Do rain gutters increase drag?

[ronallandottk]

You know what I'm referring to, those plastic deflectors mounted on the tops of our vehicles' side windows.

In other markets, they call them rain guards, vent visors, or window deflectors. Here, I think we typically call them rain gutters.

We all know that increasing wind resistance and drag can significantly increase fuel consumption, especially when traveling at highway speeds.

My question is, do rain gutters increase drag?

I tried researching this but I came up with conflicting results. It seems no one has bothered to measure the aerodynamic effects of rain gutters.

http://www.car-stuff.com/acuraventvisor.htm

Vent visors are basically considered as a type of spoiler, working to improve the aerodynamics of the automobile for higher acceleration and easily reaching top speed. Their shape reduces wind drag, aiding then to achieving better fuel mileage.

http://www.expeditenow.com/news/publ...s_AirTabs.html

To reduce air resistance and drag, the first thing you need to do is eliminate anything you can which causes resistance in the first place. Side mirrors and the brackets cause quite a bit of resistance, but you don’t want to remove those. An exterior sun visor is a major factor in wind resistance, and many people have removed it for that reason. I installed a bug shield and side window rain guards on my Sprinter and noticed an immediate hit on fuel mileage, which didn’t come as a surprise. The surprise was just how big a hit it was – more than half a mile per gallon. The Sprinter’s front end is pretty streamlined, so it didn’t take much to mess it up.

What do you guys think? Rain gutters look cool and all, but if they ruin a car's aerodynamics, then they may not be worth it.

[1D4LV]

You know what I'm referring to, those plastic deflectors mounted on the tops of our vehicles' side windows.

In other markets, they call them rain guards, vent visors, or window deflectors. Here, I think we typically call them rain gutters.

We all know that increasing wind resistance and drag can significantly increase fuel consumption, especially when traveling at highway speeds.

My question is, do rain gutters increase drag?

I tried researching this but I came up with conflicting results. It seems no one has bothered to measure the aerodynamic effects of rain gutters.

http://www.car-stuff.com/acuraventvisor.htm

Vent visors are basically considered as a type of spoiler, working to improve the aerodynamics of the automobile for higher acceleration and easily reaching top speed. Their shape reduces wind drag, aiding then to achieving better fuel mileage.

http://www.expeditenow.com/news/publ...s_AirTabs.html

To reduce air resistance and drag, the first thing you need to do is eliminate anything you can which causes resistance in the first place. Side mirrors and the brackets cause quite a bit of resistance, but you don’t want to remove those. An exterior sun visor is a major factor in wind resistance, and many people have removed it for that reason. I installed a bug shield and side window rain guards on my Sprinter and noticed an immediate hit on fuel mileage, which didn’t come as a surprise. The surprise was just how big a hit it was – more than half a mile per gallon. The Sprinter’s front end is pretty streamlined, so it didn’t take much to mess it up.

What do you guys think? Rain gutters look cool and all, but if they ruin a car's aerodynamics, then they may not be worth it.

of course they ruin a car's aerodynamics, for if they don't they would come as stock.

imho, the drag that they may cause could be insignificant for everyday driving. but could be significant if you are on a track, and microseconds really mean a lot.

which reminds me... i have to look for rain gutters for my B14....

[vernieg]

At speed beyond 40kph, you'll start hearing wind resistance and if you travel at an average of 60kph most of the time, significant na ang effect ng drag.
If these deflectors have similar design to vortex generators at its rear part, this will help lessen the air drag but I don't see one on the market. You have to make your own design to minimize air resistance.

[alwayz_yummy]

question is: do you race everyday? if so...forget that window visor....

gusto ko ung most OEM design kasi di masyado malaki ang buka unlike those mga aftermarket brands na malaki ang opening...pero ang OEM kasi ay 2x the price ng aftermarket ones...

[CVT]

OT: Never used one (although freebie ito ng 2 car purchases namin recently,- just replaced it with another freebie)... Palagi naman kasing nakasara ang car windows namin (at naka aircon).....

IMO,- negligible ang drag attributable to this, sa tipo ng city driving natin dito.

9000:snowfight1:

[ronallandottk]

question is: do you race everyday? if so...forget that window visor....

gusto ko ung most OEM design kasi di masyado malaki ang buka unlike those mga aftermarket brands na malaki ang opening...pero ang OEM kasi ay 2x the price ng aftermarket ones...

No, I don't really race...the question was more aimed at reducing drag to increase fuel economy, particularly at highway speeds (80+ Kph).

The reason this questioned popped into my head is because I recently took my week old 1.2 i10 on a 150 Km trip to break-in the engine (as well as other stuff). I was pleasantly surprised because it was pretty stable and wind noise was quite low despite 120+ Kph speeds, even though this is supposed to be a city car. I've driven a B12 and B13 Sentra at about the same speed before, and they were well planted on the road as well, though wind noise was quite higher (especially with the B12) with whistling sounds, especially around the side view mirrors and the radio antenna. I even remember an even older Ford Laser hatchback not only created a lot of wind noise, but also tended to weave left and right at high speed.

It turns out the i10 has a respectable coefficient of drag, 0.325, and the roof mounted OEM spoiler seemingly helped in reducing turbulence coming off the top of the hatch at high speed.

It was fitted with OEM rain gutters as well (casa freebie), which were pretty slim, not that much different from the pictured OEM gutters on a Civic.

Incidentally, the up and coming 2010 Mazda 3 supposedly has a .29 Cd. It would be a shame to ruin the aerodynamics of a slippery shape all because of an ill-designed rain gutter.

So I guess the consensus is that rain gutters either increase drag minimally, or even actually improving aerodynamics mildly. So along with the other benefits such as allowing you to open the windows slightly at speed or while parked in the sun, rain gutters should be reasonably useful.

[vernieg]

if ok lang sayo may nakadikit na vortex generators on your car, a similar setup like the airtabs can really help reduce drag at that speed.

http://www.airtabs.com/en/

some info on diy vortex generators:
http://www.gassavers.org/archive/ind...40/t-1482.html

No, I don't really race...the question was more aimed at reducing drag to increase fuel economy, particularly at highway speeds (80+ Kph).

[ericp]

Drag... a little bit...at high speeds.

But I like them because I can park my car with windows
partly open....cools the cabin especially when parked under the sun.

[cktlcmd]

To be honest...I only like rain guards for only one reason...so I can leave a small opening on all 4 windows when parked under the sun. I don't think there's any other use for them aside aesthetic appearances.

Ohhh....YES they do produce drag...but I would still use it for the reason above.

[oj88]

OEM visors have negligible impact on drag. In fact, Mugen (a Honda aftermarket parts manufacturer) makes them to provide aerodynamics and cabin ventilation for the Civic, including the Type-R.





This is what I have... also OEM.