Brake slotting

[boyracer]

Just wondering if anyone knew the significance of the direction of the slots cut in brake rotors. I have seen a couple of different ideas. Some cut from the outside of the disc to the inside while others are the complete opposite. Also the length of the slot, personally I would have thought that the slot would need to be long enough so that the pad does not fully cover the slot at anytime, so that the gases can escape. Any other viwepoints ??

[Dave Brand]

Originally posted by boyracer
Also the length of the slot, personally I would have thought that the slot would need to be long enough so that the pad does not fully cover the slot at anytime, so that the gases can escape.

I don't think that's necessary, as the gases will escape when the slot moves out from under the pad - as happens with drilled discs.

As for slot pattern, I suspect it's more a matter of fashion than anything else, although factors such as noise & disc strength need to be taken into account. The most important criterion is, I would think, the metal/air ratio on the disc. The latest fashion on bikes is a wavy-edged disc!

[Jukebox]

boyracer...i think you are confusing yourself with the self adjusting brakes and the normal conventional brakes. The self adjusting brakes have larger pistons and calipers.

All brake calipers and rotors have vents for the heat generated by the kinetic energy to exit.

[Dave Brand]

Originally posted by Jukebox
boyracer...i think you are confusing yourself with the self adjusting brakes and the normal conventional brakes. The self adjusting brakes have larger pistons and calipers.

I think it's you who is confused. ALL disc brakes are self-adjusting. They use a square-section piston seal, which, apart from the obvious functions of preventing fluid leaks & maintaining system pressure, performs two other functions. Firstly, in normal brake operation the seal does not move relative to the piston; this means that when the pedal is released the elasticity in the seal retracts the piston slightly. Secondly, as the pads wear the piston movement is more than the maximum deflection the seal is capable of; the seal will now move relative to the piston, which reduces the distance the piston retracts, in effect adjusting the brake. Caliper/piston size is irrelevant to the self-adjusting properties of the brake - it's a function of the piston seal design.

All brake calipers and rotors have vents for the heat generated by the kinetic energy to exit.

Calipers are designed first & foremost to perform their mechanical function. The primary heat-loss element in a disc brake system is the disc. Many low-specification cars have solid, non-vented discs on the front; only on very high-performance cars are the rear discs vented.

[Jukebox]

Dave..

I was merely suggesting that boyracer must have confused himself with the older version of disc brakes that have dual or four-piston fixed-caliper designs.

You are right about the part of vented disc brakes.

[boyracer]

How can you call fixed brake design old ?? Is still current as fas as I am aware.
But anyway, was talking about DIRECTION of slots in rotors and style.
DBA is manufacturer of disks in australia. Earlier disks (2yrs ago) had slots from inside to outside (with direction of wheel travel), newer style go from outside to inside. I also notice that AP use outside to inside. Just curious as to reason (if any).
As one reply has already susgested, is probably more fashion than anything, but still would like to hear what everyone has to say.

[Jukebox]

you'll have to learn to be more diplomatic and relaxed in your replies or end up no one wanting to reply to your threads in the future. This is a FORUM and ideas plus debate is always welcome not attacks.

[Onlooker]

With vaned disks you shouldn't have the vanes and the slot running in the same direction as a weak point will be at the point where the slot is in the center of the vane, by running opposite it eliminates this problem

[boyracer]

I thought I was being diplomatic Jukebox.
If anything I should have taken offense at your remark saying I "must"
have confused myself with the other brake design.
If you being diplomatic then why you use such wording??
I restated my question, in bold so as to draw attention to the specific question I was asking as the conversation seemed to be wondering.
I would sincerely hope that no one has taken offense to any replies that I have posted, I also realise that this is a forum and try to keep an open mind while reading and replying to postings. I'm sure everyone out there is quite intelligent, but the simple fact is you can't know everything about everything and I am quite willing to ask for help on subjects that I do not fully understand and am also quite willing to share, with anyone who asks, the knowledge that I have gained through my involvement with motorsport and the general engineering industry.
I hope that clears everything up.

[DAVID PATERSON]

Jukebox, I think you're being a little thin skinned here, Boyracer's reply seems perfectly civil to me. Or perhaps you were just confused and misunderstood him, you certainly misunderstood his initial question.

[Dave Brand]

Originally posted by boyracer
How can you call fixed brake design old ?? Is still current as fas as I am aware.

Any braking system where performance is important uses fixed calipers. Sliding caliper brakes are used for one reason - they are cheaper to make &, for most applications, they perform adequately.

[Mackmot]

Sorry i have drawn a very poor picture to help me explain what i understand of slots.
Basically they should be directional, they should start at the centre and at angle away from the direction that the disc is spinning. (someone help me this is difficult to explain)
Erm this basically forces the air to go from the centre of the disc to the outside.

Well there you go will someone who knows english better please reiterate, sorry im from yorkshire

[Andrew Kitson]

Seems pretty clear to me Mackmot.
I'll be in touch next week Wayne re: Festival pic.

[boyracer]

Thanks Mackmot, you got the right idea.
I would have thought the same and that is how the slots in the disks on my friends rally car run. However I was involved with pre-rally testing with Team Peugot (Rally Australia), good thing being you get a close look at the car (nice bunch of guys), and they had the slots facing the other way. Since then I have made a point of looking at the slot directions on all sorts of cars, all the World Rally Cars that I saw at Rally Australia ran that way and most of what I've seen in magazines also. Is it something to do with the disk hat ??
Still confused but appreciate everyones input.

[Se7en]

Have you checked both sides of the cars you're looking at, boyracer? Certainly for the aftermarket, I don't believe discs are 'handed'; they are of the same construction. That is to say, one disc will have slots running with the direction of travel, and the other side against.

I guess for racing purposes, and if the customer requested, discs could be directional with slots radiating away from the direction of travel, as per Mackmots drawing,
but in my experience, people like Bremsport just provide a grooved disc and there's no mention of left or right hand part numbers, as would be seen if grooves were directional.

Hope that's of use.

[boyracer]

Sorry se7en, close but no cigar.
The DBA rotors that we get here in Australia are left and right handed and actually come with a sticker to say so.
The really confusing bit is the slots used to face backwards but now face forwards. I can't see why they would change such a detail just for the hell of it ??

Then again maybe their sticker machine got confused

[Sparky]

Do you have a link to DBA, boyracer?

I've never seen handed discs before. I'd be really interested to see this. Are these for competition or road?

[boyracer]

Once again sorry.
No link but generic search engine should find them, big company in australia. Disk Brakes Australia (DBA).
Disks for road or competition, though maninly club level.
Have just released new version for subaru WRX which has aluminium hat, everything else just standard aftermarket disc with custom support pattern beneath rotor facings. (Hardly a rival for AP or Brembo).
Know at least 3 people who have purchased their disks from DBA, each time they come with little L and R sticker on disk. And as I have already mentioned, slots face one way on older model and opposite on new model.

[StuiE]

http://www.dba.com.au/

[Warwick]

Had a 255kw Clubsport in at work today so while we had the wheels off I took a look,same disc on both sides because the slots ran frontwards one side backwards the other.

[Se7en]

Thanks guys.

[Sparky]

http://www.dba.com.au/news/pr990527.asp

If you read this page, the second paragraph says:

"The DBA Longlife Slotted rotor received the award for its innovative unidirectional slotting (left and right) which increases pad bite, reduces fade and delivers exceptional braking performance."

Could be why some of us have never noticed these things out there! It also describes non-slotted discs as 'conventional'.

[ISK]

The slots in the friction surface of the disc are usually aranged to be tangental (i.e. if you extend the slot inwards it wouldn't pass through the disc centre). I assumed this was so that when a slot passes the leading edge of the pad it didn't chissel the edge of the pad off. If this is the case then it wouldn't matter if you had clockwise or anticlockwise slope on the slots.
On the other hand, the air passeges in vented discs are generally radial to the disc centre as the spinning disc forces the air to travel from the inside to the disc rim under centrifical action. There are exceptions some manufacturers have passeges which start radially and end up tangental i.e. they are curved. I believe it is to try to get even more air to pass through the disc.
Some group 'C' cars even combined vented discs, with passages that forced air into the disc centre, with wheels which had radial air passages that forced the air outwards under centrifical force to the outside of the wheel. Very clever as not only do you get twice the air pumping force, you also dump the hot air away from the disc inreasig cooling even further.

[boyracer]

Hi everybody, would just like to take this opportunity to thank everyone for their input.
It would seem from the posts collated so far that DBA is about the only disk manufacturer to use left and right handed disks. If anyone has any information otherwise I would still like to persue the matter.
But after having so many opinions from so many people, the consensus seems to be that it doesn't matter. I thought that may have been the case, but have had my opinion validated at least. Pirrelli guy once said that driver wouldn't notice if rally tyres were on back to front, guess it's the same for the disks.
Once again Thank you.

[con-rod]

Just to agree with the general conclusion here, i think the direction of the slots makes little difference.

Reason being because drilled discs usually have the holes in the same angled linear pattern, obviously not to move air, but to avoid having them all in-line with the centre which would weaken the disc significantly.

Similarly if the slots were in-line with the centre then, as ISK said, it would damage the pad.

ultimately the slots are there to increase surface area of disc in contact with air, thus reducing brake fade, angled for structural reasons.