The finer points of brake cooling

[ChrisL]

Is there a best way to cool brakes in competition situations? Ducting the air to the brakes is OK, but what is the most efficient use of it once its there? Should I aim to cool the caliper alone or should I aim to cool the rotor prior to it entering the caliper or after exiting the caliper. Should I aim to get the air into the vents of the rotor or onto flat surface of the rotor?

I’ve see so many different designs but I haven’t been able to get any info on the benefits of one design over the other. What would the ideal brake cooling method be if cost was not an issue?

 

[Russ Noble]

I What would the ideal brake cooling method be if cost was not an issue?

I would think the system that draws air through a series of holes cast into the upright around the bearing and discharges it mainly into the inside of the rotor. Expensive uprights to buy, I would imagine. There again obsolete race parts can often be obtained relatively cheaply. Of course you could always cast or fabricate your own. Check out Richard Timte's awesome car, I'm sure he is using some ex-IRL parts. Also Canuk40 has produced a fabricated rear with a ventilated upright as a CAV upgrade.

If you really want to know what has the best performance regardless of cost, I would say anything current in F1 would be worth checking out!

Cheers

 

[Bill D]

I have thought about this and did some research. Nearly all the cooling ducting went towards the inside of the rotor. I assume this helps cool the rotor through the vents cast into them.

Bill D

 

[Ron Earp]

If you want a well setup system I'd get a triple brake duct system and put that together. Many ways to do it as far as getting the air into the three hoses (one hole, triple NASCAR splitter, three holes, etc) but in the end the hoses are going to go to:

*One will go to a rotor hat that will get air on both sides of the disk. They don't work well if there is a large gap between the can and the rotor disk, make the gap about 0.050". Build them sturdy so they don't flex.

*One will point at the inside of the rotor if the rotor is vented. Air enters the center section and spills radially outward

*One will point at the caliper itself. A few ways to do this one, but usualy space dictates what you will do here.

 

[Lynn Larsen]

Chris,

Go here, Crawford Composites and go about ½ way down the page. You'll find examples of spindle and rear axle ducts. These should give you an idea of how you can do this.

Lynn

 

[Iain]

Hi Chris,

You may want to consider the temperature of the air you plan to dump onto your rotors, which under racing conditions should be hot to very hot, cold air onto hot metal is a good combination for prematurely cracked rotors. The new Porsche 997 Carrera Cup cars duct air from behind the radiators, this enables a more even temperature to be maintained and the rotors are not continually expanding or shrinking,

Iain

 

[ChrisL]

Seems the answer is "all of the above"

That's an interesting point Iain. I did wonder if too much cooling could be a problem too. My main cooling needs are on the rears so collecting warm air might be a bit more of a challenge... but I'm sure that the fronts will need cooling too once I solve the problem on the rears and move to stickier tyres. My intention for the rears was in fact to collect the cool air from the side scoops. Was this the original purpose for these scoops?

 

[roaldin]

Deleted due to misread.

 

[Ron Earp]

I'm open to learning about new stuff on brake cooling cause I sure need it on the cars I race! But, I've never heard of anyone having cracked rotors due to cold air. Every race car I've ever seen ducts air from the front onto the rotors/calipers etc., including all of our own. Even in 27F outside air temp in a 13 hour enduro with stock OEM rotors glowing hasn't resulted in any issues, nor issues with the other 75 odd cars in the same race. I just haven't heard of people being concerned about it myself but I'm rather new in the racing scene.

I could see it being an issue in a rain downpour with front scoops throwing water on red hot rotors. Having air from higher up or behind a radiator would help out in this situation I think.

Also over cooling with the car not being pushed could result in non-optimal brake performance, but you could change pad compound and fix that for street driving.

 

[Richard Timte]

I thought I would chime in. One reason that the cooling ducts on a modern race car are directed through the center of the upright is to keep heat out of your bearings and grease. Heat from your rotor will soak its way into the center of the upright and cause the grease to melt or coke up. Now if you put your cooling air directed directly through the upright and the amount of material to transfer the heat is minimized then the bearing will not fail. Also the vents on a rotor are designed to take air from the center and through it out to the outside edge. So the air is also being pumped by the rotor spinning from the center where the cold air is. Here is a couple of pictures of a 2000 Indy car (front and rear) without the air scoops attached. The center section of the upright are done with a wire line EDM. The webs on them support the car but allow a lot of air to flow and not much cross section of material to allow heat to soak.

 

[Richard Timte]

One thing to note on the pictures is the dust shields are not present on the car. They seal up against the upright on the outbound side and leave just enough clearance so the rotor can spin. This makes all the air flow through the rotor.

 

[Ron Earp]

Good pictures and info. I should point out that I speak of using rotor hats that are 0.050" off the disc and I'm thinking of solid discs (yes, some of us must use those for class rules) with the hats. The hats might not be used at all on a vented disc application with plenty of radial airflow from the center out.

Unfortunately with the Jensen I'm stuck with solid discs and will need all three cooling tricks to maintain brake effectiveness.

Ron

 

[Chris P.]

Another thing to notice is the leading axle design on the front suspension. It helps decrease weight transfer when the wheels are turned, but still allows enough caster to utilize its geometry benefits. This is why I am designing and making my own uprights - I don't know of any street cars with a leading axle. I never saw how much they actually used on these cars before though - wow, looks like a lot.

 

[Gary Gibbs]

I've never heard of anyone having cracked rotors due to cold air.

This is why they went to behind the radiator position for air supply on Mk. IIb vs. IIa. It is documented in the original SAE papers. I have not heard of other cases though.

 

[Ron Earp]

That is interesting on the MKII cars. I mean, I can see somewhat the concept, but one could calculate the delta T from the ambient air compared to radiator air based on a heat pump model of the system and I can't imagine it'd be huge - i.e., air coming in might be say 50F and air through radiator might be 100F, but if the 50F delta cracks the rotor it looks like you'd have serious issues.....Good thing it was isolated to those cars, else there would be literally 1000s upon 1000s of cars doing it wrong, that is for sure. But, it is what it is, I'm sure the papers are not incorrect.

Ron

 

[40 Bud]

I believe the problem was when running, in colder weather, down a long straight (giving lots of cooling) and then going to hard rotor glow braking.

 

[Ron Earp]

Thanks Bud, I think I understand now with your explination.

In that particular case, Le Mans, far too much cooling due to length of time cooled. So not particularily that the air is too cold, but that the rotor gets cooled for say a minute and goes from red hot to something far less. Then, it doesn't work for beans at the end of the straight because it is too cool. Or, gets cracked when it goes from quite cool to red hot in a matter of a second or two at the end of the straight, or cracks because it gets cooled too much and too quickly after leaving the corner and going on the long straight. Using hot air in that case keeps the rotors from getting too cool.

This isn't a problem most of us face on the race track, just the opposite for us - avoiding heat causing hub failures, hub fires, caliper seal failure, rotors warping, etc.

 

[Dave Bilyk]

Just out of interest, the following overall power dissipation under braking for a 1 ton car braking at 0.9g.

200mph Total 1058hp (789kW) , on one front disc say 317hp (237kW) if brakes are well balanced.

These figures are proportional to speed so take half for the average dissipation for braking to rest.

Even at a less insane speeds the figures give a perspective on what brakes have to endure.

Dave

 

[Ross Nicol]

Thank goodness we're not on the brakes for very long , at those power figures. I have air ducts directed to the inside centre of each rotor and the air cools the disc as it travels through the vanes and exits at the circumference.
Ross

 

[Ian Anderson]

See also
http://www.gt40s.com/forum/tech-cha...01-brake-ducting.html?highlight=brake+cooling


I posted pictures from Le Mans Classic 2004 where brakes and ducts were on display

They did not duct from behind the radiator!

Ian