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Old 24 Jul 2007, 19:14 (Ref:1972391)   #1
Alan Cherry
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Grooves in discs (rotors)

OK Gents and Ladies,
A quick question. When looking at a front disc from the outside, should the grooves go from the centre out, or the outer edge in when the disc is rotated in a forward direction.
Reason for asking - i picked up a new set of discs from Hi-spec Brakes ( Monster Brakes ) this afternoon, as my existing ones have developed a nasty crack since the last race. I'm sure poster on sales office wall showed grooves going in to out,but on checking those already on the car, they go out to in ! - have to get car ready for Lydden on sunday- any directions much appreciated.

p.s. I've been told that drilling discs is mainly for boy racers, and can cause the disc to crack- old discs were drilled , so I've specifically got vented grooved discs that have not been drilled - good move ? or not

Many Thanks
Alan
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Old 24 Jul 2007, 19:42 (Ref:1972417)   #2
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If you look at the direction of rotation the groove at 12 oclock should go from the center to the front of the car (if that makes sense)

Last edited by GORDON STREETER; 24 Jul 2007 at 19:44.
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Old 24 Jul 2007, 19:48 (Ref:1972428)   #3
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They can go either way depending on the application but Jeff at Hi Spec says have the groove going from the inside to out going backward so any water or crap is thrown out.
I don't see any point in drilling them either.
Word of warning with Hi Spec, check both discs for symmetry from one side to the other and disc to disc. I had one disc of a pair that had one face machined differently to the other so one pad started to wear with a shoulder on it.
Were your old discs from Hi Spec?
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Old 24 Jul 2007, 20:28 (Ref:1972474)   #4
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I have run rotors in both directions depending on the event duration and whether I want to encourage cooling of the rotor or retain the heat (short events or cold/wet days).

Think of the rotor as a centrifigul air pump.
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Old 24 Jul 2007, 23:48 (Ref:1972627)   #5
Alan Cherry
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Originally Posted by falcemob
They can go either way depending on the application but Jeff at Hi Spec says have the groove going from the inside to out going backward so any water or crap is thrown out.
I don't see any point in drilling them either.
Word of warning with Hi Spec, check both discs for symmetry from one side to the other and disc to disc. I had one disc of a pair that had one face machined differently to the other so one pad started to wear with a shoulder on it.
Were your old discs from Hi Spec?
Old discs were from Rally Design ( The only people who had them in stock at the time - as usual needed them quick ) I'll check the machining -never thought it may be different.
Thanks
Alan

p.s. when are you or your uncle coming back out in the fester to play falcemob?
p.p.s. No slur against Rally Design intended, but some of their stuff seems a bit 'cheap and cheerful' ahem

p.p.p.s - I like cheap !
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Old 25 Jul 2007, 05:47 (Ref:1972732)   #6
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I have bought different brands that have gone different ways, they have been coded left or right
(unless it is the right as you look at the car, or the right as you sit in the seat!)
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Old 25 Jul 2007, 07:59 (Ref:1972787)   #7
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Originally Posted by Alan Cherry
I've been told that drilling discs is mainly for boy racers, and can cause the disc to crack- old discs were drilled , so I've specifically got vented grooved discs that have not been drilled - good move ? or not
No stratight answer, but Porsche have run drilled disc on competition cars for decades, which they would not do if there was no advantage. However Porsche also seem to be able to avoid cracks, which not many others can claim I believe.
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Old 25 Jul 2007, 09:10 (Ref:1972849)   #8
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Originally Posted by phoenix
However Porsche also seem to be able to avoid cracks, which not many others can claim I believe.
They probably stress relieve them after drilling which is time consuming (thus expensive). I'm not sure of the benefits of cross drilled or grooves. The only reason they're there is to allow the gases to escape.
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Old 25 Jul 2007, 17:28 (Ref:1973241)   #9
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Originally Posted by phoenix
No stratight answer, but Porsche have run drilled disc on competition cars for decades, which they would not do if there was no advantage. However Porsche also seem to be able to avoid cracks, which not many others can claim I believe.
I do believe a lot of the drilled, milled or cast in holes has to do with marketing and give what the customer wants, not really any benifit at all. Rotors with holes in where originally designed for outgassing of asphestous brake pads back in the late 50s and 1960s.. While asphestous is no longer used in brake pads, there is no longer a need for rotors with holes in.

Most manufactures state the air should flow into the center of the hub and out the veins. This is also were the brake duct hoses from the fenders should point too, the center of the hub to cool the hub and then the air is pulled out though the rotor too cool the rotor.

So when you look at a rotor from the side, the veins should curve back at 12:00 O'clock to pull the air OUT though the rotor, Not forward and pull the air down onto the hot hub and bearing.

Does it really make a difference which way the veins curve? for the most part, no.

I have lots and lots of photos of crached rotors, drilled, slotted and plain sided, only the rotors with holes in do crack faster.
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Old 25 Jul 2007, 18:51 (Ref:1973285)   #10
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Originally Posted by AU N EGL
Rotors with holes in where originally designed for outgassing of asphestous brake pads back in the late 50s and 1960s.. While asphestous is no longer used in brake pads, there is no longer a need for rotors with holes in.
The basic composition of an organic friction material is a phenolic resin & a fibrous material, together with other ingredients, mainly in powder form, to modify the friction characteristics. Until the 1980s the main, almost universal, fibre used was asbestos. The banning of asbestos forced the use of different fibres, such as Kevlar, rockwool, glass fibre & several others. However, the resins remain the same; gassing is the result of the action of heat on the resins, so the requirement to provide an escape path for the gases is just the same for non-asbestos pads as it was for asbostos pads.
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Old 25 Jul 2007, 19:12 (Ref:1973295)   #11
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AU N EGL should be qualifying in the top 10 on the gridAU N EGL should be qualifying in the top 10 on the grid
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Originally Posted by Dave Brand
The basic composition of an organic friction material is a phenolic resin & a fibrous material, together with other ingredients, mainly in powder form, to modify the friction characteristics. Until the 1980s the main, almost universal, fibre used was asbestos. The banning of asbestos forced the use of different fibres, such as Kevlar, rockwool, glass fibre & several others. However, the resins remain the same; gassing is the result of the action of heat on the resins, so the requirement to provide an escape path for the gases is just the same for non-asbestos pads as it was for asbostos pads.
That debate can go on for ever.

If some one want to use Drilled and slotted or cast in holes that is their choice. From our reseach and many other race teams, rotors with holes in vs the same rotor without holes in has a shorter life and will crack much sooner then a disk without holes.

Plus when you really dig deep into manufactures technical pages with holes in, they say rotors should be check for damage before each race, and or for marketing purpose only.

All rotors should be check in a pre-event tech inspection anyway.
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Old 25 Jul 2007, 19:18 (Ref:1973298)   #12
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Originally Posted by AU N EGL
That debate can go on for ever.
There's nothing debatable in my original post. All I was doing was stating the fact that the requirement to provide an escape path for the gases is the same irrespective of whether or not the friction material is asbestos-based. (Unless, of course, it's a sintered metal material!) I made no comment as to how that should be achieved! It is the reason why many pads are grooved.......
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Old 28 Jul 2007, 19:21 (Ref:1975403)   #13
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Cross drillings in the discs prevent the pads aquaplaning for a couple of revolutions of the wheel when you want to brake in the wet. Not noticable on cars, but most bikers can tell you about how heartstopping that lag can be when need to slow down urgently. Most bikers use drilled discs. Slotted face discs do the same sort of thing, they just instantly clear the water from behind the pad, but aren't as pretty imho. Don't think it matters much what the pattern of holes is or what direction the grooves point, just so long as they're evenly distributed across the pad. As for the gassing thing, not got any hard info on that, but sounds likely in high temp situations like racing, and obviously needs to be cleared from behind the pad for similar reason. Do remember though, that the pad can only work on metal, not air, so don't go for discs with too many holes or slots. That'll just reduce your braking capacity. :-)

Last edited by dtype38; 28 Jul 2007 at 19:30.
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Old 28 Jul 2007, 21:03 (Ref:1975443)   #14
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Do remember though, that the pad can only work on metal, not air, so don't go for discs with too many holes or slots. That'll just reduce your braking capacity. :-)
Friction is independent of area, so that statement doesn't hold true.
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Old 29 Jul 2007, 01:04 (Ref:1975519)   #15
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Friction is independent of area, so that statement doesn't hold true.
I've never quite understood that, if the area is nil (i.e. no disc) they still work ?
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