Minimising the risk of brake fade
Discussion
All things being equal, ie to obtain the same decelaration what is the best advice to minimise the risk of brake fade at the Nurburgring on a totally std road set up (Mini Cooper S 08):
- brake hard but over a shorter distance.
- extend the braking zone but apply less braking pressure.
Or doesn't that make any difference?
The car will be driven very conservatively, ie at 6 or 7 tenths.
Thanks for any input.
- brake hard but over a shorter distance.
- extend the braking zone but apply less braking pressure.
Or doesn't that make any difference?
The car will be driven very conservatively, ie at 6 or 7 tenths.
Thanks for any input.
The only place you may risk a bit of brake fade is the tight left hander (Wehrseifen) at the bottom of the hill before the Breidscheid bridge. It's the slowest corner (comparable to Adenauer Forst) but at the bottom of the long descent.
If it's your first visit and you take your time you'll be fine.
Your brakes were probably tested there when your car was at the prototype stage!
Have fun and stay safe!
If it's your first visit and you take your time you'll be fine.
Your brakes were probably tested there when your car was at the prototype stage!
Have fun and stay safe!
nickfrog said:
Any point in also having 5.1 fluid and braided lines too eventually?
It needs changing more often. Good pads and decent heat dissipation have made more difference in my experiences.Braided lines look nice, but I've not noticed much difference due to the lines (new fluid and pistons cleaned at the same time) on motorbikes and mountain bikes.
Don't bother with 5.1, if boiling the fluid is likely to be a problem then Motul RBF600 or simular is what you want. This stuff is £20/litre and needs changing annually though. If you can get away with DOT 4 then great- for one lap at a time on the nordschlieffe I expect you'll be alright, just avoid nervously riding the brakes on the way into the faster sections because this will cook them post-haste.
I found that I was able to repeatedly cook Mintex 1144 within less than two laps of Rockingham (100bhp, 610kg) but I am reliably informed that this is because I didn't bed them in properly so be sure to do this before you arrive at the circuit (yes, there is a procedure to follow).
I found that I was able to repeatedly cook Mintex 1144 within less than two laps of Rockingham (100bhp, 610kg) but I am reliably informed that this is because I didn't bed them in properly so be sure to do this before you arrive at the circuit (yes, there is a procedure to follow).
The usual advice for ring first-timers is to treat it like a fast country road. Your 6-7 tenths will suit that just fine. Your brakes won't even begin to have a problem.
I do not believe that braded brake lines improve braking capability. In fact au contraire (Rodney), they flex and introduce le spongy pedal feel.
Bert
I do not believe that braded brake lines improve braking capability. In fact au contraire (Rodney), they flex and introduce le spongy pedal feel.
Bert
Hooli said:
BertBert said:
I do not believe that braded brake lines improve braking capability. In fact au contraire (Rodney), they flex and introduce le spongy pedal feel.
Odd, everyone fits them to bikes for exactly the opposite reason.I may well be wrong here but my experience of brake fade in a car is linked to repeated multiple hard applications (including 4 up in an e46 M3 on the ring). I'm sure to get the temperature so high as to cause fade, you have to overwhelm the systems ability to dissipate heat, this is far more likely by generating heat quickly (ie very hard breaking from high speed). Situation on a track It's different to dragging your brakes constantly on a long downhill or with a lot of weight.
I'm not sure of the theory and others seem to disagree, but this is certainly my experience.
I'm not sure of the theory and others seem to disagree, but this is certainly my experience.
Hungrymc said:
I may well be wrong here but my experience of brake fade in a car is linked to repeated multiple hard applications (including 4 up in an e46 M3 on the ring). I'm sure to get the temperature so high as to cause fade, you have to overwhelm the systems ability to dissipate heat, this is far more likely by generating heat quickly (ie very hard breaking from high speed). Situation on a track It's different to dragging your brakes constantly on a long downhill or with a lot of weight.
I'm not sure of the theory and others seem to disagree, but this is certainly my experience.
Certain levels of dissipated energy will cook the brakes no matter what! In less extreme scenarios, however, I think the 'dragging is worse' advice applies.I guess a lot of it also comes down to heat soaking through the system. if the pads are in contact with the disk for longer, there's more time for the heat to conduct back to the lines & the fluid?I'm not sure of the theory and others seem to disagree, but this is certainly my experience.
Not entirely sure of the actual answer, like most here I'm talking on experience. The worst fade I've had was coming down off culver down on the IOW in my 1.2 corsa with me + 3 mates. Got to a blind bend at the bottom, still rolling, and just had to hope for the best! That was after me lightly braking all the way down the hill to control my speed.
Actually, I'd suggest the answer is "it doesn't matter" - and certainly not for Nickfrog!
Consider the physics: If you slow down the same amount, you remove the same amount of kinetic energy from the car. That energy has to be turned into heat and noise by the brakes. Thus the brakes absorb the same amount of energy, no matter how long you take to do it, and they will have to dissipate that same energy into the air.
The only differences come from how that energy is dissipated; broadly in the shorter stop, the brakes will be hotter and will be dissipating energy into the air faster *during* the stop, once the braking is done, both cases will follow a similar curve. While you'd probably get some 'interesting' results if you considered (theoretical) limits (infinitely hard braking over an infinitely short time vs minimal braking over an infinitely long time), my gut suggests that the difference between two middle of the road cases is virtually nothing.
Plus, as noted, Nick is not planning to batter it, and the ring isn't a heavy braking circuit.
Fade can be for (broadly) 3 reasons:
1) Pad Fade
The brake pad is way over the design operating temp, out-gassing and not getting a bite on the disk. This is likely to come on *during* a stop. The pedal will remain firm.
2) 'Boiling' the fluid
The only case where DOT 5.1 may help as it's boiling point is (I think) 40deg higher than DOT4. Fairly straightforward - it gets too hot (around 260deg) becomes compressible, and you get a spongy pedal. Personally I think it's less common than folks would like to believe.
3) Fluid 'vapour' related
Brake fluid is hygroscopic. It likes to absorb water (in some ways this is good), but once it gets to 100c+ that water boils and becomes vapour. The pedal gets spongy. Not dissimilar to 2) For this reason I personally suspect most folks who swear by 'DOT5.1' would have got the same benefit by putting in fresh DOT<whatever>
As a sidenote, DOT5 (not .1) is silicone based, and not hygroscopic. It's also not compatible with 4/5.1 glycol fluids, so you can't swap!
Consider the physics: If you slow down the same amount, you remove the same amount of kinetic energy from the car. That energy has to be turned into heat and noise by the brakes. Thus the brakes absorb the same amount of energy, no matter how long you take to do it, and they will have to dissipate that same energy into the air.
The only differences come from how that energy is dissipated; broadly in the shorter stop, the brakes will be hotter and will be dissipating energy into the air faster *during* the stop, once the braking is done, both cases will follow a similar curve. While you'd probably get some 'interesting' results if you considered (theoretical) limits (infinitely hard braking over an infinitely short time vs minimal braking over an infinitely long time), my gut suggests that the difference between two middle of the road cases is virtually nothing.
Plus, as noted, Nick is not planning to batter it, and the ring isn't a heavy braking circuit.
Fade can be for (broadly) 3 reasons:
1) Pad Fade
The brake pad is way over the design operating temp, out-gassing and not getting a bite on the disk. This is likely to come on *during* a stop. The pedal will remain firm.
2) 'Boiling' the fluid
The only case where DOT 5.1 may help as it's boiling point is (I think) 40deg higher than DOT4. Fairly straightforward - it gets too hot (around 260deg) becomes compressible, and you get a spongy pedal. Personally I think it's less common than folks would like to believe.
3) Fluid 'vapour' related
Brake fluid is hygroscopic. It likes to absorb water (in some ways this is good), but once it gets to 100c+ that water boils and becomes vapour. The pedal gets spongy. Not dissimilar to 2) For this reason I personally suspect most folks who swear by 'DOT5.1' would have got the same benefit by putting in fresh DOT<whatever>
As a sidenote, DOT5 (not .1) is silicone based, and not hygroscopic. It's also not compatible with 4/5.1 glycol fluids, so you can't swap!
upsidedownmark- I think one of the reasons dragging the brakes and decelerating slowly is worse, is because braking systems are designed with a certain rate of deceleration (and therefore weight transfer) in mind. The brakes on my Caterham race car never cook in the dry, but do in the wet- the braking zones are extended, the decel 'G' is lower, and the rear brakes are working harder than usual for longer than usual. Just an observation, but if the logic carries then the same could apply to the Mini.
upsidedownmark said:
Actually, I'd suggest the answer is "it doesn't matter" - and certainly not for Nickfrog!
Consider the physics: If you slow down the same amount, you remove the same amount of kinetic energy from the car. That energy has to be turned into heat and noise by the brakes. Thus the brakes absorb the same amount of energy, no matter how long you take to do it, and they will have to dissipate that same energy into the air.
The only differences come from how that energy is dissipated; broadly in the shorter stop, the brakes will be hotter and will be dissipating energy into the air faster *during* the stop, once the braking is done, both cases will follow a similar curve.
You're wrong on several counts.Consider the physics: If you slow down the same amount, you remove the same amount of kinetic energy from the car. That energy has to be turned into heat and noise by the brakes. Thus the brakes absorb the same amount of energy, no matter how long you take to do it, and they will have to dissipate that same energy into the air.
The only differences come from how that energy is dissipated; broadly in the shorter stop, the brakes will be hotter and will be dissipating energy into the air faster *during* the stop, once the braking is done, both cases will follow a similar curve.
Firstly, if you brake later you're generally braking from a higher speed (i.e. if you kept accelerating instead of coasting).
Also at a higher speed there is greater cooling from the previous stop, before going into the next one. (Higher airflow cooling better than slower airflow, see first point.)
You're also leaving a longer TIME between braking periods, which means the brakes have more time to recover.
By spending less time on the brakes the disc and pads are not touching for so long, so the friction faces are exposed to air for more time to cool.
Also, if you're applying the brakes for longer time then the heat from the disc will permeate into the pads more. If you get off the brakes then the heat in the disc doesn't transfer to the pads/callipers/fluid as much.
The two key factors are i) Time the brakes are not applied for, and ii) Things cool much faster when there's a larger temperature differential.
mrmr96 said:
You're wrong on several counts.
Firstly, if you brake later you're generally braking from a higher speed (i.e. if you kept accelerating instead of coasting).
Also at a higher speed there is greater cooling from the previous stop, before going into the next one. (Higher airflow cooling better than slower airflow, see first point.)
You're also leaving a longer TIME between braking periods, which means the brakes have more time to recover.
By spending less time on the brakes the disc and pads are not touching for so long, so the friction faces are exposed to air for more time to cool.
Also, if you're applying the brakes for longer time then the heat from the disc will permeate into the pads more. If you get off the brakes then the heat in the disc doesn't transfer to the pads/callipers/fluid as much.
The two key factors are i) Time the brakes are not applied for, and ii) Things cool much faster when there's a larger temperature differential.
Ummm. OK:Firstly, if you brake later you're generally braking from a higher speed (i.e. if you kept accelerating instead of coasting).
Also at a higher speed there is greater cooling from the previous stop, before going into the next one. (Higher airflow cooling better than slower airflow, see first point.)
You're also leaving a longer TIME between braking periods, which means the brakes have more time to recover.
By spending less time on the brakes the disc and pads are not touching for so long, so the friction faces are exposed to air for more time to cool.
Also, if you're applying the brakes for longer time then the heat from the disc will permeate into the pads more. If you get off the brakes then the heat in the disc doesn't transfer to the pads/callipers/fluid as much.
The two key factors are i) Time the brakes are not applied for, and ii) Things cool much faster when there's a larger temperature differential.
ii) Yup, agreed. At least they do until they cool down somewhat, and then they're cooling at a lower rate. Hot things take longer to cool down than things that are cooler, which is pretty intuitive. Hot things do not cool down in a linear fashion. It's more of an asymptotic curve.
Also, note that the transfer of heat argument also applies to the heat soak into the pads and fluid. The hotter things are, the faster the heat will transfer where you don't want it - it's just another form of cooling. Overall the percentage of the energy transferred to the fluid etc., should be pretty static.
i) I'm not so sure. The system is dissipating energy ALL the time, whether the brakes are on or not. When you're actually braking, there's more energy going in than coming out, so the temp rises, that's all. You may shed slightly more when the pads aren't in contact, or you may not - I'm not so sure.
Also, you kinda missed kinetic energy.
First up, Assumptions:
A1) In any case, the turn in speed must be the same, otherwise the car will fall off the road
A2) We've just come off the start line and the brakes are nice and cool.
If you consider 2 imaginary cars, Nick 1 and Nick 2 approaching the same corner.
Nick 1 brakes at 200m, nice and steady. Nick 2 carries on AT THE SAME SPEED (just for now)
- Nick 1's brakes are getting warmer, and shedding energy a bit faster
- Nick 2's brakes are ambient, and barely shedding anything.
Now at 100m Nick 2 gets on the brakes hard. A very small time later:
- Nick 1's brakes are doing the same old thing
- Nick 2's brakes are scorching and shedding energy at a fair old rate
We reach the turn in point. Both cars come off the brakes. They've both ditched the same amount of energy into the braking system.
- Nick 1 has done it in a steady trickle and has been dissipating it into the air at a similarly steady pace over 200m.
- Nick 2 has done nothing for 100m, then a lot in 100m
Who's going to have the hotter brakes? Frankly, I think it's too close to call.
Now they're off the brakes and doing the same speed, they're going to cool very similarly.
Now we'll change the setup - this time Nick2 is going to keep it planted for an extra 90m's worth of cooling at higher speed. (Nick 2 will have to brake a smidge earlier than last time because he'll be going faster)
This time Nick 2 has a chunk more energy to get rid of - he's going faster and A1 applies. Who's going to have the hotter brakes at turn in? Given A2, I'm very sure it's Nick 2, who will therefore have hotter brakes for most of the next straight.
If we get rid of A2 and go to mrmr96's scenario, we're at some intermediate stage, and the brakes are already hot. Does 90m of cooling outweigh the additional kinetic energy we gained KE=1/2mv(squared)?
I'd suggest that for most cars the answer is a resounding NO - the engine can put energy in quicker than the brakes can shed it to the air, otherwise it would be impossible to cook the brakes. I'd also suggest that Nick 2 is a faster driver all the same
In order to get an absolute answer, you'd need to solve a pretty complex set of differential equations - beyond me, that's for sure. Personally, I favour the later and harder braking approach, but I don't believe it makes a **significant** difference, which was my original point.
What the thought experiment does prove however is that there are two ways to effectively cool the brakes:
1) Corner faster (!)
2) Arrive (a bit) slower.
If you watch F1, it might occur there's no real coincidence that when they're having brake wear/temp issues the team asks them to lift off early into some of the bigger stops.
@HustleRussell - That's really interesting, makes sense. Do you have / are you using adjustable brake bias, or is it fixed?
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