13 replies to this topic

[JimmyJamJerusalem]

Right bought a cheapo set of drilled and grooved discs.

I spoke to the supplier beforehand to make sure they were 'sided' so that the grooves etc would run in opposite directions which was confirmed.

However,

When I came to fit them I noticed that the vanes were not 'sided'. ie the vanes on each side was the same so one side was ok, but the other side wouldn't expel air.

This pic shows my understanding of how the vanes should work



I spoke to the supplier who replied with this

hi Jimmy
I understand the exact issue you are describing, but as far as I am aware all discs on the vx220 have vanes running in the same direction. We stock some BMW references that are handed, with the grooves running backwards on either side, but we have never had the vauxhall discs as handed,and we have never seen anyone selling the vx220 discs with the internal vanes handed from side to side. The external grooves etc do be handed, but not the inside.
Would this cause different cooling rates between the sides? I do not believe that it will. The internal vanes obviously do help to cool the discs, but the difference in direction will not cause a realisable difference in temps between the sides.
If you are still unsure about this, we can offer you a collection and a refund. The last thing we want is for you to be unhappy with your purchase. I can wholeheatedly say that the discs are fine, but I do understand your position too.
Thanks
Gavin

A perfectly reasonable answer, but what do I do....? Is this a significant enough issue to reject these discs..?
Are most fronts like this anyway..?

[markiii]

they should be sided as you want the vanes going the same way on all 4 wheels whether you have them face back or forwards is a matter of debate can't speak for you Jim but it would be enough for me to reject them

[rcvaughan]

Wouldn't centrifugal forces just throw all the air outwards anyway?? And the AP venting still looks a LOT better than standard. Perhaps speak to the manufacturer directly rather than suppliers Loving the ATS wheels btw Jimmy - they're what i really wanted for the Yellow Peril. Shame they've changed the regs away from R888s.

[-Dab-of-Oppo-]

(markiii)

Does not seem right to me. My old un-grooved (OEM?) discs I have just replaced had side specific internal ducts.
The new ones I fitted below where also clearly suited for left & right and where even stamped as such.



Air will naturally be forced out, but the grooves must aid this at least to some extent otherwise why bother with the increased manufacturing costs? Having them fitted the other way could possibly cause a slight buffeting and/or whistling noise?

Edited by -Dab-of-Oppo-, 26 March 2011 - 02:08 PM.

[Arno]

Wouldn't centrifugal forces just throw all the air outwards anyway?? And the AP venting still looks a LOT better than standard.

Correct. The majority (99+%) of the cooling is based on simple centrifugal forces pushing the mass of air outward from the hub.

Curved vanes inside the disc were originally only used to stop brake 'chattering' when the discs got hot.

If you use purely straight vanes inside the disc that radiate outwards without a curve then the surface of a hot disc will have a slight 'ripple' effect because of the difference in cooling and expansion between the parts of the disc exposed to air and the pieced where the metal of the vanes is located.

Because these 'ripples' are perpendicular to the brake pads they will hit the bumps head-on and this usually results in brakes that rattle and the pedal vibrating.

To combat this the manufacturers curve the vanes inside the disc. The distortion of the disc surface still remains, but now the 'edges' of the bumps are curved on the surface and as the disc rotates the pad will 'ride' more gently on each bump as it will cross the edges more diagonally.

Some manufacturers still use straight vanes, but combat the distortion by making the steel of the discs (much) thicker and reducing the air-gap. This works, but runs the risk of overheating the discs if you load them more like on track as they now have increased heat storage capacity because of the increased mass, but reduced heat shedding capacity because of the smaller air-gap and reduction in air flow between the disc surfaces.

Eg. Elise S2 OEM discs are not 'handed' and the vanes curve 'backwards' on one side. EBC's for Elises are the same AFAIK.

In motorsport applications it was found that if you make the internal vanes 'handed' so they point backwards at each side as the wheel turns then you get just a liiiiitle better/equal cooling on the discs left and right and this is a 'Good Thing ™' in this application.

So most AP, Alcon, etc. motorsport discs will have 'handed' internal vanes.

The effect is limited though and most people will probably never even notice any difference.

Grooving on the outside surface of a disc and it's direction viewed on the car is a completelty different story and not related to this...

Bye, Arno.

[Wolfstone]

If it helps, I have just checked a pair of new OEM drilled discs that I have in the garage and they are not sided.

[Tony VXR 56]

The new ones that I got recently are not sided and they are performing well.

[zx9rjason]

I bought drilled discs off ebay from seller "MTEC", whilst they look good I feel they are very heavy and have had a slight imbalance in the steering wheel ever since fitting. Wont be buying from them again, just a heads up really!

[Tony VXR 56]

I bought drilled discs off ebay from seller "MTEC", whilst they look good I feel they are very heavy and have had a slight imbalance in the steering wheel ever since fitting.

Wont be buying from them again, just a heads up really!

I have no complaints about my MTEC discs - combined with the CL5 pads I am very pleased with the performance.

I'd like a set of the more expensive AP discs but not sure my track skills really require it yet.

[Crabash]

Noticed the same and just put it down to buying cheapo disks, extra cost of making handed pairs. Put em on and no ill effects, maybe if cooling was marginal it would make a diff, not sure though. Mine been fine with RS14's and RC5+'s

Edited by Crabash, 26 March 2011 - 04:57 PM.

[JimmyJamJerusalem]

Excellent infor guys, thanks a lot (especially Arno, cheers for the info ). I think the difference will be marginal so will go with the cheapy discs. They are the MTEC discs by the way. Hopefully, I'll be hooking them up to a cold air feed anyway so that should take over the cooling duties anyway.

[Boombang]

I bought drilled discs off ebay from seller "MTEC", whilst they look good I feel they are very heavy and have had a slight imbalance in the steering wheel ever since fitting.

Had a customer long time ago who had a similar feel, then when brakes were really hot a slight judder.

Strip down revealed small amount of dirt between discs and hub.

Possibly not the issue but worth a look.

[Sammy]

Wouldn't centrifugal forces just throw all the air outwards anyway??

(I'll leave now).

[Seb.F]

Indeed, centrifugal is only present in non-inertial applications It is in fact centripetal! However, I did a bit of checking into this when I got mine, and in practice it won't make much difference and it's perfectly fine to run like that