malone

Could someone explain why slotted rotors are better than drilled for track use.

ryoung

If both sides of the holes are chamfered, drilled holes can work well on a solid rotor. This is the rotor from our Formula Continental. In this case, we drilled the rotor to reduce weight, not to increase bite; and these rotors wear without problems or cracking.

<img src="http://pictureposter.audiworld.com/17157/drilled.jpg">

However, it's not practical to chamfer the inside of the holes on a vented rotor. The sharp edge that remains inside becomes an area of high localized stress and can initiate a crack, such as you see here with a Brembo rotor that's been on track.

<img src="http://pictureposter.audiworld.com/17157/crackedbrembo.jpg">

A slotted rotor normally doesn't have these areas of high localized stress. This is what remains of my slotted Alcon rotor after ~1500 miles on track (note that the slots are 99% worn away). Though the rotor eventually did crack, none of the many cracks were initiated by the slots.

<img src="http://pictureposter.audiworld.com/17157/alcon_05.jpg">

But you can screw up even slotted rotors. Notice that the slots on my Alcons don't go to the edge of the rotor.

<img src="http://pictureposter.audiworld.com/17157/alcon_rotor.jpg">

If you mill the slots all the way to the edge, a point of high localized stress is again created, with the predictable result apparent in this Powerslot rotor.

<img src="http://pictureposter.audiworld.com/17157/crackedpowerslot.jpg">

A crack can result in catastrophic failure on track, enough of a reason IMHO to not use drilled rotors in this application. A less severe problem with drilled vented rotors is the unavoidable buildup of brake dust inside the rotor. A layer of dust on the rotor internals becomes an insulator and hurts heat transfer, the last thing you need on track.

... and our Formula Continental at the Chicago Auto Show :-)

<img src="http://pws.prserv.net/usinet.Young/photos/chicagoautoshow.jpg">

malone

Wow! That all makes sense now. I knew there had to be a good reason. Thanks for the write-up!

CP

I just checked and my Stoptech's slots don't go to the edge either. But my stock-sized Brembo rotors' slots do.

ryoung

Or were they plain face Brembo's slotted by someone else? None of the 26 different slotted Brembo's <a href="http://www.hrpworld.com/index.cfm?form_cat_id=256,164,49,363&action=catego ry">Here</a> mill to the edge of the rotor.

<img src="http://www.hrpworld.com/client_images/ecommerce/client_39/products/1000_1.jpg">


<img src="http://www.hrpworld.com/client_images/ecommerce/client_39/products/4810_1.jpg">

CP

That fit a 1991-94 Mitsubishi and are 10.1 or 10.9" stock replacement rotors...not fancy racing brakes (I use Stopetchs in the summer). All 3 sets I've got (one set vented front, 2 sets solid rear) have the slots right out to the edge.

DevilsEgg

wow i actually never seen cracked slotted, drilled yes but not slotted

ryoung

It's probably just as well that I forgot who's rotor this is :-)

<img src="http://pictureposter.audiworld.com/17157/crackedsolidrotor.jpg">

Audi_kraut

do you think drilled rotors will hold up under street use? i was considering getting a pair...

ryoung

Just don't drive aggressively down any mountains in Colorado.