Brake cooling thru wheels 6

[frankiee]

With road wheels that have a unidirectional vent pattern built into them, do the louvers draw air from the outside to the inside drawing cooling air over the brakes or
- does it draw hot air from the brake area out to the air outside?

 

[WilliamH]

Your inquiry brings back an intresting experience that happened when I was crew chief on an SCCA Trans Am series race car in the mid eighties.

We had a problem with front brake over-heating at the end of long, fast straight aways. We were running alloy wheels (10 X 16) and thought that the wheel width was not allowing the hot air to vent out fast enough.

My thought was to fabricate fins that would make the wheels fans. (BBS wheels offered this as an optional accessory at the time. We were not using BBS wheels at this time however). We did this and tested the air flow on our lathe. Lots of air flow indeed. The air moved from the outside to inside of the wheel as per design intent. We thought this would help keep tire temperatures down as versus allowing brake heat to move through the wheel.

We went to a fast race track on the west coast (Portland International Raceway) to test our brake cooling fans. After five laps the driver radioed that the engine coolant was begining to get too hot. Brakes were great though.

To get to the point, what was happening was the fans were creating so much pressure behind the engine radiator that flow was reduced considerably. We did not figure this out immediately. But that is what happened in our case. The speed at the end of long straight was approximately 190 MPH. A street driven vehicle's dynamics are not really equated to a race car.

Will

 

[frankiee]

William H
So you are saying that the flow goes from the brakes and out the wheels? Right?

 

[gwolf]

The point is, if you are trying to actively generate airflow through the wheels, suck from inside to out on the front wheels or you will be pumping high pressure air into the engine bay and preventing the radiator from functioning properly.

Suck or blow, it doesn't matter which way you do it unless you come across a situation as described by WilliamH

 

[Warpspeed]

I have seen pictures of Corvair engine cooling fans fitted to the front wheels of race cars.

These draw air from the hub outwards, and it may actually be a lot easier to do it that way. I am sure other types of aluminium centrifugal rotors with the fins inboard, could be readily adapted to do something quite similar.

 

[NormPeterson]

Air already has to flow into the rotor vents from the inside, so it seems a bit counterproductive to blow the now brake-heated air right back to the inside and have some of it become brake inlet side air again. Assuming the absence of dedicated rotor ventilation ducting and close-fitting adapters around the inside centers of the rotors, that is.

Norm

 

[GregLocock]

This is banned from F1, so it probably works!

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[InstantG]

FWIW I used to run these on my porsches in the late 80s early 90s. A company made an adapter that was affixed to the center of the factory wheels and had a large plastic center cap that screwed in place to hold the wheel fan in place. I still have a few sets of these in the basement. The fan itseld was injection molded plastic.

They worked very well and we used them in conjunction with brake cooling ducts that force fed high pressure air to the centers of the rotors.

One of the things that began happenign is that wheel weights would burn off the wheels! Yes, they worked. We stopped using them when open pattern 17" wheels became available. The fans were only made for specific 16" wheels and the guy eventiually stopped making them. I had pretty mcuh forgotten about this until recently when I bought a vintage 930 with BBS fans on it.

Steve Timmins,

http://www.instant-g.com

 

[CentralCoaster]

I think the last thing you want to be doing at high speeds is forcing more air to the wheel wells. This will build pressure under the car causing lift and drag. It'll also render your brake cooling ducts useless. The idea is to promote flow in one direction, force it in with front ducts, and evacuate it through wheels and through hood louvres.