X5 Cross Drilled Rotors? (Rotors With Holes)

TheKingSim0n · #1 03-18-2010, 06:48 PM

I was just trying to figure out what difference with brake performance is there with those cross drill rotors? I have seen a few X5s on the belt parkway with them and I was just wondering if they are any better or worst performance wise? and if not they why get them? are they cheaper?

LightWerkz · #2 03-18-2010, 06:53 PM

You wont see any benefits of using these on the street.

In fact they are actually more prone to cracking.

lemans4.8 · #3 03-18-2010, 07:15 PM

X2. The best brake set-up for the X5 is stock!

FSETH · #4 03-18-2010, 09:20 PM

Generally speaking, a big brake kit is overkill on a road car.

Now If you are talking about keeping your existing calipers and swapping out your plain rotors for cross drilled rotors of the same size, you are probably going to loose performance. Drilling reduces the metal mass of the rotor. Metal mass is what dissipates heat, so the less metal mass, the less heat can be dissipated. A big brake kit increases rotor size to compensate for the mass lost from drilling holes.

I would stick with plain rotors. If you are looking for a performance boost, try better pads, fluid, etc.

Vsmvince · #5 03-18-2010, 09:27 PM

Oem Brake rotors are your best bet. Cross drilled are all show for around town.

kishg · #6 03-18-2010, 10:29 PM

still with blank oem rotors. cross drilled is just for bling and will crack eventually.

X5 Meister · #7 03-19-2010, 05:53 PM

Oh so THAT'S what is meant by cross drilled ? Rotors with HOLES. Thanks boss.

TowX · #8 03-20-2010, 10:05 AM

When you drill holes in the rotor, you remove 20-30% of the friction surface so to stop you need 20-30% more pedal pressure. Drilled rotors are there to allow extra cooling and reduce weight. There's really no value on a normal street car at street speeds. And as others have said, a true drilled rotor must be designed to be drilled or it will crack. (ask me how I know). My race car has drilled rotors but Brembo designed them to be drilled. I tried stock rotors that had been drilled on my 528 and it was a waste of money, the increase in pedal pressure required to stop was significant. 3 months of putting up with that and they went in the trash, replaced with stock rotors.

JCL · #9 03-20-2010, 11:19 AM

Quote:

Originally Posted by TowX

When you drill holes in the rotor, you remove 20-30% of the friction surface so to stop you need 20-30% more pedal pressure. Drilled rotors are there to allow extra cooling and reduce weight. There's really no value on a normal street car at street speeds. And as others have said, a true drilled rotor must be designed to be drilled or it will crack. (ask me how I know). My race car has drilled rotors but Brembo designed them to be drilled. I tried stock rotors that had been drilled on my 528 and it was a waste of money, the increase in pedal pressure required to stop was significant. 3 months of putting up with that and they went in the trash, replaced with stock rotors.

Drilling rotors doesn't change the pedal pressure required. Friction is equal to the coefficient of friction multiplied by the normal force (pedal pressure). What can change with aftermarket rotors is the surface finish of the rotor, and this can raise the pedal pressure. Drilling is immaterial.

Agree with the rest of your comments on the complete waste in drilling rotors, and the increased tendency of drilled rotors to crack.

RMak · #10 03-20-2010, 11:41 AM

I don't recall if it's been posted here before but here's a pretty insightful article.

WHY Blank rotors are better than cross drilled and/or slotted - Honda-Tech

Article mentions that Ferrari is the only company that their brakes are cast with the holes already in them. They are not drilled. I guess that's why you pay so much for a Ferrari.