Wider wheels and the factory air curtain…discuss.

UNBROKEN · Mar 28, 2023

Someone brought this up to me…I don’t know much about it but it’s worth a free experiment. The video linked explains what I’m talking about in the first few minutes but basically with the stock wheels the air curtain exits the fender and flows out and around the tire but throw on wider, flush wheels and the air just bounces around inside the fender. Blocking the opening causes a little more drag but makes up for it in downforce but what about any effect on mpg?
I cut some closed cell rubber blocks to plug the opening…I’ll watch my mpg for a week or so to see if there’s any changes. My daily commute is identical and my car lives at 17.7mpg. Anyway…just some interesting theories and I thought we might have some smarter members that could dive deeper into it.
Also…apparently the PP2 Mustangs with wider oem wheels have the air curtain blocked from the factory.

And the little plugs I cut for free to see if there’s a change.

TMac · Mar 28, 2023

After looking at that video and the embedded link on the wind tunnel testing, I'm amazed the questions which weren't answered. I think he mentions these tests were at 100mph windspeed, but I'm not sure, since this would be relevant info.

He seems to measure efficiency of cooling as being the increase in pressure on the radiator and oil cooler. It is flow that carries the heat away, not pressure, so this cannot be an accurate way to measure cooling efficiency increases. His 1.24% increase in pressure on the face of the oil cooler in no way suggests it is now 1.24% more efficient.

He also makes a statement that without a rear wing the mustang produced 133 lbs of upforce. With a GT 350R wing, it then produced 124 lbs of downforce. He then subtracts the two with the result being there is still 9 lbs of upforce? That seems to be a pretty self-serving fuzzy math comment- don't buy the Ford wing- it doesn't help, buy mine. Flame me if you wish, but I'm a bit skeptical of some of his conclusions. Has he considered other items affected by blocking off the fender intakes such as brake cooling? It doesn't appear so.

But to answer @UNBROKEN's question- unless this made major improvements (not the 3/10s lb of drag he mentions) at 100 mph, I don't see this affecting gas mileage for any normal speeds at all.

UNBROKEN · Mar 28, 2023

Any thoughts on why the air curtain is blocked on PP2 Mustangs with the 305 square tire fitment?

TMac · Mar 28, 2023

Just looking at that part it doesn't look like a block-off. It is just restricting the amount of flow more that the stock part? Does the wider wheel fitment include other changes like brakes, fender liners, etc. I don't know any particulars about Mustang variants. Does it include a recessed vent behind the wheel openings to allow air flow out of the wheel well that might also be part of the package?

UNBROKEN · Mar 28, 2023

TMac said:

According to the guy that supplied the pic it’s a complete block off plate on his brothers car.

TMac · Mar 28, 2023

Regardless of whatever very minor effects that block off has on aero effects because I don't think 3/10s lb of drag at 100mph to be significant. I look at things holistically. I looked at the PP2 upgrades. Is it possible that the added splitter, lowering, and wider wheels (and wheel spoke design) affect the airflow in the fenderwells such that it's not needed? How about the change to the tires- perhaps rather than some aero boost, the engineers actually want a slightly higher tire temp to increases stickiness? The gentleman in the video is so interested in aero parts (which I assume he sells) that he seems blind to other possibilities. And as I posted in #2 above, he made some comments which are highly suspect- and that's giving him the benefit of the doubt.

Remember the old joke, "If you only have a hammer, then every problem is a nail!"

2020FordRaptor · Mar 28, 2023

Just a though here, could that opening be a brake duct air cooler? Thinking further could it help release pressure in the fender, kind of like a fender air extractor. Not an expert here but obviously there has to be some reason why Ford put it there.

Lightning Struck · Mar 28, 2023

Looking back through the pictures of my 2018 PP2, they do appear completely blocked. I don't have a fantastic close up of them though.

UNBROKEN · Mar 28, 2023

2020FordRaptor said:

It’s called an air curtain. Its function is to smooth airflow through the fender and down the side of the car…but with stock wheels. The question is…do wider, flush mounted tires affect the way it’s intended to work.

Lightning Struck · Mar 28, 2023

TMac said:

Higher tire temp is definitely needed with the factory Sport Cup 2's. They're down right scary when cold. Driving my car in 40* weather with the SC2's, the factory torsen diff had enough bias to slip one of the rears going around a corner with the clutch in at 25mph.

R2D2 · Mar 28, 2023

UNBROKEN said:

Yes they do. It should work even with wider tires installed. If I were you, I wouldn't close the air curtain, for safety reasons. (Imagine that added part come off and go and hit another car on the road)

But, Interesting experiment.
In a day to day use, I don't see any changes happening to mpg. More noticable change might be to the wind noice coming from the wheel well. Then again you might not notice it with all the other changes to your build.

We can't compare two vehicles (mustang vs st) for the aero. Entirely two different animals, when it comes to their performance in a wind tunnel.

R2D2 · Mar 28, 2023

2020FordRaptor said:

https://www.jdpower.com/cars/shopping-guides/what-is-an-air-curtain-on-a-car

UNBROKEN · Mar 28, 2023

R2D2 said:

The thought is the wider tire taking up the space where the air exits eliminates the usefulness of the air curtain to begin with. And I see no safety issues…nothing is coming off the car.
And I’d contend that we can compare since the air curtain is doing the same function no matter what car it’s on.

R2D2 · Mar 28, 2023

Agree that there will be a difference, but it will be too small to get noticed. When I worked on a electric vehicle body design, each teams used to make so many changes, to achieve a 20 point reduction in drag coefficient. That's 20/1000, like E.g. from 3.200 to 3.180.

As long as you are not completely closing off the wheel opening (like the rear tires areas of some old cars) there is space for the air to pass through and air curtain will continue to work. Especially, front wheels that needs lot clearance, to avoid rubbing, even when the wheels are fully turned and hit a pothole.

boiler662 · Mar 28, 2023

UNBROKEN said:

Obviously not an Explorer but you get the idea, no reason a similar setup couldn't be done to test this theory....

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