Titanium brakes?

[Chiefgroover]

http://www.suprastore.com/zmitibrki.html anyone tried these?
They sound the ticket to me, but would prefer to hear from someone who has used them.

[Alex]

Does anyone use them in racing? ie if no-one runs TI discs and hubs why not?
Do they have clamping force figures? And braking torque figures.
Do they have any technical info or just look bling?
How long do they last?
12" discs are smaller than UK's arn't they!
13" are ok but still they are mega thin - surely the heat created has to go somewhere? Ie how bad do they fade?

[Digsy]

As far as stopping power goes, the specific heat capacity (http://www.engineeringtoolbox.com/specific-heat-metals-24_152.html) of titanium is 17% higher than cast iron, so they should heat up 17% more slowly. However, mass absorbs heat and its density (http://www.engineeringtoolbox.com/metal-alloys-densities-24_50.html)is only 57% of that of steel. This means that if you took a Supra-sized rotor made of titanium and applied the same amount of braking force (energy) to it then the titanium rotor would in theory heat up much more quickly - nearly 48% more quickly in fact. :eek:

Those rotors have a lot less surface area to radiate the heat off, too, which won't help.

HOWEVER....

I did the figures again for a ceramic brake rotor (which should be a good material) and the performance comes out almost the same - in fact slightly worse (55% more temperature rise for the same energy input). So I've gone and stumped myself on that front. Bugger. :(

The other main things affecting the stopping power will be size of the rotor(meaning the radius at which the caliper sits) and the coefficient of friction between it and the pad (and the clamping force as Alex mentioned above). The size can't be any bigger than you can get inside your wheel, and the coefficient of friction can be whatever you want through the choice of pad material. Neither of these are really related to the fact that the disc is titanium rather than cast iron.

No denying the un-sprung mass benefits, though.

Edited to namecheck Alex.

[Chiefgroover]

just found this,
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"

[Chiefgroover]

Cheap as chips lol........titanium brake option!

[Chiefgroover]

http://www.caranddriver.com/article.asp?section_id=15&article_id=8723&page_number=10

[Digsy]

Not sure if this is where that quote came from, but I found it on a forum here (http://www.eng-tips.com/viewthread.cfm?qid=95224&page=1#).

Fred gets slagged a bit later on in the thread because of an error in how he defines coefficient of friction.

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).
True, friction (and coefficient of friction) has nothing to do with area, but it is braking torque which is the product of coefficient of friction, clamp force AND mean application radius (for some reason the last bit gets left out completely). Its a shame that this gaffe occurs early on in the text because (as the guy on the other forum says) it makes him look like he doesn't know what he is on about. The rest of the quote seemed OK to me.

I'm still having trouble with the specific heat issue, though, which a lot of the explanation for the Ti rotors' performance hinges on. Specific heat capacity is the energy required to rasie 1kg of a material by 1 degree C, so (as I put above and also as Fred put in his quote) a high specif heat material would be good for a brake rotor. However, this ignores the mass term. A lower mass of material will get hotter for the same energy input. Unless there is some other mechanism at play, considering specific heat alone does not explain why the rotors work better at high temperatures - especially for CF, ceramic or Al-MMC rotors, which are even lighter than titanium and yet wrok even better.

I suspect that this may have as much to do with the way that coefficient of friction changes with temperature. I was under the impression that CF brajes worked well not bcause of their ability to stay cool, but because the coefficient of friction increased as the rotor got hotter, rather than decreasing as it does with iron. I could not find any coefficient of friction versus temperature curves on the web, though, so I could not confirm whether the same was true for Ti or ceramics.

Titanium brakes certainly are being investigated for high performance road applications (I found an article on truck brakes comparing solid Ti alloy, Ti coating and ceramic rotors).

Interesting. :thumbs:

[Chiefgroover]

Seems a hot debate, and very interesting too. Maybe in time we shall find a Supra driver who has these fitted (probably in the USA) to hear how they have found them.
I fear Fred might have too much considered science applied and maybe not enough real life on the road testing. Pad match is definately going to be a sticky issue.
Mind you, if these turn out to be as good as Fred reckons, yippee!.

[Digsy]

I've been doing some digging and found some material properties for likely brake materials.

It's not conclusive:

Stainless steel (used on bikes) doesnt get as hot as iron but can only radiate the heat away half as fast and has a high exapansion coefficient.

Titanium gets hotter than steel, but only radiates the heat away at the same rate, but it doesn't expand as much.

Ceramic gets hot and doesn't give up any heat at all compared to the others. Yet ceramic brakes are used on F1 cars and aircraft.

Aluminium gets hot too, but can shed the heat energy much faster than any other material in the list. However it is not physically strong enough to be used as a brake rotor (unless you use a "filler" material).

The key could be carbon fibre, which gets F-hot, weights nothing and doesn't give up its heat. However, its coefficient of friction goes up as it gets hotter (or so I'm lead to believe). While dicsussing this with some work mates the impression was that it could be the same for ceramics.

So the thermal properties may not matter a stuff if the material is still "frictioney" when hot. Apparently titanium is not a good friction material as it tends to "tear up".

A mate said he was going to get me mu-versus-temperature curves for some of these materials.

[Stevie Boy]

Haven't had a chance to read all of this thread as it's pretty long so i hope i don't contradict anyone.
Anyway i have some experience with our customers cars such as Porsche GT2's and Turbo and Turbo S's with the Porsche PCCB (Porsche Ceramic Composite Brakes) it's not a cheap aftersales upgrade at around £4500.

Brief description of set-up 350mm (approx 13 3/4") dia 34mm wide perforated and ventillated Ceramic Composite discs. Stainless Steel carrier/bell.
Single piece aluminium 6piston calipers(front) 4piston(rear)

Heres what Porsche have to say about it:
Main advantages are:
#50% reduction in rotating and unsprung masses compared to conventional brake discs with same dia.
#Fast Brake response
#Maximum fading stability owing to constant and hi friction coefficients
#Excellent responsiveness in wet conditions
#Long service life discs up to 185,000miles

Having driven cars with this set-up braking is phenominal, however service life of 185,000miles? I'd like to know how they've come up with that figure cos i've seen a few cars after only one maybe 2 track days with the discs cracking and Ceramic Composite material breaking-up/away on the disc face, refacing not really an option and a lot of unimpressed customers with the prospect of having to fork out a couple of grand on a new set of discs.

Probly of no use to this thread but, just we're now getting customers replacing there PCCB set-ups for standard Turbo set-ups to avoid frequent replacement of expensive Ceramic Composite discs.

[Digsy]

Heres what Porsche have to say about it:
Main advantages are:
#50% reduction in rotating and unsprung masses compared to conventional brake discs with same dia.
#Fast Brake response
#Maximum fading stability owing to constant and hi friction coefficients
#Excellent responsiveness in wet conditions
#Long service life discs up to 185,000miles

That's the key then. Cool! :thumbs:

We need a mu-versus temperature curve for titanium on a brake pad.

[Stevie Boy]

You took the words right out of my mouth Digsy! :innocent: