DIY SPM S2ish aero - quantitative results
 

I think most of us know that the basic Supermiata aero formula works, but I can't recall seeing anyone post a direct before/after comparison. Since I now have some comparative data, I wanted to share it. I went from basically a stock NA with hardtop and 'R' front 'lip' to a slightly modified S2 setup. Birch splitter up front with plastic airdam, and BBFW lexan spoiler in the rear. I went beyond S2 with a 2" stickout on the splitter, Left Lane fender vents, and removed the lower portion of the rear bumper.

The car:

1992 Miata, NB VVT/6speed swapped, 4.3 torsen, hardtop. 135rwhp, 2100lbs without driver. No changes to anything between the data sets other than the aero mods. Same tires (Toyo RR) with two event days between data sets.

Pic before:

https://live.staticflickr.com/65535/...70dbf5ca_c.jpg

Pic after:

https://live.staticflickr.com/65535/...800f1cb0_c.jpg
https://live.staticflickr.com/65535/...42aff97f_c.jpg

Results:

Both data sets were taken at Arizona Motorsports Park, 2.2 mile road course in Phoenix, AZ. Before numbers are from March 2020 (in black), and After numbers are from December 2020 (in red). As noted, no changes other than the aero mods, although March was probably ~12-15deg warmer over the day. Data was gathered via Race Chrono cell phone app. I've found this app to be pretty good for straightline speeds, but the sampling rate doesn't provide good enough data to evaluate corner speeds.

https://live.staticflickr.com/65535/...46dacbd6_c.jpg

Quantitatively, the improvement was 2-3mph on every straight. The image shows a one lap comparison, but the numbers are consistent from lap to lap on both days in question. I credit most of the improvement from drag reduction, as most of the straights come after low speed corners on this track, and I wasn't seeing a definitive improvement in corner speeds. One straight (the one after the 100mph main straight) shows a 3mph improvement on a relatively short straight, and I attribute this to getting much better drive out of the carousel complex due to better stability... see below.

Qualitatively, the car is more stable in high speed corners. Previously the car was a little touchy and quick to rotate on trail braking, the aero has settled it down, and made it more predictable and easier to drive. I need a real data system in order to provide a quantitative look at corner performance.

Edited because I didn't want to give the impression that I was attributing 100% of the improvement to drag reduction.

I think this will come after you have driven a few more events with the aero.

I put splitter/wing on my NB and was surprised to only pick up 0.2secs a lap improvement. even though everyone said its much more. Car was definitely way more planted, though corner speeds weren't up much at all.
It took about 4 events to really trust and use the extra grip the aero gives, and I am now 2 secs a lap quicker at most tracks with no other changes. The time came from just getting used to the aero advantages.

And I thought my door number idea was original. People are going to think that I'm blatantly copying you..

Thanks for posting results, on the aero, though.

^ This.
It's working up to trust the car to hold where it didn't before.
Also, we made the spoiler adjustable so that you can, ahem, adjust it ;)
Take advantage of that part, try different AOA and learn what it does to the feel of the car.
Remember that while higher AOA may cost you some drag, it might also mean getting a better drive into every straight due to increased cornering speeds and at the end you may very well still come ahead.

Looking good. :likecat:

My experience is that the rear wing really helps manage exit wheel spin without having to compromise corner weight (avoiding giving up handling balance for traction). So a higher mid-straight speed. Surprisingly, I found that the rear wing allowed the rear brakes to contribute more without lock-up. With a little fine tuning, despite higher top speed, I was able to brake later.
Currently, my front splitter/dam setup serves to balance with the rear wing but I feel there is much more I can do there to contribute greater front down force and perhaps to reduce drag. A possible win-win.
A simple collection of TraqMate or Solo data showing both the low point of speed (corner entry) and high point (straight-away peak) combined with lap time will reveal a lot about aero effectiveness.

Thanks for chiming in! :likecat:

This was not the first event with the new aero, just the first one where I had before/after data that was worth comparing. I've already got the spoiler dialed in pretty well for the current setup. Definitely still learning the new 'feel' of the car.

This is a definite next step. I've been using a cellphone app, but its resolution is not good enough to parse the data that closely. Time for a real data system.

As a stop gap you can hunt down a cheap 10Hz bluetooth GPS puck and pair Race Chrono with that. It will bring up the resolution to that of dedicated systems.

Roda I actually have a Qstarz 10hz GPS unit with bluetooth. I haven't used it in forever. If I can find it, I'll ship it to you for 20 bucks if interested.