ratt_finkel

So we are putting together a plan for rear aero on the Pikes Peak car. My trusted aero advisor says as far as height: Just above the roof line is ideal. Chord length, bigger is better.

In looking at other race vettes. I notice most are similar in riser height. But some are placed forward of the rear bumper, central or even rearward.

And then I look at the C5R's and the chord length on those seem significantly thicker than popular modern aero setups. But also, it's only about about 8" off the deck. Instead of 18" plus.

Speeds will average around 70mph. Need effective range of 30-140mph.

Would love any input on what you guys have experienced in the real world.

LateBreak

Generally, my understanding is that higher and further rearward are better. I think that the pro cars have theirs mounted low and forward due to rule restriction on placement.

I built a simple 10" chord 72" long one in my garage and put it slightly above roof height. Nothing scientific beyond trying to make it look cool Thankfully, it's worked really well. The car was extremely unbalanced without it and felt very unstable when running with only a splitter up front. With the spoiler installed, the car is planted and works awesome. Unfortunately, I don't have any back-to-back track times to quantify that for you.

Picture for size/height reference

redtopz

I read a good paper on race car aerodynamics where the author showed for most production cars the optimal wing height was within 1 cord length above the deck lid. And the wing would be sitting over the deck lid and not behind it. For nasa last year I had my wing a few inches above the roof. This year for scca it's about 1" below the roof. I can't tell any difference fwiw. The angle of the wing would probably have more influence.

Also another thing to think about as far as wing placement fore and aft, is wherever the wing is located that's where the down force will be applied. So if the wing is over the rear axle, that's where the down force is applied even if the wing is attached to the frame 1' further back. Similarly, if the wing is 12" behind the car that's where the down force will be applied regardless of where it connects to the car. To prove this, get a model car and put a wing behind the car and push down on it and watch the front of the car lift up. Now put the wing in front of the rear axle and do the same thing and the car will remain planted. So wing location can also cause lift or downforce on the front tires.

ratt_finkel

I've read both of your build threads! Glad you two could chime in. Thank you for the feedback. Very helpful.

mountainbiker2

Dual Element wings will get you the most downforce your car can handle. The top Autocross guys use these kind of wings. They work extremely well at low and high speeds. Here's what I did. 8sq. ft. of wing. Dauntless Racing.



Mounted to trunk lid. The studs come up through the trunk and you bolt it down. You can still use the trunk, but you have to take off the nuts.





You will need a big splitter to compensate.

Steve