Rick

I'm needing to order rotors for my 951S race car and interested in opinions of why kinds of rotors to buy.

I ran factory/plain rotors for the first 2 years I had the car with pretty good results. Last year, I put on a set of frozen/slotted and wasn't very impressed - I did not notice any improved braking performance & they didn't last any longer than my previous sets of rotors.

So...a couple of questions:

• I'm finding a number of suppliers selling Zimmerman rotors & indicating that they're OEM...is that correct? For example, here's some on eBay: 951S Rotors
• What are the benefits of slotted vs drilled vs plain?
• Is it worthwhile to cryo-trea/freeze rotors?

Thanks much,

Rick

smlporsche

I'll give you my $0.02 for what it's worth as we have the same brakes on the front now.
I was pleased with the stock 951S rotors but I now have the frozen variety. I don't know how long they'll last but so far so good.

Zimmerman is the OEM supplier of these as far as I know.

Drilled are not for track unless your in the rain as they tend to crack more. Some pepple like slotted to aid in venting the gases that builds up under friction. At my driving level I'm still happy with the solids.

The biggest improvement I made to my braking system was to install the OG brake ducts. They do a fantastic job of maximizing cooling but they are difficult to find.

Good luck in your decision.

Mike Buck

Zimmerman makes two kinds of rotors. One comes in a Zimmerman box and one that comes in a Porsche box. They are look identical, but the Porsche box ones have a gray coating on the hat/hub area to prevent rusting. The Zimmermans are bare. Price difference is around $30 more for the Porsche box ones. Other than the the price and the coating, they should be the same physically, but for whatever reason I've found the Porsche box ones to last a little longer on my car (4-5 more weekends). Sample size is only 1 set of Porsche rotors and one set of Zimmerman box ones, so I don't have much data. My car is track only. My father drives a street only 951S. I put Zimmermans on his car last fall w/o worry and feel they'll last well in that application, but I put Porsche box ones on my car again when I needed new this year.

General rules i've heard
Street, Zimmerman ok and saves a few bucks.
Track, Porsche rotors.

Never tried drilled or cryo. Haven't felt the need to. I run just the 968 cooling ducts. Never generate a lip on my rotors from wear, just get a lot cracks that eventually lead to lots of shaking. From what I read, the cryo should help prevent this cracking or extend the life longer, but I get reasonable life as is. Drilled rotors would leave me throwing rotors out sooner if I had similar cracking.

Jim Child

I have the same brakes on my race car. I use either the Zimmermans or the factory 951S replacements from Porsche. I don't bother with cross drilled or slotting. On my car cross drilled rotors crack too easily. I've run slotted rotors, and not noticed enough difference to justify the extra $$$. I've also run cryo treated rotors and not noticed any difference in wear. The only difference between the Zimmermans and the factory replacements is the paint on the hat. The Zimmerman hats are unpainted and will collect surface rust. The factory replacement hats have high temp paint to prevent this. Its strictly a cosmetic issue which may or may not bother you. It doesn't bother me, so I generally use whatever I can find cheaper.

schwank

Hey Mike, you can just buy a 4 dollar can of high temp engine paint in whatever color you want and do it that way as well... just blue tape the rotor face and the inside of the hat and go to it. I've done several sets for the Porsche and the Audi this way and it holds up fine and prevents the ugly rust.

No reason to pay the 30 dollars more for paint only... if that is the only difference.

And no laughing at my puny NA brakes!

Mike Buck

What I was getting at is that there does appear to be some difference in terms of rotor life durability on track. Difficult to quantify, but worth it to me on a track only car. A lot of the guys I race with tend to agree. Like I said, I put Zimmermans on a street car and painted them same as you with VHT black. No issues.

Oddjob

Ive told this story several times, but this questions comes up often, so I will tell it again...

Purchased a pair of front rotors a few years back from an aftermarket supplier for my 951S. When they arrived, one rotor was an OE porsche rotor, the other was a zimmerman. Didnt think too much of it at the time. But after using for a season on the track, the Zimmerman rotor had significantly more heat/stress cracking than the OE Porsche rotor. It ended up cracking through, and the Porsche rotor still looked pretty good. Cant think of a better side-by-side comparison test.

Spoke to Bill Groschen about it (the Cyro Frozen rotor guy) at the time, and he agreed that the metallurgy of the OE Porsche rotors are better than the aftermarket Zimmerman. Apparently during their cyro/heat treat process, they noticed different material properties between them.

Again, this was half a dozen years ago, so I cant say for certain that current OE rotors are still better or different than aftermarket zimmerman, but after that experience, I have never used zimmerman rotors again - I only use solid OE Porsche rotors. And if you get them from one of the discount dealers (like Hennessy or Sunset), they are actually not much more expensive than the Zimmerman.

Also, there is not a consensus that Zimmerman is actually the OEM supplier for these rotors. Others have stated that Sebro is the OEM supplier to Porsche for rotors - although its possible that porsche gets different rotors from different suppliers, or changed suppliers over the years, or even uses multiple suppliers for the same rotors. Girling, ATE, and obviously Brembo also supply a lot of brake components to Porsche.

My thought is that, even if the cryo treatment increases rotor life, its probably still not enough to offset the increased price.

If price were no option, I would go with 968 M030 rotors (factory x-drilled, 965 part number) and get them cryo treated. But that would cost about $600 for the pair. So I wont be doing that anytime soon.

Rick

Interesting...here is the label of the rotors I was looking at - I'm not worried about the appearance but am focused on longevity & performance. I'll call Sunset this afternoon.

jerome951

I've found the same thing that Mike and Jim have. Zimmermans on my car dont' seem to last as long (heat-crack faster).

Through Sunset OEs aren't much more than Zimmermans.

And never confuse OE with OEM. OEM just means that the supplier provided a product to Porsche; doesn't necessarily mean the part was put on a 944 or were even brake rotors, and may not be the same specs (as Jim mentioned above) as the original part.

Eric in Chicago

As listed above, Zimmerman rotors dont last very long. I am running the 993 rotors (cross drilled) as they seem to last longer,(I know, strange) and are less prone to warping than the 951S rotors. I got a couple of sets from Sunset (951S) and they both warped. They were properly bedded yada, yada, yada. I have not had any problem with the 993 part #. I get about 4-5 race weekneds out of a set.

Oddjob

Eric,

What hubs/spacers are you using to fit a 993 rotor on a 944S2 spindle/hub/caliper setup? The hat height on the 993 rotors is different than 951S/928 hats.

Road America is hard on brakes. So I dont doubt that you have had various cracking/warping problems with your rotors there.

JPhillips-998

Rick I have run both and also feel that the OE rotors hold up better. For the minimal $$ difference, I would definitely go OE.

Eric in Chicago

Hi Jim,
I have the non MO30 Hub and spindle set up (Racers Edge Hubs) and the Racers Edge brake adapter. I flip the adapter around and the rotors fit without any problems. I have a set of alum hats that I am going to try this season (drop a little unsprung weight). The rotors are a bit more expensive but if I can get the 993 size and sloted instead of drilled they should last a couple more weekends (I hope). RA is a bear on brakes. After a weekend there, my pads go into the DE pile (more than 1/2 gone)

Dave in Chicago

My experience echos many above. M030 solid units, race conditions.

Zimmerman - No paint (don't really care), loose mold bits in vanes (file off, mild annoyance), but they do seem to crack rapidly for me (that's the real issue for me).
Porsche OEM - Painted, filed, nicely finished... just don't seem to crack as soon or as much under the same conditions.

I've avoided the drilled (don't need to add complexity), slotted ($$), and cryo ($$)... so no help there.

I have fresh Porsche OEM units on the workbench (installing tonight) from Sunset for about $102-105 each.

Note that the Turbo S solid rotors incorporate directional vanes and must be mounted appropriately L/R to work their best.

Van

So, in race/track conditions, how often are you replacing the Porsche rotors? I've been using the Zimmerman ones for years, and seem to get about 2 years of track duty out of them (averaging a dozen to 15 days on the track.)