Brake rotors?

[jblackburn]

Ehhhhhhhhhhhh. I've faded my ceramic brakes and drilled rotors, but they were smoking pretty good at the time.

They do make a huge difference in wet weather with how quickly they grab, though.

[instarx]

There is a very good technical discussion of drilled rotors vs solid in this BMW forum. There is even some data and references to a technical article published by GM.

http://forum.e46fanatics.com/showthread.php?t=500950

There is a lot of information and it is interesting reading (I learned a lot), but basically the discussion was summarized by this paragraph:

Street use brake heat is well below what the components can handle. Manufacturers build in a certain amount of safety margin in the generally unlikely event you need it (braking down a long grade, running from the cops, etc). So buying a rotor that is cross-drilled for the pure intent of "running cooler" is not necessary. For "looking cooler" it may be a good investment, but spend your money on better tires or pads if you want better stopping power.

Data from the GM study indicated:

• - Pad wear on cross-drilled rotors was up to 50% greater under hard use, and about 25~30% greater under street use.
  - There is no practical difference in wet weather performance [between cross-drilled and solid rotors].
  - Pad outgassing is not factor
  - Thermal fatigue life is significantly shorter for cross-drilled rotors. In the case of poorly balanced and possibly under-sized [systems], by as much as 50%.

I'm sticking to my guns that drilled rotors are a waste of money for almost everyone.

And for the ABS not being the fastest you can stop - you are absolutely correct. ABS is also inferior to locking the wheels in gravel and snow. But there is only so much room in a post so I simplified a non-critical point.

[Mad Dog Tannen]

Buy slotted or regular vented rotors. Not drilled. Especially if you care a out price. Cheap cross drilled rotors are trash.

[kcodyjr]

Re: drilled rotors not helping in wet weather. I beg to differ; my own foot and butt say otherwise.

Re: pad outgassing not being a factor, correct, but as I indicated there are other sources of gas.

Re: cheap drilled rotors. Agreed - stay away from them like the plague. I spent the bucks on some high end Zimmermans that were cross drilled and chamfered, then coated, by the manufacturer. Chamfering (countersinking, to woodworking folks) makes all the difference for resisting cracks.

Also, with any brake rotor but especially cross-drilled, it's important to let the car roll forward a few seconds after stopping, so the part of the rotor under the pads gets a chance to cool off. Warping and cracking comes from uneven heat dissipation - one part of the rotor remaining much hotter than other parts.

There's no doubt this is a hotly contested topic. If one answer was right for everyone, there would not still be such lively debate.

If your priority is to save money, then you want solid/vented rotors without any kind of slots or holes. Coating is optional. Stick with the original size and buy from a reputable vendor. Right now, for Volvo, I suggest Zimmerman, since Brembo drank the made-in-China kool-aid.

If your priority is to establish absolute confidence in your brakes, don't try to do it on the cheap.

[instarx]

My first sentence on this topic was to the effect that I knew it would be contentious! LOL I agree with everything you said kcodyjr except the last sentence. I have complete confidence in my solid vented rotor brakes (zimmerman) given the non-racing use I put them to. I see no reason to spend extra money to buy drilled or slotted rotors that may allow me to do 30 65-0 mph stops when solid rotors allow me to easily do 15 65-0 stops.

This topic and the mileage improvements of very expensive air intake filters are two things I don't follow the pack on.

[modabasi]

The physics science tells us that total friction force between the rotor and the pad does not change by the size of the contact area. This means that braking with larger pads and rotors will stop you at the same distance as smaller pads and rotors under normal conditions.

Although total friction force does not increase as the contact area increases, the heat generated by friction decreases. This is why faster cars use bigger rotors and pads, larger contact area means less heat + easier cooling and less heat + easier cooling means better braking performance under hard driving. When you use drilled and/or slotted rotors, you help the rotor to dissipate heat BUT this time you make the contact surface between the rotor and the pad smaller which makes the rotor heat up faster.

[Mad Dog Tannen]

I always thought that they used larger rotors because they get more leverage the farther the calipers are from the center. Like the Buell motorcycles have them run along and mount to the outside of the rim for that reason.

[Kirby J]

Sorry to hear of the demise of brembo. 2 years ago I installed brembo stock style rotors, w/ akebono pads on all four wheels of my 945. 125k miles later I have NO warpage, a good amount of pad left, and relatively little wear on the rotors themselves. I don't drive aggressively, but often am carrying 500 to 800 lbs of cargo in the back and I depend on my brakes. I guess i will try Zimmermans next.

Kirby J
93 940 423K and counting

[zhenya]

I'm sticking to my guns that drilled rotors are a waste of money for almost everyone.

This. Walk around the paddock at any race or track event. Drilled rotors are almost completely absent. Data has shown for years they offer no benefits and present the huge liability of cracking.

[EstVolvo]

autohausaz.com
Zimmermans