Cooling down lap(s) - reasons ?
Discussion
Hi All
Recently, I got into a discussion were some people were adamant that a cooling down period was beneficial for the life of various parts of the car (more specifically, carbon brake discs)
My understanding from a basic level of automative engineering is that a cooling down lap is mainly aimed at, and very important, for parts which are cooled by oil or water, and therefore give these parts (mainly engine parts and bearings etc) a chance for the cooling process to continue and for parts which get extremely hot (i.e. turbo's etc) not to have oiled cooked into them where it didn't get the required flow to bring them temps down
With ceramic, or otherwise, brake discs, then as they're cooled by ambient air temps, that a 'cooling down' lap would otherwise just extend the 'cooling period' as they're still receiving friction, and therefore just staying hotter for longer with no real benefits ?
I'd be interested to hear peoples thoughts on what the actual physics are for these parts to require anything other than just being parked up and left to cool naturally, rather than having another, admittedly slower, lap to just maintain those high temps a bit longer
Thanks in advance for you help
Recently, I got into a discussion were some people were adamant that a cooling down period was beneficial for the life of various parts of the car (more specifically, carbon brake discs)
My understanding from a basic level of automative engineering is that a cooling down lap is mainly aimed at, and very important, for parts which are cooled by oil or water, and therefore give these parts (mainly engine parts and bearings etc) a chance for the cooling process to continue and for parts which get extremely hot (i.e. turbo's etc) not to have oiled cooked into them where it didn't get the required flow to bring them temps down
With ceramic, or otherwise, brake discs, then as they're cooled by ambient air temps, that a 'cooling down' lap would otherwise just extend the 'cooling period' as they're still receiving friction, and therefore just staying hotter for longer with no real benefits ?
I'd be interested to hear peoples thoughts on what the actual physics are for these parts to require anything other than just being parked up and left to cool naturally, rather than having another, admittedly slower, lap to just maintain those high temps a bit longer
Thanks in advance for you help
well on a cooling down lap you shouldn't be stomping on your brakes as hard as you can from 150mph, so the energy put into them will be far far less than the previous lap/s. In addition the increased air flow of a moving car, air drawn thought disk ventilation vanes and brake cooling ducts will cool them rather more quickly than sitting on a pool of stagnant hot air in the pits (unless its a very windy day) with the pads covering 20% of them preventing an even cooling and dumping heat into the caliper and fluid.
its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
ViperDave said:
well on a cooling down lap you shouldn't be stomping on your brakes as hard as you can from 150mph, so the energy put into them will be far far less than the previous lap/s. In addition the increased air flow of a moving car, air drawn thought disk ventilation vanes and brake cooling ducts will cool them rather more quickly than sitting on a pool of stagnant hot air in the pits (unless its a very windy day) with the pads covering 20% of them preventing an even cooling and dumping heat into the caliper and fluid.
its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
]its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
But does cooling discs in this way add anything to the life of them ?
graeme4130 said:
ViperDave said:
well on a cooling down lap you shouldn't be stomping on your brakes as hard as you can from 150mph, so the energy put into them will be far far less than the previous lap/s. In addition the increased air flow of a moving car, air drawn thought disk ventilation vanes and brake cooling ducts will cool them rather more quickly than sitting on a pool of stagnant hot air in the pits (unless its a very windy day) with the pads covering 20% of them preventing an even cooling and dumping heat into the caliper and fluid.
its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
]its quite possible that on a cool down lap you could get the disks pretty cool and no worse than a stop from the motorway exit
But does cooling discs in this way add anything to the life of them ?
Cooling them on the tack will do it quickly and evenly and after all you also cooling all the other components while your out there
Park up with screaming hot brakes fresh from a fast lap and you're inviting trouble with caliper seals, wheel bearings, that sort of thing.
A cool-down lap done at lowish speeds, with minimal braking, allows a lot of the heat in the discs and pads to dissipate. They'll still be hot, but not excessively so.
As for the engine, again a gentle lap will allow the cooling system to lose some of the built-up heat from hard driving, turbo (if you have one) to cool down, oil temp to drop. All helps reduce heat soak once you've parked up, compared with stopping straight from a fast lap.
A cool-down lap done at lowish speeds, with minimal braking, allows a lot of the heat in the discs and pads to dissipate. They'll still be hot, but not excessively so.
As for the engine, again a gentle lap will allow the cooling system to lose some of the built-up heat from hard driving, turbo (if you have one) to cool down, oil temp to drop. All helps reduce heat soak once you've parked up, compared with stopping straight from a fast lap.
I had to stop on a track day with no cooling down lap, on a hill and held the car on the brakes for a short time before turning the engine off and leaving it in gear.
It cost me £540 for a pair of front discs, both had cracked.
Deffo worth a cool down lap for brakes and turbo's, of limited value for engine mechanicals in general I would say.
It cost me £540 for a pair of front discs, both had cracked.
Deffo worth a cool down lap for brakes and turbo's, of limited value for engine mechanicals in general I would say.
ViperDave said:
the pads preventing one area cooling at the same rate as the rest of the disk causes them to warp crack or otherwise destroy themselves
This is the main reason, as far as brakes are concerned. Your pad faces will be just as hot as your discs, but cool down far less effectively. If you stop really hot, the result is that a significant portion of your disc is clamped by these hot pads, making it unable to cool anywhere near as quickly as the rest of the disc, often warping or even cracking the discs due to unbalanced thermal expansion.Brakes actually heat and cool extremely quickly when in use. Here's a brake temperature graph from a little single-seat racing car, an overgrown kart really, hence it only reaching 60mph but you get the idea. Disc temp on top, vehicle speed below:
You can see how sharply the disc temperature rises in full braking, but also how quickly it drops off. On a cooldown lap you wouldn't put anywhere near as much energy into the brakes, ideally avoiding them completely, so you'd cool them dramatically. Almost all of this heat dissipation is convection, very little is due to radiation, so when stationary the heat loss is massively slower.
It's far kinder to all the components in the vicinity too. Even if you do a cooldown lap, wave your hand around your wheel well and feel just how much heat is still pumping out. Coming in hot only makes it worse for all your seals, bearings and fluids.
Personally, I'd want to do a cool-down lap for carbon brakes more than almost anything else!
Airflow over the discs (and the hot pads not sitting in the same place, thus resulting in uneven cooling) will cool the discs much more effectively than just sitting in the pits and getting heat soaked.
All the "problems" with carbon discs come from overheating and warping/de-laminating after track use! Every manufacturer out there tells you to make sure you do a cooling down lap to allow your brakes temp to come down before just parking the car.
With regards to all the fluid cool down etc, you can largely do that by just leaving the engine on in the pits for a few mins, of course the extra air flow would be better but at least they'll still be cooled by the radiator and fan... the brakes won't be cooled by anything if you're not getting airflow over them.
Ultimately, I think you're entirely wrong. In the list of reasons I'd want to do a cool-down lap, carbon ceramic brakes would be at the top.
Airflow over the discs (and the hot pads not sitting in the same place, thus resulting in uneven cooling) will cool the discs much more effectively than just sitting in the pits and getting heat soaked.
All the "problems" with carbon discs come from overheating and warping/de-laminating after track use! Every manufacturer out there tells you to make sure you do a cooling down lap to allow your brakes temp to come down before just parking the car.
With regards to all the fluid cool down etc, you can largely do that by just leaving the engine on in the pits for a few mins, of course the extra air flow would be better but at least they'll still be cooled by the radiator and fan... the brakes won't be cooled by anything if you're not getting airflow over them.
Ultimately, I think you're entirely wrong. In the list of reasons I'd want to do a cool-down lap, carbon ceramic brakes would be at the top.
braddo said:
IdiotRace said:
What about short tracks like Brands indy? I found doing a cooldown lap there barely had any affect on my oil/water temps, obviously its better for the brakes.
Two cooling laps
still shorter than one of Bedford GT. Plainly, it's about the time and distance over which you cool the car, it's not bothered how many laps it does!hufggfg said:
Personally, I'd want to do a cool-down lap for carbon brakes more than almost anything else!
Airflow over the discs (and the hot pads not sitting in the same place, thus resulting in uneven cooling) will cool the discs much more effectively than just sitting in the pits and getting heat soaked.
All the "problems" with carbon discs come from overheating and warping/de-laminating after track use! Every manufacturer out there tells you to make sure you do a cooling down lap to allow your brakes temp to come down before just parking the car.
With regards to all the fluid cool down etc, you can largely do that by just leaving the engine on in the pits for a few mins, of course the extra air flow would be better but at least they'll still be cooled by the radiator and fan... the brakes won't be cooled by anything if you're not getting airflow over them.
Ultimately, I think you're entirely wrong. In the list of reasons I'd want to do a cool-down lap, carbon ceramic brakes would be at the top.
Presumably carbon brakes suffer more as they don't conduct heat as well as steel, so where a steel disk will conduct heat away from the area under the pads to be dissipated from the free disk yet still setting up a big enough temperature gradient to warp them in some cases, with carbon disks this will be many factors worse with the disk being unable to move that heat away from the area under the pad so effectively. then throw in the composite nature of the carbon disk its just asking for trouble.Airflow over the discs (and the hot pads not sitting in the same place, thus resulting in uneven cooling) will cool the discs much more effectively than just sitting in the pits and getting heat soaked.
All the "problems" with carbon discs come from overheating and warping/de-laminating after track use! Every manufacturer out there tells you to make sure you do a cooling down lap to allow your brakes temp to come down before just parking the car.
With regards to all the fluid cool down etc, you can largely do that by just leaving the engine on in the pits for a few mins, of course the extra air flow would be better but at least they'll still be cooled by the radiator and fan... the brakes won't be cooled by anything if you're not getting airflow over them.
Ultimately, I think you're entirely wrong. In the list of reasons I'd want to do a cool-down lap, carbon ceramic brakes would be at the top.
ViperDave said:
Presumably carbon brakes suffer more as they don't conduct heat as well as steel, so where a steel disk will conduct heat away from the area under the pads to be dissipated from the free disk yet still setting up a big enough temperature gradient to warp them in some cases, with carbon disks this will be many factors worse with the disk being unable to move that heat away from the area under the pad so effectively. then throw in the composite nature of the carbon disk its just asking for trouble.
That might be true, I have to say I'm not sure on the heat conductivity. I would think it's a combination of the fact that a) the CCBs will be able to get much hotter, after all that's the whole point b) the CCBs will be more brittle, so more likely to have problems with any given heat differences. Also to consider is the just the different costs. If your discs cost 10x as much, you're going to be a lot more careful that you don't warp them.Gassing Station | Track Days | Top of Page | What's New | My Stuff