Drilled Rotors: Directional? - PeachParts Mercedes-Benz Forum

MikeyE430 · #1 09-09-2004, 05:34 PM

Trying to find a decent set of drilled replacement rotors for my 2000 E430. Looking at a set of Zimmermans. It appears that there is only one product number for the front and one for the rear. No left or right. If the drilling is directional, won't the holes be spinning backward on one side? Does this matter as far as airflow and pad wear? Won't it look goofy?

Are AMG and Brembos sold as left and right?

What say you, good peeps?

FlyDad911 · #2 09-18-2004, 09:34 PM

Replaced the rotors on a 911 recently with Brembo cross-drilled rotors, and went looking to see which way the pattern went. MB has one direction and Porsche the other. But the set has the pattern different left and right, so then it became a question of which direction was "right" - and it turns out there is no "right" direction. The purpose of the holes is to allow the gasses generated by brake operation to dissipate "more quickly" than undrilled rotors, so it really doesn't matter.

'87 300D Turbo with only 282,000 miles
'83 911SC with really great brakes

Jim's500E · #3 09-29-2004, 11:25 AM

If you get rotors that are also internally vented then it does matter which way they are installed. Usually, like on a Porsche with drilled and vented, the holes will bend/track backwards....

...this was the case on a friend's C4S...someone put a rotor designed for the left front on his right front. Fit fine but probably won't work up to its potential when needed.

MikeyE430 · #4 09-29-2004, 11:43 AM

Ended up buying a set of Brembo drilled rotors. They are drilled differently for the left and right. Also got Axxis Deluxe Plus pads and StopTech braided steel lines. Install to come. Report and pix to follow. Thanks for all your info.

yhliem · #5 10-02-2004, 09:50 AM

Quote:

Originally Posted by Jim's500E

If you get rotors that are also internally vented then it does matter which way they are installed. Usually, like on a Porsche with drilled and vented, the holes will bend/track backwards....

...this was the case on a friend's C4S...someone put a rotor designed for the left front on his right front. Fit fine but probably won't work up to its potential when needed.

Depends on what your driving style is.

R129 SL600s used directionally specific internally vented front rotors. as a result, 2 part numbers are required. MB is now in the process of phasing out the 2 PNs and supplying only one pair of identical rotors for replacement. This is already in effect in Canada. so one side is spinning "backwards".

Unless you're tracking your car, I don't think that this is much of an issue.

Cannoli · #6 10-03-2004, 08:10 PM

Good Q ... I recently upgraded my rear brakes (SL600 calipers w/Balo 300mm drilled/slotted rotors). The rotors I purchased did have specific sweep patterns that could be installed sweeping with the direction of travel, ala StopTech, or away from the direction of travel, ala Porsche.

Based on Porsche front and rear rotors that I have seen (and I've seen soooo many lately at the weekly Crystal Cove GTG in Newport Beach, CA) that have cross drilled patterns, have the hole paterns sweeping away from the direction of travel. Again, this appears to be true, front/rear and left/right.

I recently stopped by StopTech's Torrance, California facility and asked about this and why they have their rotor patterns sweeping towards the direction of travel (F/R and L/R). They told me that because of the design of the cooling vanes, the holes are drilled in such a pattern as to not drill into the vane.

Now, I recently saw a current model SL55 that had drilled rotors, and one side had a pattern sweeping away from the direction of travel, and the other side was sweeping towards the direction of travel. Hence, one Rotor part number ... not L/R specific.

So, what does all this mean? Apparently, the direction of the pattern does not matter, that is, if the rotor was designed to be L/R compatible. Porsche sweeps away, and StopTech sweeps towards.

Do you wear your watch on your left wrist or your right wrist? Which side tells the time the quickest?

yhliem · #7 10-04-2004, 12:19 AM

well...i'm no expert on fluid dynamics and aerodynamics but I think the PERCEPTION is that having the vanes sweep toward the direction of travel will "scoop" more air into the rotor thus having a greater cooling effect. However having the vanes oriented the other way would, i think, force the air out of the rotor. The resulting displacement of air would create a partial vacuum within the rotor drawing "fresh" air in from the hub area and through the holes.

In a way, the argument of cooling vane direction is somewhat moot; both theories rely on air being drawn into the rotor rather than being directed at the brakes and, as such, I would probably think that the direction of the vanes (and hence the holes) do not have that great of an effect (good, or bad) on the cooling.

If one is concerned about cooling the brakes, I would recommend the installation of ducting to take fresh COOL air from under the bumper of the car and direct that at the backside of the brakes. this air, apart from being cooler than the air that is being drawn in from around the already warm brakes, will be moving at a higher velocity and i would suspect that the added "wind chill" would have a noticable effect of rake performance.

BobK · #8 10-04-2004, 09:29 PM

Spinning vented brake rotors will exhaust warm air out along the outer edge and take air in at the center. The impeller blades can be forward or backward tilted, but the air will still go out the same way.

Tobias MB · #9 10-10-2004, 09:22 PM

There are basically three different styles of rotors, solid, straight vanes and curved vanes.
If the rotors are straight vaned then it makes no difference in the pattern or direction the rotors turn as was stated before, the air gets drawn in the
middle and out the circumference.
Now high performance or racing rotors have curved vanes inside them and even without holes (holes rarely used for racing) the rotors are directional
and it makes a huge difference which way they are installed for the best cooling efficiency. Racing rotors are usually slotted to prevent heat cracking
around the holes found in drilled rotors.
Hope this answers your question better.

Tobias MB
190/5.8

AtlBenz · #10 10-11-2004, 09:41 PM

Esthetically it looks horrible. When something has an inherent directionality its best to be thorough; detailed. It’s sloppy not to compensate for such changes.

If directionality doesn’t really matter, why don’t the holes spoke out radially. Then it really won’t matter if they are on the left or right side. Why do they have to have a "swoopy" nature in the first place?

Cannoli · #11 10-12-2004, 12:52 AM

Amen to that! I can't agree more ... I love looking at Porsches and Ferraris for that reason, among others.

Unfortunately, the Bean Counters are at it again.