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I think we are splitting hairs here, a hole, drilled or cast, is a stress riser compared to no hole, period.

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Holes in pretty much anything are evil stress risers, avoid them.

I know of a set of drilled rotors that didn't even make it 10k miles before cracking. Yeah, they were home drilled about 20 years ago. Don't care, no drilled for me. Those that want them know that I'm laughing at your ignorance.

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Now I'm laughing at your ignorance.

Holes cast into the rotor during manufacturing do not promote stress fractures.
Holes drilled into rotors after casting will lead to fractures.

That's been proven through the years.

The holes provide limited outgassing, reduce weight, and save raw materials. They also look sporty to some people. That's why they get used.

Sometimes performance oriented auto manufacturers investigate things a wee bit more thoroughly than internet keyboard warriors.

Now, would you like to revise that statement?

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I think we are splitting hairs here, a hole, drilled or cast, is a stress riser compared to no hole, period.

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The king of splitting hairs comments about others splitting hairs?






Obviously, rotors with holes are inferior to non-holed rotors. That's why you'll never see them on supercars costing hundreds of thousands of dollars.

OOPS!! I misspoke. That car cost a couple million dollars, runs 250+ mph, and has zero engineering behind it.
Stupid VW! What were they thinking?

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I was a wilwood R&D Engineer for 2 years and have been crew in many forms of racing for over 20 years. After wilwood I spent 7 years in R&D with ecomotors.com. Keyboard warrior I am not.

I guess we're both laughing. No known metal rotor has those holes cast into them, even if they are those with cast-in holes they are still stress risers. If nothing else, review "Engineer to Win". That they were drilled as opposed to being formed by some other method is a small part of the total picture. Anything that changes the stress flow path or disrupts it is a stress riser.

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As previously stated, drilled rotors are put on those cars for the buyers, because they think they're cool. Not because they're a better solution. Marketing trumps Engineering & Science every time. So those rotors prove nothing about actual performance. Can you prove that those cars set their high water marks wearing drilled rotors? We all know that they're sold with them, proves nothing. Most real Engineers have a bit better grasp of things than keyboard engineers.

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Surprise! I'm one of the guys who said drilled rotors are used because people think they're cool.

We all know that "real engineers" get their butts kicked by marketing on a regular basis. Keep spouting off with the whole engineer bit. I know a TON of engineers (worldwide) and can tell you some of those guys can't engineer their way out of a wet paper bag.

Frequently, "engineers" get caught up in minutiae. For the engineers out there, that means trivial stuff.
They go and go and go until they can't go anymore. They're measuring carbon content to the angstrom and studying the temperatures at which the base material goes from a plastic state to the liquid state despite the fact that you never want your product to get there.

Yes, all holes in rotors are stress risers.

Can you spot the stress risers in this pic?



If you said the vent holes, fastener holes, and contours around the fastener bosses you'd be partially correct.

How about this one?



See all of those slots? Those create fracture points that can not only move laterally but also across the width of the rotor by originating at the bottom of the cut.

ALL rotors have stress risers. You simply ENGINEER around them. Know that some tool paths will lead to more prevalent points of failure. Cutting will generally lead to an easier failure path than proper forming the features while casting.

You don't have to be a great engineer to know that metals have stress. All you have to do is measure a piece of flat cold rolled steel, cut into one side of it and measure the piece again. You will see deflection in the part due to stress in the steel introduced during rolling.

All formed structures are going to have some sort of stress. That stress is always looking for a way to get out. A good engineer will find the shapes and manufacturing processes that limit the failure rate of the finished product. Once you push that far away from the product's intended use it's time to call it done. In brake rotors you can limit the failure rate but you can't prevent it.

Pull the feather out of your engineer's cap and realize that other people sometimes know what they're talking about.

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I just want to say reading along with this has been SUPER FUN.

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Careful. Fun leads to a higher failure rate.

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Now now guys, keep it serious please.
How about drilled rear drums?

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That may not be too bad of an idea. It will let some of the heat trapped within the drum to leave. Just put it on the drum face. That shouldn't be a critical spot.

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Now now guys, keep it serious please.
How about drilled rear drums?

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That may not be too bad of an idea. It will let some of the heat trapped within the drum to leave. Just put it on the drum face. That shouldn't be a critical spot.

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holes for drum cooling have been around forever. mostly used in the backing plate, but i have seen holes in all areas of the drum[including the friction area] also. some applications work, some don't. i have personally seen blowed up rotors and drums with, and without holes[slots]in them. as i am no engineer[but like feets, i know a bunch of 'em and some couldn't figure out a way to walk around a post], but observe the world around me and [try to] do stuff that works for the application at hand, and avoid the things that don't. and as a side note, i have done FUN things at times, then afterward wonder if that should have happened..........

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i have done FUN things at times, then afterward wonder if that should have happened..........

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What was her name?

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Now now guys, keep it serious please.
How about drilled rear drums?

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That may not be too bad of an idea. It will let some of the heat trapped within the drum to leave. Just put it on the drum face. That shouldn't be a critical spot.

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Well if the holes are cast in the drum, maybe they would work

And to rehash, holes in rotors are less about cooling then weight reduction, looks, and pad wiping/gas venting (thought to be a minor concern with todays compounds). And cooling is more about air movement/venting, nor sure how air is induced to vent from a drum, other then the heating/expansion of the air.

And besides, you can't see holes in drums.

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holes for drum cooling have been around forever. mostly used in the backing plate,

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i have done FUN things at times, then afterward wonder if that should have happened..........

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What was her name?

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that's the problem. i can't remember........