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How much does brake rotor slot direction really matter?

Jabbit

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#1
Installed my front brakes per the Whoosh website and several articles I found. Then I looked at the rear. Which is correct and does it really matter?

20221023_195611.jpg 20221023_205239.jpg
 


jeffreylyon

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#2
The second photo is of the correct direction. The vanes act as a centrifugal pump, slinging the hot gas out. It makes no difference on a street car and plenty on a track car.
 


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Jabbit

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Thread Starter #3
The second photo is of the correct direction. The vanes act as a centrifugal pump, slinging the hot gas out. It makes no difference on a street car and plenty on a track car.
But what about this picture from the Whoosh website?

Screenshot_20221023-214103_Chrome.jpg
 


Woods247

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#4
My Stoptechs are side specific and look like the Whoosh pic:

59789F06-3340-4DAB-8898-6DC517A606A6.jpeg DAB68328-C1EC-4DF2-8BD0-8FEAB24F203D.jpeg
 


jeffreylyon

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#5
My Stoptechs are side specific and look like the Whoosh pic:

View attachment 52141 View attachment 52142
I just rabbit-holed. Apparently, some brake manufactures run the slots in the same direction as the vanes, some run them in a different direction. My Wilwood’s have slots that run in the same direction as the vanes, so opposite of the StopTechs. i think that the safe way is to check the vanes and run them in such a direction that they pump air from the hub to the rim. If the vanes are straight, do whatever you want.
 


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Jabbit

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Thread Starter #6
You make a good point - the vanes should be throwing air away from the hub. The actual slots on the rotor would be secondary. I'll pull the wheels off this week and verify the cooling vanes are correct.
 


jeffreylyon

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You make a good point - the vanes should be throwing air away from the hub. The actual slots on the rotor would be secondary. I'll pull the wheels off this week and verify the cooling vanes are correct.
I think that the Whoosh graphic that you posted show the vanes running opposite to the slots.
 


Crv

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#8
My mountune stoptechs also….I remember reading at one point that either way is viable…but the pictured option is more aggressive on pads and also has an improved effect although not a dramatic one..


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#9
It all depends on what the brake manufacture specifies on internal vane direction and not so much on the slotting.
 


Dialcaliper

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#10
It all depends on what the brake manufacture specifies on internal vane direction and not so much on the slotting.
Second this - internal vanes are sometimes curved or angled and it’s important to get them the right direction. Most OEM rotors on normal cars are just straight vanes and can go either way.

Slots/drilling on the surface don’t matter directionally and don’t really do much with modern brake pads besides look cool and wear out pads faster. Even track pads don’t need them with compounds that don’t get overheated easily. The only really useful thing they do anymore is a reference indicate the internal vane direction.

Slots and drilling came about because old asbestos and metallic pads that were not really good for track use, basically running constantly overheated so they glazed and offgasssed when pushed hard, and the solution was to have slots to scrape the pads clean and holes to vent the gasses.

As long as you’re using adequate pads and not running into pad fade (firm pedal low friction), they don’t do much. If you are trying to track on street pads, maybe it would make a difference, but it’s cheaper to just buy the right pads than burn through crappy pads.
 


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