License2Ill

iTrader: (1)

Wagner blanks from Advance auto parts.....very sweet and extra thick....will tuck out wheel slightly. MADE IN USA....fair priced but not rockbottom wear-ever price.
So spend the few extra bucks.

safemode

iTrader: (1)

I have brakemotive's slotted and drilled rotors and they are very quiet. You can feel the slots but they are no where near "pulsing" in the way that warped rotors would ....it's more of a soft discrete rubbing sound. Still miles better than the screeching school bus sound my blanks caused.

Plus, there is little that can't be said for being able to have stopping power above 100mph. Blank rotors _SUCK_ for that.... at least mine did.

License2Ill

iTrader: (1)

My understanding is the less material on the rotor the less surface friction and therefore less stopping power. So that would make the last statement there incorrect.

Holes and slots and such are purely for cooling.....and my guess is are necessary only under certain conditions.....likely not seen on the street. It is gimmick really. Stick w/ blanks.

safemode

iTrader: (1)

they're for gas venting too. which is what happens to blanks. The pads gas up and then you have a layer of gas under the pads instead of rotor. Try braking at 130mph with blanks with even decent pads and then try in someone's car with slotted rotors (drilled helps with the cooling and de-gassing too but the slots are really where the works is done).

it's like night and day


I guess if you've never gone fast enough to be really concerned that you wont be able to stop in time for an intersection then you're right, it's not something you probably need. I'm far from a crazy driver but I do like to take the car up to the limits when it's dead out and not needing a half mile to stop is awesome.

TheSilverOne

iTrader: (22)

here we go again

License2Ill

iTrader: (1)

That's interesting....I haven't taken my new setup up there just yet cuz I need an alignment....but in previous I did note spongy or harsh pedal at those speeds....that I also like to push up to every now and then when it's dead out or a bentley with a fancy radar wants to take the lead.

You've noticed this often? And feel the slot drives this gas out?
The gas is a derivative of what? the pads burning up as they hit the rotors?

License2Ill

iTrader: (1)

Lock down @ 14 pages!

Taking bets.....whoever hits deadon gets my LT1 frontend brake setups with almost new pads and all !!!!

Shockwave179

iTrader: (7)

This totally made me laugh out loud.

Gas doesn't build up between rotors and modern brake pads. That happened when brake pads were made with asbestos :rofl:

Slotting helps slightly with cooling and shedding of debris but that's about it. Pads and Calipers change stopping distance much more so than the type of rotor you run.

License2Ill

iTrader: (1)

safemode maybe what you noted in changes was attributed more to newer pads....

99FormulaM6r

iTrader: (2)

Less material = builds up heat faster. Heat is what causes brake fade under hard braking. Also, less material on the surface = less surface area, which creates a smaller swept area and decreases braking force.

As mentioned, the changes you saw were a change in pads, and probably nothing more. To find some more information, search for some of the huge threads that have blown up on here, there's a ton of good information from the people that really know how this stuff works. Also, reading the brake writeups on TireRack or most manufacturers websites is a pretty good idea as well.

EchoMirage

iTrader: (3)

i guess all the times ive hit 130-140 on track before a sharp turn with blank rotors doesnt count

and just so i can use these: and

SVThuh

iTrader: (2)

ROFL.. I was going to post the exact same thing...

I also have consistent "Peel your face off" braking ability from 130-140 on the track with my blank rotors.. Guess that doesn't count though.. Too bad for us..

License2Ill

iTrader: (1)

Music to my eyes.....I stuck to blanks all the way around recently and resisted everyone's stupid notion and beliefs on cheap lines and holes in their rotors.

You guys should try hearing that kind of stuff from your local meineke store manager who recut a pair of my blanks.....I just stood quietly and didnt even bother while he went on and on about getting slotted and vented rotors and yada yada.....I shook my head and said sorry im not going to do it.......this is a Z28 not a 350Z.

Brakemotive

iTrader: (73)

You're wrong about the less material = heat build up. A typical 20+ lb rotor will usually lose about .1 lb of iron during the drilling process. Cross-drilling increases the wetted surface area of the rotor thereby improving itscooling ability. Convection heat transfer is second only to radiation in terms of energy conversion. Conductive heat transfer which you're implying is negatively affected by drilling; is responsible for the lowest percentage of energy conversion. The more airflow through the vanes, the cooler they will run.

The reduction in surface from drilling has no affect on braking force - your master cylinder bore, pedal fulcrum, line pressure, number of caliper pistons, their size and their position relative to the center of the hub is what determines braking force.

At any given moment the only surface area that matters is what's directly under the puck. The reduction in surface area of a typical pad due to slotting and chamfering is much greater than the area lost by drilling.

I do agree with you that the pad compound will have the biggest effect on rate of deceleration.

mitchntx

iTrader: (14)

What's the over/under on when some one posts that F1 race cars and Lambos have drilled and slotted rotors?

License2Ill

iTrader: (1)

Seems a little contradictary.

Please explain why loss from drilling would not equate loss in surface area?
When your talking about a hole vs. thin lines. Either way material is being taken away.

It's easy to say loss of surface area is loss of surface area is loss of surface area. I'm certain the holes equate to some loss of surface area.

99FormulaM6r

iTrader: (2)

Points in bold. I'm not saying that drilling/slotting a rotor will make a huge difference, but physics don't lie. When you factor in the increase in stress points in the rotor and the fact that pad life is decreased, I don't see any tangible benefit to a drilled/slotted rotor (unless you're racing and want something to scrape at your pad to keep the surface fresh, where some race cars have small slots cut into the surface).

Chris_B

The benefits are primarily in the initial "bite". The extra leading edges from cross-drilled hole increase the effectiveness of the pad as well as raise its temperature more quickly. This advantage starts to normalize after a second or two, but the difference can be felt in most cars. I've felt it and I have test results from vehicle data acquisition and brake dyno results that back it up. We used to hacksaw slots into race pads to get more initial bite on tracks where we had trouble keeping heat in the brakes. Again, more leading edges equate to just a little more bite.

I have also worked with professional racing drivers who can definitely feel the difference. Once during qualifying at Daytona, drilled rotors were put on the car. Before the morning race warmup, the crew swapped them for slotted rotors in preparation for the 24 hour race -- but neglected to tell the driver. He then blew right through the back straight chicane when there was much less bite. Race pads take longer to heat up and he was surprised there was not enough heat in them yet due to the rotor change.

Are there additional stress risers? You bet. But that makes little difference on the street. I've been in the industry for over 20 years and hardly ever see (properly manufactured) drilled rotors that cracked before they wore out -- unless severely abused or tracked hard. I have seen MANY poor quality rotors (bad casting, substandard materials, wrong thermal post-processing, incorrect drill patterns, poor finishing, etc.) like the typical eBay garbage crack, but that has nothing to do with the drilling question.

Decreased pad life? Yes, a little anyway, but not severe at all. Most street pads are so low in friction that the extra bite that the drilled rotors gets out of them is well worth the trade-off. Pads are relatively cheap and quick and easy to change out, so I've never found it to be an issue.

Contrary to some of the points laid out in this thread, reducing the surface area has absolutely no effect on brake torque. But it does cause the pad and rotor to heat up a bit quicker from cold. The effective torque arm can be viewed at the center of pressure for the pad for calculation purposes. This does not change by drilling the rotor, so no torque is lost.

Also, drilling a rotor typically removes .35 - .70 pounds, depending on the size of the rotor, its design and plate thickness. This is relatively insignificant as far as temperature rise is concerned. Yes, the rotor will run slightly hotter, but good luck actually measuring the change without an on-board data acquisition system.

Chris

mitchntx

iTrader: (14)

Thanks, Chris.

So if I'm trying to set FTD between my house and the parking lot at work, then holes and slots are the way to go, eh?

Chris_B

Depends on your route. I've had commutes where riding a bike was faster. Another one was a 12 mile canyon route. Not sure why, but I went through brake pads at least once a year in the canyon...

But if it helps, all but one of my street vehicles has cross-drilled rotors on it right now. The odd man out is slotted-only, but that vehicle is large and can put lots of heat into the brakes very quickly. Even the family van has drilled rotors, which my wife likes the feel ("oooh, grippy!") of over the stock stuff I took off. Yeah, the pads were 80% of the improvement, but the rotors do contribute some. It may only stop 5 or 10 feet shorter, but that can make all the difference in the world when needed.

For track cars, I prefer the J-Hook pattern. It has the bite of a cross-drilled rotor without the stress risers.

Chris