Stock street car vs stock street car with aero… how much is aero worth in a lap time?
Aerodynamic downforce adds load relative to speed. The faster you go, the more downforce you get. But downforce is often accompanied by drag, and drag increases greatly at speed. The result is that aerodynamic downforce often gives you a faster lap time, but a lower top speed. In the end, it’s safe to say you’ll go faster by ignoring drag and going after as much downforce as possible.
But how much faster you go depends on the track. On a straight drag strip, you’d actually go slower. On a flat, circular track, you’d go a shit ton faster. Most tracks are a combination of straights and curves, and how much aero helps varies greatly on the layout.
To find out how much aerodynamic downforce is worth, I ran some simulations in OptimumLap. For the stock street car build I used Cd 0.39, Cl-0.1. For the aero version, I used Cd 0.43, Cl 1.1. This represents a lot of downforce, and something that is probably not achievable by the average person, but allows you to average the two extremes for most cars that land in between. These are reasonable values for drag and lift, and I’m just spitballing here anyway. So how much of an advantage is worth aero at different tracks?
| Track | Aero |
| Willow Springs | 105.4% |
| Mosport | 104.7% |
| Lime Rock | 104.6% |
| Thunderbolt | 104.4% |
| Watkins Glen | 104.1% |
| Palmer | 103.7% |
| Summit Main | 103.6% |
| Thunderhill 3 mile | 103.5% |
| Road Atlanta | 103.5% |
| Club Motorsports | 103.5% |
| Waterford | 103.3% |
| Mid-Ohio | 103.3% |
| Thunderhill 2-mile | 103.2% |
| NYST | 102.9% |
| Gingerman | 102.9% |
| VIR | 102.8% |
| Thompson | 102.7% |
| Canaan | 102.6% |
| Laguna Seca | 102.4% |
| PV extension | 102.3% |
| SCCA Nats 2010 | 101.9% |
| PV original | 101.7% |
There are some surprises here, notably VIR. I thought VIR would be an aero track, but it’s close to the bottom of the list. This is partially the result of two long straights where drag plays a role, but also some tighter corners where there isn’t much downforce.
I’m also surprised by Lime Rock and Thunderbolt. I don’t think of them as aero tracks, but they are. I don’t have a track map for Nelson Ledges, but it would be close to the top, and probably above Watkins Glen.
If I average all the tracks out, aero is about 3.3% faster. But this includes the autocross track from SCCA Solo Nationals in 2010, and Pineview Run’s long and short courses. These are not normal race tracks, and if we remove them, 3.5% is the mean, the median, and the mode.
I’ve often heard people say “Aero is worth 3 seconds per lap,” and that’s actually a really good rule of thumb. If you are doing a 1:30 lap time on a race track with a good mix of corners and straights, 3.5% faster comes out to exactly 3 seconds. But you can see that it really does depend on the track layout: how many fast corners, and the length of the straights.
| Note: I can only run simulations on tracks I have in OptimumLap. If you want me to include your favorite track in some future article, sends me your 10-hz GPS data. It can be difficult to get an accurate map at full speed, so if you can drive on the racing line at half speed, it will result in the most accurate track map. |
Occam's Racer 