dackp143

iTrader: (3)

Wow there is some great information on that. I honestly feel more educated about everything even though I will still use drilled rotors as the look is IMO great. I personally don't mind spending an extra $100 a year on pads, I like to work on my car plus this gives me the chance to actually inspect my wheel wells and calipers for leaks or to make sure none of the calipers have a seized piston (happened to my last IS300).

Great info!

Kurtz

iTrader: (1)

Yeah.... carbon ceramic is a bit different.... though those also don't change your braking distance. There's a bunch of tests that have been done on the PCCB upgrade and they stop the car exactly the same as the stock brakes do unless you've completely abused the hell out of them (like 20+ laps at 3-digit speeds with lots of braking and no time in between laps)....but in general the carbon rotors are vastly more durable so cracking around drilled holes won't be anywhere near the issue it is in metal rotors... course you're paying as much as a new Kia just for the brakes in that case, and still seeing no benefit in street driving.

Mostly they put metal drilled rotors on some "expensive" cars because the average person doesn't know anything about brakes but knows that drilled rotors look cool. Plus if you're dropping 100k+ on a car you won't notice having to replace your cracked rotors occasionally right?


I don't think "we" are because warping is still commonly thrown out there with people thinking the rotors are warping...your own post earlier in the thread for example mentioned "warping" brakes, not experiencing uneven pad transfer... and if you bed the pads properly and don't abuse the brakes the uneven transfer doesn't happen- the fact it kept happening to you suggests common sense isn't as common as you suggest. Likewise there's rarely any good reason to "machine" rotors but you seem to keep having that happen to you too.

You can do a search and see the cracks on the OEM Lexus IS-F rotor that Lobuxracer has posted after just one track visit though....and he's hardly the only one.

Feel? Sure.

Have any actual difference in stopping distance? Nope.

that'd violate some fairly basic laws of physics.

By ALL means use slotted or drilled if you like the look, and that look is worth eating through pads 25% faster and having to replace rotors more often. But don't ever suggest they "stop better" because they don't


Funny, my OEM low-dust pads are perfectly quiet. Guess I'm just lucky

jet350

Wow lots of info thanks guys from what I've read most say that unless I'm going for looks my oem rotors are just fine, I think I may go with a slotted set up though I don't drive the car that often pretty much only on weekends trying to save mileage, so don't really have to worry about wearing out my pads that fast, and I think they look bad ***
Thanks

lobuxracer

iTrader: (2)

That's the best possible reason for getting those rotors! Well done!

FWIW, I'm totally cool with someone getting something for looks. I call it Visual Performance. Just don't use a Mechanical Performance argument as the reason why you're doing something purely for visual performance.

Truth be told, 99.9999% of street drivers can run drilled rotors without issues. 0.0000% of track drivers can run drilled without issues - and all this BS about holes being cast in or drilled or drilled and chamfered is nothing but BS. Drilled rotors are going to crack under severe duty. But it is nearly impossible to have this happen on the street unless you live at the top of a mountain and have to drive down it every day (yes, there are a few people who do this).

So if you want to get drilled rotors because they look cool, rock on. BTW, one of the problems in the paper was they showed better heat transfer from the drilled rotors, which is true, however, in service, drilled rotors run hotter than blanks. It makes no sense until you realize drilling removes material which would normally be a heat sink, so despite the ability to shed heat a little quicker, the lighter weight means they'll run hotter at the track, and hotter is not better.

Once again - rotors DON'T WARP. They get uneven pad transfer and under track conditions will develop cementite to further make the rotor worthless, but they really don't warp. Cementite is easy to see - black spots on the rotor face will show you exactly where it is developing.

Last of all, turning rotors is a disaster unless they're resurfaced with a centerless grinder (the same technology the factory uses for final finish). I put a set of turned rotors on the front of my F and nearly wrecked the car because the driver's side worked normally, and the passenger's side did not - I hit the brakes hard at freeway speed to dive into a spot for an exit, and the car pulled hard left to the point I had to countersteer a 1/4 turn to keep the car going straight. I'll never put a lathe turned rotor on anything again.

06isDriver

I understand that drilled and slotted give almost no advantages besides looks, but carbon ceramic (while they MAY not actual improve braking distance or whatever) should weigh significantly less than their iron counterparts. Reduction of unsprung weight , especially on a rotating assembly WILL increase performance in acceleration at the least.

This is why i was excited when that company came on here claiming a 7-9 lb reduction in weight per rotor over stock, but they havent followed up with a rear fitment so I'm still waiting.

lobuxracer

iTrader: (2)

The biggest benefit isn't rotational inertia loss, it's improved suspension compliance by reducing unsprung weight. If you're concerned about rotational inertia, you'd have to start with the lightest rims and tires you can get because they're much farther out in the rotational plane than the disc is. But reducing unsprung weight is ALWAYS good because you can make the suspension more compliant which means the tire is in better contact with the road more often.

Contrary to popular fashion, in racing series with big budgets the teams will put smaller brakes on cars at tracks where braking is less important to improve the sprung to unsprung weight ratio. It does also reduce overall mass (but often this means they need to run more ballast) and may improve measured acceleration depending on a lot of factors, but mostly it gives the team the ability to move weight around in the car to get the chassis set up right.

brociouz

iTrader: (65)

Back to the OP's question. Read this thread: https://www.clublexus.com/forums/sus...r-options.html

CleverName

Years ago I got in this very argument on another forum. Back then I would have easily sided with your comments, and in fact made them myself while slapping my knee and arguing with those that told me I was wrong.
I kinda had to hand it to some of them that really knew physics and thermal dynamics way beyond my understanding. It was enough to make me re-think what I thought I understood, and slowly walk to their side of the argument.
You are correct that the paper is mus-representing the issue as heat transfer, but I have seen thermal imaging showing that cross drilled rotor do in fact run cooler than blanks. This was a shock to me to learn that air actually plays a larger role in cooling than physical conduction through a larger heat-sink. Turns out that due rotation, a high vacuum resides at the outer circumference of the disk. This vacuum draws cold air into those holes, allowing a more even cooling across the face of the disk. The thermal imagery took me by surprise as i had not envisioned that possibility. I now understand the benefits of cross drilling, and why they are offered on high end exotics. As it was pointed out... "Heat is never a friend in brake components"

That said I agree that poor and cheap cross drilling done on a poor and cheap Chinese cast blanks is next to worthless and a slotted or blank design will be a smarter choice. But done right, by a top of the line manufacturer, I now believe there is a distinct advantage to cross drilling.
As I live in a low to mid-range world, I'll stay with slotted for now as my best option, but if i had deep pockets to do it right, I would find those good manufactures and jump on the cross drilled bandwagon in a heart beat. (Of course I could replace them each time I found a new crack as well! Anyone wanna loan me 6 grand?)

Just food for thought... For me, i can no longer take the stand I once did, but the new thinking also comes with the realization that the good stuff is never cheap...

V

lobuxracer

iTrader: (2)

OK, but if there were airflow through the holes, they would not be clogged with pad material on the F's Brembo rotors. They fill up at the track and I have to clean them with a 5/32" drill to get the pad material out. I have to do this after every track weekend, so the concept doesn't ring true with my real world experience.

"Vacuum" doesn't exist at the edges, there's a pressure differential between the root and edge because the rotors is turning and the linear velocity of the outside edge is much higher than the root edge which is why ducting always goes to the root of the rotor, not the edge. Bernoulli's principle in action. Airflow is critical to temperature reduction, and it is definitely conduction, not radiation or convection. The air pressure at the holes is the same as the root, but the farther from the root the hole is, the lower the pressure differential, so flow through the holes will be less than from root to edge. Practical experience (clogged holes) says the differential isn't enough to displace pad dust.

I've had a few discussions with brake engineers over the years including the whole debate over curved vanes vs. straight (from the Supra's curved vanes and the left/right question - did Toyota get it right or not with their left and right designations). All the engineers say drilled rotors run hotter (using thermal paint on the edges of the rotors to measure maximum heat in service). All the manufacturers do not recommend drilled rotors for track bound applications - they all say round slots are best, and interestingly enough, slots never seem to get clogged with brake dust.