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Project #YAE92 M3: Part 5 – Basic Aerodynamics

by Mike Bonanni

Now that we’ve brought you back up to speed on the Yost Autosport E92 M3 endurance race car in our last article, it’s time to start diving into details on the current version of this beast. I figured we would start with the part of any race car that is the most intriguing to me; aero. Aero, like any other aera of a race car build is not simple. If you bolt on a set of super expensive triple adjustable coilovers to your car that doesn’t mean your car will go faster, in fact it may make it slower. You have to know how to use them, how to adjust them, how to set them up to where they are working properly. It’s the same with aerodynamics. Using self tapping screws to mount a “splitter” to the bottom of your plastic bumper cover just doesn’t work yet you see it all the time.

We are fortunate enough that the race class we run our car in for endurance racing is virtually unlimited in the field of aerodynamics. So why don’t we see cars that look like Unlimited class time attack cars racing around at the 25 Hours of Thunderhill? I think there’s multiple reasons for this; First, I think that the area of aerodynamics has not yet cought on hugely in grassroots racing outside of time attack. Second, there’s not many easy bolt-on aftermarket parts that actually work proper for most platforms. There’s always some sort of fabrication involved in most cases and that shys people away especially if they’re not experts in aero.

 


This photo of the BMW Team RLL E92 M3 race car to me is the ulitmate endurance racing aero design. All you really see that adds downforce are a wing, splitter, and tiny little canards.The rest of the areo is designed for efficency. Reduce drag, reduce lift, add a little downforce.

When people think aero they think downforce, more is better, but in endurance racing everything is a compromise. With a time attack car it’s easy, add as much downforce as possible, counteract the drag with more horsepower. Cars only have to run 1-2 laps at a time in clean air. For endurance racing it’s much more complicated. We have to think about fuel mileage, tire wear, susceptibility to damage, and the fact that we’re almost always driving in traffic. Not only that but we have to be extra sensitive to what effect any change has on our car as the smallest change can have a huge impact over the course of 25 Hours. A couple tenths of a second each lap adds up tremendously over the course of 550+ laps that we run in the 25 Hour.

So our aero goals are simple; reduce drag as much as possible and add a little downforce. Version 1 of our aero package attacks the low hanging fruit so to speak. Is there room for improvement? Of course, and we’ll get to it down the road. For now, let's look at the basics.

 


A front splitter is a common sight at any track day or grassroots race, but how many of them are mounted properly? An adult male should be able to stand on it and the only thing that should move is the front suspension. APR Performance made a custom carbon honeycomb splitter for us using a template we gave them that does the job beautifully. Now you can call them up and ask for the same one we have! Extra bonus shot of our new LED strip we use during night races so our crew in the pit can tell which car is ours out on track.

We’ll start at the front of the car with our splitter. I see time and time again splitters that are mounted to the plastic or fiberglass bumper covers of the car and this just simply doesn’t work well. What a splitter does, is provide a flat surface area for high pressure air at the front bumper to push down on. You have to think of what that splitter is then pulling on. You want the forces generated to transfer to the tires where they’re benefitial for handling and braking. If your splitter is mounted to your flimsy bumper cover you’re not transfering much, if any of that downforce to your tires. You want to mount it directly to the chassis. Companies generally don’t sell them like this because it makes production of the parts much more difficult, requires drilling or welding in most cases, and the reality is that would turn most people off from buying them. It’s much easier to sell a flat piece of carbon or composite. If done properly a normal sized adult male should be able to stand on the splitter and the only thing that should move is the front suspension.

 


Here you can see the sub structure of our splitter. There’s a subframe like creation that provides a wide footprint to mount the actual splitter itself to. The structure transfers load across the splitter and connects to the chassis at 4 points. You can also see our brake ducting here which pulls air from under the splitter. This is a low pressure area so you’re not pulling tons of air through the brake ducts but packaging was an issue for us while brake cooling was not. We ran the entire 25 Hours of Thunderhill without brake ducting at all without problems but a little extra cooling can help them last even longer. This setup allows us to keep the front end of the car more streamlined and create very little drag.
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Comments
Rick14
Rick14link
Tuesday, August 11, 2015 2:19 AM
I'm sharing it on reddit
8695Beaters
8695Beaterslink
Tuesday, August 11, 2015 5:14 AM
I really dig the LED strip in the splitter. What a great idea! Well until everyone else copies it and does the same... Also, you could have just had three pages on the rear wing structure and would have still made an awesome article. Any chance of seeing more of it?
spdracerut
spdracerutlink
Tuesday, August 11, 2015 10:41 PM
Well thought out mods! Love it!
warmmilk
warmmilklink
Wednesday, August 12, 2015 12:41 PM
do you really have BC coilovers on this?
M.Bonanni
M.Bonannilink
Wednesday, August 12, 2015 12:59 PM
Thanks everyone!

warmmilk - Absolutely.
mistermike
mistermikelink
Friday, August 14, 2015 3:24 PM
awesome doable and keeping it simple and legit. To work on my aero after the swap :)
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