Slotted vs Plain Discs

[major quicknap]

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.

[wparsons]

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.

[ZionsWrath]

Originally Posted by wparsons

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%.

[STV3]

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.

[STV3]

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

[gramicci101]

Originally Posted by ZionsWrath

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%.

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.

[supramkivtt2jz]

This thread is vomit inducing.

[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.

[wparsons]

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

[mikepaul21]

Originally Posted by gramicci101

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.

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.

[2point0]

Originally Posted by wparsons

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

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

[zooki]

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.

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

[gramicci101]

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 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!

[finch1750]

Originally Posted by gramicci101

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!

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