Titanium Brakes

[MysticLlama]

Has anyone seen the titanium brakes that Bavarian Autosport has in for the M3?

I was flipping through a catalog at a firends house this weekend and came across them.

They seem really cool, the only thing is that by looking at them they look really thin. Could they really dissapate heat so fast that they can use that much less material?

Seems like the way to go for weight savings if they work well.

"The rotors are made from titanium for superior strength, better heat dispersion and amazing weight savings. (Example: for a 97 M3, a 13” rotor weighs about 5 lb. vs. 17 lb. for stock) The billet aluminum calipers (7 lb. vs. 12 lb. for stock) feature internal porting for safer fluid transfer. "

[Emission]

The rotors don't have much surface area.

How much?

[jpnovak]

I looked... $8K for front/rear kit.

Ouch!! That's a big brake kit and a lot of Pagids for that much.

Great idea though! I wonder if those slots are chamfered to reduce milling of the pads away?

I'd like to see some feedback from a track session comparing identical cars with std brembo type kit and this Ti system.

[ChrisBennet]

Back in 1996 Peter Albrecht addresses this issue on the long gone Porschefans mailing list. I thought it was very enlightening so I saved it.
-Chris

From: PLAlbrecht@aol.com
To: porschefans-911@ioio.com
Subject: Re: Titanium brake rotors

Jim Nelson asked

<< Has anyone here tried Titanium brake rotors on their race vehicles? We
are probably going to try these (on the bone-stock, street-tired RS
America that finished 8th in class, 23rd overall at Sebring this year).
Next year, we go to 993 bodywork, real wheels and tires, and a serious
diet to try to improve our competitiveness.
>>

Rob Channel replies

>I've never used these and I'm not a materials expert, but I thought titanium
was VERY susceptible to nicks and scratches becoming stress fractures. I
suppose you would try to stay on the track and replace them after every race
anyway, though. :-)

Rob's right. Andy Warren pointed it out too. Titanium in the hands of
somebody who doesn't know what he's doing is pure evil. I have motorcycling
friends who popped for titanium hardware for their Ducatis and they were
amazed to find that they were snapping heads off everything, at very low
torques even. ("But...but... it's TITANIUM!! It's expensive!!! It MUST be
good or it wouldn't be expensive!!!") It's used for military and race car
applications because those things have the budgets to check things over much
more frequently (like tear down everything after every race and send it out
for crack testing). Titanium is used if you need lightness at all costs, and
high temperature strength. Neither of these is a factor in disc brake design.
The cast iron works just fine at the relatively low (!!!) temperatures
experienced by brakes (dull cherry red hot ain't hot. White hot is hot). The
special cast iron used in discs is better at getting rid of the heat.
Titanium is not as good from a heat transfer standpoint because its heat
capacity is lower and its thermal conductivity is lower. That may be good in
a jet engine but not in a brake. We WANT the things to soak up heat. The disc
is a big "heat sink" and a titanium disc is just won't take up as much heat,
as quickly, as a dumb old lump of iron. We WANT the disc to be a big heat
buffer during the stop, so that it can radiate and conduct away the heat
AFTER the stop. Blowing more air or ducting air to the rotor helps this. You
don't get rid of the kinetic energy during the stop, you store it somewhere
else in the form of heat and then gradually transfer it to the air
afterwards. If you consider that model, you see that titanium is absolutely
the wrong material for this.

Also, titanium is, as Rob pointed out, extremely notch sensitive. And guess
what happens when a pad scrapes around a rotor. Hundreds, thousands of tiny
scratches, each a wonderful stress riser. And then if you cross drill or
groove the rotor, it gets even worse.

Looking at the specs, titanium has about 1/4 the thermal conductivity of cast
iron, and just marginally (6%) less heat capacity per unit mass but since its
density is 62% that of cast iron, the overall heat capacity for an
identically dimensioned disc would be only about 58% that of an otherwise
identical cast iron disc.

If the heat isn't going into your rotor because it won't conduct or absorb as
much heat, it's going into your pad, caliper and fluid. Also not good.

Pete

[Emission]

You've got to wonder if they are really "that good" or more "bling" factor.

Porsche has gone ceramic, when they could have easily gone titanium. I wonder what the arguments are for/against. Do you think the titanium rotor has the friction like iron/ceramic?

[MysticLlama]

That post is rather enlightening, and brings up some of the points I was thinking about.

One of the guys I used to work with worked at Boeing as an engineer for years and told me that titanium has some weird properties.

Unlike other metals that distort or pick up new properties when heated or cooled, or banged on with a hammer, Ti has those, but also does weird things at speed.

He said that some of the planes are 10 inches longer in flight due to the speed and even a couple of the stealth bombers leak while on the ground, but have a perfect seal in flight.

Strange stuff, none of which sounded like it would help braking any. The weight is cool, but the heat capacity may not be there.

Definately Blingin' though.

[Wrecked944]

Seems like Ti is a poor choice for brake rotors. But I hear it's perfect for gas pedals.

[ChrisBennet]

Originally posted by JanusCole
Seems like Ti is a poor choice for brake rotors. But I hear it's perfect for gas pedals.

I'm never going to live that down am I?
-Chris

[masraum]

Hmm, I wonder how many people are going to be really screwed by those Ti rotors??

Chris B, that's cool, I must have missed a post somewhere.

[chrisp]

Very high bling bling factor. Very low performance factor. Ti galls very easily and has poor heat sink capabilites. Currently used in caliper pistons to insulate fluid from heat. Why then put it in rotors? They are supposed to absorb heat.

Funny stuff.

The aluminum case is probably pretty nice though.

[Emission]

I bet titanium calipers would work. Keep the rotors ceramic or iron.

[Jack Olsen]

What the heck is the briefcase for? Are they so valuable that you cuff them to your wrist and bring them separately to the track?

[Emission]

Originally posted by JackOlsen
What the heck is the briefcase for? Are they so valuable that you cuff them to your wrist and bring them separately to the track?

Once the rotors fail at speed... the metal case is for remains....

[Randy Webb]

Hmmm, interesting - I'd like to hear what Bill V. has to say about this.

The quoted post above is mostly correct. There are some (newer) alloys of Ti with better resistance to stress crack failure. Also, you can polish it, tho that doesn't seem like a good solution for the face of a rotor.... The main thing holding back the use of Ti is the high cost to refine it and to work the material (the latter is just like the case with SS years ago). Ti is extremely abundant however, more so than most metals, and the costs are coming down. You can get some sense of the way the Ti industry is going by reading the annual reports of Ti "smelting" companies -- and many of these are posted on the web.

Thermal conductivity and heat capacity are not always a benefit in rotor design -- witness PAGs ceramic brakes, which surely have very low values of both those effects. These are not much more costly than the Ti option above, and will likely be cheaper in the future - the use of them seems to be expanding despite the initial problems.

[porcupine911]

Originally posted by MysticLlama
...
Unlike other metals that distort or pick up new properties when heated or cooled, or banged on with a hammer, Ti has those, but also does weird things at speed.

He said that some of the planes are 10 inches longer in flight due to the speed and even a couple of the stealth bombers leak while on the ground, but have a perfect seal in flight.
...

this isn't that strange... just simple thermal expansion due to friction with the air molecules at high mach numbers. the plane you mention is the sr-71 that leaks fuel like crazy on the ground and seals up due to thermal expansion when in flight.

[Wrecked944]

Originally posted by masraum
Chris B, that's cool, I must have missed a post somewhere.

I tease him a lot over his Ti gas pedal. But it is all from jealousy. Chris knows I'd electroplate my car in Ti if I could. Bring on the bling, baby !!

[Wayne 962]

Originally posted by MysticLlama
He said that some of the planes are 10 inches longer in flight due to the speed and even a couple of the stealth bombers leak while on the ground, but have a perfect seal in flight.

The SR-71 was (is?) famous for this. Used to leak like a sieve on the ground.

If titanium were so great, then Porsche would be using it (or have used it) in their competition braking systems a long time ago...

No one's talked about the Aluminum calipers?

-Wayne

[Bill Verburg]

The Ti rotors are available in the usual 13, 14 and 15" sizes for our cars they run ~$1400/ea. they generally incorporate a ceramic coating which needs to be reapplied after each weekends use. The Nextel guys are experimenting w/ them, but the verdict isn't in. Mostly on Super speedway rotors which are surprisingly small anyway(non vented).

They are used by a lot of the Sprint and midget guys w/ good success in lighter less stressed applications. Replaced regularly of course.

For our cars cast iron is an almost ideal meaterial despite its mass.

The PCCBs are all being pulled in favor of good old cast iron for track use.

[David]

I remember the aluminum rotors that were out a few years ago. I guess they had a metal spray coating for wear resistance. I saw some at a shop and the mechanic said they didn't work and were being pulled off the car. Anyone have experience with these?

As a side note, it looks like F1 maybe pulling the carbon/carbon brakes to reduce costs. I've felt for years that this one change would improve races dramitically by making passing possible.

[Bill Verburg]

The aluminim metal matrix rotors were just that , an aluminum composite structure. They were not up to the task.