What's the best design: disc brake rotors

[bull]

I'd like to discuss some info I've been mulling over as it relates to disc brake rotors. There are several different types and I'd like to get some opinions on what you think is best. Basically when it comes to rotors the idea behind the slots and holes is to cool the rotor by exhausting gases more quickly. But which design does it best?

There are about five types of generalized rotors, four subtypes of drilled rotors and four subtypes of slotted rotors I am aware of with the most common (IMO) being OE followed by drilled and slotted rotors:

General
1. OE flat
2. drilled
3. slotted
4. drilled and slotted
5. dimpled

Slotted rotors
1. rounded slots
2. knife edge slots
3. continuous slots (pic 2)
4. open slots (slots go off the edge as in pic 3)

Drilled rotors
1. straight lip
2. champhered lip
3. straight rows
4. curved rows



[img'http://www.gruppe-s.com/Ben/Brakes/Evo_Brakes/PFCStiRotor.jpg[/img]http://

[bull]

And then later, if this gets real interesting, we can talk about vane designs too.

[b5blue]

I like mine scattered and smothered with a .......oh wait that's Waffle House. 

[Mr.Woolery]

-Drilled rotors are just bling.  The only thing they do is allow opportunity for cracking and increased pad wear.  Whenever I see drilled rotors, I'm disappointed.

-Slots are okay, but the only real reason for slotting rotors is to assist in reducing the water sheeting/hydroplaning effect if they get doused. 

-Directional vanes help to reduce pad wear and "chunking" the pads (by having the slots go past the pads at an angle to the pad's leading edge).  Vane direction doesn't make much, if any, difference at all.

The order in which I'd put rotors from best to worst:
-slotted, directional or solid (best)
-dimpled (bling with less pad wear)
-drilled (bling with more pad wear
-combo slotted and drilled or slotted, radial (worst)

[thedodgeboys]

there is something about letting gases from the pads and better cooling with all the holes but that stuff doesn't apply on the street.

now if your going to auto-cross or road race you may look at some of that stuff or if just want the bling.

[Q-ship]

For the most part, appearance is the only real difference. However a couple of the pics you posted are of questionable functionality.

The idea is to vent the gases that can build up between the pad and rotor which can cause "green fade", so any version that can vent the gasses away is a vast improvement.

A couple of the pictures show appearance only designs that couldn't actually vent the gasses. I would avoid them.

I have read that drilled rotors can crack at the holes, but I have never seen/had it happen, and since most ultra high performance exotic cars have drilled/slotted rotors. I'm guessing that the cracking is an internet myth.

As for the cooling vanes, either design will do the same thing, so I doubt that one is any noticeable improvement over the other.

A slotted and/or drilled rotor will offer a big advantage over a flat rotor with any pad that is available nowdays, so I only use, and recommend them to anyone buying new rotors.

[bull]

A couple of the pictures show appearance only designs that couldn't actually vent the gasses. I would avoid them.

Such as which? I'm thinking pic #2 would fit that description but at the same time I would think it would function about the same as a rounded-end slot.

I have read that drilled rotors can crack at the holes, but I have never seen/had it happen, and since most ultra high performance exotic cars have drilled/slotted rotors. I'm guessing that the cracking is an internet myth.

I've seen them crack but the cracks I've usually seen are exacerbated by the holes, not caused by them. Usually it's the typical stress/heat cracks you'd see in a flat rotor which still occur in drilled rotors only they follow the path of least resistance.

[bull]

there is something about letting gases from the pads and better cooling with all the holes but that stuff doesn't apply on the street.

now if your going to auto-cross or road race you may look at some of that stuff or if just want the bling.

So if I'm going down a steep hill, maybe towing an RV with my Durango on the freeway, you're saying there's zero advantage to a rotor design that lets gases out better and keeps the rotors cooler? Or maybe I get slotted rotors for my 68 Charger and I'm coming back from a car show in 95-degree heat and six people cut me off within a 15-minute period... no advantage?

[E5 Charger]

I've gone through this with my 97 Dodge Avenger on an Avenger forum. Unfortunately everyone you ask will give you a different answer. I was considering them because the Avenger rotors warp easily. The more I researched the more frustrating it became. In the end I bought a set of OE style Wagner rotors. I would like slotted for my Charger only because the plating will keep them rust free longer. Unless someone is selling OE style with a zinc plating?

[thedodgeboys]

there is something about letting gases from the pads and better cooling with all the holes but that stuff doesn't apply on the street.

now if your going to auto-cross or road race you may look at some of that stuff or if just want the bling.

So if I'm going down a steep hill, maybe towing an RV with my Durango on the freeway, you're saying there's zero advantage to a rotor design that lets gases out better and keeps the rotors cooler? Or maybe I get slotted rotors for my 68 Charger and I'm coming back from a car show in 95-degree heat and six people cut me off within a 15-minute period... no advantage?

I am no expert however I would say no advantage or little in eather case, the way I understand is the brakes need to be at a certin temp in order for them to show an advantage over none drilled or slotted. I don't recall ever seeing any heavy over the road trucks with em if they were better wouldn't they use them?
What about stock cars if They were better wouldn't  NASCAR use them? They spend cubic dollars on brakes.

I don't don't know about f1 those cars over the top.

.

[bull]

I've yet to see many disc brakes on trucks at all. I know they exist and therefore I bet drilled and/or slotted rotors for them exist. And seeing as how they have the advantage over passenger cars by using exhaust brakes and transmission retarders there doesn't seem to be a big push for them out of necessity.

Beyond that though I don't understand your self-opposing opinion that basically says yes, slotted/drilled rotors dissipate heat better but why would the average guy want to do that. Especially when the cost in many cases is pretty much a wash. What does it matter what the temperature is? The idea is to get rid of heat more efficiently so wouldn't the slotted/drilled rotors still dissipate heat better no matter what the temperature?

[thedodgeboys]

Sorry I'm no expert


Check this out
http://www.perfectbrakes.com/brakesforhighlytunedcars.asp

More good info
http://www.google.com/search?q=are+there+advantages+to+slotted+rotors&hl=en&client=safari&ei=Zo18TK-mH9jnnQf55bGdCw&start=0&sa=N

[bull]

More good info
http://www.google.com/search?q=are+there+advantages+to+slotted+rotors&hl=en&client=safari&ei=Zo18TK-mH9jnnQf55bGdCw&start=0&sa=N

I've read a bunch of those forum opinions already and I've seen guys swear OE stuff is just as good or better and I've seen other guys swear drilled and/or slotted rotors are superior. Basically it looks like nothing more in the realm of expertise than what we have here. So I've decided to research it more by looking for actual unbiased studies rather than forum opinions. So far the only thing I've run across deals with the vane designs rather than slots, holes or a combination thereof.

And FWIW, the forum opinions generally state that an OE design is adequate (and I agree). They also state that there are some advantages to a slotted design such as improved initial grab, less glazing and better brake dust/water expulsion. One disadvantage mentioned about the slotted rotors compared to an OE rotor is that they tend to wear out faster. Some say much faster, some say it's almost the same as OE. I'm sure there are many unseen factors involved in that scenario. Also, I've yet to read about any advantage to drilled rotors.

[bull]

The idea is to vent the gases that can build up between the pad and rotor which can cause "green fade", so any version that can vent the gasses away is a vast improvement.

Based on what I've been reading there's no such thing as green fade anymore due to the materials being used in today's brake pads. Apparently the only gas being vented these days is hot air.

[HPP]

Slotting on the pads themselves usually serves the purpose of venting as well as and much more easily done than slotting rotors for any street applciations. I would also tend to agree that pad compounds have changed so much in recent years that they have become very specialized for applications that require less hardware alterations than in years past. But the whole drilled and slotted look still screams purpose built int eh minds of many car enthusiasts.

When you talk about high end sports cars and racing applications using drilled rotors, that actually is a bit of a dis-service as these rotors are actually formed with the holes in them. They are not drilled. Similarly, real high end stuff is made of carbon, not steel, and certainly not iron.

[bull]

When you talk about high end sports cars and racing applications using drilled rotors, that actually is a bit of a dis-service as these rotors are actually formed with the holes in them. They are not drilled.

I did some reading on that too and no one could find a company that actually cast the holes in during production, and some questioned whether it's even possible to do that. I think some of the dimpled rotors are cast that way but I'm not so sure about the through holes being cast. Maybe, I just don't know.

[Mr.Woolery]

The idea that slotted brakes allow for venting pad gases used to apply, but brake pad technology has come a long way.  Brake pads no longer produce gases like they used to, and now the only reason for slots is for water shedding.

[b5blue]

How about that "cryo-treatment" that super freezes and all that?   

[bull]

How about that "cryo-treatment" that super freezes and all that?   

I read a little about that but I don't know what it does to improve them.

[HPP]

Ultimately, there is no ultimate rotor. There is only best for the intended application rotors. Street rotors will have different requirements than drag rotors, which differ from road race rotors, which differ from short track oval course rotors. I also think it is safe to say that the ultimate in any of these catagories for a stock spindled mopar is not happening either.

If you want to improve braking performance, the single biggest change/improvement you can make is to increase the diameter of the rotor, which will provide greater mechanical leverage for stopping. This is part of the reason why there has been a movement towards larger diameter rims in the past 20 years. The biggest rotor you can fit inside a 15" rim is 12.19", and it won't fit inside of all 15" rims. Step up to a 17" rim and now you have 13" rotors, or a huge increase in leverage over many OEM provided 10.5" rotors.

Since application helps determine the best, there are also considerations about heat dissipation, unsprung weight, moment of inertia, swept area, clamp force, pad compound, effective operating temps, so on and so on.

[suntech]

My opinion is that the slotted directional vaned ones are the best, and ofcause in the biggest possible diameter you can fit in.

The slots has just one purpose, and that is to evacuate water from the disc. ( without increasing pad wear to much)

The vanes has just one purpose, and that is to move most possible air through the disc, to cool it. For that reason the shape is important, and on modern hi performance brakes we see shapes on vanes that reminds a lot about turbine vanes, to reduce turbulence, hence increase flow, hence increase cooling. Same thing we can see on sofisticated water pump impellers. ( take a look at the pump impellers Boyesen Engineering has made for dirtbikes.......almost doubled the flow, just by reducing turbulence!! )
In my mind there is no doubt that it does make a difference, but if we use them hard enaugh to FEEL any difference........that´s another story!

The diameter is easy, since increased distance from wheel center decreases the forces needed to do the same braking job, hence reducing heat build up.

just my 

[thedodgeboys]

Ultimately, there is no ultimate rotor. There is only best for the intended application rotors. Street rotors will have different requirements than drag rotors, which differ from road race rotors, which differ from short track oval course rotors. I also think it is safe to say that the ultimate in any of these catagories for a stock spindled mopar is not happening either.

If you want to improve braking performance, the single biggest change/improvement you can make is to increase the diameter of the rotor, which will provide greater mechanical leverage for stopping. This is part of the reason why there has been a movement towards larger diameter rims in the past 20 years. The biggest rotor you can fit inside a 15" rim is 12.19", and it won't fit inside of all 15" rims. Step up to a 17" rim and now you have 13" rotors, or a huge increase in leverage over many OEM provided 10.5" rotors.







I wish I had said that   that sums it up pretty darn good
Since application helps determine the best, there are also considerations about heat dissipation, unsprung weight, moment of inertia, swept area, clamp force, pad compound, effective operating temps, so on and so on.

[elacruze]

Over-the-road trucks and railroad disc systems do not use slots or holes. That should say something.

Racing systems need venting because they get so much hotter than 'normal' brakes. I'm sure you've seen clips/photos of cars with red-hot rotors at the track. Consider the 24 hour races at LeMans or Sebring.

These are not conditions that merit consideration on the street, the rotors available for our stuff are worlds away in material composition. Basically the holes/slots are merely for appearance. There may be some small benefit during pad break-in and extremely wet conditions.
My rotors are slotted, but only because it came with the package. I bought expensive Powerstop rotors and had them Cryo treated; you get what you pay for in rotor material, and the Cryo insures that there are no stress areas or hard spots through the rotor.

[HPP]

The vanes has just one purpose, and that is to move most possible air through the disc, to cool it. For that reason the shape is important, and on modern hi performance brakes we see shapes on vanes that reminds a lot about turbine vanes, to reduce turbulence, hence increase flow, hence increase cooling.

Only problem with this line of reasoning is that when you buy these directional vaned rotors, are they asking you for right and left applications or are they just throwing a new rotor on the table? If they aren't differentiating between right and left, then one set of vanes is pointing backwards, so your efficiency drops on one side.

[suntech]

Only problem with this line of reasoning is that when you buy these directional vaned rotors, are they asking you for right and left applications or are they just throwing a new rotor on the table? If they aren't differentiating between right and left, then one set of vanes is pointing backwards, so your efficiency drops on one side.

If they have directional vanes, i would have to be a lefty and a righty for each axle.....