| BIGSKYWRX | 05-11-2006 08:30 PM |
Lower coefficient pad = less heat in rotors?
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The last couple of HPDE's I've run DS3000's- they brake like the dickens :devil: and have a high operating range (vs 2500's) BUT are they increasing heat into my rotors (over a lower friction pad)?
I'm on the brakes a shorter time w/ the 3000's vs the 2500's- don't know if this outweighs the higher vs lower friction?
I'm on stock size (WRX) rotors and would prefer not to over tax them. I looked into the 3000 endurance pads (high operating temp, but lower friction) but these are not available for the FHI 4/2 pots.
I'm going to switch to R compounds this years for most of my events and am afraid this may exasberate the heat situation further.
I'll probably try a little experimenting w/ some rotor temperature paint, but maybe someone already knows the answer :)
TIA
I'm on the brakes a shorter time w/ the 3000's vs the 2500's- don't know if this outweighs the higher vs lower friction?
I'm on stock size (WRX) rotors and would prefer not to over tax them. I looked into the 3000 endurance pads (high operating temp, but lower friction) but these are not available for the FHI 4/2 pots.
I'm going to switch to R compounds this years for most of my events and am afraid this may exasberate the heat situation further.
I'll probably try a little experimenting w/ some rotor temperature paint, but maybe someone already knows the answer :)
TIA
| adhowe70 | 05-11-2006 09:54 PM |
Its simple: more braking = more friction = more heat. It doesn't really matter whether you distribute that friction out over 5 seconds or 6... the end temperature will be nearly identical if you're doing the same braking.
| BIGSKYWRX | 05-11-2006 11:20 PM |
It must not be that simple because I guess I'm still not getting it :) One brake pad has a higher coefficient, one lower- I know which one brake "better". One brakes in a shorter distance ( but shorter duration), the other a longer distance (but longer duration)- are you saying they will both produce the same amount of heat in the rotors?
If you are- then it's a easy choice- I'll continue on w/ the 3000's for track days :).
If you are- then it's a easy choice- I'll continue on w/ the 3000's for track days :).
| trhoppe | 05-11-2006 11:24 PM |
[QUOTE=BIGSKYWRX]It must not be that simple because I guess I'm still not getting it :) One brake pad has a higher coefficient, one lower- I know which one brake "better". One brakes in a shorter distance ( but shorter duration), the other a longer distance (but longer duration)- are you saying they will both produce the same amount of heat in the rotors?
If you are- then it's a easy choice- I'll continue on w/ the 3000's for track days :).[/QUOTE]
That is exactly what he is saying. Braking from 120mph whether it takes 200ft to get to 50mph, or 100ft to get to 50mph, will produce the same amount of heat.
-Tom
If you are- then it's a easy choice- I'll continue on w/ the 3000's for track days :).[/QUOTE]
That is exactly what he is saying. Braking from 120mph whether it takes 200ft to get to 50mph, or 100ft to get to 50mph, will produce the same amount of heat.
-Tom
| adhowe70 | 05-11-2006 11:34 PM |
Yup... that's what I'm saying. If you have a heat problem, add metal (make a larger heat sink) or add ducting (capacity to cool the brakes between corners). Changing pads will just make it take longer to brake.
| AndrewSS | 05-11-2006 11:56 PM |
for what its worth, I took my STi to the track twice on hawk HPS pads and then when I switched to the performance friction 01 pads (race pads) after that first trackday on them my brembos gold finish turned noticably darker and then the red "brembo" text turned dark brown. Could be a result of more heat from using that pad, but could be more variables to it, I dunno... just thought I would mention it :)
| ChrisDP | 05-12-2006 12:12 AM |
FWIW, any time you can compress a braking zone, you're lowering your average rotor temperature... you're giving the rotors more "off" time to cool down. Your heat load hasn't changed because you're still stopping the same amount of weight moving at the same velocity, BUT your temps will be lower if you can stop for a shorter period of time. That said, a higher temp pad will allow you to heat the rotors up more because it'll keep generating friction above the temperature that a lower-temp pad fades and gives up.
| BIGSKYWRX | 05-12-2006 09:11 AM |
Good info guys! Thanks :)
| jweiss | 05-12-2006 09:15 AM |
[QUOTE=ChrisDP]FWIW, any time you can compress a braking zone, you're lowering your average rotor temperature... you're giving the rotors more "off" time to cool down. Your heat load hasn't changed because you're still stopping the same amount of weight moving at the same velocity, BUT your temps will be lower if you can stop for a shorter period of time. That said, a higher temp pad will allow you to heat the rotors up more because it'll keep generating friction above the temperature that a lower-temp pad fades and gives up.[/QUOTE]
I agree completely. Even if you consider the same pads, stopping harder over a shorter distance is actually easier on your brakes than a longer, lighter brake application on a multi-lap basis.
I agree completely. Even if you consider the same pads, stopping harder over a shorter distance is actually easier on your brakes than a longer, lighter brake application on a multi-lap basis.
| maxQ | 05-12-2006 09:36 AM |
[QUOTE=ChrisDP]FWIW, any time you can compress a braking zone, you're lowering your average rotor temperature... you're giving the rotors more "off" time to cool down. Your heat load hasn't changed because you're still stopping the same amount of weight moving at the same velocity, BUT your temps will be lower if you can stop for a shorter period of time. That said, a higher temp pad will allow you to heat the rotors up more because it'll keep generating friction above the temperature that a lower-temp pad fades and gives up.[/QUOTE]
Right, especially the last part. If the higher temp pad starts melting other things, like balljoint boots, etc... then it's maybe a better idea to use the lower temp pad... or just replace your balljoints more often.
But the disadvantage, obviously, is a higher average rotor temp... which can cause worse problems... like not stopping. Like everything else, it's a tradeoff.
Right, especially the last part. If the higher temp pad starts melting other things, like balljoint boots, etc... then it's maybe a better idea to use the lower temp pad... or just replace your balljoints more often.
But the disadvantage, obviously, is a higher average rotor temp... which can cause worse problems... like not stopping. Like everything else, it's a tradeoff.
| Homemade WRX | 05-12-2006 12:24 PM |
[QUOTE=adhowe70]Its simple: more braking = more friction = more heat. It doesn't really matter whether you distribute that friction out over 5 seconds or 6... the end temperature will be nearly identical if you're doing the same braking.[/QUOTE]
but over the longer braking period how much heat disipates from the rotor...
temp's are lower...just got done testing polymatrix A's and E's on our Formula car...the E's were cooler at then end of the brake zone...but over the entire course they were about level...
but over the longer braking period how much heat disipates from the rotor...
temp's are lower...just got done testing polymatrix A's and E's on our Formula car...the E's were cooler at then end of the brake zone...but over the entire course they were about level...
| remowgn | 05-12-2006 12:59 PM |
[QUOTE=Homemade WRX]but over the longer braking period how much heat disipates from the rotor...
temp's are lower...just got done testing polymatrix A's and E's on our Formula car...the E's were cooler at then end of the brake zone...but over the entire course they were about level...[/QUOTE]
My thoughts exactly. Not only that, you're not putting as much temperature "shock" into the system, because of the longer time constant.
I'd say go for the ducting though, that's the right way to fix the problem. :)
temp's are lower...just got done testing polymatrix A's and E's on our Formula car...the E's were cooler at then end of the brake zone...but over the entire course they were about level...[/QUOTE]
My thoughts exactly. Not only that, you're not putting as much temperature "shock" into the system, because of the longer time constant.
I'd say go for the ducting though, that's the right way to fix the problem. :)
| zzyzx | 05-12-2006 01:07 PM |
[QUOTE=ChrisDP]FWIW, any time you can compress a braking zone, you're lowering your average rotor temperature... you're giving the rotors more "off" time to cool down. Your heat load hasn't changed because you're still stopping the same amount of weight moving at the same velocity, BUT your temps will be lower if you can stop for a shorter period of time. That said, a higher temp pad will allow you to heat the rotors up more because it'll keep generating friction above the temperature that a lower-temp pad fades and gives up.[/QUOTE]
Um... hrm.
The laws of physics don't change. Given this the same amount of heat is generated from the same amount of kinetic energy, right?
If you compress this dissipation of energy onto a smaller timescale, it just means that the materials in question have to absorb the energy faster.
This obviously means that peak temperatures get higher.
It also means the components involved experience more "shock" then they would otherwise, and hence more fatigue.
Perhaps somebody could outline where I've gone wrong here? :confused:
Um... hrm.
The laws of physics don't change. Given this the same amount of heat is generated from the same amount of kinetic energy, right?
If you compress this dissipation of energy onto a smaller timescale, it just means that the materials in question have to absorb the energy faster.
This obviously means that peak temperatures get higher.
It also means the components involved experience more "shock" then they would otherwise, and hence more fatigue.
Perhaps somebody could outline where I've gone wrong here? :confused:
| Chromer | 05-12-2006 01:37 PM |
[QUOTE=zzyzx]Perhaps somebody could outline where I've gone wrong here? :confused:[/QUOTE]
power = accelleration * mass / time
(In a vacuum it) Takes the same amount of power to slow the car at 1.5g's under braking as it does at 0.1g's.
And watts * .86-ish * hours = kilocalories
The system as a whole will absorb the same amount of heat. Localized heating, yeah, will probably be more.
However - pad abrasion probably plays a part too. If the hottest material is constantly removed from the pad via abrasion, then it is removed from the system and doesn't have much time to transfer its heat to the calipers and into the fluid...
power = accelleration * mass / time
(In a vacuum it) Takes the same amount of power to slow the car at 1.5g's under braking as it does at 0.1g's.
And watts * .86-ish * hours = kilocalories
The system as a whole will absorb the same amount of heat. Localized heating, yeah, will probably be more.
However - pad abrasion probably plays a part too. If the hottest material is constantly removed from the pad via abrasion, then it is removed from the system and doesn't have much time to transfer its heat to the calipers and into the fluid...
| BIGSKYWRX | 05-12-2006 02:34 PM |
damn- it's never an easy answer :)
| Northwest Tan | 05-12-2006 02:34 PM |
[QUOTE=Chromer]power = accelleration * mass / time
(In a vacuum it) Takes the same amount of power to slow the car at 1.5g's under braking as it does at 0.1g's.
And watts * .86-ish * hours = kilocalories
The system as a whole will absorb the same amount of heat. Localized heating, yeah, will probably be more.
However - pad abrasion probably plays a part too. If the hottest material is constantly removed from the pad via abrasion, then it is removed from the system and doesn't have much time to transfer its heat to the calipers and into the fluid...[/QUOTE]
Your power equation is wrong...you spelled ACCELERATION wrong :D
Power = (m*a*s)/t
m=mass
a=acceleration
s=distance
t=time
Now I have to question the rest of your post...
(In a vacuum it) Takes the same amount of power to slow the car at 1.5g's under braking as it does at 0.1g's.
And watts * .86-ish * hours = kilocalories
The system as a whole will absorb the same amount of heat. Localized heating, yeah, will probably be more.
However - pad abrasion probably plays a part too. If the hottest material is constantly removed from the pad via abrasion, then it is removed from the system and doesn't have much time to transfer its heat to the calipers and into the fluid...[/QUOTE]
Your power equation is wrong...you spelled ACCELERATION wrong :D
Power = (m*a*s)/t
m=mass
a=acceleration
s=distance
t=time
Now I have to question the rest of your post...
| maxQ | 05-12-2006 02:39 PM |
[QUOTE=zzyzx]
Perhaps somebody could outline where I've gone wrong here? :confused:[/QUOTE]
What Chris is saying: the AVERAGE rotor temperature over a lap will be lower if you compress your braking zones because the rotor has more time to dissipate heat.
In a given lap, you generate 150 kJ (WAG at a number, don't yell...) under braking, regardless of brake pad. With a lower coefficient pad, you spend 26 seconds of a 1:20 lap putting energy INTO the rotor and 54 seconds letting it out.
If you have a higher temp pad, you can spend 24 seconds under braking and 56 seconds radiating... resulting in a lower AVERAGE temperature with higher PEAK temperatures.
Perhaps somebody could outline where I've gone wrong here? :confused:[/QUOTE]
What Chris is saying: the AVERAGE rotor temperature over a lap will be lower if you compress your braking zones because the rotor has more time to dissipate heat.
In a given lap, you generate 150 kJ (WAG at a number, don't yell...) under braking, regardless of brake pad. With a lower coefficient pad, you spend 26 seconds of a 1:20 lap putting energy INTO the rotor and 54 seconds letting it out.
If you have a higher temp pad, you can spend 24 seconds under braking and 56 seconds radiating... resulting in a lower AVERAGE temperature with higher PEAK temperatures.
| WRX 2002 | 05-12-2006 03:32 PM |
If you are braking later (compressing braking times) means you will be braking later, therefore you have more time to accelerate to the corner thus increasing your peak track speed requiring more energy to dissipate via the brakes. So not only increasing peak temperatures but also requiring more cooling due to increased speed.
Extra cooling time available by braking later is really minimal in the swing of things, so you brake later by 1sec so theoretically you have an extra second of cooling before the next corner, the benefit is near zero but you also increase the amount of speed/energy you need to dissipate which would easily offset any advantage you might get.
But then again, higher peak temperatures will disapate heat quicker than lower temperatures. The heat dissipate is not linear across the temperature spectrum.
As normal it is not very simple.
probably best to have a very good handling car so you can take the corners without braking.
Extra cooling time available by braking later is really minimal in the swing of things, so you brake later by 1sec so theoretically you have an extra second of cooling before the next corner, the benefit is near zero but you also increase the amount of speed/energy you need to dissipate which would easily offset any advantage you might get.
But then again, higher peak temperatures will disapate heat quicker than lower temperatures. The heat dissipate is not linear across the temperature spectrum.
As normal it is not very simple.
probably best to have a very good handling car so you can take the corners without braking.
| Chromer | 05-12-2006 03:33 PM |
[QUOTE=Northwest Tan]Your power equation is wrong...you spelled ACCELERATION wrong :D
Power = (m*a*s)/t
m=mass
a=acceleration
s=distance
t=time
Now I have to question the rest of your post...[/QUOTE]
Can't be, I looked it up on teh internets...
Crap, back to first principles for me.
Power = (m*a*s)/t
m=mass
a=acceleration
s=distance
t=time
Now I have to question the rest of your post...[/QUOTE]
Can't be, I looked it up on teh internets...
Crap, back to first principles for me.
| davis10 | 05-12-2006 03:47 PM |
brakes convert rotational kinetic energy to energy in the form of heat the amount of heat you produce depends on your change in velocity not what the coefficient of friction of the pads and rotors is. If the coefficient of friction is higher it allows the brakes to convert more kinetic energy into heat quicker but the same amount of heat is produced. If it takes longer to brake it allows more heat to get dissapated into the area in surrounding the rotors, sot the rotor do infact get hotter.
However the more rapid change in temperature also probably puts more of a strain on the rotors too.
However the more rapid change in temperature also probably puts more of a strain on the rotors too.
| remowgn | 05-12-2006 04:58 PM |
[QUOTE=maxQ]
If you have a higher temp pad, you can spend 24 seconds under braking and 56 seconds radiating... [B]resulting in a lower AVERAGE temperature with higher PEAK temperatures.[/B][/QUOTE]
This is the core of the issue- which is worse? higher average temperatures or higher peak temperatures? My instinct says higher peak temperatures.
If you have a higher temp pad, you can spend 24 seconds under braking and 56 seconds radiating... [B]resulting in a lower AVERAGE temperature with higher PEAK temperatures.[/B][/QUOTE]
This is the core of the issue- which is worse? higher average temperatures or higher peak temperatures? My instinct says higher peak temperatures.
| WRX 2002 | 05-12-2006 06:00 PM |
[QUOTE=remowgn]This is the core of the issue- which is worse? higher average temperatures or higher peak temperatures? My instinct says higher peak temperatures.[/QUOTE]
Don't forget if you are not braking you are probably still accelerating therefore going faster which means more energy / heat to get out of the system.
Don't forget if you are not braking you are probably still accelerating therefore going faster which means more energy / heat to get out of the system.
| Freon | 05-12-2006 06:13 PM |
[QUOTE=maxQ]What Chris is saying: the AVERAGE rotor temperature over a lap will be lower if you compress your braking zones because the rotor has more time to dissipate heat.[/QUOTE]
Where does this time come from? The 5th dimension? Your rotors are dissapating heat even when heat is being added! There is no change in time dissipating at all!
Actually, I'd argue the opposite. If your lap time goes down 1 second due to better pads, you have 1 second less per lap for your rotors to cool down.
Anyway, several of you have it right. Braking from 90mph to 20mph should create about the same total heat regardless of if you do it in 5 seconds or 15. Your peak temperature on the faster braking should be higher since you're adding in energy faster.
Where does this time come from? The 5th dimension? Your rotors are dissapating heat even when heat is being added! There is no change in time dissipating at all!
Actually, I'd argue the opposite. If your lap time goes down 1 second due to better pads, you have 1 second less per lap for your rotors to cool down.
Anyway, several of you have it right. Braking from 90mph to 20mph should create about the same total heat regardless of if you do it in 5 seconds or 15. Your peak temperature on the faster braking should be higher since you're adding in energy faster.
| WRX 2002 | 05-12-2006 06:24 PM |
[QUOTE=Freon]Where does this time come from? The 5th dimension? Your rotors are dissapating heat even when heat is being added! There is no change in time dissipating at all!
[/QUOTE]
Very good point!
Its a bit like saying that 2 piece rotors run cooler with most things been equal. The bearings, hubs and wheels should be cooler but the heat that used to be transfered to the hub, bearings and the wheels are now left in the smaller mass rotor, so the temperature of the rotors will actually increase.
the only way to reduce the temperature is via external cooling (brake ducts) or larger rotors.
[/QUOTE]
Very good point!
Its a bit like saying that 2 piece rotors run cooler with most things been equal. The bearings, hubs and wheels should be cooler but the heat that used to be transfered to the hub, bearings and the wheels are now left in the smaller mass rotor, so the temperature of the rotors will actually increase.
the only way to reduce the temperature is via external cooling (brake ducts) or larger rotors.
| Northwest Tan | 05-12-2006 06:40 PM |
[U]Force of Friction[/U]= (coefficient of friction)*(normal force)
If mu goes up then less normal force is required to develop the same mount of brake torque.
If mu goes up then less normal force is required to develop the same mount of brake torque.
| BIGSKYWRX | 05-12-2006 07:56 PM |
[QUOTE=BIGSKYWRX]damn- it's never an easy answer :)[/QUOTE] :lol:
It appears I may have to try out my experiment afterall :)
It appears I may have to try out my experiment afterall :)
| ChrisDP | 05-13-2006 09:44 AM |
The rate at which a rotor sheds heat during braking is MUCH less than the rate at which heat goes into it due to the pad dragging against it.
Anyone here ever driven down a mountain? Try it sometime... use short hard bursts on the brakes to slow the car for every corner 1 run, repeat the run and drag the brakes to slow down the same amount.
hint: the second run you're going to want to do alone...
Anyone here ever driven down a mountain? Try it sometime... use short hard bursts on the brakes to slow the car for every corner 1 run, repeat the run and drag the brakes to slow down the same amount.
hint: the second run you're going to want to do alone...
| BIGSKYWRX | 05-13-2006 10:57 AM |
From DBASteve
The kinetic energy generated from braking will not change with pad compounds. The method in which this energy is processed and the
resulting temperature can change but it is dependant on the mass of the disc rotor, the mass of the pad, and the thermal conductivity of both materials.
You can have two pad compounds with the same or similar friction coefficient but different disc operating temperatures. Why? Materials like ceramic, Kevlar, carbon, ECT can insulate the pad material and force more heat into the disc rotor.
This is not a simple question of friction coefficient when you dig deep into
the reasons how and why brake temperatures are achieved. It gave me plenty of headaches in the past.
The kinetic energy generated from braking will not change with pad compounds. The method in which this energy is processed and the
resulting temperature can change but it is dependant on the mass of the disc rotor, the mass of the pad, and the thermal conductivity of both materials.
You can have two pad compounds with the same or similar friction coefficient but different disc operating temperatures. Why? Materials like ceramic, Kevlar, carbon, ECT can insulate the pad material and force more heat into the disc rotor.
This is not a simple question of friction coefficient when you dig deep into
the reasons how and why brake temperatures are achieved. It gave me plenty of headaches in the past.
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