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Old 03-27-2009, 10:57 AM   #1 (permalink)
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Fender flares, instead of wheel well covers?

Would a set of fender flares help improve highway mpg or create down-force and make it worse? I noticed on the top gear car they held up some flares and said more mpg, but I didn't follow up to see if that would help or if it's more worth-while to just make full wheel well covers.

Any input on this?

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Old 03-27-2009, 01:19 PM   #2 (permalink)
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Drive Stick -

The fender flare will increase frontal area. Unless it's covered to help the air flow over the tire, it won't "pay" for itself, aerodynamically speaking.

IMO, (shallow) fender flares can probably make a good "mount system" for wheel skirts.

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Old 03-27-2009, 03:21 PM   #3 (permalink)
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bad, unless they look like this:
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Old 03-27-2009, 03:36 PM   #4 (permalink)
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The answer to your question can be found in all the low drag vehicles with open wheel wells. You won't find flares on the bodywork (not counting spats to direct flow around the tread face of the exposed tire).

I expect someone may chime in here with the example of the newest Prius bumper bodywork ahead of the front wheel arches, which is claimed to help. I'm on the fence on that one until I can learn more about it. But it's not really a flare - definitely doesn't increase frontal area.

The flares on the Top Gear Rabbit may get air away from the tread face of a wider tire, but I bet you a donut the flow behind the aft edge of the arch is a mess.

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Old 03-27-2009, 05:15 PM   #5 (permalink)
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i suppose flares MIGHT help IF the increase in frontal area is compensated be the reduction in drag.... i'm not sure if that's mathematicly possible, because frontal area is more important than Cd in cda... that is, nocking off a mirror is easier than reduceing your Cd by 0.01...

however on some cars the bodywork curves in near the bottom and exposes some of the tires
like this

in this case "fender flares" down there won't really add frontal area!

here's another thing to think about

the toyota IQ... 0.299 Cd... those bumps are there for a reason

i think a lot depends on what happens before the fenders... older more square cars, or cars with a shorter nose, might have less attached flow before the wheel arches so perhaps there these flares might help somehow....

just some guesses though.
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Old 03-27-2009, 05:58 PM   #6 (permalink)
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This is my issue:



In order to remedy this I'd really have to cover the lower portion of the entire front bumper and bring it down at the correct angle to block the lower grille, and extend the sides out to where the tire is no longer directly in the wind. This would help a lot, but obviously would look rough since I'm no fiberglass expert.

Hmm..
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Old 03-28-2009, 07:50 AM   #7 (permalink)
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Anybody see this as a problem? Also if I were to block my front grille opening (lower portion) and make something to push air outward around the front wheels would I see increased mpg possibly?
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Old 03-28-2009, 01:04 PM   #8 (permalink)
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flares

Hucho's book addresses this issue.I believe a one-size-fits-all reply wouldn't apply here.Each vehicle will be different,some will gain,some will lose.Cardboard, duct tape, a Scan-Gauge or tank mileage would tell for your car.
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Old 03-29-2009, 12:10 AM   #9 (permalink)
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Some cars have their fenders set up to deflect air around the wheel wells.

Flares would make sense if they're more aerodynamic than the tire and wheel well. The problem with having a flare direct air around the front of the tire is you also have a flare at the back acting like a parachute. So how about a half flare?

More frontal area doesn't necessarily increase drag. In this case the wheel wells could be causing airflow to fan out or at least become turbulent. You can have an object sticking into airflow that makes a huge wake behind it, but it's not apparent in frontal area calculations.
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Old 03-30-2009, 12:00 AM   #10 (permalink)
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I'd say no on the flares, lowering your car and exposing less tire would certainly help. 2" lower would get rid of about 40% of your visible tire from that front view...

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