JPhillips-998

The holes are for brake dust and gasses. I use solid rotors that are vaned. If the vanes are directional then it is very important that they be mounted on the correct side. A fellow racer mounted both of their fronts backwards, they had no cooling and cooked their brakes within a few laps.

smokey

The holes were there originally to expell the gas build-up between the pad and rotor. Modern racing pads don't emit much gas. Porsche puts the drilled rotors on their street cars because they look cool, and because they can.

penguinking

maybe because you can't shave drilled rotors, so if theres ever a problem with them you have to replace them instead...

kurt M

Bingo. The holes also reduce friction, heat load storage mass as well as rotor life via cracking and uneven wear. I have one of Tony's old Zimmermans out in my shop. Little if any surface wear but 3 big a$$ cracks at 2, 5 and 9 O-clock. I think Zimmerman has now changed the hole placement so as to not have two in radial line with each other.

Larry Herman

Mine seem to be more for brake dust COLLECTION! They are plugged solid after every track event.

A930Rocket

I'd like to find GOOD slotted front rotors for my 930. Know anybody that makes them for the Big Reds with 993TT rotors?

I've found that the pagid oranges clog the holes more than the blacks, but I couldn't get them in time for the last event at VIR.

RedlineMan

I respectfully beg to differ, strongly. They may reduce surface area, but they INCREASE friction. The pad scraping over all those holes INCREASES friction. In some applications, you can HEAR the pads moaning as they rip across the pad face. I hear this sound on my mountain bikes with disc brakes.

If you do not get the radial grooves with your holed rotors, you obviously don't generate enough brake stress to need them.

Unless you have extremely effective duct work, you might be better of keeping the extra heat sink in the rotors. That is where you WANT the heat to be. If it cannot dissipate through the air, and doesn't stay in the rotor, the next stop is the pads and calipers, where you DON'T want it.

I STILL am not convinced they do anything better than slotted rotors. I slot my own OE rotors and they work extremely well.

Glen

Why not, You can turn them just like any other rotor.

trumperZ06

Yeah, even the General... F#*Ked up the C-6 Vette with the...

bling-bling drilled rotors !!!

NAPA sells the C-5 solid rotors for ~ $ 26.00/each !

RedlineMan

Hmmm....

Too bad that GM - in reflecting on the 968 when designing the C5 - did not take note of the braking potential therein. The US car makers are not as genetically predisposed to under-braking their cars as the Japanese, but it's close at times.

I don't know why I did not think of it before, but there is another reason I can think of for holing rotors; Lessening Rotational Mass.

penguinking

how much mass do you save by drilling rotors? anyonne actually measure this somehow? i'm guessing a pound at most?

kurt M

This runs against what I have read in the past. Not to hijack a thread and not a point of contention, I am only curious as how holes do this. They are not acting like a cheese grater or are sticking up in any way. Does the pad material deform into the holes as they pass by? Unless there is deformation of the pad or rotor the holes are only a place where there is air rather than metal and air has a lower friction coefficient than the rotor surface.
Is the moaning a high frequency harmonic that sets in from the differing friction coefficients or air making a sound as the holes open and close? When rotors wear what does the wear pattern look like? Does the rotor wear fasteer where the holes are or does the rotor wear faster where the holes are not?

Rather than adding holes (AKA stress risers) to a rotor to reduce mass why not make the rotor thinner? Yes, less mass for thermal storage but holes do same thing unless you drive air through them to utilise the added surface area they provide. A pound per rotor would be a great savings as the weight saved is of the best kind to not have. Unsprung rotating. More cooling potental = smaller lighter brakes needed= faster.

RedlineMan

Yes Kurt;

These are all good questions you are raising, and I too am speaking partially from my understanding. Also partly from direct experience.

It seems the holes DO cause increased friction. Whether this is from pad deformation or not is a good question. It seems plausible, now that you mention it. The end result is that the holes wear grooves in the pad surface, which are effectively then low spots and do not then contact the rotor surface as forcefully as the "high spots" that are wearing normally on the flat face of the rotor. Because the grooved areas of the pad are not pressuring the rotor surface as hard, the higher portions of the pad then wear radial grooves in the rotor face (where the holes are not). It is my obvious assumption that the rotor and pad would be wearing evenly if the holes were not there.

This suggests to me that, regardless of its cause, there is increased friction as a result of the holes. Stands to reason... I think.

Given the above, it seems it must be the cadence of the pad getting ripped by the holes. I have experienced some cars that made a vibrating, moaning hamonic when you stood on the brakes. This can come from either holes or slots. I think it has a lot to do with how the reliefs are rendered as to position, size, pattern, etc. My mountain bikes with Hayes hydraulic disc do this too.

Incidentally, my own slotted rotors - which I machine myself - do not cause any of these occurences.

It would seem to be a thin line between enough mass and too much. There must be a point of diminishing return for thickness, either way, and I might assume holing bridges that gap successfully, if indeed they are put there to decrease rotational inertia.

In the end, the fact that they do not last as long as solid or slotted rotors in most applications makes my decision. I'm cheap!

kurt M

"The end result is that the holes wear grooves in the pad surface, which are effectively then low spots and do not then contact the rotor surface as forcefully as the "high spots" that are wearing normally on the flat face of the rotor. Because the grooved areas of the pad are not pressuring the rotor surface as hard, the higher portions of the pad then wear radial grooves in the rotor face (where the holes are not). It is my obvious assumption that the rotor and pad would be wearing evenly if the holes were not there."


That would lead me to think that there will be less friction as there is less contact surface. You describe a condition where the pad area over the holes is compromised by the holes and making less contact with the rotor. The best friction is obtained by even contact between the two surfaces X the clamping pressure. I would think that using holes to grind material away does not make more friction over all and increases pad consumption rate.

I have seen setups that use the holes to increase cooling and I can see where in theory they might do so from the increased surface area they provide. The setups forced air through the holes from the sides, as well as from center to edge passing through the existing vents.

Damn, now I have to look into this one and find out what is really going on. There has to be true test data on this.