X5 Cross Drilled Rotors? (Rotors With Holes)

[wallyx5]

I have the brembo cross drilled rotors and they do look damn nice of the X. They cost about the same is the oems. No cracking issues and they have about 80,000+ miles on them. They just look nice that's why I got them. And I drive my X really hard so the additional cooling is a benifit.

[butundo]

I have the Brembo's as well. I do think they look good on the vehicle. I also intended to do a lot of towing, so I figured that it would help with cooling, but I haven't installed the hitch yet.

[kishg]

what makes you guys think the holes improve cooling? cooling in a brake rotor is from the heat being radiated off the rotor surface area. holes actually reduce that surface area. the only way holes are useful is to reduce rotating mass in a race car and those typically have brake cooling ducts.

[n2red]

No matter which philosophy you subscribe to, there are manufacturers that do put drilled rotors standard. A good example is Mecedes, and it's performance arm, AMG.

I suppose there are pros and cons either way but in the end, 600 hp means nothing if you can't stop.

[FSETH]

Originally Posted by n2red

No matter which philosophy you subscribe to, there are manufacturers that do put drilled rotors standard. A good example is Mecedes, and it's performance arm, AMG.

I suppose there are pros and cons either way but in the end, 600 hp means nothing if you can't stop.

This is not the same as replacing blank rotors with drilled of the same size though. That is more like a big brake kit.

[FSETH]

Originally Posted by butundo

I have the Brembo's as well. I do think they look good on the vehicle. I also intended to do a lot of towing, so I figured that it would help with cooling, but I haven't installed the hitch yet.

If your drilled rotors are the same size as the OEM blank rotors, they will not cool as well as the plain ones due to less metal mass to dissipate the heat. The holes are not there for heat issues. They are there to allow the gasses that form between the pad and the rotor to escape. However, that is not a big deal these days with newer pad materials. The cooling comes from the metal mass of the rotor, the internal veins of the rotor and and air ducting. In short, you get less cooling with cross drilled direct replacement rotors.

I would not personally do any heavy towing with drilled direct replacement rotors.

[fraserp]

IMO do your home work --- too many experts here - research and re-research take a look herehttp://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-rotors1.htm

[TowX]

I would never drill a rotor that wasn't designed from the manufacturer to be drilled. A Brembo rotor on a Porsche that's drilled was part of entire brake package that was designed for the car. And the rotor was produced to be drilled.

Drilling a stock rotor is dangerous and does nothing to improve braking. Think about it. When you drill holes, you've removed 20-25% of the friction surface that the pad contacts. So on a street car that doesn't build up the heat of a race car, you can give up brake performance in a big way.

Also, having talked with a Brembo engineer a number of years ago, he also said that someone who drills their front rotors but leaves the rear alone is messing up the brake balance and the ABS. He said that with a front that has 20% less surface friction area, the driver has to apply more pedal pressure to get the same braking force from the front than they did with the stock rotors. But, the rears get the same increase in pedal pressure and still maintain the stock friction surface. So in the wet, you know have a vehicle that's going engage the rear ABS before the front, which isn't the way the ABS system was programmed. It'll work in almost all conditions, but as he said, do you really want to test your homemade brake balance in a panic situation when your life depends on it?

Oh, and I've seen stock rotors that have been drilled ultimately crack. I foolishly went against my own best judgment and decided to try a set of 4 drilled Zimmerman rotors for my 911 a couple of years ago in an effort to find a competitive advantage. Keep in mind Zimmerman makes the stock factory rotors for the earlier 911's so these aren't no-name brand rotors being drilled. Here's what happened after just 8 track days. And when I pulled the other front one off, there were cracks forming too. Note that the big crack followed a line from hole to hole. And note the cracks around every other hole migrating outward. This crack was all the way through the rotor. I threw the stock undrilled ones back on, my brake temps went down over 100 degrees, and I could go deeper into each turn before standing on the brakes. Drilled stock size rotors took away brake performance, increased brake temps significanty, and could have caused a major accident if the rotor had cracked at a part of the track other than a slow speed turn. Oh, and when it broke, it sounded like a sledge hammer hit the right front wheel well it was that loud. If I'd been hard on the brakes just one turn earlier (VIR, 140 into turn 1, a 2nd gear right hander) rather than T3 which just requires a light tap on the brakes to scrub just a few mph, I would have locked that right front tire and at least gone straight off into the field, or worse, could have spun the car at triple digit speeds.

[wallyx5]

This is a fun subject. Maybe it depends on the manufacturer. All Brembo Big Brake kits comes with drilled rotors. I have had my brembo drilled rotors on now for over 112,000 miles and never had any issues with cracking or vibration from warped rotors. And they still look sweet. I will buy another set in the near future.

[TowX]

The key there is "big brake kit" from Brembo. Those are rotors that Brembo makes for being drilled. And the piston sizes in the calipers are probably optimized for the application as well. I know with the Brembo BBK's for Porsches that the calipers pistons are sized so the pedal pressure required to stop is unchanged from stock. When you spend $3000+ for a set of brakes from Brembo, you're buying their engineering and their quality.

FWIW, the brakes on my race car have drilled rotors again- but now they're factory 996 Twin Turbo calipers and rotors (by Brembo) for all 4 corners of the car. On a 2400 lb car they're overkill but I can get through 2 seasons of racing on a set of rotors, and 20-22 days on the pads, which is double what the stock size components gave me. And temps are way down too.