toklas

no worries just trying to educate. I've seen first hand how drilled rotors can fail. I wouldn't put them on my truck. You would have had the same increase in stopping power with just the pads and slotted rotors. it is not recommended to put drilled rotors on any heavy duty braking application, which is why you only really see them on street cars that want to look cool. You wont see them on any race cars, semi trucks. Formula 1 used to use them but too many issues with no real advantage.

If its a light duty truck sure go ahead, but if you're towing/hauling please don't

this is a very common failure when drilled rotors are put under stress.

ALTAJAVA

Several things here. I hope no one is dumb enough to put these on a cup car, that would be my only concern with having them fail. Comparing them to a race car application is highly irrelevant. The only possible exception would be a drag car. Second, and more importantly, if a round hole is a point of failure why are we taught to drill a hole to stop a stress crack from propagating? Fact is a hole/rounded radius is used to avoid a stress crack from even starting. Having drilled/slotted allows the gasses created from the heat build up to escape. That has been proven far more benificial than losing the minimal amount of swept area from having the holes/slots. I didn't buy these for the "cool factor". I bought these because they work better than anything the factory used for about the same price as factory brakes. Not all cross drilled rotors are the same quality, which I highly suspect is the case with your example, which appeare to be highly worn based on the ridge about a 1/4" from the edge. They look like they've seen several sets of pads without resurfacing and I would be amazed if the bottom of the grove is at minimal thickness. I have never seen such an example when using a good product, and I have seen some horror stories while working in a garage.

toklas

i apologize just to clear things up. the pic is not of my personal experience. It was just an example of the sort of fractures i have seen on multiple rotors. this particular pic is from another tech article which can be read here.

http://automotivethinker.com/brakes-...d-and-warping/

as for comparing to race cars being irrelevant i disagree. Many of today's advancements in vehicle technology are directly related to testing done on the track. The fact that drilled rotors used to be prominent and have since been removed should be an indicator as to their effectiveness.

The concept of needing to vent gas is antiquated based on pad materials in the past. most modern pads use materials which mitigate that issue.

ALTAJAVA

Advancements based off of racing are one thing, you directly compared a performance STREET brake to a race brake. The differences couldn't be further apart than night and day. Unless you had the rotor pictured metallurgically tested you have no idea what caused the stress crack. I highly suspect what caused the crack is its out of spec meaning it's too thin. I base that on the wear pattern and real world experience. Not something I read somewhere, but knowledge has to start somewhere and that's usually a book. Personally I've seen plenty normal rotors crack the same way that I could argue having a non drilled rotor caused the problem. While newer pad material may have mitigated the gas issue, it hasn't completely eliminated it. There is still the fact that holes are not a source of stress cracks. I have no desire to turn this into a pissing match, but you saying these brakes are a waste of money doesn't hold up. No worries, just trying to educate.

ALTAJAVA

Having thought about this further I will add, a quality cross drilled rotor has beveled holes. In the picture provided, it appears to be the main evidence of the article you linked, there are no beveled holes. This means one of two things, 1; it was of poor quality to begin with, or B; the rotor was highly worn out as I first suspected. There are a lot of "theoretically" in that article. As I earlier pointed out, it's easy to prove one thing on a blackboard and be unable to prove it in the real world. At this point I am done beating this horse.

toklas

your right dead horse, glue at this point. as i've stated a few times. personal experience not "blackboard". do what you wish.

Bremsen

She ain't dead yet, I'll take a good strong swing at it.....

Toklas, your points are correct. All discs can crack, but due to the holes in the middle of the friction face a drilled disc will crack earlier and at a much lower temperatures. When the brakes are applied the friction surface heats up, but the hub area does not. This temperature differential means that the friction surface is expanding and trying to pull away from the hub. When you have a void (hole, slot, etc) in the surface that is being heated, that void will be the first place a crack will form. Yes, racing discs use slots to increase bite and clean the pad surface to prevent glazing, but the discs are generally "floating" and therefore the iron is allowed to expand evenly and separately from the hub/hat to prevent stress cracks from occurring.

Brake systems are actually pretty simple and the primary differences between a racing brake system and road car system are mostly in their efficiency and materials. Brakes are basically energy conversion systems. Racing brake systems are just designed to handle and transfer that energy much more efficiently and account for thermal expansion at much greater levels.

Seeing as the OP is asking about heavy towing brakes I would strongly recommend a good quality plain faced disc and good brake pads/fluid. When towing you are adding mass, which increases inertia and the energy the brakes will need to handle. A 6+ ton vehicle going 70mph is actually not much different than a 3400lb stock car going 125mph in the amount of energy. Yes, the trailer brakes will take up some of that slack but the truck brakes will be taxed. Since we can't really change the thermal efficiency of the OE brake system, you want a good high temp performance pad and good fluid so they don't fade with the increased heat, but also a high quality plain face disc that will be less likely to fail with the increase in thermal expansion.

acdii

There is too much mis-information here.

First of all, cheap pads and cheap rotors WILL crack. Properly drilled and beveled rotors that are designed to absorb heat, with the properly matched pads will not crack unless abused beyond the tolerances they were designed for. The PowerStop kits are properly matched pads and rotors and will last a long time without cracking. Powerstop races their products and continue to improve them to reduce these tendencies to crack.

Second, slots are not for "bite", they are to release the gases that can get trapped between the pad and rotor that causes brake fade.

I put the Z36 tow kit on my truck and they work perfectly to slow the truck and trailer without any fade. I have only one complaint and that is the first couple stops when cold take more pedal effort, but after that, they are very light on the pedal. After my 3175 mile round trip up and over the mountains of Colorado and Utah pulling 6300# of trailer, I can say with 100% certainty that the powerStop brakes work as designed without overheating, or getting hot enough to crack.

brown1

just got the z36 installed, going to break them in tomorrow. unfortunately no test towing until next spring due to um's home football schedule and my daughters fall travel softball schedule.