16 replies to this topic

[Spitz]

Which way should this rotate?
Would forward direction ( by the picture ) be to the left or right?

Thanks


edit!
Just found the answer.
There is a label still visible on the rotor ( for us idiots ) that this is for the right side of the car.

Edited by Spitz, 30 July 2012 - 10:11 PM.

[L400RAS]

Imagine the grooves to "fling" the brake dust outwards when driving. This is a passenger side disc for UK cars (RHD), or a drivers side for left hand drive.

[tiger99]

I agree. The label is wrong. That is very clearly for anticlockwise rotation.

[Spitz]

mmmmm....label clearly states "for right side of car" for the pictured one ( Left side is labelled on the other ), So that is the way I installed.
Not looking forward to having to swap them around if this is wrong.

[tiger99]

It is definitely wrong, and will impair the cooling.

[Spitz]

According to this, I have them correct. ( although this shows vented...mine aren't vented )



(not mine...just an example )

[tiger99]

This is now quite different!

The diagram is correct, if the red lines are the vent slots. The blind ended grooves in the latest picture are not for cooling air, they are for pad glaze busting, squeal suppression etc, and because they don't carry much air they are facing the wrong way, to tend to force the pad inwards. The picture of the disc on the car is the same, the slots are blind ended. In your very first picture, the surface slots were open ended and therefore for cooling, and were wrong.

There are two ways of thinking about it, firstly the centrifugal force (a popular myth, but never mind, it helps explain the facts) throws the cooling air outwards, so the exit must be backwards with respect to rotation, otherwise ram effect would bring air in to oppose the air which was trying to get out.

The other way gets involved in conservation of angular momentum. The air moves outwards, and for constant angular momentum must lose rotational speed, so again the slot must exit backwards.

I assume that the discs are vented as well as being grooved. The orientation of the internal vents is far more important than that of the surface grooves. Poke something down the holes and check that, if they are handed, the exits are facing backwards. Original Metro vented discs were handed, they later changed to straight vanes, not quite so efficient, but only needs one part to be stocked,

[jaydee]

Why half disc is drilled?

[Spitz]

Why half disc is drilled?

The others are just in the shadows and blocked by the wheelnut.
So I have them on right then.....as per the labels on them. In the very first picture...rotation is to the right..(.as in...that is on the right side of the car )

I installed these ( bought used ) to get rid of the horrible brake sqeel...it has worked

Tiger....mine ( very first pic ) are not vented discs

Edited by Spitz, 02 August 2012 - 08:50 PM.

[tiger99]

If you are very sure that the grooves are not for cooling, then they would be correct, but if the grooves are for cooling, wrong.

[jaydee]

The grooves are supposed to clear the pad surface from dust, but installed that way, where dust will escape from during the rotation?
dust will be took to the center of the disc by the groove, and not out of the disc, if you get what i mean.
I dont want to say its a manifacturer error as they are supposed to be better engineers than me and there should be a reason why the choose that direction. But, air or dust or whatever flows in those grooves makes no difference in the concept and what tiger is saying sounds more correct to me...
If you put the disc in the very first pic on the left side, once it rotates air will flow from the centre of the disc to the outside, cleaning brake pad dust away from disc surface minimising brake fade and pad glazing.

[tiger99]

jaydee, I agree with that, and as you know, the dust will follow the air flow, which is plain wrong in that orientation, but was thinking that there was also another factor at work. If you orient the discs correctly for air and dust flow, you also apply outwards pressure to the pads, which are retained by relatively weak fixings, while the other way the pads are pulled inwards, and either bottom in the caliper or at least on the hub if the retainers break, rather than being ejected. Now I know that the chance of that happening is almost zero, but it is likely why they chose to do it that way.

Another factor is brake squeal, which is very poorly understood, and as many people here will have experienced, difficult to eliminate sometimes. Possibly they found by trial and error that they squeal one way and not the other.

[Ethel]

There are 2 edges to each groove, why would the 2nd throw the pad inwards more than the 1st throws them out?
If it does, why would that be an advantage? The further the pad is from the axis the greater leverage.
Surely any groove is open ended unless it's totally covered by the pad?

Not that I can understand how removing a large part of the surface area improves a frictional brake anyway


.....I can just about see the logic in the ejecting pads. What about slide calipers, are posey performance discs different for them?

[The Principal]

Hope this helps, borrowed from the EBC website - EBC’s Turbo Groove Brake Discs feature a unique wide “high volume” slot design that runs to the outside edge of the disc allowing the dust, debris, gasses and carbon deposits to be “spun off” from the braking disc surface, further improving braking. The blind holes prevent cracking and help to break down surface gasses of the brake disc/rotor to further improve braking under heavy load.

[tiger99]

Ethel, both edges of the groove will throw the pad in the same direction, although the leading edge of the groove will have much less effect than the trailing edge.

As to whether the slots are open-ended or not, it looks to me as if in some cases they will be fully covered by the pad.

The actual frictional force is not dependent on area to a first approximation, only the product of applied force and pad to disk coefficient of friction, so grooves will not reduce the braking torque. I see that the railway industry actually uses disks which are made in two semicircular sections, with a small gap in between, and they don't seem to cause any judder at twice wheel rotation frequency, even under heavy braking. Of course, a smaller area means less ultimate heat capacity.

The Principal, the EBC web site which you refer to is very interesting. As a mainstream brake manufacturer their products are seriously impressive, unlike certain aftermarket suppliers. See link below for a picture which clearly shows the outer ends of the grooves facing backwards with respect to wheel rotation, as simple physics says they should, if the purpose is to eject air.

http://www.ebcbrakes...rt_rotors.shtml

"EBC Turbo Groove and Spotty Discs are directional “LEFT and RIGHT” which is nearside and offside of your vehicle. The spotted pattern and the sweeping grooves should be pointing to the rear of the vehicle."