Brake ducting

#1

Since brake ducting is allowed, is it legal to replace the backing plates with a custom plate to accomodate the ducting? (e.g. sheet metal with round tube welded to it, or carbon fiber piece with round tube molded into it)

#2

yep. see section 9.3.13.7, which allows ducting "to the brakes" via the "passage of up to a three inch diameter duct leading to each front brake". attaching the duct to a modified or aftermarket backing plate is "leading to each front brake" in my book, otherwise there’s no way to actually ‘lead it to the brake’. the small cost of doing this will save you big-time in break pads over the long run.

#3

The easy route is to get the RRT/Bimmerworld backing plates – not the cheapest option, but very easy to install and very effective when coupled with 4-5 feet of hose and a duct on each side.

#4

I’ve noticed that my outside disc gets a lot more spider cracks on it than the inside disc. This would seem to be due to the venting on the inside disc keeping it cooler. If there was only a way to get the vent to blow on both sides… There’s got to be a way, no??

#5

Are you ducting the air onto the face of the rotor or into the vanes on the center? If you duct it into the vanes, it should cool both sides evenly. If it’s hitting the face of the rotor, I could see some issues. I’m surprised you aren’t getting some warping.

#6

My Bimmerworld ducts do aim the airflow somewhat at the inside face of the rotor but I haven’t had any warping. I haven’t checked either surface since installing the ducts but I will.

And I have certainly seen less brake pad wear.

Carter

#7

Run TD Pro Race Wheels or Kosei’s. They have a ton of rotor/caliper clearance to promote airflow. I wouldn’t worry so much about cracking. Rotors are cheap and the brakes are tiny, it’s going to happen no matter what you do. The only way to fix the outside cracking first is to go to floating rotor like the Motorsport rotors on later M cars. And that would cost a ton. Rotors tend to twist somewhat as the inside friction surface have a different amount of expansion compared to the outside due to it’s attachment on the hat.

#8

DriverGT5 wrote:

Aren’t the vanes designed to flow air from the center of the rotor to the outside? I may be misunderstanding the design, but I would think that trying to blow in from the edge of the rotor would be analagous to blowing into a fan?

I was thinking more so of a C-shaped piece that would attach at one end to the top of the duct blowing on the inside disc, and would bend over the disc to blow onto the outside disc. Theoretically this seems like a more uniform way to cool each side of the rotor, but I can’t help but think this would present some sort of safety issues (ie the add-on piece braking off & getting stock in the wheel spokes). Brainstorming here folks - it’s a dangerous pasttime!!!

#9

Yeah, you’re correct. Rotors are designed to "flick" air out from the inner radius to the outer radius. Based on that, air will always be sucked in from the inboard side of the rotor (regardless of where your duct is aimed) and propelled out. To get airflow to the outboard side, you need a floating rotor which allows air to be sucked in from both sides of the rotor. Also, a wheel spoke pattern that is designed like a propeller (like some of the Porsche 996’s) will help the airflow.