zoso_turbo

First and foremost...thanks to all for your feedback...I apprecaite the feedback and hope that othjers are benefitting from these posts.....

So...at this point here is a quick summary of the varioujs posts:
* Slotted and Solids seem to be more ideal for "hard braking" scenarios - track events
** Cross drilled will perform better in wet weather, but may not hold up to track days as the slotted and/or solids will, they may develop hairline cracks.
*** Ceramic is not in the same category to compare, seem to be too costly for this comparison.

One observation I would like to point out is this....It seems that when you compare the type of rotors I have mentioned, using data points from "supercars" seems to be inapplicable. I am having a difficult time thinking about spending more than the typical price of a slotted or solid rotor from ZImmerman or Brembo. So, anyway, like I said, I am open to any and all relative feedback.

Thx again.....

Please feel free to add/update my summary.

ZT

azmi951

This is an excellent article all about the science of brakes. It is from 1991 but many of the facts are still present.
I do wonder if the race teams that run stock brakes that were originaly drilled have switched to slotted rotors.

http://www.scirocco.org/faq/brakes/p...n/pfpage1.html

Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it.

The one glaring exception here is in the rare situation where the rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car, for an example.) While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life, at the expense of higher weight. It's all about tradeoffs.

Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)

zerMATT951

On the topic of good reading, Don Istook was sponsored by StopTech for a few years while his team was racing Audi S4's in the Grand Am series. Those guys know a lot about brakes and have written quite a bit of technical information about all aspects of braking.

This is their FAQ page that mixes pretty good technical info with a little product info:
http://www.stoptech.com/tech_info/faqs.shtml

This is their white paper index with some REALY good technical reading about brakes, but they don't get any more in-depth on slotted vs drilled. Each is great reading on it's on merit though:
http://www.stoptech.com/tech_info/te...e_papers.shtml

zoso_turbo

Is there an area on this BB where one can place white papers and links of reference? If not, we will lose a valuable exchange of information as it related to this particular topic.

Thx...I hope someone can answer my question.

ZT

Stuttgart

Here is a couple definitions that are of the utmost importance when taking a look at braking.

“Bite” describes the response time or initial reaction the pad’s have when first engaged. This characteristic is designed into c pads to maximize deceleration in the first ½ second of the stopping event while both aero and dynamic grip-traction of the racecar are at their optimum.

“Torque” is the amount of decel during the braking event for the given amount of driver effort. An important area of improvement for is how smooth the torque delivery is for the given driver’s input.

“Release” or modulation, is the ability to control the release or time response of the decrease in braking power to prevent overwhelming the available mechanical grip of the tire’s traction with the track surface allowing the driver to optimize tire adhesion without locking wheels. Release characteristics are ultimately important in technical corners and high speed finesse braking.

“Feel” is how dynamically, the bite, torque, pedal travel, and release interact with both the brake system components and the vehicle’s grip-traction level. This interaction, and the subsequent effects and their value are subject to debate from driver to driver. Certainly a moving target for all racing brake manufacturers.


A proper racing slot pattern has two purposes, improved bite and improved release. Gas dischage is not an issue. People often believe that the slot in brake pads are for the same reason, but in reality they are there to releive stress much like an expansion joint in the side walk.

You would be extremely surprised to find out how big of a role marketing plays in designing brake systems for auto manufacturers, often times to the detriment of performance, look no further than the brakes on the 997 cup.

The single biggest factor in disc quality is casting technology and metallurgy, and unfortunately it is the hardest for the consumer to determine. Look for machined ID and OD, many manufacturers will cut costs by machining only the OD or neither. Anytime you see a balance cut or weight clip, you should be warned that the casting is junk, inconsistent vane thickness and metallurgy.

Chris White

Hmmm...all the 993 turbo rotors I have used have balance cuts....

Chris White

Oddjob

I recall every Turbo S/M030 rotor that I have ever looked at, also has the balancing cuts/machining on them - both Porsche and Zimmerman.

Stuttgart

They are poor quality castings, balance cuts adjust the mass which negatively effects the thermal stability.

What would you think if you got a set of tires with a chunk of tread removed to balance it?

Oddjob

You can equalize rotational mass by various methods - adding mass to the light side, or reducing mass on the heavy side. For balacing purposes it does not matter, for pratical purposes it does matter.

All tires require balancing. But its done once they are mounted on the wheels, so the balancing is done for the wheel and tire combination. Since the tire is in contact with the road surface, of course the tread surface cannot have mass removed for balance. Thats not a pratical method for balancing, so tape-on or clip-on weights are used.

A couple questions:

- Have you ever seen a cast rotor that does not require balancing? Brand/make?

- How does machining the edge of a cast rotor for rotational balancing affect the thermal stability. And what do you specifically mean by thermal stability?

In the end, it doesnt matter. Since we own and drive Porsches, and Porsche rotors are either machined for balancing or use clip-on weights, we have no other option than use these "poor quality castings" (?).

f1rocks

There is no way a sand cast rotor can be consistently produced without some variation in weight requiring a machine cut or weight added.

Investment cast may come close enough but still would probably be far too costly to produce.

Stuttgart

Yes, I see cast rotors every day that do not require balance cuts but I don't want to over step Rennlist's adv. policy.

By thermal stability I mean how the rotor reacts to changes in temperature. Uneven mass results in uneven expansion and contraction rates. A casting with inconsistent vane thickness, cheek thickness, etc. will require balance cuts. Post machining, the rotor may have minimal runout and thickness variation with a good surface finish but as soon as you add heat to the situation, the tolerances go down hill fast.

"There is no way a sand cast rotor can be consistently produced without some variation in weight requiring a machine cut or weight added."

With a certain casting technologies you can consistently get rotors that only need ID and OD machined, no balance cuts. At the end of the day it comes down to scrap rates, many manufacturers get greedy scrapping very little thinking that the customer will never know the difference, and accordingly the consumer has become accustom to a little noise, coning and warping coming from poor quality castings.

Not trying to be argumentative guys, just trying to point out some things that people outside the industry never get to hear about.

zerMATT951

It *sounds* like you are saying that there are quality products available out there, but you don't want to tell us because you think it will violate a Rennlist policy?? Are you implying that some special company out there is making such perfect castings, and that they are so special, that by simply saying their name, you will get your hand slapped? That's total BS.

What it comes down to is this: We all buy brake rotors from the major OEM brands or directly from Porsche. That list of brands is very short (ATE, Zimmerman, etc). Are you saying they are all crap? So I guess we are all just buying crap cars and crap parts with our heads in the sand because there's *some* magical company out there that makes perfect stuff... we just won't ever know who they are. That's useful advise.

It sounds like we've moved from discussing common car parts to discussing brake rotors for the space shuttle or something... they (NASA) have an endless supply of money (ours) to sit around and wait for their vendors to make perfect castings. The rest of us have to buy what is commonly available from automotive suppliers. That is, unless you decide to share your secret with the rest of us.

Sam Lin

I've also seen rotors with no balance cuts or clips on them. I throw them away, as it means the manufacturer was too cheap too balance them at the end of the production process.

No casting process can produce a perfectly balanced rotor. Either its balanced by material removal via machining, or by the addition of weight via a wire balancing clip clipped into the vanes from the center outward.

Sam

Cory9584

dont slotted rotors eat up pads?

Guns951

Drilled rotors are better as aforementioned, in the wet. That's about the only advantage...maybe some cooling effects as well but that's debatable all day long depending on your side of the fence.

I went with drilled because to me they represent the Porsche image 100% and help with the look i'm going for with my RS project...that's my $.02