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gen1dak
Dodge Dakota
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12/26/2007
00:54:04
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 Subject: RE: rotors bad after 10k
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Geeez .boB, sometimes you can be such a .....pussy.
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Dan M
Dodge Dakota
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12/26/2007
06:15:27
| RE: rotors bad after 10k
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drilled rotors are designed and best used in racing applicatons, not street use. The holes are designed to let gases escape. The drilling weakens the rotors. This is not such a big deal with race applications because they are tossed after the race.
it's all about brake fade. How do the brakes work when hot. Brakes work on friction, more importantly, the transfer of heat.
Slotted rotors do not do much except provide a little room for gases to escape. Gases come from heating of rotors/pads causing the resin in the pad to break down due to heat. The resin releases gas. This is why when your brakes are hot they don't stop as well. You're compressing the pads on a "bed of gas" instead of compressing the pads on the rotors.
This is also why the rubber ring on my caliper burnt when my caliper locked up. My caliper wouldn't relase all the way and therefor my brakes could not cool down. The rotor heated up so much it transferred heat to my caliper. When my caliper heated up too much, it transferred heat to rubber piston. This is why it smoked. By the time I got my stock jack out, my truck jacked up and my front tire off, my rotors were 195 degrees.
Ever noticed F1 cars have air ducts near tires to direct air onto rotor? This helps cool rotors down. F1 racers brake a lot vs indy and nascar.
If you're doing a lot of braking (city traffic, towing, mountains/hills), stick with slotted or dual ventilated (new brake compounds release less gas than compounds 20 years ago). I would never use nor recommend a drilled rotor for street use.
also, why do you think larger vehicles or vehicles with higher hp motors come with larger rotors and calipers? more surface area to grab for pads and more surface area for heat to disipate.
- Dan M
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Dan M
Dodge Dakota
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12/26/2007
06:20:06
| RE: rotors bad after 10k
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I should say that vehicles these days come with dual ventilated rotors.
This is where the area the caliper clamps pads on are 2 different pieces of metal separated by supports. It's hard to describe, but if you saw it you would understand.
think of it like an oreo cookie. The black cookies are the surface areas where the calipers clamp the brake pads and the cream in the middle is the support. this design helps dissipate heat than a single black cookie design.
mmm oreos.. i will have to stop by kroger and pick some up on the way home LOL
- Dan M
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miltonwaddums
Dodge Dakota
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12/26/2007
14:07:25
| RE: rotors bad after 10k
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My $.02 on the subject:
.boB, I've usually found myself in agreement with you, but not this time.
As someone else on this thread has already stated, brake systems work my changing the kinetic energy of the vehicle into thermal energy. This is accomplished through friction. Friction, by definition, theory, and practice is unaffected by surface area. Friction Force = Coefficient of Friction x Normal Force Applied (in this case, the force between the pad and rotor). Thus, the limiting factor in braking performance is the ability to transfer heat from the braking system, not contact patch area between the pad and the rotor. By giving superheated gases a place to go, you have increased the systems ability to reject heat. Slotting or drilling also greatly increases heat transfer surface area for forced convection. Solid rotors do not have a good way to convect heat or allow gases to escape.
Cross drilling holes do provide a stress riser, but have you seen how thick the rotors are? They will not crack, neck, for fail under any conditions.
Another way to reduce brake fade is to use a high temp brake fluid that exceeds DOT standards. When brake fluid begins to boil under extreme braking conditions (for us that would only be emergency braking while towing) the braking effectiveness will decrease.
Alrighty, I think I've wandered far enough off topic from the original post.
One of the things (I think at least) that causes rotor warp is our lack of understanding of fatigue loading and failure modes. Combine that with cheap crappy materials and you can have all sorts of permanent deformation that causes warpage and pulsating with cheap rotors. Mind you, however, that even "good" rotors can warp. The only real way to avoid / delay warping is to brake softly. Obviously, this is much easier with a manual tranny that can disengage when close to a stop (instead of applying torque like an automatic tranny) and using the engine to do some of the braking. But I guess this is something we all know.
Jay
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Dan M
Dodge Dakota
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12/26/2007
17:22:54
| RE: rotors bad after 10k
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I disagree somewhat. You are saying that the size of a rotor/pad has no effect on it's ability to apply force? Try stopping a 5500 lb dakota on half a brake pad with the same piston as a full brake pad. The size of the rotor and pad do come into play. The full size pad will stop faster than half size. It's simple physics as you tried to explain.
Your explanation comes more into play for single piston vs dual piston - more force applied to same surface area. This applies more friction which is more stopping power.
Look at 02 dakota vs 03 dakota. 02 is single pistion dakota, 03 dual. 03 has larger rotor. 03 has more towing capacity than 02.
- Dan M
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.boB
Dodge Dakota
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12/26/2007
18:00:07
| RE: rotors bad after 10k
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>> Friction, by definition, theory, and practice is unaffected by surface area. <<
So.... 1 square inch of pad will produce the same friction and energy conversion as 20 square inches? If that were true you could make the pads 1/10th their current size, lose a lot of unsprung weight, and yet still maintain the same braking force. So why don't the race car builders do that?
>> Slotting or drilling also greatly increases heat transfer surface area for forced convection. <<
Really? According to Wilwood, "Drilling diminishes a rotor's durability and cooling capacity."
The purpose of cross drilling was not for cooling. It was for outgassing. Since modern pads don't outgas that much, it's no longer needed. That's especially true with a ceramic pad. Cheap street pads do, but only at temps encountered during road racing. If you're using your stock brakes for road racing, you're making a big mistake that no amount of holes is going to fix. If you're abusing you brakes that much while on the road, you've got some real problems.
Remember, as Dan said, we're talking about a solid surface rotor, which is really two solid surface rotors sandwiched around an air gap with cooling fins. I havn't seen an actual solid steel single disc in a long time. But I don't work on small/cheap imports, so you might find some there.
Dan is also right about cooling ducts. Most race cars have them. Why? Because that's the most efficient way to cool brakes - direct ambient air onto them in a steady stream. NASCAR not only has cooling ducts, they also have fans in the ducts to blow in more air when the car isn't moving as fast.
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miltonwaddums
Dodge Dakota
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12/26/2007
22:47:34
| RE: rotors bad after 10k
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Dan:
I agree with you about the size of the rotor, as a greater diameter rotor will offer more stopping torque with the same amount of friction force. This increases stopping ability.
.boB:
Most race car builders do select the smallest caliper and pad that will stop the car. And then be able to stop the car again. My point is, pad wear is the reason for not being able to drop below a certain amount of surface area.
I completely stand behind my point of friction is unaffected by surface area. This is physics 101, just google it. One factor that SLIGHTLY makes me lean your way is the fact that a smaller pad has a smaller heat transfer surface area, but most of the heat goes through the rotor.
As for cross drilling rotors, if nothing else, it is a good way to reduce rotating and unsprung mass.
Not trying to flame here, just seeing if someone can learn me something here. - Jay
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Kowalski
GenIII
12/27/2007
17:02:39
|  RE: rotors bad after 10k
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"miltonwaddums" - no one can learn you anything here; but we might be able to teach you something if you keep an open mind. While it's been 30+ years since I took physics 101 (and some more advanced physics too) - what you claim is not what I was taught. Surface area does matter in friction - otherwise we'd all be rolling on skinny bicycle tires for less rolling resistance and better milage. But that size contact patch just doesn't have the friction to turn or stop our vehicles - hope you can understand that real world example. Reducing unsprung mass can have handling adavatages, at least you are right about that. By the way, I'm still awaiting a response on another thread from you - when I said I'll bet you can't explain how a bad IAC could cause hard cranking. That was when you declared another poster's answer was correct; while my answer that a bad battery could be the culprit for both hard cranking and poor idle was slighted. Seems you have a habbit of suggesting others are wrong while you don't know what you are talking about...
Lead, follow, or get out of the way
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Mario
Dodge Dakota
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12/30/2007
21:38:01
| RE: rotors bad after 10k
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Buy American - raybestos
https://www.rockauto.com/dbphp/mfr,RAYBESTOS
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miltonwaddums
Dodge Dakota
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1/02/2008
14:59:31
|  RE: rotors bad after 10k
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Kowalski,
WTF? Why attack me here because of something else I wrote on another thread? Not to mention it was because I declared someone else RIGHT rather than wrong. Someone else made the point I was going for after you posted your question anyways, so there was no point posting back with the same post as the last guy. As for having an open mind I'd be amazed if ANYONE on this forum has one.
As for Physics 101, your professor was wrong. I stand by what I said about friction being unrelated to surface area. Again, just google it. As for tires and TRACTION (not FRICTION - two different animals) contact patch IS critical. I do understand this real world scenario, however it has nothing to do with braking.
I am simply posting what I have learnt over the years. If someone else has a disagreement, I welcome it because I do learn some things. If all you have to offer is slander, then piss off.
- Jay
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