82 replies to this topic

[GeorgeTheCar]

I was a dinner last night with a person senior in the FIA circuit community.

He very positively stated that changing to steel brakes would result in braking distances 5 times as long as with the current carbon/carbon brakes.

I have read several times that the gap is less then 2 to 1.

Can anyone document that or provide solid data of the actual performance gap?

[rms]

Just shows how deluded or ill informed 'senior' FIA officials are !

[primer]

I was under the impression that the biggest benefit with carbon brakes (in F1 cars) was how much useful life they provided (for minimum weight).

[rookie]

I was under the impression that the biggest benefit with carbon brakes (in F1 cars) was how much useful life they provided (for minimum weight).

Agreed. It's for weight mostly, not perfromance.

Zanardi ran steel brakes for a few races in 99 because he couldn't get a feel for the carbon jobbies....it's not like he was braking at the 500m marker...

http://www.atlasf1.c...99/aug/1561.htm

[GeorgeTheCar]

AS I think more about it, the biggest impact of low unsprung weight of carbon carbon brakes is on the high aspect ratios of the current tires.

If the new tire supplier moves to lower aspect ratio tires they, by design, will be more highly damped and a little extra weight will not not have such deleterious effect.

[desmo]

I suggest outing the name of this person as nobody in such a position should be that astonishingly poorly informed. And by poorly informed I mean fecking stupid.

[Fat Boy]

He very positively stated that changing to steel brakes would result in braking distances 5 times as long as with the current carbon/carbon brakes.

incorrect

[BritishV8]

I agree that the number sounds absurd... but before calling someone "fecking stupid" I'd be very interested to hear their rationale. This isn't a topic I know much about, or have ever read or thought a lot about, but there are obviously multiple factors here. Brake rotors are flywheels, so making them lighter will make them easier to slow down. Just how much lighter are carbon rotors anyhow? Do carbon rotors have a favorable coefficient of friction? Do they run cooler and/or/thus provide more resistance to fade? (The difference in stopping distance might be quite different from different starting temperatures, right?) Is he assuming that the car isn't getting any engine-braking effect and that the cars KERS system has been turned off? The 5-to-1 figure must be some sort of absolute worst-case scenario.

Please pardon me for showing my ignorance, but are "steel brakes" really steel? What sort of alloy? I thought good old-fashioned iron was actually preferred over steel for brake rotors. I want carbon rotors for handling reasons...

[Fat Boy]

I agree that the number sounds absurd... but before calling someone "fecking stupid" I'd be very interested to hear their rationale.

I wouldn't. Because someone throwing around numbers like that is "fecking stupid".

[desmo]

Stopping/braking distances will be only very fractionally different between C-C and ferrous rotored brakes. Depending on the testing methodology I wouldn't be at all surprised if one could find a way (perhaps cold brakes) to get results where the metal rotored brakes stop in a shorter distance as the primary limiting factor in braking distances for racing brakes is traction rather than available braking torque.

[Lee Nicolle]

From all accounts carbon gives very marginal braking increases at greatly increased cost.But if the opposition has a 5/100th a lap advantage you have to have it too. Carbon is considerably lighter though probably less durable.
The only thing 5 times greater would be the budget savings. Same for carbon clutches too.

[MattPete]

As someone said above, the limiting factor is tire grip, not the brakes.

Having said that, I think I heard somewhere that carbon brakes have an advantage in initial bite, or how quickly they go from no friction (brake not depressed) to maximum friction. But I don't think the advantage is worth pursuing -- on the timeline of milliseconds. Instead, as someone mentioned above, the advantage is in unsprung weight.

[Ross Stonefeld]

Well the limiting factor at the far end of the scale will be tires yeah, but C-C are going to be better at slowing you down than blocks of wood.

Wooden brakes and bias-ply tires. That would give you something akin to overtaking. In a "I wasn't trying to pass him, I was trying not to crash into him" sort of way.

[GeorgeTheCar]

Well the limiting factor at the far end of the scale will be tires yeah, but C-C are going to be better at slowing you down than blocks of wood.

Wooden brakes and bias-ply tires. That would give you something akin to overtaking. In a "I wasn't trying to pass him, I was trying not to crash into him" sort of way.

Am I correct in thinking that general improvements in materials science have given us a wider choice of friction materials to allow iron or steel rotors to give braking performance that approximates that of C-C systems?

[DaveW]

I was a dinner last night with a person senior in the FIA circuit community.

He very positively stated that changing to steel brakes would result in braking distances 5 times as long as with the current carbon/carbon brakes.

I have read several times that the gap is less then 2 to 1.

Can anyone document that or provide solid data of the actual performance gap?

I suspect that context is all.

I dimly recall descending the Hardknot pass (a brilliant, narrow & winding mountain road in Cumbria, UK) in an automatic car, ending with both feet on the brake pedal & using the handbrake & searching for every puddle. Also, there appears to be a fashion for using carbon-ceramic brake disks in high end sports cars... I believe they don't make much difference on the first stop, but thereafter....

[desmo]

I suspect that context is all.

I dimly recall descending the Hardknot pass (a brilliant, narrow & winding mountain road in Cumbria, UK) in an automatic car, ending with both feet on the brake pedal & using the handbrake & searching for every puddle. Also, there appears to be a fashion for using carbon-ceramic brake disks in high end sports cars... I believe they don't make much difference on the first stop, but thereafter....

I'm interested in hearing what possible context you think might have made that 5 to 1 braking distance utterance even minimally plausible.

[DaveW]

I'm interested in hearing what possible context you think might have made that 5 to 1 braking distance utterance even minimally plausible.

I tried to suggest that excessive temperature can cause serious brake fade, which "boils down" I suppose to the superior heat dissipation characteristics of carbon compared with steel.

[Fat Boy]

Carbon brakes reduce weight by a big chunk. They also reduce rotating mass, which will make a quicker accelerating car (in any direction). The actual braking characteristics of C-C in terms of friction coeff. is very similar to conventional brakes. Yes, most conventional disks are cast iron as opposed to steel. It's been a while since I've done a direct comparison of the two, since I haven't had the chance to run a C-C car lately. A few years ago, though, The mu of a conventional brake setup was maybe 0.65 and the C-C setup was maybe 0.55. They both had good 'bite' when hot. The conventional setup had much better modulation and release characteristics. The conventional setup also had much, much better cold characteristics. The C-C manages the heat better (although it can still very easily have overheating problems). In the end, over a 100 second lap, the C-C setup was maybe a couple tenths faster. It allowed for slightly less ducting or slightly hotter temps, which is a big deal on an F-1 car, but much less so on a less optimized aero package.

Incidentally, C-C brakes are often touted as being less expensive over the course of a season than conventional brakes. I did not necessarily find this to be the case. We would had have to been on a very short R/R schedule with conventional brakes to match the money spent on C-C brakes. They're cool in a tech-geek sense, but certainly not necessary.

I do like them for ovals, because they work well enough and taking those huge spinning chunks of steel out of the equation has to be safer in event of a crash. I think the IRL made the right call there.

[Fat Boy]

I tried to suggest that excessive temperature can cause serious brake fade, which "boils down" I suppose to the superior heat dissipation characteristics of carbon compared with steel.

I've found that carbon brakes tend to be harder on things like caliper seals, wheel bearings, etc. The heat does dissipate better off the rotor and into everything else! I'd like to get RDV's take. He's got a ton more experience than I do with them (or hell, with anything).

[Scotracer]

I was a dinner last night with a person senior in the FIA circuit community.

He very positively stated that changing to steel brakes would result in braking distances 5 times as long as with the current carbon/carbon brakes.

I have read several times that the gap is less then 2 to 1.

Can anyone document that or provide solid data of the actual performance gap?

5 times?

To brake for Rettifilio at Monza would require somewhere close to 600m braking distance

According to what I've heard, Steel brakes offer just as much braking effort as Carbon but steel ones are heavier (increasing unsprung and rotational mass) and fade faster.

Edited by Scotracer, 19 November 2009 - 18:01.

[GeorgeTheCar]

Thanks for the comments

I'm glad I wasn't the idiot at dinner!

[McGuire]

Don't wish to be the village pedant but really we are talking about iron brakes. Steel rotors would really suck.

[BullHead]

steel though, better endurance over race distance for same thickness?

[Fat Boy]

steel though, better endurance over race distance for same thickness?

No. Brake disc life is about themal properties, not mechanical ones. Cast Iron wins when it comes to thermal stability. I don't even know where to get steel rotor should I want to try them. AFAIK, they don't exist unless you want to make them yourself.

[RDV]

C-C can be cheaper in certain applications, at least where I tried them, but not by a huge amount...it ends up subject to series regulations...in the Japanese GT we spend a fortune on rotors (probably the biggest cast-iron ones in the world) as specified by rules, as you use a new set for qualifying, and usualy a new set before the race, just because of bite and response..knock off being a big factor as they warp, not to talk of cracking at difficult tracks (Lemans used to be a bitch...enough cooling for the hard braking would overcool on straights, even today blanking on intakes for day and night running can be iffy). Pads are carbon-metalic anyway, so no big difference...
A set of C-C that can do three races is cheaper than two sets of iron rotors per race, plus cutting unsprung weight...
C-C used to be changed mid-race at LeMans 24h, but now you just breeze through with a single set and don't even think about them.

Initial bite can be better on C-C if you stomp on them hard enough, but takes a lot of driver training depending on their style, and as mentioned above, ultimate limiting factor is tire grip...hence usefulness on aero cars for high speed braking..low speed modulation a bit more tricky.

Have evaluated C-C against iron and as FB says, lap time difference minimal depending on driver.
Downside of doing that is that drivers that come to iron from C-C complain of no braking, but that is only initial bite...
As for Carbon-Ceramic...zero experience...

[DOF_power]

So people forgot about the Monaco 67 ?!
Graham Hill blocked Bandini for most of the race as payback for Mexico 64.
On circuits like Monaco with blocking drivers there wasn't any passing in the good old days just like there isn't today.
Now with every circuit being a Monaco and with the drivers blocking things are bad.

[McGuire]

steel though, better endurance over race distance for same thickness?

No, gray cast iron is the ticket for (ferrous) brake rotors. Its heat absorption and thermal conductivity are far superior to steel. Also vibration damping. There are about 20 standard classes of gray cast iron and generally you want something right around the middle for silicon and carbon content.

Motorcycles use steel or stainless rotors but that is mainly for appearance as gray iron tends to rust and flake so badly. These are solid, non-vented rotors and not very taxed. A vented steel rotor is not practical.

As FB notes, for a light street rod, go-kart, or other low-grade application for solid brake rotors, you can cut and grind them from steel plate... around 1080 will work. Rather farmer-ish, though. Would be the perfect approach for, say, fabbing up a driveshaft-mounted parking brake.

If they could ever get the manufacturing cost down, CGI (compacted graphite iron, aka vermicular iron) would make a nice material for brake rotors and drums. Lighter and stronger than gray cast iron with attractive thermal properties.

[primer]

C-C used to be changed mid-race at LeMans 24h, but now you just breeze through with a single set and don't even think about them.

What changed?

[h4887]

What I don't understand is this: coal is made of carbon and it burns quite merrily. Carbon rotors glow white-hot so why don't they just burn away?

[Kalmake]

What I don't understand is this: coal is made of carbon and it burns quite merrily. Carbon rotors glow white-hot so why don't they just burn away?

Carbon comes in many forms. You wouldn't expect diamonds to burn either.

http://en.wikipedia....ropes_of_carbon
http://en.wikipedia....d_carbon-carbon

[McGuire]

While we are at it... in the usual case, brake rotors don't really "warp" in the sense of a thermally induced distortion. The actual mechanism: Pad material desposits itself unevenly on the rotor faces, causing an eventual variation in thickness sufficient to produce vibration etc. (Trade term: "judder.")

If you want to see pad deposition for yourself with your own car, get the brakes good and hot and then do a long, hard stop, bringing the car to a dead standstill, but then keep your foot firmly clamped on the brake pedal for oh, 60 seconds with the vehicle stationary. Then roll the vehicle forward about one half wheel rotation and then get out and look at the rotor through the wheel spokes. You should see a clear outline of the brake pad imprinted on the face of the rotor, including rivet holes if so equipped. You don't want to do this too hard or too often, though. It will "warp" the rotor, har.

[Fat Boy]

What I don't understand is this: coal is made of carbon and it burns quite merrily. Carbon rotors glow white-hot so why don't they just burn away?

Get them hot enough and they oxidize. They don't really burn, per say, they just turn to carbon dioxide. Not all at once, mind you, just the hottest portion at the surface.

[Lee Nicolle]

No, gray cast iron is the ticket for (ferrous) brake rotors. Its heat absorption and thermal conductivity are far superior to steel. Also vibration damping. There are about 20 standard classes of gray cast iron and generally you want something right around the middle for silicon and carbon content.

Motorcycles use steel or stainless rotors but that is mainly for appearance as gray iron tends to rust and flake so badly. These are solid, non-vented rotors and not very taxed. A vented steel rotor is not practical.

As FB notes, for a light street rod, go-kart, or other low-grade application for solid brake rotors, you can cut and grind them from steel plate... around 1080 will work. Rather farmer-ish, though. Would be the perfect approach for, say, fabbing up a driveshaft-mounted parking brake.

If they could ever get the manufacturing cost down, CGI (compacted graphite iron, aka vermicular iron) would make a nice material for brake rotors and drums. Lighter and stronger than gray cast iron with attractive thermal properties.

Quite a few Euro cars have cast steel rotors, In street use it does not seem to warp as badly but they do wear out a whole lot quicker. Some pad material is recommended for steel rotors too.
Apart from Karts and slow bikes and the ocasional dirt tracker I have never seen steel used in any race application, though there is a heap of minor variations in cast iron materials.
Some midgets and Sprintcars use scalloped out steel and or alloy but they are trying to make things light but the brakes are normally rubbish.
The smart guys are running proper [lightweight] race rotors with a decent calliper set up and are winning races and advoiding accidents.But are 10-20 k heavier.

[OfficeLinebacker]

While we are at it... in the usual case, brake rotors don't really "warp" in the sense of a thermally induced distortion. The actual mechanism: Pad material desposits itself unevenly on the rotor faces, causing an eventual variation in thickness sufficient to produce vibration etc. (Trade term: "judder.")

If you want to see pad deposition for yourself with your own car, get the brakes good and hot and then do a long, hard stop, bringing the car to a dead standstill, but then keep your foot firmly clamped on the brake pedal for oh, 60 seconds with the vehicle stationary. Then roll the vehicle forward about one half wheel rotation and then get out and look at the rotor through the wheel spokes. You should see a clear outline of the brake pad imprinted on the face of the rotor, including rivet holes if so equipped. You don't want to do this too hard or too often, though. It will "warp" the rotor, har.

yep. I read some really detailed paper about brake noise including judder and ever since, I always creep a bit at stop signs. I try to leave a little extra space so when I come to a stop I can spend the time between when I stop and the light turns green again creeping. Or if it's perfectly level I keep the car in neutral and take my foot off the brake.

Been working like a charm.

[primer]

Been working like a charm.

Parking brake.

[kikiturbo2]

While we are at it... in the usual case, brake rotors don't really "warp" in the sense of a thermally induced distortion. The actual mechanism: Pad material desposits itself unevenly on the rotor faces, causing an eventual variation in thickness sufficient to produce vibration etc. (Trade term: "judder.")

If you want to see pad deposition for yourself with your own car, get the brakes good and hot and then do a long, hard stop, bringing the car to a dead standstill, but then keep your foot firmly clamped on the brake pedal for oh, 60 seconds with the vehicle stationary. Then roll the vehicle forward about one half wheel rotation and then get out and look at the rotor through the wheel spokes. You should see a clear outline of the brake pad imprinted on the face of the rotor, including rivet holes if so equipped. You don't want to do this too hard or too often, though. It will "warp" the rotor, har.

I have always been a proponent of "brake rotors don't really "warp" " camp, although the common theory is they really bend like a pretzel.. and I am just trying to cure a set of almost new very expensive two piece discs from DBA that had the wrong pads and wrong driving style subjected onto them.. I have put on a set of very agressive pads, and they judder much less, but I can still notice some judder under light braking.. . time to visit the track..

[mariner]

It may be buried somewhere in the F1 rules but how about setting a very thin maximum disc thickness to aid overtaking plus a fail safe warning system to prevent actual disc break up?

He who canes his brakes early gets to retire for safety reasons and everybody has to brake early so there are more opportunities to "out judge" people on braking and overtake.

Without always eulogisiing people like Jim Clark, in the days when brakes did not last well his usage was apparently way below his less skilled team mates so a maximum disc thickness hopefully driving skill would be rewarded.

[OfficeLinebacker]

It may be buried somewhere in the F1 rules but how about setting a very thin maximum disc thickness to aid overtaking plus a fail safe warning system to prevent actual disc break up?

He who canes his brakes early gets to retire for safety reasons and everybody has to brake early so there are more opportunities to "out judge" people on braking and overtake.

Without always eulogisiing people like Jim Clark, in the days when brakes did not last well his usage was apparently way below his less skilled team mates so a maximum disc thickness hopefully driving skill would be rewarded.

How about a max. PAD thickness? Seems a safer option.

[mariner]

I only said discs because they might be slower to change than pads if pitstops were still allowed. If you banned disc or pad changes then I agree pads would be much better.

[Greg Locock]

I have always been a proponent of "brake rotors don't really "warp" " camp, although the common theory is they really bend like a pretzel.. and I am just trying to cure a set of almost new very expensive two piece discs from DBA that had the wrong pads and wrong driving style subjected onto them.. I have put on a set of very agressive pads, and they judder much less, but I can still notice some judder under light braking.. . time to visit the track..

They do warp (run out) a bit, but the main driver for brake shudder in production is thickness variation. The stiffness of the system is high so the forces you can generate wth small thickness variations is large. Backing off on system stiffness is one possible cure, but it feels like soft pedal.

[kikiturbo2]

They do warp (run out) a bit, but the main driver for brake shudder in production is thickness variation. The stiffness of the system is high so the forces you can generate wth small thickness variations is large. Backing off on system stiffness is one possible cure, but it feels like soft pedal.

I am sure they do run out a bit, especially the non floating kind, but I would also wonder if the shudder is also down to the different friction coefficient between the pad and different parts of the disc (in case of non even pad material transfer on to the disc..)

[Greg Locock]

I am sure they do run out a bit, especially the non floating kind, but I would also wonder if the shudder is also down to the different friction coefficient between the pad and different parts of the disc (in case of non even pad material transfer on to the disc..)

I'm sure it is in part. Now I'm wondering if we have a good theory for how the thickness variation is formed. I know they track it during durability tests.

[McGuire]

Not theory, fact. When you identify the "fat spots" in a so-called "warped" rotor, these typically appear as "hard spots" or "blue spots" -- cementite inclusions. These regions of the rotor face have effectively turned to carbide.

[Fat Boy]

Not theory, fact. When you identify the "fat spots" in a so-called "warped" rotor, these typically appear as "hard spots" or "blue spots" -- cementite inclusions. These regions of the rotor face have effectively turned to carbide.

Do you have some sort of tech paper on this? I'm curious, because I've ran into the situation many times where the effectiveness of a rotor/pad combo just kind of goes to ****. It's not a glazed or wear issue, but it is related to mileage. The only answer I've been able to come up with is to put new stuff on. No big deal for me, but at times I've heard kind of a metal-on-metal sound coming from team managers / owners about it. You're throwing rotors in the bin that visually look and measure fine. The driver reports poor modulation and overall friction levels, though.

I've never figured out what it is and haven't ever had the budget to go down that particular rabbit hole. I'd be interested to know if someone else already has.

[Greg Locock]

Not theory, fact. When you identify the "fat spots" in a so-called "warped" rotor, these typically appear as "hard spots" or "blue spots" -- cementite inclusions. These regions of the rotor face have effectively turned to carbide.

So, should be easy enough to hardness test them and spot the difference?

[DOF_power]

Steel brakes won't make a **** of a difference.

When equally prepared drivers in Speedcar, with equally performing cars, got near one another they didn't pass each, they did synchronized late braking combined with waving the the car around/blocking .
I remember Alesi, Herbert and Frentzen doing this for 30 minutes till Alesi missed the braking and took himself and Herbert out.

There was no passing at all.

Steel brakes are a myth, a false-belief from an era when the likes of Fangio and Senna took physical preparation seriously while the rest didn't and when the fastest cars could have a 2-3 second advantage into the first corner.



To see why it is a myth look at Mexico 64 and Monaco 67; 2 words Hill - Bandini.

Edited by DOF_power, 23 November 2009 - 09:56.

[Fat Boy]

Steel brakes won't make a **** of a difference.

Weird post. Anyway, they won't make a difference versus what?

[McGuire]

So, should be easy enough to hardness test them and spot the difference?

Sure, and I presume your brake people are doing so. Oftimes the evidence is visible to the naked eye:



The above photo is figure 4 from Carroll Smith's notorious, frequently quoted monograph on brake rotors, which invites quibbles (it's his absolutist tone) but is essentially solid. It is fashionable these days to sharpshoot Smith... maybe it's an Oedipal thing. Link to story: http://www.stoptech....brakedisk.shtml

[McGuire]

Do you have some sort of tech paper on this? I'm curious, because I've ran into the situation many times where the effectiveness of a rotor/pad combo just kind of goes to ****. It's not a glazed or wear issue, but it is related to mileage. The only answer I've been able to come up with is to put new stuff on. No big deal for me, but at times I've heard kind of a metal-on-metal sound coming from team managers / owners about it. You're throwing rotors in the bin that visually look and measure fine. The driver reports poor modulation and overall friction levels, though.

I've never figured out what it is and haven't ever had the budget to go down that particular rabbit hole. I'd be interested to know if someone else already has.

Sounds like it is related to buildup but not carbide inclusions or you would get vibration. Dumb question probably, but did you try scuffing the rotors?

[Tony Matthews]

]

The above photo is figure 4 from Carroll Smith's notorious, frequently quoted monograph on brake rotors, which invites quibbles (it's his absolutist tone) but is essentially solid. It is fashionable these days to sharpshoot Smith... maybe it's an Oedipal thing. Link to story: http://www.stoptech....brakedisk.shtml

Well, that was a fascinating read, thanks for the link. I am ashamed to say that I have never read any of Carroll Smith's books - I intend to rectify that ASAP.