Yeah You win!! Thats a pretty decent pit crew you got there!

Mine is a girl though. My wife really doesn't want our daughter to be a hunter or a grease monkey so now we have a boy on the way.

 

Trust me, me stop at two!!!!!!

I love my kids, but three is just such a handfull.

 

WOW!!!
That is what everybody I know who has 3 kids tells me.
To quote my cousin... "Once you're outnumbered you're SCREWED!!"

 

 

Drilled or slotted rotors do NOT increase braking force AT ALL. They DO allow better heat dissipation, which reduces fade and fluid boiling under hard use. Unless you are using your truck for racing, they are a waste of money for posers.

If you want to increase braking performance, get better pads, and braided lines for the calipers, which will expand less and decrease pedal effort.

 

And you got your degree in performance braking where?

The increased heat dissipation alone increase the ability of the brake system to perform better than stock. My 8000# SUV stops about 15-20 feet quicker with the crossdrilled/slotted rotors and EBC pads up to three times in a row in immediate testing, before getting any fade out.

 

my question on the whole drilled/slotted rotor issue is simple-- wouldn't it be harder (or impossible) to turn the rotors when the time comes? I don't know, but it seems like that would hamper the ability to reuse them on the next brake change.

Not that this matters much, though because I just replaced my rotors last week-- used OEM replacements. The ones that were on there were OEM, and even after 150K it wouldn't surprise me one bit if they were the ones Ford installed when my truck was built.

For my money (which in this case is more than just an expression, unfortunately) keeping it original is the way to go on brakes-- just too important to mess with. If it's good enough for Ford and a bazillion other f-150 drivers out there, with no reports of recalls/etc, then it's good enough for me! Why fix a problem that doesn't exist to begin with (and then risk introducing new ones)?

Plus, OEM rotors, OEM pads, and I probably won't have to mess with anything again for 5 years, I bet.

Except of course to flush the fluid every year or so. Just 'for the record'- brake fluid is hygroscopic, will absorb moisture, and it isn't that the water compresses, it's that it boils. Once the water boils out you're left with gas pockets and those are what compresses. Trust me, I know this from firsthand experience.

You wanna talk about brake fade, try driving a 60's station wagon (with drum brakes all the way around and brake fluid that's 20 years old if it's a day) through the mountains-- scary stuff there!

 

I'm an engineer. Braking force is friction force. Friction force is a function of the coefficient of kinetic friction between the two materials (pad & rotor) and the force applied at the contact surface. Period.

No it doesn't. Contact area and temperature do not enter into the equation. The heat dissipation increases the effective operating range of the brake fluid by preventing it from boiling.

That's because the coefficient of friction between the EBC pads & the rotors is higher than that of the stockers. Rotor configuration has nothing to do with it.

As I said before, if you race, or subject your vehicle's brakes to very hard use (i.e.: drive like an idiot), fancy rotors will help prevent fade and fluid deterioration. Otherwise they are a waste of money. But they sure LOOK cool, don't they?

I can think of some freeways that are beginning to resemble racetracks.. , but seriously, you really need to be beating the hell out of your truck to get the brakes hot enough to get fade on a properly sized disc system

 

Shouldn't be a maintenance issue. A brake lathe turns pretty slowly and takes off very little material at a pass. Holes/slots shouldn't interfere.

As to the latter, been there, done that... drums get hot quick when you hold the pedal down and don't cool off very quickly.... that's why they have runaway truck ramps.

 

No, drilled rotors do not dissipate heat more rapidly.

That is a statement by Willwood, a company that has manufactured performance brake systems for about three decades.

http://www.wilwood.com/Centers/Infor..._answer/07.asp

 

I'm no engineer. Not implying to be. BUT,
I do know a thing about shooting and to me a slot in a rotor is very similar to the slots in a fluted barrel on a rifle. The point being that increased surface area increases the ammount of metal that is in contact with the outside air. That same air that our brakes rely on to cool off. The same basic concept is also seen in radiators that also increase the ammount of surface areafor air to cool. IMO slotted rotors will cool easier than non. Will this make a practical or noticeable difference if yo keep your brake fluid fresh,,,,, Definitely Debatable!!!!

my.02

 

Interesting link Aaron.

Maddog's intuition is correct. From a strictly thermodynamic standpoint, more surface area = better heat transfer, so slots & holes SHOULD allow the rotor to shed heat more efficiently. This, as has been pointed out, is the principle behind all heat sinks, radiators, etc..

It's possible that something to do with the specific application (brake rotors) makes the extra surface area ineffective as a heat sink. I'll look into it & post back.

It's true (as the Wilwood link states) that slots & holes compromise the structural integrity of the rotor and reduce it's service life.

The point about weight reduction is also true, but really, on a 4500# vehicle, are a few holes in the rotor gonna help?.

 

Here ya go Aaron..... it appears Wilwood isn't quite sure WHAT the holes do...

From the same site (here)http://www.wilwood.com/Products/002-...-SRP/index.asp :

"The venting and cleaning action of the holes and slots will reduce pad glaze and disperse gasses and heat generated during the pad to rotor interface."

It's pretty obvious that the statement you found is erroneous.

 

As an engineer, you should realize that the increased capacity of air flow through the drilled holes and into the slots will reduce the operating temperature. Its a simple concept, not to unsimilair to the K&N intake. Take away the restriction, get better airflow, and hence better performance.

The first street application by a manufacturer was the Porsche 930 (911 Turbo) in 1979. Porsche has continued to install cross-drilled rotors on their cars since. If they were ineffective, or worthless, why wouldn’t they have been removed years ago? Mercedes Benz continues to install them on their highest performance models. They have a worldwide renowned brake system, and called by most the best stock brakes in the world. BMW is in the same place, using the crossdrilled on their high performance models.

Take a 12x12 piece of metal. Put a hair dryer in front of it and continue (a heat gun would work better) to heat it. Test the temp. Now, drill a multitude of holes in it and do the same. Which has a lower temperature? The concentration of heat can now go through the metal instead of building up on the face. I am being serious, not trying to chastize your degree. Does it not seem that you would decrease heat in such an experiement? Granted, when you change to crossdrilled (or at least when race teams do) they increase the size of the rotor to maintain the same amount of surface area. I know nascar uses a slot type system, as they cannot run increased size rotors.

 

98Navi:
Well… there’s a lot here… you have some basic misconceptions about how thermodynamics works… and mechanics too. But that’s ok, it’s hard stuff.. and no offense intended to you either.

I’ll take another shot here (kind of long, sorry, you started it… ), but this would be a hell of a lot easier with a chalkboard.


Lets do the mechanics first:
Like I said above, brakes work by producing friction force. That friction occurs at the pad/rotor interface and is the product of a constant (the previously mentioned and very complicated sounding “coefficient of kinetic friction” of the two materials), and the clamping force of the caliper… a very simple equation.. multiply two numbers.

Two things that DON’T affect braking (friction) force at the contact surface are:
1. Temperature - within reason.. obviously if things start to melt you have a structural problem, and the properties of the materials change. Under about 1000º F, the properties of the pad & rotor are pretty consistent.. the heat itself does not cause a change in the friction coefficient, and hence no change in the braking capacity. Ever see night racing where you can see the rotors glowing orange? Cast iron starts to glow at about 900º... those cars can still stop fine, as long as the brake fluid is kept under about 450º... that's where the slots & holes come in (more on this below).

2. Contact area – This is a tough one to get. It doesn’t matter whether the pad contact area is 2 square inches or 2 square feet – as long as the materials don’t change, and the clamping force is the same, the friction (braking force) is the same. Think about it this way: It takes the same effort to slide the sofa across the floor whether it has feet on it or whether it is sitting on a large flat surface… vastly different contact area, but same materials, same sofa.. same friction force.

Theoretically, the pads could be as small as pinpoints, and as long as they could withstand the clamping force without a structural failure, the braking force would be the same. But they would wear out very quickly, so that is not a very practical situation.

As far as rotor size: Stopping a rotating mass (the wheel, which is being driven around by the momentum of the vehicle’s mass that it’s attached to at its center) requires torque, just the same as making the wheel turn requires torque.

Torque is measured in terms of force times distance. For braking, the force is the friction force generated by the pad at the rotor, and the distance is from the center of the wheel to the centroid of the pad. Multiply these, and you have torque. If you increase one or the other, you have greater braking torque. This is why larger diameter rotors stop the vehicle more effectively, NOT because the pad contact area may be larger. Larger pad area will result in slower wear, but NOT greater braking force.


On to the thermodynamics:

The experiment you suggest is sort of on the right track. I’ll try to clarify what you seem to realize already.

Heat transfer between an object and its surroundings is governed largely by the ratio of its surface area to its volume (and some other things which aren’t pertinent here). Now, obviously, at the moment you remove the heat source (the hair dryer, as you suggest), two objects with similar volumes but very different surface areas (one plate with holes in it, one without, in your trial) will have the same temperature. I think what you are getting at is that the one with the larger surface area will cool more quickly over a given time. That is correct, but it has nothing to do with airflow, or local concentration of heat.. it’s simply a result of the larger surface area/volume ratio.

The airflow thing you talk about at the beginning of your post is sort of right, but again, I get the feeling you’re not quite there…. The idea behind generating airflow is simply to reduce the ambient temperature around the rotor. This gives a large thermal gradient between the rotor and its surroundings, and makes the rotor cool more quickly. The air filter thing isn’t the best analogy.. a better one would be the wind chill you feel in the winter. If the air is calm, your warm body creates a warm layer of air at its surface (same deal as the brakes.. you’re transferring heat energy to the atmosphere). Now when the wind blows, that layer of warm air becomes thinner, so you lose heat more efficiently, and freeze your *** off. It has nothing to do with the FLOW per se, just that the flow is causing the thermal gradient between your body and the atmosphere to be steeper.


Anyway, I hope this helps.