[artichoke]

When looking for replacement pads / rotors for my Benz ML430, which also goes thru them at a goodly clip, I saw a website advertising cryo-treated rotors. Apparently freezing the rotors to a very cold temperature aligns the molecules into a more crystalline structure which remains even after they are heated to operating temperature. The site claimed much longer wear (like 2x as long) and same or better stopping performance because the rotor surface stays flatter. The idea was that then you would change rotor only on every other pad change. The added cost of cryo-treated rotors would be more than compensated by having to buy only half as many of them.

Hypothetically, I guess pad wear could also be slightly reduced if the rotor is less rough surfaced. I don't know if they claimed this.

We ended up not using them because I didn't get around to ordering them in time before we needed brake work.

Is anyone aware of cryo-treated rotors for 300C and/or SRT8?

 

[cbutler32]

choker (sorry man)...
at some point someone had to say it...
let it be me...
as I am ALWAYS KIDDING!!!

there was some talk back on this on the board...
in might be in one of the other sections...
do a search...
I even think someone did it...
later ARTICHOKE!
damn that sounds good right now with a little butter and mayo...
mmmm...

 

[artichoke]

ARTICHOKE!
damn that sounds good right now with a little butter and mayo...
mmmm...

Yeah I didn't find any appropriate on-theme avatars -- was looking! Lemme know if you find any. (burp)

Yes you're right about the other thread, it's here:

http://www.300cforums.com/forums/srt-8-general-discussion/10532-srt8-rotor-grooving-problem-possible-solution.html?highlight=cryo

and my apologies for splitting the thread. Goddardzilla and some others liked cryo treated parts, Zeckhausen and a couple others thought they were hype. Zeckhausen is the first credible person I've heard say it is not a useful technique.

What was missing was any links to manufacturers selling ready-to-use cryo treated rotors. Maybe soon in time for my first brake job on the CSRT?

 

[marnepup]

cryo treated rotors are junk science...no more helpful (except for the person making a bundle of money) than nitrogen in your tires.

 

[DZeckhausen]

cryo treated rotors are junk science...no more helpful (except for the person making a bundle of money) than nitrogen in your tires.

Agreed. Rather than write this all up again, here's a link to my thoughts on the subject: http://www.300cforums.com/forums/120089-post11.html

And to save you a mouse click, here's the text of that post:

If you don't know anything about cryo treated rotors you should research it. Just FYI this is used by tons of race teams. I used them on my Suburban to decrease rotors temps by over 200 degrees. Tested by Truckin magazine on their 3/4 ton Suburban with the same results.
This is not snake oil, it's a proven process that works.

It's not possible for cryo tempering alone to reduce rotor temperatures by over 200 degrees. Vendors' claims of 200% and even 400% reduction in rotor wear are also completely false. The marketing brochures are full of testimonials from race teams about how wonderful these rotors are - testimonials from teams who get their rotors free and will say anything to keep free stuff coming. What you do not see is a double-blind test supporting any of the marketing claims. Nothing personal, but I doubt "Truckin Magazine" followed the scientific process in their evaluation of cryo tempering, particularly since they were probably given product to evaluate by one of their advertisers.

Let's examine the claim of a 200 degree reduction in rotor temperature. The primary function of the brake system is to convert the energy of motion of the vehicle (kinetic energy) into heat (thermal energy). Next, it must dissipate that heat. Heat is dissipated from brake rotors by radiation, convection, and conduction. The percentage contribution of each form of heat dissipation on an unducted brake system (like on a street car) is approximately 50%, 25%, and 25% respectively.

With that as background, let's look at how rotor temperature is influenced. The kinetic energy of the car is a function of the square of the velocity. It's equal to 1/2 mass times the velocity squared. In a full stop, you are converting all the kinetic energy of the car into thermal energy stored in the rotors. The temperature rise in the rotors is a function of how much mass the rotors contain. The heavier the rotors (greater mass), the lower the temperature at the end of the stop. For a moment, let's ignore cooling. If you put heavier rotors on a car and change nothing else, then the temperature of the brakes at the end of a stop will be lower than it would have been with lighter rotors. But cryo tempering doesn't change the mass of the rotors. So the energy density of the rotors (energy stored per unit of mass) is unchanged by cryo tempering. Thus, the only way cryo tempering could drop rotor temperatures by 200 degrees is to increase the rate of cooling.

So let's move on to the mechanisms by which rotors shed heat:

Radiation is the predominant mechanism for heat loss and is a function of the surface area of the rotors. A characteristic called emissivity influences the efficiency of the radiation process and is changed very slightly by bedding rotors. But any change in emissivity due to cryo tempering is unmeasurable. So if the cryo tempering doesn't change the surface area of the rotors (which it obviously doesn't!) and it doesn't change the emissivity, then it can't increase the rate of cooling by that mechanism.

Moving on to Convection, we have a mechanism that is a function of airflow around and through the inside (assuming vented) of the rotors. This is influenced by the size of the air gap and the design of the internal cooling fins. Neither of these are affected by cryo tempering, so we're left only with:

Conduction. This is the transfer of heat into your wheel bearings and through the backing plates of your brake pads into the calipers and brake fluid. This is the "bad" kind of heat transfer. If cryo tempering really reduced rotor temperatures by 200 degrees, then this must be where that heat goes. If true, it would mean you would be boiling your brake fluid and cooking the grease in your wheel bearings. Fortunately, it's not true.

I challenge anyone here to have cryo tempered rotors installed on one side of your car and a normal rotors (of otherwise identical construction) installed on the other side, with the stipulation that the installer not tell you which is which. Take your car to the track and do some high speed braking, then use a pyrometer to take rotor temperatures. See if you can find a significant difference in temperature between the two sides, enough to identify which one is the cryo rotor and which one is not. If there really is as big a difference in performance between normal and cryo rotors as claimed by the vendors, then it should be obvious which one is cryo tempered. Next, you can leave the rotors on your car for the next 30,000 miles, then use a micrometer to measure rotor thickness. See if the cryo tempered rotor exhibit less wear. I'll go out on a limb here and predict that you will find no significant difference.

Cryo tempering does not even come close to meeting the claims made by the vendors. Your hard earned money is better spent elsewhere.

 

[artichoke]

Agreed. Rather than write this all up again, here's a link to my thoughts on the subject: http://www.300cforums.com/forums/120089-post11.html

And to save you a mouse click, here's the text of that post:

It's not possible for cryo tempering alone to reduce rotor temperatures by over 200 degrees. ...

I agree, it seems quite unlikely. Perhaps less heat is generated if the stronger molecular structure of the cryo rotor gains less internal heat (not from friction with the rotor) but it wouldn't be much and I'm really stretching here ...

This wasn't my point however. My reason for getting them would be to get rotors that last longer, to change the rotors less often. I am looking for not-worse performance than stock, that is all. You predict that they won't last measurably longer, but unlike your comments about heat dissipation, I don't see a logical argument to support you there "out on the limb". I'm still looking for evidence of actual results on this one.

Also I have to wonder if many race teams would use them (as has been claimed by Goddardzilla iirc -- I don't know this independently) if they weren't the best. This is a major safety issue. Redline claims racing teams use their motor oil even if they advertise Mobil 1 on the car, because Redline is the best. Same here -- actual use by racing teams constitutes an endorsement that I take seriously. How they would work in a non-racing Brembo system -- that's another story I haven't thought about.

 

[DZeckhausen]

I agree, it seems quite unlikely. Perhaps less heat is generated if the stronger molecular structure of the cryo rotor gains less internal heat (not from friction with the rotor) but it wouldn't be much and I'm really stretching here ...

That would defy physics. Energy can not be created or destroyed. It can only be converted from one form to another.

The brakes stop your car by converting kinetic energy into thermal energy. When your car is going V mph, it has a kinetic energy equal to 1/2 times the mass (of the vehicle) times the square of the velocity V. So E=1/2*m*V^2. This energy is converted into thermal energy (heat) when you stop your car. And this thermal energy is stored in the cast iron rotors. The energy density (or temperature) is the amount of energy stored divided by the amount of material storing the energy. The more material the energy is stored in, the lower the temperature of the rotors. So for the rotors to be cooler after cryo-tempering, the rotors would have to weigh more. But they don't. So we know that's not true. And we also know that cryo-tempering does not change the rate at which thermal energy is dissipated from the rotors (radiation, convection, or conduction.) The claim of lower temperatures is false.

This wasn't my point however. My reason for getting them would be to get rotors that last longer, to change the rotors less often. I am looking for not-worse performance than stock, that is all. You predict that they won't last measurably longer, but unlike your comments about heat dissipation, I don't see a logical argument to support you there "out on the limb". I'm still looking for evidence of actual results on this one.

If this claim was true, the vendors of cryo-tempered rotors would welcome a double blind test that would prove their claims. But such a test has not been done by them. Instead, they give you anecdotal stories. It would be easy to prove their claim by setting up a fleet of taxis or police cars with new rotors, some of them treated and some not. After some reasonable mileage interval, the wear rates could be compared. If these claims were true, every vehicle manufacturer would equip their cars with these rotors, especially brands like BMW who regularly replace rotors under their free 4-year maintenance plan.

Also I have to wonder if many race teams would use them (as has been claimed by Goddardzilla iirc -- I don't know this independently) if they weren't the best. This is a major safety issue.

I never said cryo-tempering harms the rotors. I just said it does not improve their performance. If a race team is getting free consumables in exchange for saying a few nice things about them and running the logo on the side of their car, then they will do so, as long as it doesn't hurt their chances of winning races.

 

[artichoke]

That would defy physics. Energy can not be created or destroyed. It can only be converted from one form to another.

Yes I know but (maybe I didn't express it very well) I am talking about extra heat energy created within the rotor, in addition to that caused by the pad - rotor friction. That is, hysteresis loss as the rotor deforms. As I said, there wouldn't be much of it. You're preaching to the choir on the basic physics of energy conservation, my friend.

Regarding the cryo rotors -- aren't there some testing results? I wish there were. When I was looking for brakes for the Benz ML, there were at least testimonials.

 

[SRTEight]

Radiation is the predominant mechanism for heat loss and is a function of the surface area of the rotors and the temperature difference between the rotors and the surrounding air. A characteristic called emmissivity influences the efficiency of the radiation process and is changed very slightly by bedding rotors. But any change in emmissivity due to cryo tempering is unmeasurable. So if the cryo tempering doesn't change the surface area of the rotors (which it obviously doesn't!) and it doesn't change the emmissivity, then it can't increase the rate of cooling by that mechanism.

Hey DZeckhausen
Thermodynamics was a LONG time ago, so this post is to help me remember, not argue with you. For my simple mind, and those who read that haven't had the joy of Thermo class, let me explain Radiation this way.
All of the heat we get from the Sun is radiation. There is no air in space for convection to bring the heat. And no metal pole connecting us for heat transfer by conduction. So all of the heat is transferred by radiation. From one mass unit (the sun) to another piece of mass (the earth). I don't recall that air temp around the brakes would have anything to do with radiation. It is simply the mass and characteristics of that mass (the emmissivity) that determines radiation heat transfer.
I was really surprised to hear that 50% of rotor cooling is by radiation. Because they are surrounded by so many objects. I guess the heat is transferred to the wheel, the suspension, frame and everything else "visible" to the rotor. I guess this must be true. The heat load of a house is about 4 times more influenced by radiation than ambient temps.
So two things. I don't think surrounding air temp has anything to do with radiation. and I agree that cryo tempering must change emmissivity to help cool. and whether or not it does, I haven't a clue.
Enlighten me further Master.

 

[BobCav]

I'm no metallurgist, nor do I play one on TV, but it would seem to me that tempering, either by heat or cryo, would only affect the surface hardness possibly increasing durability but have nothing to do with heat dissipation.

Thoughts? Comments? Talk amongst yourselves....

 

[DZeckhausen]

I was really surprised to hear that 50% of rotor cooling is by radiation. Because they are surrounded by so many objects. I guess the heat is transferred to the wheel, the suspension, frame and everything else "visible" to the rotor. I guess this must be true. The heat load of a house is about 4 times more influenced by radiation than ambient temps.
So two things. I don't think surrounding air temp has anything to do with radiation. and I agree that cryo tempering must change emmissivity to help cool. and whether or not it does, I haven't a clue.
Enlighten me further Master.

You're absolutly right. The ambient temperature does not affect the amount of energy radiated from a rotor. I was careless and mis-typed. Convective and conductive cooling are affected by delta T (the difference in temperature between ambient and the rotor). Radiation cooling is not.

If you want to be very precise, radiation (in Joules per second) from a body is equal to emissivity times the Stefan-Boltzmann constant (5.67 x 10^-8) times the surface area times the fourth power of the temperature (in degrees Kelvin).

This also means that the percentages I quoted make a bunch of assumptions. Assumption one is that the car is moving at a good clip on a race track under heavy braking conditions. Assumption two is that the rotor is not ducted with an air tube that forces cold air from the bumper through a custom backing plate and through the center of the rotor. Such ducting would decrease the role of radiation and increase the role of convection.

All else being equal, at slower speeds/lower temperatures, the radiation component of cooling becomes very much less predominant.

If cryo-tempering were to affect the amount of cooling due to radiation, it would have to change the emissivity. It certainly wouldn't change the surface area or the Stefan-Boltzmann constant!

 

[DZeckhausen]

Yes I know but (maybe I didn't express it very well) I am talking about extra heat energy created within the rotor, in addition to that caused by the pad - rotor friction. That is, hysteresis loss as the rotor deforms. As I said, there wouldn't be much of it. You're preaching to the choir on the basic physics of energy conservation, my friend.

I get it now! You're talking about heat built up in the rotors as they are squished and relieved. Conservation of energy would not be violated because the energy is coming from the driver's leg, not from the 1/2 * mass * velocity squared. This heat build-up would also occur in the brake pads and the brake lines and even the brake pedal. But the amount of heat generated is so small that there would be no practical way to measure it. If significant heat was generated in this manner, it would be felt in the driver's foot, like a spring.

The assumption here is that cryo-tempering makes the rotors so much more dense that they don't deflect as much. Cryo-tempering does not change the grain structure, so the density is constant. It may affect the surface hardness, but that is a small contributor to overall rotor stiffness. And since there are no reports of improved pedal feel (nor claims of such by the vendors), there is no evidence supporting this theory.

Regarding the cryo rotors -- aren't there some testing results? I wish there were. When I was looking for brakes for the Benz ML, there were at least testimonials.

None that I've ever seen and none that the vendors are touting.

 

[artichoke]

I get it now! You're talking about heat built up in the rotors as they are squished and relieved. Conservation of energy would not be violated because the energy is coming from the driver's leg, not from the 1/2 * mass * velocity squared. This heat build-up would also occur in the brake pads and the brake lines and even the brake pedal. But the amount of heat generated is so small that there would be no practical way to measure it. If significant heat was generated in this manner, it would be felt in the driver's foot, like a spring.

Well, whatever causes rotor deformation. As I said a long time ago, the amount of deformation would be very small, but I'll continue with this topic if you like to. Energy comes from the perpendicular force of the brake pads, but that's true of all the energy flows we are talking about. Due to friction, the energies involved are the energy contributed by the braking system, plus the rotational energy of the wheel and a share of the translational kinetic energy of the whole car.

I believe that with power assisted brakes, the brake system contributes a different amount (generally more) than the driver exerts with his foot. As for brake pedal feel, the power brakes will have much to do with this. For example, you note in your adverts for your special brake lines that they improve pedal feel, I believe. I don't know how much the rotors have to do with brake pedal feel -- not much I imagine, because they will "feel" like hard metal to the pads in any case.

The assumption here is that cryo-tempering makes the rotors so much more dense that they don't deflect as much. Cryo-tempering does not change the grain structure, so the density is constant. It may affect the surface hardness, but that is a small contributor to overall rotor stiffness. And since there are no reports of improved pedal feel (nor claims of such by the vendors), there is no evidence supporting this theory.

None that I've ever seen and none that the vendors are touting.

Doesn't cryo treatment change the structure of all the metal not just the surface? That (with or without evidence) is indeed what the vendors I saw were touting. I am sure it's treated long enough for all the metal to reach cold temperature, not just the surface.

 

[marnepup]

I'd say that if (and it's a mile-wide "if") cryo-treatment slows rotor wear, it's brobably by a couple percent, at best. Certainly not worth the price.

 

[DZeckhausen]

Well, whatever causes rotor deformation. As I said a long time ago, the amount of deformation would be very small, but I'll continue with this topic if you like to. Energy comes from the perpendicular force of the brake pads, but that's true of all the energy flows we are talking about. Due to friction, the energies involved are the energy contributed by the braking system, plus the rotational energy of the wheel and a share of the translational kinetic energy of the whole car.

I believe that with power assisted brakes, the brake system contributes a different amount (generally more) than the driver exerts with his foot. As for brake pedal feel, the power brakes will have much to do with this. For example, you note in your adverts for your special brake lines that they improve pedal feel, I believe. I don't know how much the rotors have to do with brake pedal feel -- not much I imagine, because they will "feel" like hard metal to the pads in any case.

As I said before, the amount of heat generated in this manner is so small as to be unmeasurable. Yes, there is a mechanical advantage at the caliper due to the brake pedal assembly ratio, the vacuum assist, and the ratio of master cylinder bore to caliper piston area. But you can sit in your car (engine running) and pump the brake pedal repeatedly and you will not measure a temperature increase at the rotors becuase of this action. In a practical sense, it's not relevent.

Doesn't cryo treatment change the structure of all the metal not just the surface? That (with or without evidence) is indeed what the vendors I saw were touting. I am sure it's treated long enough for all the metal to reach cold temperature, not just the surface.

I can think of just one situation where you might gain a significant improvement in rotor longevity under racing conditions. Under racing conditions (repeated high speed braking, R-compound race tires, rapid cooling during a long straight section of race track) all rotors will eventually develop micro-surface cracks. These cracks will slowly expand and eventually require replacement of the rotors. It happens much faster with drilled rotors than it does with slotted or plain rotors. And it happens faster with 1-piece rotors than it does with floating rotors. So, let's assume we have a race car equipped with poorly made 1-piece rotors from a boutique foundary in Mainland China that did not do any heat treating to relieve stresses. These crappy rotors will quickly be destroyed on the race track. If you send them off to be cryo-treated, the process (which also involves slowly heating them) will relieve stresses from manufacturing and the rotor might last longer before cracking.

This would not be the case with quality rotors from any major aftermarket supplier such as Brembo, Balo, Zimmerman, ate, PowerSlot, StopTech, EBC or from the OEM rotor supplier for Chrysler. These suppliers heat treat their rotors after they are manufactured. It would only be the case that cryo-tempering would help for "no-name" rotors picked up off eBay or the cheapest available rotors at your local auto parts store. (Auto parts stores usually have a "premium" and a "budget" brand of rotors.) And it would only apply to racing conditions and the delay of the onset of cracking. It would not apply to the rate of rotor wear and the time/mileage required to reach minimum thickness.

Under street conditions, the claims of 200 to 400 percent improvement in longevity are false. The claims of dramatic temperature reduction are false.

 

[GNSCOTT]

Can you guys do some neat graphics like they do on Myth Busters. :wink1:

 

[DZeckhausen]

Can you guys do some neat graphics like they do on Myth Busters. :wink1:

I can do better than that. I'm working with StopTech to arrange some double-blind testing of cryo-tempered rotors. The testing may not be done until summer, but it will happen. And the methodology will be documented so that readers can be confident there was no bias in the conducting of the test, collecting of the data, or interpretation of the results.

Just be patient, because they have lots of stuff on their plate. When we are close, I will resurrect this thread. This won't happen in the next few days or weeks.

 

[artichoke]

... I'm working with StopTech to arrange some double-blind testing of cryo-tempered rotors. The testing may not be done until summer, but it will happen. And the methodology will be documented so that readers can be confident there was no bias in the conducting of the test, collecting of the data, or interpretation of the results.

Just be patient, because they have lots of stuff on their plate. When we are close, I will resurrect this thread. This won't happen in the next few days or weeks.

Cool, thanks!

 

[marnepup]

Fantastic! ...can't wait for the cryo-scammers to scream bloodymurder...:bigrin:

 

[DrKevSRT]

Sorry guys, had to chime in. I am an instructor with the BMW clubs of America and Canada, and have been attending driving schools for over 20 years. I first tried cryogenically treating my rotors on my '01 BMW M5, which was NOTORIOUS for eating rotors after two driving schools. I successfully completed 7 schools before any warping was noted. I currently have completed 6 schools on my M3 with absolutely NO warping. This stuff works incredibly well. Sorry to bust any flame bubbles!