Brake Discs - rotation for front slotted discs

[kiwipetrolhead 1]

Hi there,

I have a pair of new slotted front discs for my e21. Problem is, because the slots are angled, I'm not sure which is the correct rotation. Please see pic - should "A" or "B" be the front of the car?

Hopefully this and a few other things will prevent the brakes from overheating around Manfeild, so long as the rotation is correct.

Thanks

Paul

[Yuen 16]

Hi there,

I have a pair of new slotted front discs for my e21. Problem is, because the slots are angled, I'm not sure which is the correct rotation. Please see pic - should "A" or "B" be the front of the car?

Hopefully this and a few other things will prevent the brakes from overheating around Manfeild, so long as the rotation is correct.

Thanks

Paul

"the easiest way to verify correct usage is to install the rotors on the side of the vehicle that results in the end of the slot nearest the outer edge of the rotor always contacting the brake pads first."

Taken from: http://www.tirerack.com/brakes/brakes.jsp?...t+Slotted+Rotor

So it sounds to me like B.

[btccm3 1]

iv got slotted rotors on my m3 and they spin anti clockwise in your diagram.

the idea is the slots free themselves of debris when spining

the ones on mine are side specific so you cant get them wrong

and they had a little L on the left one and a little R on the right one.

Edited February 5, 2007 by btccm3

[kerrynzl 3]

Yuen is correct [Accordng to the Brembo article]

On my race car, I have Curved Vane Rotors [vented], the brake cooling ducts go to the centre of the rotor and the directional spinning acts like a cooling fan in the rotor [early 80's F1 cars had wheels that were similar] so on my race car the answer would be 'A'

[cainchapman 0]

McMillans fitted mine and 'A' to the front of the car is how they. On the rears.

[E30-323ti 66]

Curved Vane rotors are quite different, and yes vent from the centre out so rotation direction is very important.

Slotted rotors (ie. surface treatment) isn't as critical, but I'd install them with A to the front of the car.

Are both rotors slotted the same direction?? or one of each for left & right sides??

[kiwipetrolhead 1]

Yuen says "B" and he is supported by the Brembo webpage which states...

"Brembo Sport slotted brake rotors are sold in axle pairs and the easiest way to verify correct usage is to install the rotors on the side of the vehicle that results in the end of the slot nearest the outer edge of the rotor always contacting the brake pads first."

btccm3 says "A" (based on what he says) and a pair on his car are fitted according to an "L" or "R". Mine don't have any "L" or "R" to indicate.

kerrynzl says that Yuen is "correct [Accordng to the Brembo article]" (so that's "B"), but then he goes on to say that "A" is the correct rotation. Hmmm...

cainchapman thinks "A" too, based on McMillans fitting of his pair on the rear.

E30-323ti mentions curved vanes, which I agree are different - mine also have the centre vanes which I think are slightly curved, but it's hard to tell for sure if they are curved. So while it might be true that the rotation of slotted discs is less important than the rotation of curved vanes, I have to get the direction correct because of the vanes in mine. But E30-323ti also thinks "A" is correct - again different to the Brembo brake article.

So you see my dilemma now? I think I will go for "B" then, thanks to Yuen's help, despite the majority of 'votes' (and kerrynzl's apparent confusion being for "A". More comments welcome though, I'll be fitting them this weekend.

[kerrynzl 3]

Mine Isn't confusion Mate!

I stated that on curved vane [with vented rotors] it is opposite because of a cooling system [similar to a centrifugal impellor]

Slots on rotors serve two purposes:[the vanes are for cooling]

1: to clean residue

2: more importantly remove the gas build-up between the pad & rotor [commonly known as Green-Fade]

When Brembo makes a statement, they are using their products are a direct replacement for stock rotors [so I'd assume the backing plate is left intact, which changes airflow compared with ducting]

[E30-323ti 66]

I would have them in the A direction due to the same centrifugal (or is it centripetal!?!?) reasoning behind the curved vane rotation direction.

Why would you want any pad deposits, gases, whatever to be ushered to the inside of the rotor, where they can only disperse back past the rotor face!?!?! But I'm sure it doesn't matter that much either way.

If the literature say's "B" then "B" it is.

I'd put them on "backwards" but thats just me.

[kerrynzl 3]

90% of Vented Rotors are Straight Vane [easier to manufacture] but the same principles apply.

I can only assume Brembos comments are in relation to the using of a backing plate [where air enters from the outside and moves towards the centre]

[Yuen 16]

A subject of much debate! Tried to find some more info for you:

http://www.stoptech.com/tech_info/faqs.shtml#16

"The direction of the slots or hole pattern should not be used to determine what side of the vehicle to place a rotor. Different manufacturers may have different strategies for slot and hole patterns.

The only correct way to determine what side a directional rotor goes on is the internal vane direction. "

http://www.buybrakes.com/brembo/faq.html#q28

"Which direction should the discs rotate?

It is a popular misconception that the slots or drillings in a disc determine the direction of rotation. In truth, for an internally vented disc, the geometry of the vanes dictates the direction of rotation. There are three vane types in use:

1. Straight

2. Pillar vane (comprised of many small posts)

3. Curved vane

The first two vane types are non-directional, and can be used on either side of the vehicle. The curved vane disc, however, is directional. A curved vane disc must be installed with the vanes running back from the inside to outside diameters in the direction of rotation. Please see figure. Orienting the disc in the manner creates a centrifugal pump. The rotation of the disc causes air to be pumped from the center of the disc, through the vanes, and out through the outside diameter of the disc. This greatly enhances the disc's ability to dissipate heat.

Additionally, all of Brembo's slotted discs are directional as well, regardless of the vane geometry. The discs should be installed such that the end of the slot nearest the outer edge of the disc contacts the pad first. Please see figure."

[kiwipetrolhead 1]

A subject of much debate! Tried to find some more info for you:

http://www.stoptech.com/tech_info/faqs.shtml#16

"The direction of the slots or hole pattern should not be used to determine what side of the vehicle to place a rotor. Different manufacturers may have different strategies for slot and hole patterns.

The only correct way to determine what side a directional rotor goes on is the internal vane direction. "

http://www.buybrakes.com/brembo/faq.html#q28

"Which direction should the discs rotate?

It is a popular misconception that the slots or drillings in a disc determine the direction of rotation. In truth, for an internally vented disc, the geometry of the vanes dictates the direction of rotation. There are three vane types in use:

1. Straight

2. Pillar vane (comprised of many small posts)

3. Curved vane

The first two vane types are non-directional, and can be used on either side of the vehicle. The curved vane disc, however, is directional. A curved vane disc must be installed with the vanes running back from the inside to outside diameters in the direction of rotation. Please see figure. Orienting the disc in the manner creates a centrifugal pump. The rotation of the disc causes air to be pumped from the center of the disc, through the vanes, and out through the outside diameter of the disc. This greatly enhances the disc's ability to dissipate heat.

Additionally, all of Brembo's slotted discs are directional as well, regardless of the vane geometry. The discs should be installed such that the end of the slot nearest the outer edge of the disc contacts the pad first. Please see figure."

Excellent, thanks Yuen,

I have checked and the vanes in my discs are straight, so the correct answer to my question, based on what you said already as well as this new info is indeed "B" (although there is some debate in the industry...). I put them on over the weekend, but as per "A". Still, according to Race Brakes (Auckland) who I emailed late on Friday, it does not matter too much which way slotted discs rotate (so long as the internal vanes are straight).

So while it does not really matter, I will switch them over as per "B" sometime soon anyway.

FYI, here's a 'Copy And Paste' from Race Brakes' reply...

Steve Currie of Race Brakes 0800 Brakes said...

"Assuming they are not curved vane rotors, and I don’t see why they would be, I would normally advise that B is forward i.e. right hand rotor in photo. This is the short answer.

DBA’s website will contradict this, but that now becomes the long answer. Truth is, it doesn’t really matter unless you are an F1 team looking for 100ths of a second. Then you wouldn’t be using cast iron rotors anyway."

(I don't know who DBA are exactly, but I assume they are some other brake manufacturer.)

So, "B" it is, but really it does not matter too much.

Thanks for everyone's comments, much appreciated and I think we all learned something new out of this thread.

Paul

[kiwipetrolhead 1]

A bit more on this topic, more sutff I just received from Race Brakes (they are very helpful guys)...

"If you care, I’ll give you the long answer.

All the serious race rotor manufacturers (Brembo, Alcon, AP Racing) go “B†for increased bite. Although most have gone away from straight slots and now use a variety of patterns that can look like fish hooks or spaghetti. If you are using curved vane rotors, you are obliged to fit them one way only and the slot pattern ends up where it will (always B that I have seen).

DBA in Australia are the only company that recommends A. When I questioned them as to why they thought they knew better than F1 manufacturers, their (feasible) reply was that since most of their rotors go onto road cars, having the slots the “wrong way around†helped to decrease noise and didn’t throw brake dust onto the wheels as badly. I do notice however that any curved vane rotors that they make, such as the 355mm FPV GTP fronts, have the slots going the normal motorsport "B" way when fitted with the curved vanes going in the right direction i.e. discharging the hot air like a water pump impellor, not scooping it in as a lot of people (race car owners) seem to think.

Cheers,

Steve

Race Brakes 0800 Brakes

351 New North Road

Eden Terrace

Auckland

New Zealand

Ph: ++64 9 377 2000 or 0800 Brakes (272537)

Fax: ++64 9 377 2100

Web: www.racebrakes.co.nz

E-mail: info@racebrakes.co.nz"