In a previous post I put various wings and spoilers on my Veloster N and tested them at Pineview Run. What I found was that a ducktail spoiler or single wing was about .7 seconds faster than the OEM N spoiler/wing. And then I tried a dual element wing, which was another .6 seconds faster.
Pineview is a small, slow track, and there are only a couple corners where aero matters, and so 1.3 seconds is a significant difference. I opined that on a longer track with faster corner speeds, the lap time delta might double.
I got a chance to put my money where my mouth is at private open track day at NYST. The track closed for the season a couple weeks prior, but somehow Brad at S2K Takeover got his group a bonus round, and they invited me along. It was cold and damp at the start of the day, and this affected things slightly, but I got in a lot of consistent runs as well.
Rear aero options
For this event, I didn’t have much front aero on my Veloster N, just a hood vent and an aluminum undertray. Those are mostly for cooling, but they might provide around 60 lbs of front downforce at 100 mph. I have splitters and canards aplenty, and can get five times the downforce with those, but I wanted to test the exact same car I was using at Pineview last time.
Well, not exactly the same, because I didn’t bring the ducktail spoiler. At Pineview, the single wing was about the same performance, and so I left the ducktail at home. This would allow me to make faster setup changes, as I could keep the same roof extension on for every configuration.
If you are a regular reader, you know I’m a shit disturber; I like to challenge the status quo, and disprove common misconceptions using data. That’s another reason there’s no front aero on the car. Adding rear aero alone on a FWD car throws the aerodynamic balance out the window, and is the opposite of what most aerodynamic pundits suggest.
The rule of thumb is to match your aero balance to the chassis balance, so that you don’t change the balance of grip as the car changes speeds. And so if your car has a 50/50 weight distribution, then you add the same amount of downforce front and rear. Or in the case of this FWD hatchback, if you have 67% of the weight on the front, then you should add twice as much downforce on the front as on the rear. But I purposefully didn’t do that; I only added downforce to the ass end.
I tested seven rear aero options:
- No aero – The base model Veloster didn’t come with a wing or spoiler, just a roofline extension. I built my wing mounts on top of this, and so the no-wing setup has two vertical wing supports. This might provide some stability in yaw, but they wouldn’t add downforce or affect the lap times much.
- Single wing, 0 degrees – This is my DIY S1223 wing, which I recently modified with glassed-in endplates. This is also the lower wing for all of the dual element wing tests.
- Dual wing 0/0 – This setting adds an upper wing element at zero degrees. This represents a dual wing at the lowest drag setting.
- Dual wing 0/26, standard gap – I then set the upper wing to 26 degrees. This is a fairly conservative angle of attack for a dual element wing.
- Dual wing 0/26, small gap – I kept the angle the same, but moved the upper wing down (closer to the main wing) and forward, so there was more overlap between the wings. This is the only wing setting where I used this gap and overlap.
- Dual wing 0/40 – I put the gap and overlap into the original position, and then raked the upper wing to 40 degrees, which is typically the maximum angle you can use with a dual element. At this AOA I’m flirting with flow separation, but what can I say, I’m a flirt.
- Dual wing 0/40 Gurney – I added a 1/4” Gurney flap. At high angles of attack, a Gurney flap can often help keep air attached. This setting should have the highest downforce, but also the most drag.
Let’s see how these compared in lap times, from slowest to fastest.
No wing 1:41.546
I tested the wingless car on the last run of the day. The track was in perfect condition by this time, now completely dry and warmed by the sun. I was also driving at my best, with enough laps under my belt that I wasn’t losing time anywhere for silly mistakes or a lack of reference points. And yet I set my slowest lap time.
The problem was mostly that I’d gotten used to rear aero, and without it, the car felt sketchy. On my best lap, the rear end got scary loose while braking on the front straight. And then I almost shit my pants braking into T5, as the car skidded in a way I hadn’t experienced before. I intentionally drive a tenth under the limit at this track, and I honestly thought I was about to put it in the grass.
That nervousness braking into downhill corners may be partially down to the Hyundai’s dynamic brake bias, which senses wheel speeds on each corner and then loads more and more front bias as the rears sense lock. This can put up to 93% of the bias on the front tires, making the rear end rather irrelevant. Without rear aero, that balance shifts earlier.
So let’s move on from braking zones to corners, and in the slower ones, the non-aero car handled the best and was the most fun to drive. Rather than forcing the car into rotation early in the corner, I could just lift a little and get a mid-corner pivot.
From start/finish to T5, the cars were very evenly matched, but from the downhill braking zone in T5 to T11, the car was 1.5 seconds faster with a single wing than without. Sans wing, I had less confidence in turns 8 through 11. From T12 to the end of the lap, the cars were again very evenly matched.
If you look at the speed trace, you’ll see that right around 52-54 mph is where the difference is; go faster than that, and you want a wing, go slower, and you don’t. Ergo, using rear aero alone on an autocross course could be useless, but on a race track, you definitely want it.
Double wing 0/0 1:40.370
Most people wouldn’t set their dual wing to zero degrees top and bottom, it doesn’t take advantage of the convergent gap, which allows more secondary wing angle. Where you see this setting is in Formula 1, when the upper wing goes into DRS mode.
And that’s exactly why I wanted to test this setting. Next year I plan to build a DRS upper wing, and I wanted to see what the speed advantage was on the front straight. So here’s how that shakes out.
The DRS 0/0 double wing had an average top speed of 107.4 mph, while the 0/26 setting had an average of 106.8 mph, and the 0/40 had an average top speed of 106.4 mph. So DRS was worth about 1 mph from the highest to lowest drag settings. This doesn’t take into account that the higher downforce wings would have a higher min speed through T18, so let’s call DRS a 2 mph advantage on this track.
Surprisingly, that’s not worth a lot in a lap time, as the reduction in drag isn’t noticeable until about 88 mph, which happens about half way up the front straight on the 3rd to 4th gear shift. From there until the braking zone is where DRS makes a difference. Still, DRS sounds like a fun project, and on a track like Watkins Glen or VIR, the drag reduction would be more worthwhile.
Single wing 1:40.081
The single wing is the bottom wing for all the dual wing setups. It’s my DIY S1223 with a 1/2” Gurney flap. In the wind tunnel, it was nearly the same downforce as a 55” 9 Lives Racing wing (185.4 lbs) and 55” PCI wing (182.5 lbs).
With the wing on, the car was much more planted in the braking zones and in the fast esses. The downside is that is the wing took away some of the fun in the low and medium speed corners. For the gain in lap time, and especially the braking stability, I’ll take that trade.
If I look at the theoretical lap times, there’s a full 2 seconds between the single wing and no wing. And this is without changing wing angle at all. If I had added more wing angle, the car would have turned an even faster lap time.
But let’s get back to the real data, and that was that the single wing at zero degrees was 1.5 seconds faster than no wing. This is just over double the delta I saw at Pineview, and so I guess I was right about that prediction. And with that, I’ll make another prediction, which is that this wing would be worth 3 seconds at Watkins Glen.
Double wing 0/40 Gurney flap 1:39.970
You may recall that the lower wing has a Gurney flap on it already, and for this run I put a 1/4″ Gurney flap on the upper wing as well. The upper wing measures 4.7″ chord, and so the wicker is about 5% of the chord, which is a typical size.
This configuration drew the short straw, because the track was cold and damp when I tested it. Top speed was down a hair from the other 0/40 test runs, but not as much as I thought it would be.
I’d like to re-test this one at Pineview Run, as the extra downforce might have some benefit in slower speed corners. But given that the 0/26 setting was faster, I don’t think there’s a reason to use double Gurney flaps and a 40 degree angle on this car, unless I add front aero.
Double wing 0/40 1:39.447 and 1:39.435
I did several laps with the Gurney flap on and then quickly pitted, ripped it off (it was duct taped on, just like I would in a wind tunnel), and went right back out on track again. Although the track was still damp, the conditions wouldn’t have changed much in those 60 seconds, and so I feel the comparative data here is really good between with and without the Gurney flap on the upper wing. The data shows that there’s about a half second between them, and no Gurney on the upper wing was faster .
On the second to last run of the day, just before testing the single wing, I retested the 0/40 dual wing, because I didn’t feel I gave it a fair shake on a partially damp track. The best lap was only .012 seconds faster, and so I think there wasn’t that much time deficit in the damp track after all.
Double wing 0/26 small gap 1:39.230
I wanted to see what would happen if I changed the size of the gap between the wings, and the amount the top wing overlaps the bottom wing. It would be better to run a sweep of offsets in a wind tunnel, but I figured what the heck, I’ll make one radical change and maybe I’ll notice a clear signal in the deltas. I did not.
The smaller gap had a slightly faster top speed on the front and back straight, but the differences were so minor I can’t attribute it to drag reduction. But the minimum corner speeds were all slightly less than with the larger gap, and maybe this is a lower drag, lower downforce arrangement after all. I can’t say for sure, and with lap times this close, kinda don’t need to retest this one.
Subjectively, I can’t say I felt huge difference between any of the 0/26 settings and 0/40 settings. They all made the car a little more stable, and required a little more effort to turn the car. But if you changed wing angle or Gurney on me without knowing, and sent me out on track, I wouldn’t know which I was using.
Double wing 0/26 1:39.104
The fastest laps were set with the top wing at 26 degrees with the standard upper wing gap. These laps are shown here in blue vs the 0/40 runs in red.
A – You can see the 26-degree angle has less drag and a higher top speed than the 40-degree.
B – The only place the 40-degree angle has a clear advantage is in the carousel before wheelie hill. More downforce means a higher minimum speed all the way around.
C – For whatever reason, the lower wing angle carried a higher speed through the esses.
Other than those areas, there wasn’t a lot to choose between them. Given that, there’s enough evidence to say that somewhere around 26 degrees is the best setting. Certainly the 40 degree angle was slower, as was zero degrees.
It’s funny, that when I originally built this wing I set the upper wing to 30 degrees and made no provision for adjustment. I was simply testing a proof of concept at that time, but damnit that might actually have been the best setting.
Conclusions
Here are all the fastest laps and theoretical laps for each configuration.
| Aero | Best lap | Theoretical | Front MPH | Conditions |
| No wing | 1:41.546 | 1:41.192 | 108.3 | Dry |
| Dual 0/0 DRS | 1:40.370 | 1:39.903 | 107.6 | Dry-ish |
| Single wing 0 | 1:40.081 | 1:39.217 | 107.3 | Dry |
| Dual 0/40 Gurney | 1:39.970 | 1:39.693 | 107.0 | Damp |
| Dual 0/40 | 1:39.447 | 1:39.061 | 106.8 | Damp |
| Dual 0/40 retest | 1:39.435 | 1:38.785 | 107.2 | Dry |
| Dual 0/26 small gap | 1:39.230 | 1:38.651 | 107.7 | Dry |
| Dual 0/26 | 1:39.104 | 1:38.506 | 107.6 | Dry-ish |
In the previous article, I forecasted that the single wing’s .7 second advantage and the dual wing’s 1.3 second advantage at Pineview might be worth double at a longer track, and it was almost exactly that. Like Pineview, NYST had only has a few corners where aero matters, and on a track with more fast sweepers, the advantage might double again
So I would also guess that the single wing’s 1.5 second advantage at NYST might be 3 seconds at Watkins Glen. However, I wouldn’t extrapolate this and say that the dual element wing would go 5 seconds faster at Watkins Glen, because the double wing is pretty draggy.
A single wing is more efficient, and a longer wing span might give similar downforce as the double wing at 0/26, while also having less drag. A single wing is also a lot easier to optimize, with just the angle of attack, height, and setback distance to monkey with. The dual wing has twice as many variables, and hitting the sweet spot may be down to luck. I’ve started building a larger MSHD, and I’ll test that next year, along with a new DRS wing.
Speaking of DRS, it seems like I’d want to have three settings:
- Low speed – In slow corners, the car doesn’t benefit from rear aero, and it’s more fun to drive without it. I’d activate DRS at 50 mph and under.
- Medium speed – For corners above 50 mph, I’d put the wing into full downforce mode.
- DRS – On any significant straight, I’d go back to the low-drag setting.
Another discovery from this test is that I’ve found the tipping point where adding rear aero stops making the car go faster. This will help me figure out how much rear downforce I need when I put my splitter and canards back on. Those items are worth about 300 lbs of front downforce at 100 mph, so in order to achieve the same balance I found in this test, I’ll need to add at least that much more downforce in the back. Here’s why.
My car weighs 3200 lbs with me in it, and because I’ve removed some weight from the rear, the weight balance is about 67/33. So that’s 2144 lbs on the front tires and 1056 on the rear. The typical aero rule of thumb is that if I add 300 lbs of aerodynamic downforce, then I should split that 200 front and 100 rear. This retains the same chassis balance and mechanical grip that the engineers designed.
However, the fastest configuration I tested was with 60 lbs of downforce on the front (the hood vents and undertray) and probably 240 lbs on the rear. This adds up to 2204 lbs on the front and 1296 lbs on the rear, which works out to a 63/37 balance. Mathematically, I’ve moved the grip 4% rearwards at speed, using aerodynamic downforce. When I add my splitter and canards, I’ll want to be in the same range.
Now of course none of this make logical sense. When you put rear downforce on a FWD car, it takes away from the front tires, which is a problem because they are doing all of the steering and accelerating. But logic be damned, the reality is that I went 2.5 seconds faster with way too much rear aero bias.
If I did this same experiment on a RWD car, the results would likely be even more dramatic, because the rear wheels are responsible for acceleration and have more weight on them for braking. This supports the case for having heavily rear biased aero on a RWD car as well.
When you load a car with too much rear aero, it understeers in fast corners, but also makes for a safer and more stable car that requires fewer corrections when you lose control. The downside is the car will be boring to drive and harder to turn. But that’s what the brakes are for.
If you don’t care about lap times and want a car that is fun to drive, set your aero balance however you want. But if you care about lap times, ignore the rule of thumb and see what happens when you keep adding more and more rear downforce.
One day I’ll have enough information to write an in-depth article on aerodynamic balance, but until then, chew on this nugget: if you like the way your car handles, you don’t have enough rear downforce.
Occam's Racer 