Mounting drilled rotors

I recently replaced rotors on my RF98K front brakes with drilled rotors (LD20's) from Primus. The rotors have a lightly drilled pattern sweeping from the inside, to the outside. When I Googled "Mounting drilled rotors" I found different articles on which direction the sweep of holes goes, both forward and back. All of the responses I found dealt with finned, two-layer rotors which are common on heavier street cars. Does it matter which direction the sweep goes on the single -layer formula car rotors, and why??
Thanks in advance!!!
Cheers
John
480-250-4727

I'm no authority, but I imagine if the holes sweep inside to outside you might get a little better air flow through them. OTOH, if there is any sort of leading edge on the holes you'd get a cheese grater effect on the outside pad. If the holes sweep the other way the grater is on the inside pad and dust may tend to accumulate.

Look forward to more informed opinion..

The direction of the hole pattern is inconsequential. What is important is that as the holes sweep past the pad, they cover the entire pad. The holes are to clean the material that is worn off the pad as the pad presses against the rotor. The theory is that the holes will improve braking because it removes loose material between the pad and the rotor and they will reduce taper ware for the same reason.

But there is a down side. The holes will cause cracking and as the rotor wares you must insure that the edges of the holes are chamfered, other wise pad ware will become excessive. The rotor will also operate at a higher temperature because there is less rotor mass and friction surface for the pads to operate against. This also reduces the braking potential. With the newer type friction materials, keeping pad and rotor temperature up can be an issue with brake performance. With the holes, the rotor cools more rapidly after each application setting up the potential for thermal shock which will lead to cracking.

Primus is a reputable supplier. When you buy drilled rotors you want very good materials or the rotor won't last the season. Some suppliers have gone to steel rotors but the coefficient of friction is way less than with cast iron so the brake won't perform as well.

I have made very good money making and selling drilled rotors but my preference is for groves instead of holes to clean the pad surface. You have a lot more rotor surface to operate against. You can't stop a car by squeezing air.

Quote:

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Originally Posted by S Lathrop

The direction of the hole pattern is inconsequential. What is important is that as the holes sweep past the pad, they cover the entire pad. The holes are to clean the material that is worn off the pad as the pad presses against the rotor. The theory is that the holes will improve braking because it removes loose material between the pad and the rotor and they will reduce taper ware for the same reason.

But there is a down side. The holes will cause cracking and as the rotor wares you must insure that the edges of the holes are chamfered, other wise pad ware will become excessive. The rotor will also operate at a higher temperature because there is less rotor mass and friction surface for the pads to operate against. This also reduces the braking potential. With the newer type friction materials, keeping pad and rotor temperature up can be an issue with brake performance. With the holes, the rotor cools more rapidly after each application setting up the potential for thermal shock which will lead to cracking.

Primus is a reputable supplier. When you buy drilled rotors you want very good materials or the rotor won't last the season. Some suppliers have gone to steel rotors but the coefficient of friction is way less than with cast iron so the brake won't perform as well.

I have made very good money making and selling drilled rotors but my preference is for groves instead of holes to clean the pad surface. You have a lot more rotor surface to operate against. You can't stop a car by squeezing air.

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Hey Steve,

I just mounted a set of drilled and slotted rotors on an '04 Z06 street car. The holes were nicely chamfered, and the company touted much better cooling with the drilled holes, and the slots would wipe the gas and debris giving the pad a clean surface to act upon. This is not a track car, and so far the brakes feel much better than OEM Z06 stuff.

I realize there is less total rotor area and you can't stop by compressing air, but so far, so good on this street application.

Regards,
Bill

Bill;

In a street application, this stuff looks cool and zoomy. And the cleaning process of the pad and rotor is more of an issue for good street brakes. But race cars are a different applications.

In racing, brake heat management is critical, especially with pads like PCFs. The coefficient of friction changes a lot with temperature. You need to keep the pads in an operating zone to get good performance. The worse thing you can do is run the pads too cool and have the brake performance changing during the brake application. An example is brakes that lock up just as you start to release them.

This release issue was a problem with the FF in the early years of using PFC pads. The cure was to elevate the operating temperature to where the brakes were operating at maximum designed friction levels through out the braking cycle. We now check brake rotor temperature as an indication of where the brakes are operating temperature wise. We adjust cooling accordingly.