Grooved Discs Rotation Pattern

[Ruddmeister]

There are 2 piece discs I have seen with curved vanes in the disc which are designed to evacuate heat.

These are single piece disc's and the vanes in the centre of the disc are straight not curved if I recall? these types of vanes are more about structural rigidity and have very little ability to evacuate heat in the way described above AFAIK

 

[CupraString]

http://i662.photobucket.com/albums/uu349/Cuprastrin/Leon030.jpg

 

[james.l]

well that is quite a lot of science to take in on a wed afternoon, trying to get my head around this, will inspect my discs later and try and work this out.

 

[Paul D]

The direction of curve of the vanes in the inside the vented disc wont matter (neither if its flat) in terms of direction of air flow.

In centrifugal fans you can have forward curved, backward curved or flat blades, it just changes the characteristic of the fan - more pressure developed vs airflow etc. The air will still flow from inside to outside.

Think of the disc rotating at speed. The inner edge moves more slowly than the outer edge. This causes a pressure difference which then causes the air to move from inside to outside (the faster moving air is evacuating the disc too quickly to be replaced by the slower moving inner air). Thus more air is drawn into the disc.

To answer the OP question though, if the discs are marked left/right then follow this, if they aren't ask the manufacturer. If they are unsure, then take your pick - and see my previous post about performance, noise, pad wear!

As such the forward curved blades will not 'scoop' air in - that defies physics as the air will be forced the opposite way by centrifugal force.

 

[Ruddmeister]

I can see the theory but don't think there is a great deal of 'airflow' in practice, certainly not compared to the volume of air cooling the surface of the disc via ducts etc. I think the vanes design are all about strength, weight reduction, separating the faces the two pads make contact with and reduction of warping. The airflow may be a added extra benefit but I'd guess it's small

I understand the R8 has curved internal vanes that are in opposite direction O/S to N/S (front)suggesting that the cost of changing the casting moulds is way more expensive than any benefit from this 'airflow' theory

it's an interesting question for sure

 

[Slimy]

Think of the disc rotating at speed. The inner edge moves more slowly than the outer edge. This causes a pressure difference which then causes the air to move from inside to outside (the faster moving air is evacuating the disc too quickly to be replaced by the slower moving inner air). Thus more air is drawn into the disc.

As such the forward curved blades will not 'scoop' air in - that defies physics as the air will be forced the opposite way by centrifugal force.

Have a look at my 'Whirly' link, they actually dismiss the pressure difference theory as being negligible, compared to the force of air flow made by centrifugal force. I made that mistake initially, but then reading about it suggested that while it does happen, it's not the main factor.

Ruddmeister, I'm not convinced there is only a little cooling effect coming from the vents. If there wasn't an airflow, why would they be called 'vented' discs?

 

[Ruddmeister]

why would they be called 'vented' discs?

Marketing?

Lets just say the jury seems to be out on effectiveness although I can appreciate the theory it seems to be just that

I'm not ruling anything in or out.......seems to be very little definitive info on this

 

[Muttley]

Well, for what it's worth (about 2p in old money) I think the main advantage of vented discs is the increase in surface area. In the same way that a double radiator on your central heating can put a lot more heat into the room, the vented disc has twice the surface area of a solid disc and can radiate a lot more heat energy into the surrounding air. In order to be reasonably efficient the air in the vents has to move, so that cool air replaces the air heated by the disc, but as has been said above, just spinning the disc will do that. There may be some advantage at the very edge of performance, but none of us is ever going to approach that on the road.

 

[DPJ]

Well, for what it's worth (about 2p in old money) I think the main advantage of vented discs is the increase in surface area.

Good point.

 

[Slimy]

Well, for what it's worth (about 2p in old money) I think the main advantage of vented discs is the increase in surface area.

Never really thought about it like that, that probably makes the most sense! In fact, it's not just double the surface area, each vane would add more surface area, and so make it even more efficient at cooling down.

 

[james.l]

just checked my discs again, there is definatly no left or right, they are EBC plain discs grooved by CRN, does it matter if the fronts are on differantly to the back?

 

[james.l]

am still really confused as what to do with the fitting of these. Will try and phone CRN or EBC

 

[Slimy]

If they're EBC plain discs, then they're not 'handed', so EBC won't be able to help. As most of this talk has been related to the internal vents, and the EBC discs don't care which way round the vents go, I'd just put them on so the grooves sweep outwards as they turn.

 

[ibizacupra]

Not necessarily always the case, the disc could be designed to use rotational force to suck in air from the centre and disperse it outwards.

Not in the case of the ones here

The EBC or Std Brembo vents are not directional at all
Competition Rotors (like I use on mt 2-piece setups) are directional cooling vanes, and it is the cooling vane which sets the disk handing.. so ducted air from the curved internal vent pulls air in from the inside and spills it on the outside edge

Lean back grooves are said to be less aggressive
I usually put them on lean back as pictured on my earlier post

 

[ibizacupra]

I could see that a disc would suck air in at the centre and blow it out at the circumference if there were fan type blades at the centre - but I havent seen any that have that.....

My 2-piece rotors are like this

 

[Gezzy]

i thinks people do fit them with the groove leading away from direction of rotation simply for the asthetics as it does look better but it doesnt really matter

 

[Gezzy]

the reason they are vented is to keep them cooler vent dust away and also gives water a chanel to filter out instead of it being sat on the face of the disc

 

[ibizacupra]

for DPJ:
this one shown, with internal curved venting would be a NS disk
Note the grooves in that instance would be deemed "backwards" to the norm as they face fwds in the more "aggressive" & noisier way

I reccommend eliptical and Ultimax to most people as they are quieter running disks, and eliptical are simples as they are omnidirectional

 

[DPJ]

for DPJ:

Not sure what you're trying to explain to me here, Bill.

 

[ibizacupra]

Not sure what you're trying to explain to me here, Bill.

groovey baby