Side mirror drag & effect on fuel economy - quantified

[stevet47]

It certainly isn't going to pull your car to one side. It would be like sticking your hand out the window and expecting that you pull your car to the side...it just wont happen.

And folding it in should be better for aero then leaving it alone as long as folding it doesn't create an ugly open area in the front that will trap the air and create turbulence.

[Eddles]

Originally Posted by ojman873

This is my first post here and I wanted to express my appreciation for all the valuable and useful tips and hints posted throughout the site from all of you.

I had a few questions regarding the mirror topic. I have folding mirrors on both sides of my 4-door 2007 Hyundai Accent GLS. I was considering folding in the passenger side one after having read about the FE/aero benefits. But are there any negative effects resulting from lopsided airflow when only one mirror is extended? For instance, might the car pull to one side or something? Also, is folding in just the passenger mirror better for FE/aero than not doing anything at all? What I mean is could the uneven airflow somehow have a negative FE effect? I appreciate any input. Thanks.

OJ

Don't worry too much about it. In the UK, side mirrors were optional on most cars until the late 80's. I grew up with my dad's old Nova, a B-reg one (1984) and it didn't have a passenger side mirror at all. His next Nova, a K-reg one (1993) had a passenger side mirror and that was novel!

Look at this A-reg Nova (1982) and you can clearly see that it doesn't have a passenger side mirror.

[ojman873]

Thanks for the input!

[mrk]

Hi guys,

Maybe you are interested in some aero tests done to mirrors
check here --> http://www.racemirrors.com/engineering.html
The idea is using an aerodynamic shape but also to add a clear attachment to the mirror, in order to reduce back area (as kammback does)
I think this attachment must reduce Cd in all mirrors, and also it is good for DIY and it may be done in many cases
Worth trying?

Cheers,
Mrk

[Frank Lee]

Here's that article that had the comment about '94-up Chevys having more aero drag with the mirrors removed: Car Aerodynamics - Hot Rod Magazine

I trust the article cuz the aero guy has good credentials.

[tasdrouille]

Originally Posted by Frank Lee

Here's that article that had the comment about '94-up Chevys having more aero drag with the mirrors removed: Car Aerodynamics - Hot Rod Magazine

I trust the article cuz the aero guy has good credentials.

I will quote the article...

The '94-up Chevy Impalas and Caprices are notable exceptions; on those cars, the Cd actually gets worse when you remove the mirrors.

lets read that again, but just the interesting part...

the Cd actually gets worse

What is aerodynamic drag? CdA. The Cd can be higher, but that doesn't mean the drag forces go up overall. Mirrors are more or less 5% of the frontal area. On a .30 Cd car that's a 15 points Cd increase needed to offset the gains from the reduction in area.

[Frank Lee]

That is a good point. It would have been helpful if they'd given more detail.

Still, given the context (most likely, racing or pursuing and top speed) and the desire to put things in layman's terms, I'm guessing the CdA was taken into account for that comment and the car remains better off with.

[dwtaylorpdx]

The reason the caprice mirror nets a loss when removed is the mirror reduces the laminar flow across all those window edges and gaps behind it. I used to own one and I got the mirror broken in a parking lot, I immediately noticed the wind noise and the difference is where the sides got dirty. If you fabricated small gasket areo parts over each glas and window frame transition it might make a difference ?

YOu can see this on most cars if you take some grease like teh red wheel bearing grease and place small bb sized globs over teh area you want ot see the wind flow on and do a quick freeway run on a reasonably hot day, the grease will get streaked down the car according to the wind currents.

Looks aero is not always aero.

Dave

[j12piprius]

Originally Posted by mrk

The idea is using an aerodynamic shape but also to add a clear attachment to the mirror

Also a good idea for a car, instead of having a long tail.

[aerohead]

Originally Posted by tasdrouille

I will quote the article...



lets read that again, but just the interesting part...



What is aerodynamic drag? CdA. The Cd can be higher, but that doesn't mean the drag forces go up overall. Mirrors are more or less 5% of the frontal area. On a .30 Cd car that's a 15 points Cd increase needed to offset the gains from the reduction in area.

I won't be able to put my hands on it anytime soon,but in the past it has been reported that the EPA ignores mirrors and their frontal area in certification of new cars.
If the Cd reflected the drag of the mirrors,it would skew the CdA of the car,as the CdA would be figured on the smaller frontal area of the car sans mirrors.
It's kind of a book-keeping foible.I'll try and dredge that up.