bowser1724

So, I've gone through as much as I can tolerate so I am going to post what I know, what I've found, and hope you all can fill in the rest.

I've got a 1987 944S. It needs some front brakes. There are 100's of options out there, ranging in price from $20 to $300 per rotor. Drilled, slotted, black zinc, gold zinc, dimpled, casted, oe style... How do you decide?

First I read many comments here in RL, many seem to like Zimmermann, but the problem I see is that each commenter has there own driving style and objectives. This leads to other comments, for example Centric - are they good? "they're crap" "they warp" "I was unhappy with them" "they worked fine for me" "7k miles, still work fine". None of these comments have any factual basis behind them.

Here is my facts list:
More metal = more heat dissipation - *simple* thermodynamics
Cross drilling = cosmetic only, not for track use because it weakens the disc.
Cross drilling and casting are different
You get what you pay for, except when you don't.
Actual materials make a difference
Zinc wears off the braking surface, prevents rusty looking hubs.

Decision Process
Step 1: year and model / submodel
Step 2: which brake option do you have? Do you have M758 (944 S2)?
Step 3: to track or not to track
Step 4: do you care about looks?

Take a look at clark's garage:
http://www.clarks-garage.com/shop-manual/brake-04.htm

The OE spec for most 944 and 944s (non turbo) is 20.5mm (0.8")
This seems to be the vast majority of rotors out there.
If you are running an S2, then you will want to look at the specs to ensure you are getting the thicker rotor.
If you have the M758, you will have a much beefier rotor, at 32mm

If you are going to track it, and you are going to run it hard, I STRONGLY recommend NOT getting cross drilled rotors, unless you like your rotors to crack. You can find plenty of stories. I have a personal one myself. Rotors didn't fail, but they ate the pads up, and the drill holes cracked, leading to poor rotor and pad life. At the track, no one cares how cool your rotors look. Make sure you can stop. As far as slotting - see end of post questions.

If you are NOT going to track it, then get whatever cool look or color floats your boat.

Finally, metallurgy. I know very little about it, but it seems that a better process and better materials lead to longer life. How to know this about your target manufacturer, well, that is another story.

In an effort to better assess how much metal is present, check the shipping weight. This is not a fail-proof method, but I've found that most of the 20.5mm rotors come in at 13.3 lbs. Once you get them out of the box, we'll see.

List of well known manufacturers:
Zimmermann
Sebro
ACDELCO
Brembo
Centric / StopTech
Bosch


Open Questions:

Can the caliper on a normal 944 / 944s fit the 28mm rotor thickness + new pad?

Slotted rotors - are they worth it? Anyone with some facts on braking power, pad life, rotor life?

Info Request:
If you agree with the points in the post, perhaps you can post the thickness and weight of the rotors when you get them new, and of course the manufacturer, and if inclined where purchased and price.

AgLiftPilot

Lot to discuss here.

I race a 944Spec car for 14 or so week ends a year. The car has the late spindle with floating rotor which slips onto the wheel studs and not the rotor that bolts to the inside of the early style hub. My race car has brake cooling ducts on both side through holes cut into the backing plates.

I got my car in 2012 and ran on those rotors until the summer of 2015. These rotors were Brembo stamped and already decently worn. There was a good sized ridge on the inside and outside edges, but very little cracking. Braking performance was good so I continued with them until I had a decent amount of heat checking and more ridge than I was comfortable with. About 15 or so events were done on these rotors. I replaced the pads maybe twice in the process.

In the summer of 2015, I refreshed my car in preparation of the national championship event. At the Amateur Motorsports Expo 15 I met reps from a company who had a brake bedding service where you could send them new rotors and pads, then they would install them on their brake dyno for bedding in. This would impregnate the rotor with the pad material which is what apparently is the purpose of bedding in new brakes. In essence, you can install these rotors and pads and they are race ready. I can say the process does help. It may not make a huge difference in the level of racing I compete in, but since the brakes which went on the dyno after mine was the Corvette Racing brakes, it must be worth something.

The rotors I ended up getting bed in were at the recommendation of the brake shop, which were Centric/Stoptech slotted rotors. I have been running Hawk pads since I got my car in the DTC-60 Front and Blue Rear combo since after the first pads wore out.

I will agree that the more material the better, so cross drilling isn't worth it since modern pads don't gas out like the olden days. I was told that slotted rotors do help in cleaning the surface of the pad allowing fresh compound to always be in contact with the surface of the rotor.

Metallurgy is very important, but if you are buying a quality rotor, I think you are getting as good as can be expected. If the car isnt ever going to see the track, then I would go as cheap as possible unless the looks care to you.

The final thing Ill say is that I didnt see anything mentioned about the vane direction within the rotor. Modern rotors are ventillated, and serve as an air pump with the way the rotor vanes are positioned within the rotor. Cheap rotors dont matter which side they go on, but the more expensive rotors can include directional vanes which require you install the rotor on the correct side for them to work properly.

Dave951

Since AgLiftPilot brought up the subject of pad bedding, I felt I should add a few more thoughts on that. It seems that every pad/rotor company has a different recommended procedure for how they think the bedding procedure should take place. I've tried a good number of them but the procedure which I feel is the best was the one from Wilwood. Here

V2Rocket

I have regular Zimmerman rotors for the past 10 years/50,000 miles, just put the 2nd set of pads on a few months ago. Thickness of rotors seemed fine for the next 50,000...Pads since 2006 have been "Mintex" OE replacement basic Organic...

No "wheel wobble" (from warped rotors), nothing but good stopping.

Car is long distance commuter, around-town errand runner, canyon blaster, wanna-be street racer, everything...no problems.

Smike

Old post but lots of relevant info.

http://www.evolutionm.net/forums/evo...ct-thread.html

To be clear, "warping" is uneven pad material transfer. This creates high and low variations on the rotor surface that in turn (no pun intended) causes the brake pad to ungulate as it passes these spots. Often yo will see heat spots where the deposits are. Turning rotors will remove uneven deposits. Review pads and how you are using them (e.g. street pads overheating in HPDE use or race pads operating at too low of a temperature on the street).

curtisr

Would this help? As one might imagine, brakes are the stuff of research galore.

Thermomechanical Behaviour of Dry Contacts in Disc Brake Rotor with a Grey Cast Iron Composition

Van

I use Sebro solid rotors. I usually get 2-3 seasons out of them in the front. And many, many seasons out of the rear.

To the OP, I think you're over thinking it for an NA car. The Sebro rotors for $45~ish are fantastic bang-for-the-buck. Could you argue that slotted, dimpled, cross-drilled, plated, etc. have some marginally beneficial attributes? Sure... but are they worth the additional cost? I don't think so.

mikey_audiogeek

You missed one - Porsche.

OE "Porsche spec" discs are better and last longer than OEM discs.
None of the manufacturers above are allowed to sell OE "Porsche spec" discs, even though they might be the OEM.

Not saying they're worth the extra bucks, but you should be aware that OE spec and OEM spec are different.

Cheers,
Mike

thomasmryan

Yes, I believe this to be the original non-M030 968 front rotor. Notice the extra bump between the vanes to increase surface area/cooling.

Arominus

I run sebros up front and recently acquired a set of OEMs for the rear that will likely last until the world explodes. The solid sebros have been... Solid.

mikey_audiogeek

Yep, that's Porsche OE, one of the visible differences.

Another obvious difference is the superior method of balancing the disc.

Wonder how many differences there are that we CAN'T see?

Jon951

Yes I replaced multiple sets of cross drilled Big Reds which were needed at the time for the pads out gassing I now use solid rotars and modern pads (more swept surface = more braking). Another level of voodoo is to have the calipers, pads and rotars cryogenically frozen. This is alleged to increase their durability which can be a critical factor in endurance racing.

Tiger03447

One note on the cryo treatment..After the part has been stress relieved by the cryo treatment, the tolerances go haywire.as well as the grain of the material...for absolute precision in the rod/crank area, the surfaces have to be re-machined after the treatment..every solution..breeds new problems..

fnel1771

Got 35 days out of my Sebro Slotted in 08 CS, using PFC08. Running in Instructor group mostly at The Glen and Tremblant.

Installing another set on the weekend!

bowser1724

Is Porsche really the manufacturer? I thought Zimmerman made the "Porsche" OEM. I can't seem to find my reference now though. Do you have anything to point at?