Titanium Brakes

[Dave K]

Just curious on your opinions/thoughts on the ZMI Brake system, with Titanium rotors.

http://www.zmibrakes.com

The rotor is really thin, compared to a Brembo, etc., with no center vanes, so the weight is very low, but so is the mass to absorb heat.

Any thoughts?

-Dave
"Everything should be designed as simple as possible, but not simpler"

 

[CoryPad]

Fascinating that titanium is used in a wear application. I guess the intermetallic coating is something like TiAl and has better wear resistance. I don't think the low mass is a problem - convection appears to be the main heat transfer mechanism, and the extremely high surface area to volume ratio enables this.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TChronos]

I bet the pads wouldn't last long.

 

[ejit]

As long as the caliper has a good air path or heat sink it should work.
The inertial and unsprung losses should be impressive.

 

[phatmouty]

Those seem very interesting. They claim that they may be the only brake rotors that you may ever have to buy. That is a hefty claim. I wonder how well they would work in a high speed situation such as drag racing where saving on weight is a plus. That's just from my point of view from where I am an avid drag racer and these look very nice.

The cooling system on these brakes looks like it would eat the brake pads up more quickly than usual, but I'm not sure because I would have to put them to the test on my own vehicle. They might be something worth a try.

 

[Dave K]

From another forum, this reply came from the inventor at ZMI:

"My name is Fred Callahan and I am the inventor of the rotors you see posted. The rotors are Intermetallic coated titanium (international patent), and have been in use for over 10 years. Starting from the top, the swept area is actually more than a current Corvette rotor. Coefficient of friction does not depend on surface area, but rather the friction value, multiplied by the force applied (by the caliper pistons to the pad). Surface area has a lot to do with pad wear, or think of a rotor that has a ¼" swept area. It will still stop the car the same amount, but the pads won't last as long. The heat generated is from the material thermal conductivity and mass of the rotor. Nice for show, but useless for the track? Rocky Moran Jr. won the last Formula Atlantic race he ran using four rotors half as thick as these at Laguna Seca. You can either ask him or Price Cobb who owned the car at the time. Review this race and you will see he won by a fairly large margin and was able to easily pull away from the field. In fact, it was so easy that after the race they tore his engine down thinking he was cheating. These rotors have been in many races from SCCA, Late Model Dirt cars, World of Outlaws, many different styles of cars, both ovals and road courses. Brake rotors do not need to store energy, cast iron brake rotors need to be massive because they store energy, and if you cool a cast iron rotor too quickly, it cracks. Ask yourself why would you want a brake rotor to remain hot - wouldn't it make more sense to cool it quickly before applying the brakes again, and inducing more energy? The Specific Heat for titanium is .14 BTU/Lbs/°F, while cast iron is .10 and carbon fiber is .16, so you can see titanium is closer to carbon than it is to iron. If aluminum could withstand the temperature, it would be the best rotor with a .23 specific heat, which is why all of the money was dumped into aluminum metal matrix rotors, but at the end of the day, aluminum is aluminum. The open slot design (US patent pending) performs two functions. First, the slots on the rotor pictured have just about the same surface area as a cast iron rotor, and surface area is the important factor for cooling, which is why heat sinks are usually aluminum, and have a lot of machined surfaces and protrusions, to increase the surface area to allow for radiant cooling. Secondly, the angle of the slots are important for initial bite. Depending on the situation, you may want a higher or lower initial bite, most street cars would require less. The most important factor I haven't seen mentioned yet (probably because it is a pro and not a con) is the lower inertia these rotors offer over cast iron. It may be only 50 lbs. static weight, but this translates to hundreds of pounds rotating weight - which allows the car to accelerate quicker (not having to spin up the heavy cast iron rotors), decelerate quicker (not having to stop spinning the heavy cast iron rotors), quicker response time for the suspension (less weight means the spring isn't compressed as far over a bump and keeps the wheel planted to the road), and less spring rate required, for the same reason, allowing greater flexibility in vehicle set-up. An example of inertia, two kegs of beer are rolling down a hill at you, one is empty and the other is full, which one do you want to get in front of?
Now, LG is mad at me because of a comment I made to him at the SEMA show, and Lou, if you want to go over that in public forum, I'd be happy to accomodate you. Andy was given a free set for his car to try. I have e-mails stating the first few tracks went fine, but eventually, 35-40 minutes into a race, the pads would get too hot and begin to fade - I also have the e-mail where the rear blades were continued to being used, and the cast iron vented rotors were back on the front only. I offered a set of vented titanium rotors, but not for free this time, and received no response.

The blade rotors are certainly not for every application, which is why we offer vented rotors to some, and blades to others. The Mosler car was interested in competing in performance, with acceleration/deceleration as a primary goal, not running the 24 hours of LeMans - if that was the case, we would have put vented rotors all the way around. If you think the rotors are too expensive, find me an inexpensive source for titanium. Nobody is getting rich off of these things, I still have a day job, this isn't what I do for a living. I hope I've answered some of your questions."

-Dave
"Everything should be designed as simple as possible, but not simpler"

 

[fdizz]

I was wondering what kind of brake pad would be used with titanium rotors. Apparently, ZMI sells Mintex Performance brake pads in the kits, but i saw nothing at Mintex's website about pads for titanium rotors.

Thanks for your help

Mike

 

[49078]

I think the pads would be used up quickly, because Ti is such a poor conductor of heat so all the heat would be transferred to the pad. This can be a problem with tool life when machining Ti, all the heat is absorbed by the tool and eventually leads to failure.

I think I once heard that Ti was used in F1 brakes, I don't know if that was true or not because I didn't follow it enough at the time. Nowadays they use CC brakes though.

 

[ntsqd]

URL didn't work for me. Is it now dead?

That whole qouted statement leaves me with the impression he doesn't really know all that he's talking about. In my two years designing at Wilwood what I had yet to learn about brakes was frequently made obvious to me by my various projects.
This statement: "Coefficient of friction does not depend on surface area, but rather the friction value, multiplied by the force applied (by the caliper pistons to the pad)." sounds good but is less than meaningless. It tells me that there may not be a formal Engineering or Physics background behind it.

What about the auto-ignition possibility when using Ti in this type of application? I know insurance to cover machine shops usually excludes the machining of Ti & Mag unless they are specified and then the rates go up. This is b/c auto-ignition has happened during machining often enough that the Insurance industry recognizes it as an above normal risk. Seems to me that using it here may not be the best idea.

 

[ZoRG]

F1 problably use Ti as the hats, although, I would think Aluminium would suffice.

To be honest, personally, I still think the only way to go for a street car is carbon/ceramic, it might be difficult to find some currently though, but the cost would be the same if not cheaper than the titanium alternative.

ntsqd, thumbs up for you guys at wilwood, good prices! good products! I noticed you are becomming very popular lately.

 

[sprintcar]

I've been running a cast titanium vented rotor with a friction coating for the past 2 race seasons. It was a bit expensive to get the right coating on the rotor, but aside from normal heat checking, everything is still ready to go. I used the same set of brake pads and they still have another season in them. This is a single rotor on the rear axle of a 1350lb sprint car on dirt and the rotor will get cherry red on a short track.

Keep the wheels on the ground
Bob
showshine@aol.com

 

[BarneyD]

A customer of mine has ZMI brakes on his 2002 NSX. He has the front and rear rotors/calipers. He loves the kit. It has given him the little edge needed to stay ahead of the other all motor NSX's. It's amazing how loosing the rotaional mass and unsprung weight can make such an impressive difference. I'm thinking about putting a set on my Integra. Matter of fact, I need to go to the website to make sure I can get a set for my integra.
Nice to be part of this group. Nice to meet you all.
Have a great weekend,
Barney D.

Barney Demonbreun
Technician for Gary Force Acura, and owner of;
Ashland Motorsports
1304 Big Marrowbone Rd.
Ashland City, Tn. 37015

 

[stambee]

Sprintcar,

We have just begun using a non-vented ceramic coated titanium rotor on our sprint car (red devil brand), and have noted a few interesting characteristics: First the pad material transfers to the rotor and the rotor actually picks up a few thousandths of an inch of thickness after the first race. This does not appear to be a problem although the material does not transfer evenly (radially). While it appears to have worn grooves into the coating, it is actually built-up pad material. Secondly, the system does not dissipate heat very well. On a short track with a lot of grip, the rotor tends to carry a lot of heat and will glow cherry red. Due to this, it is important to use heat shields between the caliper pistons and the pads. We must also use a high quality brake fluid and change it often. Have you noticed any of these issues?

This is a great website and this is my first post.

 

[BarneyD]

Unfortuately, my customer has yet to sign up to a track event. He's more of a drag racer that wanted to loose some rotational mass. I don't think the unsprung weight was a big issue for him, just the roattional mass. I kinda makes me sick. In my humble opinion, NSX's weren't designed to drag race. Put them on a roadcoarse and let them shine! The brakes on the NSX are the weak point. At least if your running stock weight. NSX's can be reduced to around 2600 lbs with the right mods/weight reductions and still be a comfy street car. Once the car has been lightened a bit, the brakes aren't as much of an issue. Ducting helps out a bunch also.
I'm trying to find out why ZMI's site is down. Are they out of business? There is another customer of mine who is looking to purchase a set of their rotors for his NSX. If anyone knows how I can get in touch with them it would be greatly appreciated.

Have a great week guys,
Barney

Barney Demonbreun
Technician for Gary Force Acura, and owner of;
Ashland Motorsports
1304 Big Marrowbone Rd.
Ashland City, Tn. 37015

 

[ntsqd]

Stambee,
It is normal for newer pad compounds to transfer some material to the rotor's surface. Though it sounds like you are getting an excessive transfer. Is the transfer the same regardless of compound used?

 

[BarneyD]

If I'm not mistaken, the slots that acutally go all the way through the rotors are watter cut. This *should* keep the danger of machining TI down to a minimum risk would think. I'm trying to get in touch with the guy that actually makes the Ti rotors for the now defunct ZMI. I'll keep everyone in the loop on what I find out.
The reason TI would be a better material to use for the cost difference. The carbon rotors on the prancing pony cars are around 8k each last I heard. The total kit (all 4 corners) for an NSX is around 7k including the aluminum calipers. Not bad if you want that little extra edge. Weight reduction is my favorite modification. It's *usually* cheap, makes the car handle better, and most people don't realize that loosing weight is free horsepower. (10 lbs weight loss equals 1 horsepower from what I've been told....I could be wrong...please tell me if I am). Not to mention the ability to stop quicker.
Have a great week all, enjoy the gas prices.
Barney

Barney Demonbreun
Technician for Gary Force Acura, and owner of;
Ashland Motorsports
1304 Big Marrowbone Rd.
Ashland City, Tn. 37015

 

[stambee]

I only have tried the compound recommended by the manufacturer. Even with the material transfer, the brakes work well.

I'm a bit concerned about the heat transfer however, since it seems that most of the heat is transferred to my axle and rear end bearings. Does anyone know at what temperature 4AL6V titanium allow glows red hot? From what I can find, it is well below 800F. Any help would be appreciated.

 

[ntsqd]

Can't help with TI temp vs color. Perhaps google?
What sort of heat dams are employed? Floating or fixed rotors? I'm presuming an aluminum hat of some sort.
Are you measuring temps at the hsg?

 

[stambee]

The manufacturer recommends heat shields between the pads and the pistons, which seem to help even though they are only about .062" thick. The rotor floats on "buttons" since the caliper is fixed to the rear housing. The hat and hub are also ti for max rotating weight savings. The whole unit works well and I think that the ultimate solution is a well designed duct to blow cool air across the rotor. Oh, and to change the fluid often. I'm not sure if you are familiar with sprint cars, but working on them is no big deal. We race for about 30 minutes and work for about 30 hours.

 

[patprimmer]

Colour radiation at higher temperatures is pretty well independent of the material. Red hot is red hot, iron, steel, chrome, brass, glass or titanium.

Regards

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