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Old 08-12-2022, 03:05 AM   #481 (permalink)
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https://mdpi-res.com/d_attachment/ap...ion=1649919194

New article study from March of this year showing that diffusers add drag slightly, but definitely increase downforce

Yet the Mercedes eqxx says their diffuser lowers drag

So confusing!!! No doughy across the board that diffusers increase downforce, but now Iím seeing mixed things about lowering drag. I donít care about extra downforce. Iím not taking mountain turns at 90 miles per hour or drag racing!

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Old 08-12-2022, 09:45 AM   #482 (permalink)
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Loosely: anything affects drag but some things affect body flow in a positive way by either diffusing that flow or blocking a higher drag thing with turbulent air. Problem with this concept: hard to model accurately even in large fast computers. Just gotta do it.
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Old 08-12-2022, 11:04 AM   #483 (permalink)
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Quote:
Originally Posted by Phase View Post
https://www.autonews.com/article/201...-in-other-ways

They are claiming my wheel skirts add drag lol
Ironically, the GM EV1 had rear fender skirts... to reduce drag.

Regarding the diffuser, it may or may not reduce drag. Depends on the application.
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Old 08-12-2022, 03:27 PM   #484 (permalink)
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Quote:
Originally Posted by Blacktree View Post
Ironically, the GM EV1 had rear fender skirts... to reduce drag.

Regarding the diffuser, it may or may not reduce drag. Depends on the application.
Yeah but that was back in the day. My wheel skirts bulge out a little but they reduce drag because they keep air flow attached and increase pressure in the wake. Smooth air flow is going to have lower drag than hitting a whole turbulent wheel well and detaching. So idk why they are saying that.

And now Iím confused about the diffuser part and it seems expensive now to try and do real testing to see if drag is reduced or not. Cardboard isnít going to hold up for a coast down or throttle stop test at super high speeds. And i donít think pressure gauges would show if drag is reduced and fuel economy is improved.
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Old 08-13-2022, 02:46 PM   #485 (permalink)
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Quote:
Originally Posted by Phase View Post
They are claiming my wheel skirts add drag lol
Not exactly. They are claiming:

Welburn said pulling the body out, essentially widening the body where the rear tires are located, increases aerodynamic drag.

To widen the body at the rear to accommodate skirts without making compromises to the rear tires or rear track, would introduce a pressure spike in the turbulent airflow zone. This should add drag in most cases.

If the skirts are flush with the body and don't bulge out, generally they should reduce drag.

For a front drive car, I don't see why they'd be an issue regarding rear tire size or rear track width. Having narrower tires in the rear or a narrower track in the rear shouldn't adversely effect the performance of a front drive car given that the important tires are up front and can be as thick as needed.

For an AWD vehicle, having a rear track more narrow than the front track also isn't much of an issue, especially if the vehicle is electric and has the ability to do near-instantaneous slip detection.

It is rear drive layouts where they can be problematic. BUT if you design both front and rear track to be sufficiently narrow that both front and rear wheel skirts can be accommodated, then this shouldn't be an issue either.
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Old 08-13-2022, 04:26 PM   #486 (permalink)
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Cardboard isn’t going to hold up for a coast down or throttle stop test at super high speeds.
You need better cardboard.

Triple-wall corrugated painted with Copal varnish. Drifter stitched with Zip ties.
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Old 08-14-2022, 03:44 PM   #487 (permalink)
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Quote:
Originally Posted by The Toecutter View Post
Not exactly. They are claiming:

Welburn said pulling the body out, essentially widening the body where the rear tires are located, increases aerodynamic drag.

To widen the body at the rear to accommodate skirts without making compromises to the rear tires or rear track, would introduce a pressure spike in the turbulent airflow zone. This should add drag in most cases.

If the skirts are flush with the body and don't bulge out, generally they should reduce drag.

For a front drive car, I don't see why they'd be an issue regarding rear tire size or rear track width. Having narrower tires in the rear or a narrower track in the rear shouldn't adversely effect the performance of a front drive car given that the important tires are up front and can be as thick as needed.

For an AWD vehicle, having a rear track more narrow than the front track also isn't much of an issue, especially if the vehicle is electric and has the ability to do near-instantaneous slip detection.

It is rear drive layouts where they can be problematic. BUT if you design both front and rear track to be sufficiently narrow that both front and rear wheel skirts can be accommodated, then this shouldn't be an issue either.
My rear wheel skirts buldge out though, like little bubbles. But they maintain attached air flow
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Old 08-14-2022, 07:04 PM   #488 (permalink)
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A properly designed skirt (no reflection on yours) will have an agressive leading edge, shroud the tire to the limit of breakover and departure angles and extend rearward to the separation edge.


https://kustomrama.com/wiki/Fileick-bailey-dreamboat.jpg

Ignore the side pipes. That's like wearing an onion on your belt, just something they did back in the day.
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Old 08-14-2022, 09:20 PM   #489 (permalink)
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Quote:
Originally Posted by freebeard View Post
A properly designed skirt (no reflection on yours) will have an agressive leading edge, shroud the tire to the limit of breakover and departure angles and extend rearward to the separation edge.


https://kustomrama.com/wiki/Fileick-bailey-dreamboat.jpg

Ignore the side pipes. That's like wearing an onion on your belt, just something they did back in the day.
yeah my side skirts have the bigger bubble in the leading edge and then are smoother and less curved going back. they are not perfectly symmetrical and even
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Old 08-15-2022, 11:42 AM   #490 (permalink)
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diffuser drag

Quote:
Originally Posted by Phase View Post
https://mdpi-res.com/d_attachment/ap...ion=1649919194

New article study from March of this year showing that diffusers add drag slightly, but definitely increase downforce

Yet the Mercedes eqxx says their diffuser lowers drag

So confusing!!! No doughy across the board that diffusers increase downforce, but now Iím seeing mixed things about lowering drag. I donít care about extra downforce. Iím not taking mountain turns at 90 miles per hour or drag racing!
On page-22 they comment:
' for angles lower than 8-degrees the improvement in aerodynamic drag can reach up to 2.5%.'

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