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Tbolt
29-03-2018, 16:29
Driving the 911 Carrera RSR 2.8 I'm having problems keeping the brakes warm on tracks with longer straights because it doesn't have brake ducts you can tape up, so I watched the brake temps under brake and noticed a strange behaviour which seems to be on all the cars I've tried. When braking the temp obviously go up quite quickly on the brakes, but then they stop and start to cool, all while I still have my foot on the brake pedal and braking the car hard.

Now on some cars if you accelerate and drag the brake hard the brakes continue to heat up but on the RSR 2.8 ( and probably some others I haven't tried many yet ) the brakes will heat up, then stop and start to cool, all while dragging the brakes, they then become very cold and all the heat has transferred to the tyres turning them red. But now the brakes are cold and the tyres are getting hotter so where is that heat coming from? Seem a bit odd to me.

Sorry if this has been brought up before but doing a search for brake temps obviously bring up a lot of hits.

Tbolt
31-03-2018, 10:02
Since no one has replied can anyone confirm they are seeing the same behaviour of the brakes? My brake pedal appears to be working correctly so I don't think it's just me.

hkraft300
31-03-2018, 12:05
Energy (kinetic) = 0.5 x mass x velocity^2

Say a car is braking from 250kmh. Brake temp rises then plateaus because rate of heating of brake discs = rate of cooling.

Heating of brake discs is the conversion of the kinetic energy of the vehicle.

Once you slow to, say 150kmh for example, yourself putting a lot less energy into the brakes discs. So then rate of energy input (heating) to brake discs < rate of energy dissipation (cooling) from brake discs. So the temperature drops even if you're on full brake pressure.

That's all I got for an explanation.

Zaskarspants
31-03-2018, 12:11
It will take a finite amount of time to heat the tyres via hot brakes. The heat pulse must be conducted to the tyre structure via the wheel and other components and this will take some time, hence the delayed heating you are observing.

micmansour
31-03-2018, 13:43
Energy (kinetic) = 0.5 x mass x velocity^2

Say a car is braking from 250kmh. Brake temp rises then plateaus because rate of heating of brake discs = rate of cooling.

Heating of brake discs is the conversion of the kinetic energy of the vehicle.

Once you slow to, say 150kmh for example, yourself putting a lot less energy into the brakes discs. So then rate of energy input (heating) to brake discs < rate of energy dissipation (cooling) from brake discs. So the temperature drops even if you're on full brake pressure.

That's all I got for an explanation.

Exactamondo, it's because the kinetic energy quadruples every time your speed doubles, so slowing from real high speed, the brakes absorb more heat than they can dissipate.

For the rear brake temps, I would say because the car has no ABS, with the caliper clamped on to the disc with no relative differential in speed between static and rotary part, there is no heat generated. It sounds like your rear wheels are dragging due to being locked up, hence why they get hot

Tbolt
31-03-2018, 14:29
Exactamondo, it's because the kinetic energy quadruples every time your speed doubles, so slowing from real high speed, the brakes absorb more heat than they can dissipate.

For the rear brake temps, I would say because the car has no ABS, with the caliper clamped on to the disc with no relative differential in speed between static and rotary part, there is no heat generated. It sounds like your rear wheels are dragging due to being locked up, hence why they get hot

Like you say I think what happening is I'm locking the brakes without realizing it. The car didn't feel like it was locking up, the cars still feels under control, no smoke ( has that been reduce because of the smoke pouring off the tyres in corners we had before the last patch? ) and I can't feel it through the wheel. I'm use to it being obvious when I lock up. Maybe I need to tweak my FF.

Tbolt
31-03-2018, 15:00
So I tried the RSR 2.8 again, reduced my braking even more than usual as the car slowed down and the brakes did not cool down, just as I would expect. I guess the few cars I had this problem with it's not very obvious when you are locking up. I'll keep more of an eye on the brake temperature to try and improve my braking on these cars. Or I need some better driving gear ;)

Tbolt
31-03-2018, 15:07
Energy (kinetic) = 0.5 x mass x velocity^2

Say a car is braking from 250kmh. Brake temp rises then plateaus because rate of heating of brake discs = rate of cooling.

Heating of brake discs is the conversion of the kinetic energy of the vehicle.

Once you slow to, say 150kmh for example, yourself putting a lot less energy into the brakes discs. So then rate of energy input (heating) to brake discs < rate of energy dissipation (cooling) from brake discs. So the temperature drops even if you're on full brake pressure.

That's all I got for an explanation.

I think as you slow down the rate of temperature rise will decrease, the temperature would only decrease if you have massive amounts cooling.

Tbolt
31-03-2018, 15:43
So I tried brake dragging again and if you apply the pedal enough to lock the front wheels you can drive along without any smoke from the tyres, but if at the same speed you apply more brake pressure then smoke start pouring off the front tyres, but surely a locked wheel can't get anymore locked by applying more brake pressure?! The wheel is either locked or not.

So does this mean we are not getting any feedback from a brake lock up if you only go slightly over pressure?

David Slute
31-03-2018, 16:44
You might want to play with your ffb settings or wheel if you cant feel lock ups. I can tell which tire is locking up on my Thrustmaster tx using the stock immersive settings as the wheel pulls to that side plus audio cues.

Tbolt
31-03-2018, 16:55
You might want to play with your ffb settings or wheel if you cant feel lock ups. I can tell which tire is locking up on my Thrustmaster tx using the stock immersive settings as the wheel pulls to that side plus audio cues.

Yes I'll have to play around with it, though there is something wrong with the physics for the smoke, but are you getting feel through your wheel even for a "low pressure" ( which only exsists in this sim ) lock up? A "high pressure" lock up i can feel, though in the real world these are the same thing.

MaximusN
31-03-2018, 17:27
So I tried brake dragging again and if you apply the pedal enough to lock the front wheels you can drive along without any smoke from the tyres, but if at the same speed you apply more brake pressure then smoke start pouring off the front tyres, but surely a locked wheel can't get anymore locked by applying more brake pressure?! The wheel is either locked or not.

So does this mean we are not getting any feedback from a brake lock up if you only go slightly over pressure?
Are you sure your tyres are locking when you think they are? Tyre squeal could also come into effect when they are at their peak grip. The same reason you should aim for the 'good' squeal when cornering. It is when they are about to break traction, but giving the best grip they can.

Tbolt
31-03-2018, 17:52
Are you sure your tyres are locking when you think they are? Tyre squeal could also come into effect when they are at their peak grip. The same reason you should aim for the 'good' squeal when cornering. It is when they are about to break traction, but giving the best grip they can.

Well to start with i didn't but when I look outside at the car the front wheels don't seem to be turning and the fact that the brakes temps are coming down - releasing the brake pedal a little and the brake temps start going up and the front wheels start turning again.

I ran out if time to test it any more but give it ago yourself and see what you think. Drive along and apply throttle and brake until the front tyres start smoking then release the brake pedal a bit until the smoke stops but the brake temp are still coming down and look at your front wheels.

Casey Ringley
02-04-2018, 14:57
Energy (kinetic) = 0.5 x mass x velocity^2

Say a car is braking from 250kmh. Brake temp rises then plateaus because rate of heating of brake discs = rate of cooling.

Heating of brake discs is the conversion of the kinetic energy of the vehicle.

Once you slow to, say 150kmh for example, yourself putting a lot less energy into the brakes discs. So then rate of energy input (heating) to brake discs < rate of energy dissipation (cooling) from brake discs. So the temperature drops even if you're on full brake pressure.

That's all I got for an explanation.

In addition to this, we do multi-layer heat transfer modeling of the brakes. The temperature you see is the outer surface as that's what matters most for braking performance (and it equalizes with the 'core' temperature rapidly when you let off the brakes). So you will see a big spike in temperatures when applying lots of brake pressure at high speed and then two things happen: 1.) The large difference in surface to core temperature of the brake rotor means heat energy moves more quickly from surface to core and 2.) the amount of heat generation is reduced because the car is now slower. So the temperature will peak, stabilize, and then start to reduce even if you continue to slow for a corner. A typical application might look like this - braking from high speed for 1s, then coasting at the new velocity.

252497

It was new tech we added primarily to make the glowing disc effect look better, but turned out to be a good improvement to braking feel too. Calibrating cars to carbon-carbon material properties in the new model felt much more like modern carbon-carbon race brakes to our pro-driver consultant team.

As for the 911 Carrera RSR, its iron brakes don't need a ton of temperature to work at optimum. That type of brake is perfectly happy entering a big braking zone at 200-250C and spiking up no higher than 600C or so. Modern iron race brakes (GT3, for example) start to drop off in performance over 750C and so entering the biggest braking one of a track around 300C is best to maximize time around the peak-mu temperature of 550C. Carbon-Carbon brakes, such as on the modern IndyCars, also want to be at 300-350C before heavy braking so they hit the sweet spot for friction coefficient while not getting so hot to cause excessive component wear.

Tbolt
02-04-2018, 16:05
In addition to this, we do multi-layer heat transfer modeling of the brakes. The temperature you see is the outer surface as that's what matters most for braking performance (and it equalizes with the 'core' temperature rapidly when you let off the brakes). So you will see a big spike in temperatures when applying lots of brake pressure at high speed and then two things happen: 1.) The large difference in surface to core temperature of the brake rotor means heat energy moves more quickly from surface to core and 2.) the amount of heat generation is reduced because the car is now slower. So the temperature will peak, stabilize, and then start to reduce even if you continue to slow for a corner. A typical application might look like this - braking from high speed for 1s, then coasting at the new velocity.


It was new tech we added primarily to make the glowing disc effect look better, but turned out to be a good improvement to braking feel too. Calibrating cars to carbon-carbon material properties in the new model felt much more like modern carbon-carbon race brakes to our pro-driver consultant team.

As for the 911 Carrera RSR, its iron brakes don't need a ton of temperature to work at optimum. That type of brake is perfectly happy entering a big braking zone at 200-250C and spiking up no higher than 600C or so. Modern iron race brakes (GT3, for example) start to drop off in performance over 750C and so entering the biggest braking one of a track around 300C is best to maximize time around the peak-mu temperature of 550C. Carbon-Carbon brakes, such as on the modern IndyCars, also want to be at 300-350C before heavy braking so they hit the sweet spot for friction coefficient while not getting so hot to cause excessive component wear.

Thanks for the info which gives a some more detail of how the sim works.

Having had a bit more of a play I've realised that what I thought was the brakes locking but not producing smoke is not actually a full lock up - the wheels are still turning very slowly, with the brakes cooling very quickly. This wasn't easy to see because of one of the annoying features of the game where the external camera always wants to reset to the rear of the car when on the external chase view, I wish we could have a key to turn this off, or do away with it completely as it makes it hard to view you car from other angles even in replay.

What made me think the brakes were a bit cool on the RSR 2.8 was the fact that they start at 549 degrees at the beginning of a TT, but I've realised all cars have the same temp at start and the fact they they are blue and drop into the 150's after a few laps.