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Old 06-07-2022, 12:59 PM   #321 (permalink)
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Originally Posted by aerohead View Post
1) While you're experiencing a 'trend' in the data, the test methodology isn't rigorous enough, nor data points of sufficient extent to enable the use of the mathematics.
2) Coastdowns must be conducted just as proscribed in the SAE Handbook.
3) Every rotating component in the car must be quantified for moment of inertia, or estimated according to SAE instructions.
4) You need your own weather station, or, perhaps timely AWOS ( automated weather observation service ) updates from a local airport, adjusted to raw barometer. ( I paid CAR and DRIVER road warriors to test my CRX at the Chrysler Proving grounds for top speed, and coastdowns. They threw in skidpad testing for free ). Chrysler has a sheltered straightaway, designated specifically for coastdown testing. Cost was equivalent to 1-hour in a wind tunnel, in 2014-2017 dollars ( DARKO or A2 ).
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5) We don't know what happens to the IONIQ's engine BSFC when the cars' drag is reduced at a constant test speed.
6) We don't know anything about it's actual rolling resistance.
7) We don't actually know if it's published Cd was @ radiator shutters fully-closed, zero-yaw, crosswind-averaged, etc.. We do know that the wheels were rotating in the wind tunnel.
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8) MPG data would only help, fully-warmed, at a constant speed, without any hybrid function, in both directions, just the engine operating at a constant speed, with weather monitoring. And at an accuracy you're comfortable with.
Yeah it’s really hard to do some of these tests in the real world in crowded places. Wish I had a test track but nope

Sure the data points were limited and the test was quick

But all I can say is the car did feel smoother and more stable, acceleration felt slightly faster, barely, when I put the car in sport mode and stomped the pedal to the metal to get up to speed as fast as possible, and wind noise went down a little bit. Obviously these aren’t reliable data point, but the car felt like it glided a little better even within those few minutes of driving with the skirts on. I’ve put 107k miles on my Ioniq in 2 abs a half years. I practically live in it. So I know how it feels. It’s like an extension of my body. It definitely felt different with the skirts on. I would have left them on the remainder of the road trip, but I didn’t want to risk possibly getting pulled over for cardboard skirts from a cop that’s in a bad mood or possibly ignorant. Was already driving without side mirrors and “ technically illegal” tinted windows. I want to fabricate the metal and permanent black rear wheel skirts though this summer. Just really hard to tell how much it helped mpg

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Old 06-09-2022, 11:10 AM   #322 (permalink)
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hard to tell

The only comfort I can provide is that, since 1974, I've never experienced any document supporting the notion that adding rear skirts could ever INCREASE drag, only the opposite.
If you choose to do any elongation at all, the skirts will be part of your insurance policy, delivering a healthy onset flow, a prerequisite, if any downstream pressure recovery is to be expected.
Even without elongation, you're limiting turbulence, which is pure entropy. 'Poison' to mpg.
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Old 06-09-2022, 06:40 PM   #323 (permalink)
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The only comfort I can provide is that, since 1974, I've never experienced any document supporting the notion that adding rear skirts could ever INCREASE drag, only the opposite.
If you choose to do any elongation at all, the skirts will be part of your insurance policy, delivering a healthy onset flow, a prerequisite, if any downstream pressure recovery is to be expected.
Even without elongation, you're limiting turbulence, which is pure entropy. 'Poison' to mpg.
i agree that they cant hurt. i think car designers have gotten a lot better at limiting the drag that occurs from the back wheels versus decades ago. so wheel skirts still can give improvements, just not as big as on an older model car. for instance, the light year one car says the wheel skirts can be optional and only provide 15 extra km of range. or about 10 miles. thats barely anything, but its something! im definitely going to go thru with the rear wheel covers, and then after that i can actually add a mini box cavity flare thing coming off the back of it to creat a separation edge at the lower part of the car. ill post mock up pics when it stops raining and i can tape them on. right now im trying to reduce the sound of wind noise where my side mirrors were but since took them off
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Old 06-10-2022, 12:43 AM   #324 (permalink)
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image i found of the hybrid ioniq i have versus the EV version and its rear diffuser, incase that helps anyone. interesting image
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Old 06-10-2022, 01:05 AM   #325 (permalink)
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One notices the EV has a downsized cooling system, but it needs no exhaust at all.

That profile with the Automobilemag watermark over it seems to be what works for the front (see EcoVan's thread), but it seems a little steep for the rear.
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Old 06-10-2022, 02:00 AM   #326 (permalink)
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One notices the EV has a downsized cooling system, but it needs no exhaust at all.

That profile with the Automobilemag watermark over it seems to be what works for the front (see EcoVan's thread), but it seems a little steep for the rear.
i agree. it looks way too steep. wonder why hyundai would do that. obviously my diffuser will be more gradual since i need to have clearance over the muffler and will be extending my rear diffuser out past the rear bumper by about a foot

its interesting how the prius and corolla hybrids both have rear diffusers already built in under the car, and side skirts, yet the ioniq doesnt use any. dont know if it was ignorance with hyundais development team or just budget costs or styling... no idea
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Old 06-10-2022, 09:32 PM   #327 (permalink)
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bonneville ioniq using front air dam, while hyper mod uses splitter. both use some type of minor side skirt...

both lowered

bonneville even taped up the cracks and door handles...

only aero mod i dont get is the rear hyper spoiler. its pretty much an air brake being that steep
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Old 06-10-2022, 09:45 PM   #328 (permalink)
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Wickerbill, or Gurney Flap. It's a vortex generator, a small-scale localized feature that 'pulls the air around a corner' to reduce the size of the wake.

Vekke's Solidworks CFD thread shows that a reflex curve can have similar effect.

I'm favoring the splitter for my XFi. I have a blank cut out of 1/8" ABS for when the motivation strikes.
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Old 06-10-2022, 09:54 PM   #329 (permalink)
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Wickerbill, or Gurney Flap. It's a vortex generator, a small-scale localized feature that 'pulls the air around a corner' to reduce the size of the wake.

Vekke's Solidworks CFD thread shows that a reflex curve can have similar effect.

I'm favoring the splitter for my XFi. I have a blank cut out of 1/8" ABS for when the motivation strikes.
ideally id like to extend my spoiler down and out a little farther to reduce wake size, then the last few inches, flip it up gurney style

julian was always saying in his videos to avoid front splitters because you want air to flow under the car if its got a smooth underbody. so confusing!
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Old 06-10-2022, 11:22 PM   #330 (permalink)
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Likely either misquoted or wrong misspoken?

What do you think of the clear plastic tailfins and wing on his Insight?

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