Topic: Weird drilled disc question

[Scott S]

 Is there an actual function to the direction of the slots or holes on a drilled rotor? Should the sweep or arc be facing forward or backwards (CW or CCW)? Or is it purely aesthetics?

[Xnavylfr]

I don't think it has to have a PATTERN! The reason they are drilled is to help remove some water from floating on the disc and causing them from HYDRO-PLANING in a sense.

Xnavylfr(CHUCK)

[Scott S]

 Right, I understand all that. I just wondered if there was a "backwards" and "forwards" or Left and Right, etc.

[Scott S]

 To clarify: I'm talking about when there's a pattern, like this for example.

[Harsh]

I believe the rotation should go forward.  For example, the rotor on the left (in your pic) would go on the right hand side and the other on the left hand side.

[Thousandson]

I have heard other wise. I talked to one shop owner he said CW.  I also drilled my disks like this.

[Cabilao]

It doesnt matter cw or ccw. the holes help you to get rid of water much quicker and helps also with cooling the disks if used on the race track or on long rides downhill when a lot of braking is needed. Normal disks tend to fading and drilled ones not. Dirt is also removed faster and some people say the pads last longer. dont know bout this. But drilled rotors in combination with braided hoses should improve the brakes.
just my 2 cents.

[wvshooter]

As far as function is concerned the pattern doesn't matter. What you want it to look like after it's finished does matter. If you like it, it's ok.

Two things you don't want to do. Don't use too many holes or such large holes that the rotor won't be able to stay straight or will become too weak. Also, don't drill holes in a way that will cause your wheel to become unbalanced. In other words, too many holes on one half of the rotor and too few holes on the other half. 

[TS250]

Pattern direction doesn't matter at all.  The holes help with brake action in wet conditions, and lightening the rotor (unsprung weight).  They don't help much at all with brake fade; I've had horrendous fade on a drilled single rotor (with steel line) 550 going downhill.  Dual discs help with fade, or at least extending the time it takes to heat the rotor/pad/fluid enough to fade.

One could make an argument that a drilled single rotor will fade quicker than a non-drilled rotor.  Less mass takes less time to heat.

[Viktor.J]

One could make an argument that a drilled single rotor will fade quicker than a non-drilled rotor.  Less mass takes less time to heat.

And many holes makes a bigger area for heat transfer. BUT Whether the new heat transfer area affects more then the decreased volume and therefor easier convection I don't know. Think you'll have to run some simulations and different cases to be really sure.

(Bigger heat transfer area > decreased convection or Bigger heat transfer area < decreased convection)

(hope you understand what I mean, English is not my mother tounge)

To answer the question: No, it doesn't matter if you made them identical. Is a wheel harder to spin clockwise or counter clockwise ? The wheel ( a circle) doesn't have a end, therefor no beginning, therefor no front or back ( you still have rotation direction on tires and such)

[TS250]

Oh for sure more surface area decreases cooling time.  They'll still heat up faster.  It's a compromise.

[zoolion]

I'm pretty sure the holes are to vent gasses created during the braking process that are released as the pad material wears. The layer of gas between the rotor and pad reduces friction, pad rides on a cushion of air. I think water gets boiled off pretty quickly, although the steam created could contribute to the gas effect.
I may be mistaken and this may only apply to carbon racing brakes.

[Stev-o]

Ever notice how high performance race cars [F1] do not have drilled rotors?

[Thousandson]

F1, and many others cars, including most commuter vehicles, don't have drilled disks. But they do have vented holes running in between two flat disks. More interrupted surface area = Less braking power.

[alancop]

In the world of autoX sometimes rotors are drilled and the holes are lightly filed in order to make them bite into the pad, giving you a massive amount of braking power, however this also wears the pads insanely fast, like 1 set per 3 or 4 runs.

[Viktor.J]

as mentioned disc for cars are already "ventilated". But however, take a look at the superbike bikes, all of them have drilled holes .... must be some reason:)

[cb650]

Also the "super cars" are carbon fiber and replaced frequently.

[TS250]

as mentioned disc for cars are already "ventilated". But however, take a look at the superbike bikes, all of them have drilled holes .... must be some reason:)

With the exception of the top-of-the-line MotoGP bikes.  Their carbon rotors aren't drilled. 

[Viktor.J]

I know ! But still they can make a disc of what they want
Superbikes dont, right ? Wonder why they drill, if Any racingrider know th
at would be great !

[Scott S]

 This wasn't really a question of WHAT the holes do or don't do....kinda got a grasp of that. I was just wondering if the DIRECTION of the holes/pattern has an effect. Apparently, No. Which is good: Now I can run one on each of my CB's!

[Stev-o]

Scott - just curious, why are you doing it?

[Harsh]

Well looking at my Triumph (that came with drilled rotors) my previous reply in regards to direction is incorrect.  I also looked at my buddies GSXR and SV, both of them follow how my Triumph is.  I don't know if it makes a difference or not, but manufacturers appear to do it that way so I would pressume there is a reason for it.

[Scott S]

Scott - just curious, why are you doing it?

 Becuase I'm sick of trying to get the RH side of my dual disc conversion to work properly. Three master cylinders, two different brands of pads, two different calipers, shims, spacers, grinding, alignment, etc.
 I either have very spongy, weak brakes, or the RH side drags. I can NOT get it straightened out. I'm going back to one disc and will use the other drilled disc on another bike.

[wvshooter]

Becuase I'm sick of trying to get the RH side of my dual disc conversion to work properly. Three master cylinders, two different brands of pads, two different calipers, shims, spacers, grinding, alignment, etc.
 I either have very spongy, weak brakes, or the RH side drags. I can NOT get it straightened out.

Sorry to hear about your problem. Sometimes things just blow up in your face.

I'm going back to one disc

I'm kind of old fashion, being old myself, but I like the "look" of the single rotor on the cb's. And as far as braking power goes who want's to lock up a tire anyway?