Brake temperatures

[ChrisGB]

So, here's a question for you. Do we reckon it would be possible to attain higher brake temperatures on road than on track? My thinking, take a reasonably powerful MR2, punt it around somewhere like Brands Hatch, you will be on the brakes for around 12 second a lap, around 20% duty cycle. Now take the same car down a gnarly mountain B road, short straights and tight bends, all low gear stuff, braking as hard, but lower speeds = lower airflow, but 50% duty cycle.

Discuss.

[Ardent]

Possible mmm yes
Probable mmm no

So many variables. I think if you set out to do it then perhaps achievable. But would still need planetary alignment of all the variables in your favour.
The road to yourself for a start. Round my way, no chance.

[StuC]

In theory the road could be worse, specifically the mountain pass you mentioned, especially headed downhill with higher inertia headed forwards making these front brakes work harder. You'd have to be giving it some welly though and it would depend on the lengths of the straights.

Are you thinking of this in respect to brake fade Chris?

I am sure there is some nasty homologation brake fade test where you have to accelerate up to 70, then brake to zero. Then repeat 4 times on the bounce. Its a difficult one to pass as the heat doesn't get chance to dissipate.

[Alex Knight]

You need to think of the amount of energy you are converting into heat.

On a lot of tracks, there are several big stops from 100+ mph. A car travelling at those speeds before braking has a huge amount of kinetic energy, much more so than 99.9% of road driving. You need to dissipate that massive energy very quickly on track (through friction) which creates massive amount of heat as a by product.

Try rubbing your hands together slowly, but for 10 seconds (road). See how hot your hands get.
Now try running your hands together very quickly, but for 5 seconds. See how much hotter your hands get.

You mentioned duty cycles of 20 and 50%. What you are not factoring is the difference in brake force applied. You brake *significantly* harder on track than you should ever do on a road, maybe for less time, but you are still generating way more heat due to significantly more energy needing converting.

[Ardent]

taking the point of braking hard from a 100 on track. In my simple mind. Whilst the car is building up to and traveling at a 100. The air flow around the brakes will be providing much cooling prior to the application of the brakes.
So many variables.

[Alex Knight]

There is precious little airflow over road car brakes I'm afraid.

[JoeCool]

I've set fire to road car brakes on the road, and I've yet to manage that on track.

Milton Keynes is pretty good for it: Just do roundabouts from 70 to 20ish over and over until you end up in the flower beds.

Overall, I think track is harder, because the speeds are higher and the duty cycle harsher. But there's no reason why you can't overheat the brakes under exceptional conditions on the road.

[Jrichards20]

I've managed to destroy pads on both track and mountain passes. So don't know about heat, but can come to the same outcome in both... Shitting yourself as you realise you now have a whole different type of turn to.  s:) s:)

[ChrisGB]

Was thinking about this as on the three occasions I've had pad related fade, it has been on country roads, usually sustained heavy braking from about half way down many short straights.

My thinking is that on fast road use you have a longer duration of braking, relative to the length of the straights. If you are on it, you are probably going 9/10ths, but also there will be a lot more "partial braking". This is because you will be having brake checks while you wait for visibility and lighter braking where surface or camber are less than optimal. The overall effect is that you heat the pads for longer per mile, while working then very nearly as hard. This means that although the thermal gradient across the pad will not be as steep as on track, the overall heat energy in the pad could easily be greater.

Work the same pad on track and on most longer straights, you will get big speeds, but longer periods where the pad is losing heat. The temperature gradient is bigger, but the overall heat load may not be as great. The greater gradient and higher surface temperature will increase the heat dissipation.

I've read theories that not braking hard enough / late enough on track can increase brake temperature more than going harder on the brakes.

[stupink]

you have so much more grip between tyres+tarmac on track, so the brakes can/do work a lot harder regardless of the fact you start at near double the speed and drop 120>50 not 70>20.   Easy enough to overheat on both that said, stupidly small disks on both front+back and its the disks that do the storage+cooling(hence vented, it acts like a pump and flows air, so you do get a lot of airflow over the disc on both road and track)

[Alex Knight]

you heat the pads for longer per mile, while working then very nearly as hard.

If you are braking nearly as hard on the road as you do on track, then I don't want to be anywhere near you on a road.

I can honestly say that I have probably never driven quicker than 6/10ths on the road. Any more is irresponsible imho.

Braking on track is brutal. I've never gotten anywhere near that on a road, and I pray that I never have to.

[tommyzoom99]

So, here's a question for you. Do we reckon it would be possible to attain higher brake temperatures on road than on track? My thinking, take a reasonably powerful MR2, punt it around somewhere like Brands Hatch, you will be on the brakes for around 12 second a lap, around 20% duty cycle. Now take the same car down a gnarly mountain B road, short straights and tight bends, all low gear stuff, braking as hard, but lower speeds = lower airflow, but 50% duty cycle.

Discuss.

Just my 2 pence

I am the lead design engineer for a Carbon ceramic brake company called Surface Transforms ( go check us out) so i have a reasonable amount of experience when it comes to brakes

On road in many cars we have tested you will never see brake temps as high as on the track, average road temps around 150 to 300 degrees C on  track 500 to 700 degrees C now this is for Carbon ceramics

On the road you cant do the speeds and break hard and long enough to generate high temp, there are certain situations describe where if your going down a hill for 10 mins constantly on the brakes them they will get hot yes but general spirited driving on the road i would be highly surprised to see higher temps than on track,

now this depends how fast you are willing to go on the road, me not very fast, know where near fasted enough to get my brakes any where near what i would call hot, compared to on the track

Braking from 70 to 30 or 60 to 20 for example wont generate much heat your not braking for long enough its generally the big stops the produce the heat, which are alot more frequent on track and constant lap after lap, some track obviously are more brake oriented and alot harder on brakes but still i have never seen any data showing higher brake temps on the road

cheers tommy

[shnazzle]

Funny, when I read the first post I thought of the same analogy mentioned later; rub hands together slowly for 20 mins and you'll get some heat, rub hands really hard for 10 seconds...tons of heat. I think that basically sums it up!
You'd have to be doing some pretty "special" road driving to get the brake temps as hot as on a track. Although I have to admit having experienced fade on a choice public road before. I used a bit more engine braking and the problem disappeared.

[Jrichards20]

So, here's a question for you. Do we reckon it would be possible to attain higher brake temperatures on road than on track? My thinking, take a reasonably powerful MR2, punt it around somewhere like Brands Hatch, you will be on the brakes for around 12 second a lap, around 20% duty cycle. Now take the same car down a gnarly mountain B road, short straights and tight bends, all low gear stuff, braking as hard, but lower speeds = lower airflow, but 50% duty cycle.

Discuss.

Just my 2 pence

I am the lead design engineer for a Carbon ceramic brake company called Surface Transforms ( go check us out) so i have a reasonable amount of experience when it comes to brakes

On road in many cars we have tested you will never see brake temps as high as on the track, average road temps around 150 to 300 degrees C on  track 500 to 700 degrees C now this is for Carbon ceramics

On the road you cant do the speeds and break hard and long enough to generate high temp, there are certain situations describe where if your going down a hill for 10 mins constantly on the brakes them they will get hot yes but general spirited driving on the road i would be highly surprised to see higher temps than on track,

now this depends how fast you are willing to go on the road, me not very fast, know where near fasted enough to get my brakes any where near what i would call hot, compared to on the track

Braking from 70 to 30 or 60 to 20 for example wont generate much heat your not braking for long enough its generally the big stops the produce the heat, which are alot more frequent on track and constant lap after lap, some track obviously are more brake oriented and alot harder on brakes but still i have never seen any data showing higher brake temps on the road

cheers tommy

From the horses mouth  s:) s:)  Ok, so that is purely temperature on the pads/discs. What about brake fluid? Does the difference in type of braking effect the temperature of the brake fluid differently, I would imagine the fluid not having as quick as cooling period, and not being subject to force? and air flow. Possibly the contributes to brake fade on the road, compared to brake fade on the track caused by heated pads and disks?

[tommyzoom99]

So, here's a question for you. Do we reckon it would be possible to attain higher brake temperatures on road than on track? My thinking, take a reasonably powerful MR2, punt it around somewhere like Brands Hatch, you will be on the brakes for around 12 second a lap, around 20% duty cycle. Now take the same car down a gnarly mountain B road, short straights and tight bends, all low gear stuff, braking as hard, but lower speeds = lower airflow, but 50% duty cycle.

Discuss.

Just my 2 pence

I am the lead design engineer for a Carbon ceramic brake company called Surface Transforms ( go check us out) so i have a reasonable amount of experience when it comes to brakes

On road in many cars we have tested you will never see brake temps as high as on the track, average road temps around 150 to 300 degrees C on  track 500 to 700 degrees C now this is for Carbon ceramics

On the road you cant do the speeds and break hard and long enough to generate high temp, there are certain situations describe where if your going down a hill for 10 mins constantly on the brakes them they will get hot yes but general spirited driving on the road i would be highly surprised to see higher temps than on track,

now this depends how fast you are willing to go on the road, me not very fast, know where near fasted enough to get my brakes any where near what i would call hot, compared to on the track

Braking from 70 to 30 or 60 to 20 for example wont generate much heat your not braking for long enough its generally the big stops the produce the heat, which are alot more frequent on track and constant lap after lap, some track obviously are more brake oriented and alot harder on brakes but still i have never seen any data showing higher brake temps on the road

cheers tommy

From the horses mouth  s:) s:)  Ok, so that is purely temperature on the pads/discs. What about brake fluid? Does the difference in type of braking effect the temperature of the brake fluid differently, I would imagine the fluid not having as quick as cooling period, and not being subject to force? and air flow. Possibly the contributes to brake fade on the road, compared to brake fade on the track caused by heated pads and disks?

brake fluid temp are normally directly related to temp of the disc and pads, as the heat radiates from the disc and pads into the calliper, the calliper gets hot heating the brake fluid as well, some heat is generated by the fluid being pushed through the lines from friction alone but its not a compressible fluid so it doesn't get hot like compressing a compressible fluid when braking.

For example if the disc and pads get to 300 degrees the calliper will heat up to around this temp usually slightly less say 250 degrees for argument sake, as the calliper is cooled by air flow as well, this then heats the fluid up to this temp also but it generally doesn't get hotter than the pads/disc, this is due to the fact if only 300 degrees on heat is going into the calliper from the disc/pads it cant get hotter than 300 also the fluid is running through meters of brake lines which do dissipate alot of heat as there is alot of surface area covered by the brake line if you imagine running hot fluid through a long metal tube even with minimal air running over it it does dissipate quite alot of heat.

cheers tommy

[nathanMR2]

Not that i have done much track time but the only time ive ever really got serious brake fade was at the ring. Never been able to achieve this on the road despite some fairly sprited driving.

I guess on the road i try to avoid being on the brakes too much, whereas on track you cant really avoid being on the brakes harder and for longer periods of time