Brake Ducts, Tire Cooling, and beyond

[AR3-GP]

I wonder if more attention can be paid to how the heat radiates outward from the back of the car. There are many external heat sources including the engine, the cooling system, the exhaust pipes, the front brake duct exits and the rear brake ducts exits. How do they conduct and convect heat towards the back of the rear tires? If you take a thermal snapshot, what is the temperature of the air entering the rear brake ducts, the air hitting the face of the tire, and the temperature of the air near the inner sidewall?

[dialtone]

Here's my analysis/theory: You know how Laptops uses specially designed copper pipes, with thermal pads under the heatsink with big openings for the fan's airflow, to allow for heat extraction in the rear and sides?

If you look at the Mclaren brakes, it's not that far off from my analogy.

That’s what I wrote as well a few pages back, but those copper pipes contain a PCM that wouldn’t be usable here perhaps.

Aside from that the name of the game is either improve airflow or transfer heat where there’s more airflow, not much else can really be done.

[dialtone]

I wonder if more attention can be paid to how the heat radiates outward from the back of the car. There are many external heat sources including the engine, the cooling system, the exhaust pipes, the front brake duct exits and the rear brake ducts exits. How do they conduct and convect heat towards the back of the rear tires? If you take a thermal snapshot, what is the temperature of the air entering the rear brake ducts, the air hitting the face of the tire, and the temperature of the air near the inner sidewall?

Without forced air or a heat exchanger to increase surface there’s no way you can heat a tire with so little contact time just by airflow escaping to the back of the car.

[AR3-GP]

I wonder if more attention can be paid to how the heat radiates outward from the back of the car. There are many external heat sources including the engine, the cooling system, the exhaust pipes, the front brake duct exits and the rear brake ducts exits. How do they conduct and convect heat towards the back of the rear tires? If you take a thermal snapshot, what is the temperature of the air entering the rear brake ducts, the air hitting the face of the tire, and the temperature of the air near the inner sidewall?

Without forced air or a heat exchanger to increase surface there’s no way you can heat a tire with so little contact time just by airflow escaping to the back of the car.

The tire is always in contact with the airflow. The brake duct exits, the exhaust pipes, and other hot components are constant heat sources. They warm the air at speed because heat flows from hot to cold. For the same reason, there is a tire cooling effect when air hits the tire as long as that air temperature is below the temperature of the tire. Without this, the tire would just get hotter and hotter until it melted because there would be no mechanism for heat added from friction at the contact patch, deformation of the sidewall, and the brakes/rim to leave the rubber.

That means the temperature of the air surrounding the tire is important. It establishes the thermal gradient which extracts heat from the tire. The greater the temperature difference, the greater the heat transfer. In other words, if you send warmer air to the tires, the tires cool less. This can happen on a hot day when the air temperature is high, or if for some reason you aim all of your hot air exits at the tires. So that's why I commented on the brake duct and the air curtain effect. If you aim a hot air gun at the sidewall (i.e a brake disc collector outlet), then the sidewall will be heated by some amount. It's a constant heat source like putting a hair dryer in your face. We're talking about incremental gains here, not silver bullets. An optimization of the hot air outlets may lead to incremental gains in the cooling of the tires. Optimization of aero balance may lead to less slip/heat. Improvement of the brake tins may lead to more cooling from the inside.

[SB15]

Here's my analysis/theory: You know how Laptops uses specially designed copper pipes, with thermal pads under the heatsink with big openings for the fan's airflow, to allow for heat extraction in the rear and sides?

If you look at the Mclaren brakes, it's not that far off from my analogy.

That’s what I wrote as well a few pages back, but those copper pipes contain a PCM that wouldn’t be usable here perhaps.

Aside from that the name of the game is either improve airflow or transfer heat where there’s more airflow, not much else can really be done.

Some laptops don’t have liquid infused water in the cooling pipes because some have really good airflow for heat extraction while others uses PCM given the airflow constraints.

What I’m getting at is that the reason why McLaren’s entry for the rear brake duct is soo huge is that it uses the 3 pipes to keep the tyres in order.

The main one cools the brakes while the other 2 pipes loops inside the brake drum itself and if use something like copper or GOLD in the pipes, no PCM, it maintains temperature.

[dialtone]

Hold on, I’m not saying that triple exit with hot air separation isn’t a good idea, I agree with you here. Just that what that creates behind the car isn’t enough to heat the tire.

[SB15]

Hold on, I’m not saying that triple exit with hot air separation isn’t a good idea, I agree with you here. Just that what that creates behind the car isn’t enough to heat the tire.

My mistake for the confusion, I was just adding on what I said early wasn't saying you were wrong either.

Yes indeed it won't heat the tyre, but it will keep it under the control because the rear brake duct exits Mclaren are running is 3 channels that are pretty much the biggest on the grid. For Mclaren, there is a complete imbalance between straightline speed and rear tyre cooling that it's almost like the straight-line speed is negligible.

Random thought: So what other team do I think would implement be able to this and possibly make a better version? It would have to be Mercedes because I'm very confident that if theirs anyone to develop something even remotely similar, it's James Allison and the Merc because the W16 suffers a lot from rear tyre overheating due to a woeful design in the brake drums and how tiny the cooling entry and exits are. It's almost inevitable for them to do it somewhere within the next 2 races.

[vorticism]

The brake ducts are like the '17 formula barge boards of the ’22 formula. Merc’s caliper ducting is unique compared to what I’ve seen of Mclaren and Red Bull’s. It's routed around and beneath the upright before making a 180* turn just in front of the caliper. Viewed from the rear showing the exit ducting:

Same angle showing the rear disc intake and collector arrangement:

How they fit together:


In common with other teams, they are using the intake paths to cool the cake-tin/drum by routing them along the outside, using the caketin itself to help form the pathways.

[vorticism]

It almost looks like variable size blanking panels can be installed on the RB21 front brake bodywork. Could this be done to control the amount of heating of the tires with brake disc heat?

https://i.postimg.cc/kGQ1hnjP/image.png

https://i.postimg.cc/V6YWLjgp/image.png

I too thought they were just inspection holes that would get covers when assembled, but looking closely at the second photo in the more assembled state, you can see there's a directionality to the opening, opening to the outboard, with a duct outlet just inboard of it, suggesting they are doing something there similar to what I mentioned about the W16 rear disc collector diluting. On RB21, directing a portion (via the hole/portal) of the front disc outflow here instead of directly to the main outlet, while diluting it with the flow from that other small duct beside it. So this implies they are trying to heat this portion of cake-tin/drum on the front axle. The cake tin would be forming the outer confines of this duct.

Yet on the rear axle all the talk is of, and I'll I've seen in photos, is that they focus on cooling the cake-tin/drum.

[AR3-GP]

I too thought they were just inspection holes that would get covers when assembled, but looking closely at the second photo in the more assembled state, you can see there's a directionality to the opening, opening to the outboard, with a duct outlet just inboard of it, suggesting they are doing something there similar to what I mentioned about the W16 rear disc collector diluting. On RB21, directing a portion (via the hole/portal) of the front disc outflow here instead of directly to the main outlet, while diluting it with the flow from that other small duct beside it. So this implies they are trying to heat this portion of cake-tin/drum on the front axle. The cake tin would be forming the outer confines of this duct.

Yet on the rear axle all the talk is of, and I'll I've seen in photos, is that they focus on cooling the cake-tin/drum.

I agree with you on this theory. They can mix hot brake exhaust with fresh air to create a warm air layer under the outermost cake tin layer in order to warm the wheel rim/tyre. I was able to find the fully blanked brake exhaust outlet in one of the photos from Spain, so they also have the option to go to a "maximum rim cooling" configuration by blocking the hot brake exhaust from entering that outermost shell.

[AR3-GP]

Mclaren front duct seems very complicated.




Their treatment seems much more advanced.

[Watto]

Mclaren front duct seems very complicated.
https://i.postimg.cc/fTXGLH3J/image.png

https://external-preview.redd.it/tobi-g ... d989210ca7

Their treatment seems much more advanced.

I'd imagine it makes things hard to work out exactly what is going on where they are being routed though i wonder if the thermal camera they used helps, iirc somewhere was mentioned the cool spots lined up with vent locations (which makes enough sense obviously) but having that imagine may help decipher what is going on.

[AR3-GP]

I too thought they were just inspection holes that would get covers when assembled, but looking closely at the second photo in the more assembled state, you can see there's a directionality to the opening, opening to the outboard, with a duct outlet just inboard of it, suggesting they are doing something there similar to what I mentioned about the W16 rear disc collector diluting. On RB21, directing a portion (via the hole/portal) of the front disc outflow here instead of directly to the main outlet, while diluting it with the flow from that other small duct beside it. So this implies they are trying to heat this portion of cake-tin/drum on the front axle. The cake tin would be forming the outer confines of this duct.

Yet on the rear axle all the talk is of, and I'll I've seen in photos, is that they focus on cooling the cake-tin/drum.

I also think your theory could fit what they are doing with the rear collector (RBR). The rear brake disc collector on the Red Bull has a large mushroom shape. What would the excess volume be fore? Perhaps the extra volume is used for mixing... The Mclaren brake disc collector is much smaller, narrower and crucially has less surface area. There's no mixing phenomena there. It's possble Mclaren focused intensely on the heat isolation of the brake disc and that's where Red Bull made a mistake. Their brake disc collector has a lot of surface area. Surface area increases heat transfer to the outer shells of the brake tin. Obviously have not run any numbers, but it seems smart to minimize the surface area of the collector, and attempt to eject majority of the heat out of the duct exits, rather than to have large surfaces where it can radiate to the shell interiors.




If you compare Mclaren's rear brake drums from 2024 to 2025, it appears that they improved the heat insulating properties of the brake disc collector by using new fiber materials. I think one of the things that Mclaren does better than others is keeping more of the heat from the rear brake disc inside of the collector and not allowing it to radiate towards the outer shells of the cake tins.


It also just struck me. Mclaren's rear brake disc collector looks the most like a turbocharger

[SiLo]

I wonder if one of the channels is just a free air channel, it doesn't cool anything specifically, but by injecting unblocked airflow into a exit right next to the other, it help increase the speed of the exiting air surrounding it, making it more efficient?

It could be. I also wonder if the more outboard channel(s) (closer to the tire sidewall), are more likely to be a free air channels, creating an "air curtain" to limit the amount of brake duct heat which is flowing against the sidewall of the tire. If the brake duct exhaust were being exposed directly to the sidewall, I think that would contribute to more heating of the tires. If this is true, then one can see how the Mercedes design seems less optimal. They mix the brake disc exhaust and a free stream in the brake disc collector, but that air is heated and expelled right next to the sidewall of the tire. It seems to lack the air curtain.

https://i.postimg.cc/3r98yD5g/image.png

It might also explain why Red Bull claim the Mclaren brake ducts were noticeably cooler than other teams. They are extracting heat more effectively, but also passing through cooler free stream air that is not directly heated inside the caliper area of brake drum.

[AR3-GP]

I wonder if one of the channels is just a free air channel, it doesn't cool anything specifically, but by injecting unblocked airflow into a exit right next to the other, it help increase the speed of the exiting air surrounding it, making it more efficient?

It could be. I also wonder if the more outboard channel(s) (closer to the tire sidewall), are more likely to be a free air channels, creating an "air curtain" to limit the amount of brake duct heat which is flowing against the sidewall of the tire. If the brake duct exhaust were being exposed directly to the sidewall, I think that would contribute to more heating of the tires. If this is true, then one can see how the Mercedes design seems less optimal. They mix the brake disc exhaust and a free stream in the brake disc collector, but that air is heated and expelled right next to the sidewall of the tire. It seems to lack the air curtain.

https://i.postimg.cc/3r98yD5g/image.png

It might also explain why Red Bull claim the Mclaren brake ducts were noticeably cooler than other teams. They are extracting heat more effectively, but also passing through cooler free stream air that is not directly heated inside the caliper area of brake drum.

Yeah it's a fairly reasonable explanation for why the outer cake tin would have "blue spots". Clearly something like this is not that easy because 9 other teams didn't have any blue spots, and it's seems logical to pass cool air to the outer shell. Perhaps the other struggle to actually prevent the brake disc heat from "heat soaking" the air in the outer shell.