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 Post subject: Disc Brake Rotor Slot Direction: Pinwheels and Buzzsaws
Unread postPosted: Mon Jan 14, 2013 12:41 pm 
Moar Dew.
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Joined: Wed May 16, 2007 6:17 am
Posts: 8301
Location: North Syracuse, NY
Lots of misconceptions regarding slot rotation... I wrote the following material on the SVX Network ~5 years ago, and I posted it on Miata.net earlier. I refreshed the links and quotes, which still hold true. Keep in mind that the vanes are inside the rotor (when not solid, of course) - not to be confused with the slots.

The material I've read in forums as well as name-brand pages (StopTech, Baer, etc.) indicates that the direction of the slots is often inconsequential, so long as the vanes are appropriately oriented.

Regarding StopTech's Power Slot: <Power Slot install .pdf>
StopTech wrote:
Unless the vehicle manufacturer specified otherwise, rotors with directional vanes are to be installed so that at the top edge of the rotor, the vanes sweep toward the back of the car.
...
Slots perform their function identically regardless of direction. Only in the case of "straight" vane or solid rotors, if a customer prefers the appearance, rotors may be installed with the slot direction reversed.

Brembo says half 'n' half of that, too: <linky>
Brembo wrote:
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:
■Straight
■Pillar vane (comprised of many small posts)
■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. 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.

It's probably safest to go by application, by brand.

Considering that the amount of gas that the slots are responsible for capturing is slight, that both ends of each slot are open to atmosphere, and that most of the way around, the slots are completely exposed, I'd follow the vanes first, manufacturer's guidance second, and (in indifference expressed by the components and their manufacturer) aesthetics third.



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