposed, pipe can get damaged during a wheel change, or by road/track debris (rocks, pieces of other cars, etc.).
• Adds a slight amount of weight
• limits caliper design to a more conventional rectangular shape

Internal crossover tubes / pipes

Pros

• Allows for asymmetrical caliper design (AP Racing Radi-Cal is a good example)
• Reduces possibility of crossover being changed during a wheel swap or by debris (this is one of the reasons why you see internal in a race series with frequent wheel changes (NASCAR), or in rallying).
• Reduces weight- Also critical at the higher levels of racing
• Reduces number of spare parts to hold on hand

Cons

• Can be more difficult to bleed- air bubbles can get trapped in the recesses of the calipers, and generally tougher to get that air out
• Caliper is more intricate and expensive to manufacture
• Can't easily be swapped from leading to trailing.
• Would be more difficult to remove any contaminants if they got inside
• Caliper is trashed if crossover section gets crushed

I bought a BBK from Wilwood and really wanted the drilled rotors for the bling, but y'all convinced me that they crack, so I settled for slotted rotors for just a bit of bling, while staying as stong as possible.

I really like the idea of using the slots as a gauge for rotor replacement.

I had a hard tim tracking down the specific silicon ones locally.

Ended up finding at bed bath and beyond $10 each.

Didnt like how all the walmart ones couldnt be bent as desired

I just ordered some replica ebay spatulas.
Full review in 60 days when they get here from China.

Will you be making pancakes? I want pancakes!