Slotted or Drilled?

[DZeckhausen]

Originally Posted by stevesrt8

BTW, I can't believe a car like the ZO6 has any issues with brakes. They are massive, and the car is surprisingly light.

Remember that energy goes up with the square of the velocity, but only linerarly with weight. So, although the exotic materials in the C6 Z06 make it a couple hundred pounds lighter than the "normal" C6, the astonishing power to weight ratio allow it to go faster at the track, and that's where it runs into brake trouble.

The standard brakes on the regular C6 are OK, but even the upgraded ones are still NOTHING like what I see on the ZO6.

One of the most popular cars for StopTech big brake upgrades is the new Corvette C6 Z06. It's not because the passenger side directional rotors are backwards. It's due to a fundamental issue with the front 6-piston calipers that results in accelerated pad wear at the track.

Each OEM Z06 caliper holds 6 "padlets" and each padlet has a piston pressing against it from behind. With a normal 4 or 6-piston caliper with two pads per caliper, the pistons are staggered in size in order to apply a differential force to counter the pads' tendency to want to rotate and nose dive into the rotor. It's analogous to applying more weight to your back leg when surfing, in order to keep the front of the board from digging into the water. With the 6 pistons on the Z06 caliper each centered on a padlet, the padlets dig in and wear (under track conditions) at a severe tapered angle. So you get down to metal on metal much earlier than if the pads had worn evenly. The StopTech 6-piston front brakes (identical to what I have on my SRT8 now) have two gigantic pads per caliper and staggered pistons that hold the pads parallel to the rotors for even wear. One of the first track mods many C6 Z06 owners do is to replace those OEM front brakes (and usually the rears too) with StopTech brakes.

As an aside, the Brembo 4-piston front calipers on the SRT8 have four 44mm pistons, so they are not staggered either. Thus, tapered pad wear at the track is an issue for the SRT8 too, but nowhere near as bad as the Z06. More "serious" OEM Brembo brakes, such as those found on Ferrari, Lamborghini, and even Subaru WRX STi have staggered pistons and much better pad wear characteristics at the track.

[stevesrt8]

thanks, Dave.

Once again, a surprisingly clear explanation of things not well known.

[AlexDestructive]

well said ^

[NM08SRT8]

Remember guys, the weakness in "drilled" rotors are from buying either 1) cheap drilled rotors, 2) getting blanks and drilling them yourselves.

If you buy rotors that were formed from solid steel in a mold with the holes built in it, you will have a more solid rotor that isn't AS weak as the drilled rotors. Like stated in another post, dozens of other car manufactures used Drilled OE rotors with no problems....

[DZeckhausen]

Originally Posted by NM08SRT8

If you buy rotors that were formed from solid steel in a mold with the holes built in it, you will have a more solid rotor that isn't AS weak as the drilled rotors. Like stated in another post, dozens of other car manufactures used Drilled OE rotors with no problems....

Actually, the drilled rotors that come OE on Porsche will crack during track use just as quickly as other drilled rotors (excluding eBay junk). There's nothing magic about Porsche, Ferrari, or AMG rotors that allows them to violate the laws of physics. Drilled holes create stress risers in the iron and act as "magnets" for cracks to form around. If the rules of a particular race allow it, Porsche drivers will opt for slotted rotors in a heartbeat. The myth of the "cast-in holes" has been circulating for a long time. But those holes are machined just like any other quality drilled rotor. I think Todd at TCE even has a cash reward out for anyone who can provide photographs of a Porsche rotor mold that shows the holes being cast!

Drilled rotors do provide the best wet bite, reducing that seemingly eternal delay before the brakes start working in torrential rain. They also have a measurable increase in bite over slotted rotors and they save 1/4 to 1/3 pound of weight per rotor. So there are compelling reasons to use them on a street car that will never be tracked.

[hansmathews]

Dave,

What an articulate and intellignet way you have for instruction. Just a thank you from one engineer to what I assume is another.

I was wondering what is the problem with the original rotors on the SRT-8's. My rotors looked like the pads had been driven down to the rivets at 6000 miles even though that wasn't the case. I have just assumed there was an issue with material composition, though the slots in the replacements pique my interest.

I just got the new rotors ~250 miles ago. Should have done it earlier, as I was past the 12K mark and had to pay for new pads, but they did give me the rotors at n/c. Would you recommend replacing the OE pads in the near term, and with what, or just run them till they need replacement?

I would like to get a more normal life from the brakes and reduced dusting would be nice (though that is already greatly improved with the new rotors).

Hans

[DZeckhausen]

Originally Posted by hansmathews

Just a thank you from one engineer to what I assume is another.

Good catch. BSEE at UNH. MSEE @ Duke University and then 15 years at Bell Labs.

I was wondering what is the problem with the original rotors on the SRT-8's. My rotors looked like the pads had been driven down to the rivets at 6000 miles even though that wasn't the case. I have just assumed there was an issue with material composition, though the slots in the replacements pique my interest.

Nothing wrong with the rotors. It's the OEM pads that are too abrasive and chew through the rotors with amazing ferocity.

I just got the new rotors ~250 miles ago. Should have done it earlier, as I was past the 12K mark and had to pay for new pads, but they did give me the rotors at n/c. Would you recommend replacing the OE pads in the near term, and with what, or just run them till they need replacement?

I would like to get a more normal life from the brakes and reduced dusting would be nice (though that is already greatly improved with the new rotors).

Unless you want the new rotors to start looking like the old rotors soon, and the wheels to be permanently stained by brake dust in between the polished spokes, you should swap to the pads described here: How-To: Installing low-dust brake pads on an SRT8

[hansmathews]

Great info. I'll get my order in in tomorrow.

Would you expect to need to clean the rotors up already / break any glaze with say 300 miles by the time I get the parts? Visually, they look new at this point.

Cool stuff on the career. I'm a BSME and 16 years around the natural gas industry. Today I run an engineering group that provides upgrade and retrofit services for large gas engines. Some of these monsters are 11,000 Hp on 20 cylinders at 345 RPM. You can stand in the cylinder. I do some teaching at industry confrences and enjoy teaching the technical stuff. Too bad you can't make a living at it (stand alone).

It's a good thing to do something you enjoy.

I'll call tomorrow and place the order.

Hans

[nazab]

What about the 300C 5.7 , which rotors and pads do you recommend as I am not happy with the OE. I have changed rotors and pads under waranty and still hear a braking noise ( hmmm ) under hard braking at 100 mph or more.
Also suffered from rotors wraping at only 15000 miles !

[DZeckhausen]

Originally Posted by nazab

What about the 300C 5.7 , which rotors and pads do you recommend as I am not happy with the OE. I have changed rotors and pads under waranty and still hear a braking noise ( hmmm ) under hard braking at 100 mph or more.
Also suffered from rotors wraping at only 15000 miles !

It's normal to hear a low frequency hum from your brakes when braking hard from speeds in excess of 100mph. So I'm not sure a different pad choice is going to help you here.

The amount of heat you put into the brakes is proportional to the square of the velocity. For example, slowing the car from 120 to 104 (a 16mph reduction) puts as much heat into the rotors as coming to a complete stop from 60mph. So it's not much of a surprise that your brakes had some issues. You probably overheated your pads and they deposited material unevenly onto your rotors, resulting in judder. The rotors weren't really "warped". See this excellent white paper by the late Carroll Smith that goes into the detailed physics: The "Warped" Brake Disc and Other Myths of the Braking System

If that low frequency noise during high-speed braking bothers you, then you might want to avoid slotted or drilled rotors. Personally I like it, since it reminds me of the sound of my brakes at the race track. And, of course, I prefer the extra bite of slotted rotors.