E36 - Drilled and/or slotted rotors - Worth the money or just a scam?

"Karl North" wrote

Unless you are tracking the car, drilled rotors are not worth it. In fact, just replacing the stock rotors with drilled can actually lengthen stopping distances, since the swept area is reduced! There was an article in Car & Driver about a year ago that was interesting - you can probably find it online...

FloydR

In a recent Shelby Mustang GT (that's 475 hp, by the way) pre-test Ford was asked why they were not using drilled rotors. Answer was that drilled rotors have a tendency to crack in heavy use and are not worth the trouble.

Hi, I'm not going to "Track" the car. I'm just looking to improve the performance of the braking system.

Thanks, Karl

So what is the model and year of your auto? If performance increase is what you are after then rotors alone are not the answer.

BMW is a parts-bin company. In other words you can mount parts from the larger cars onto your car. For instance I have a 635csi and I can bolt on 750i calipers, rotors, and master cylinder. I had to buy larger wheels but the the performance was awesome. Another thing I did to improve pedal feedback was to replace the old rubber brake hoses with Stainless braided hoses. What this does is reduce the amount of expansion (balloning), thus making the pedal feel less spongy.

Slotted and drilled rotors will eat brake pads and create lots of dust. These rotors should be used with the pads the rotor manufacturer recommend or poor performance will result.

Cheers. Blake

You've answered the question yourself. If those discs improved a standard setup for normal use, the maker would fit them from new.

No. All current BMW brakes would lock the wheels if the ABS didn't prevent them. If your car doesn't have ventilated disks (air gap in the middle) then it may be worth fitting those if you intend to rally the car or do long alpine descents. Otherwise I would not bother.

The only road application that I am aware of them being useful for is motorbikes, where the disks are outboard, get wet and the slots clear away water allowing some braking effort on the first revolution.

Aircraft sometimes have them (in stacks), but the issue here is the huge amount of energy to be dispersed in bringing tens of tons of aircraft to a halt from 240kmph+ on very few wheels.

If you are experiencing fade in your BMW then you have a problem, probably damp brake fluid.

The scams have it.

Unless you are racing, the slotted rotors are not very good for your car. The same mentality that put the muffler system on your car is the one that drives a person to slotted discs. You don't like the muffler, odds are you won't like slotted discs either. The difference being, somebody else put the muffler on ...

You'll need to define what "better performance" means to you in order to fully answer your question. Slotted or drilled have only a few advantages over standard solid discs.

Upside: The holes or slots allow gasses which are put out by the pads from the high heat of heavy braking to escape. So under this very limited situation (this is the track thing everyone's been talking about) it may improve braking. They also will help void brake dust or water should either of these get onto the swept surface of the rotor. And of course, they look *really* cool (like you are a racer even if you're not).

Downside: You actually *reduce* the contact area between each pad and the disk surface therefore reducing the normal-condition braking performance. They can act as a cheese grater on your pads causing them to wear out significantly faster. They can cause your brakes to be somewhat noisier (grinding sort of noise). Drilled holes can cause uneven heating and cooling of the disk resulting in premature warping and the development of cracks.

Moral: If you drive the car on the street, the only way to really get improved brake performance is to get more or increased friction contact area with the disk, which means either a different brake pad compound, or bigger brake rotors and calipers (big brake kit), which will undoubtedly also require larger diameter wheels to clear them. We're talking many, many hard earned samoleans here...

To my way of thinking, the BMW brakes are already some of the best performing available, and one of the many reasons that I buy my BMWs in the first place. I'd try a few different types of brake pads and see what you can find that you like. They are much cheaper and will have more benefits and fewer liabilities that drilled or slotted rotors. I don't know about you, but I've got (many) more important things to spend my money on than a big-brake upgrade for a street driven BMW.

Now OTOH, if you *are* planning to race or autocross the car (and money should be no object) by all means upgrade to Big Brakes with slots and/or cross drilling. As the old adage goes; the fastest car around the track is usually the one that can stop the quickest.

-Fred W

Rather than slotted/drilled rotors consider the diamond/slotted rotors!They are better in my opinion over slotted/drilled rotors and have had substantially longer pad life due to better heat dissipation from the diamond shaped (holes)!