Will mud flaps adversely affect mpg?

alex_tdi

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May 15, 2001
Location
Los Angeles, CA
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TDI GLS, 2001, Blue
Hi,

Thinking about putting on front and rear mud flaps.

Would there be any aerodynamic effects? I'm not sure cuz it's low to the ground and right behind the wheels.

Bottom line is... would it affect my drag and thereby decrease my MPG?

Thanks.
 

MOGolf

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In theory there would be a slight increase in wind drag and increase in vehicle weight.

However, you probably wouldn't notice. Natural wind speed variance, your weight variance, your other load weight variance, the weight of the vehicle variance (as you use fuel it gets lighter), how many bugs are smashed on the front and windshield, how much dust and dirt are stuck on the car, etc., are more likely to affect your MPG.
 

OmegaMan

Active member
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Jul 8, 2001
Location
Honolulu, HI
My 9 year old niece has decided that "Mud-Flap" is her word for passing gas!

I suppose, if you hooked up some contraption in the driver's seat, you could use good healthy Mud-Flaps to INCREASE your fuel economy!
 

BratscheMan

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Oct 18, 2000
Location
Watertown, WI
TDI
none at present
Will mud flaps adversely affect MPG?

I suppose so--if you shred them up and put the fragments in your gas tank.
That would tend to clog the fuel filter, and you know it would not be very beneficial to mileage efficiency.


Also consider this--the amount of mud caked on the flaps would have to be factored in. Come to think of it--some of the Forum members who are getting tired of sending in oil analyses could scoop the debris off their flaps and get a chemical breakdown (maybe Turbo Steve would volunteer for this project). We could start a whole new topic and call it:

Getting the Real Dirt on the TDI
 

alex_tdi

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TDI GLS, 2001, Blue
You guys crack me up.


I just thought I was going to learn some aerodynamics theory... I know that I've learned a great deal of chemistry with all the synthetic oil discussions.

Alex
 

MOGolf

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Well if it is aerodynamics theory you want...

A properly installed mudflap will be positioned completely behind the tire (as viewed from the front of the car). As a result the coefficient of drag will not increase (as calculated by the vehicle manufacturer). I've temporarily misplaced the formula or I would post it.

Once you install the mudflaps, you will have to take your vehicle to a wind tunnel for testing. The facility must allow for the wheels to be spinning during the test. (Caution: you must have deep pockets of money for this as wind tunnel testing is very expensive. Most auto manufacturers don't even have their own. They share or rent time from an independent company.) In the wind tunnel testing, you must test for a change in the turbulence of the air around the spinning wheel/tire assembly. If an increase is found in the turbulence, then expect a decrease in the MPG for your vehicle.

Your individual vehicle must be tested since the slightest variance in position of installation will affect the results of aerodynamic change.

And one other thing: consider what you paid for this opinion. It may be worth exactly that.
 

BRUSSELS BELGIAN

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alex_tdi: Actually, on a serious note, I was asking myself the same queestion. But I think I am going to "play it safe" for my 70 mpg fuel economy run to Florida and NOT install them until after I get back. I know what the car can do now (66 mpg) and I am afraid I may start going down the back side of the efficiency curve if I fool around much more with the car
 

RabbitGTI

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I saw a TUV study on mudflaps years ago and the mileage penalty was less than 1% if I remember right. Put mudflaps on the front and they will prevent a gravel rash on your car. You don't need them on the rear. Another thing mudflaps can do is cause rust if you mount them by drilling your fender lips.
 
M

mickey

Guest
It might. But the fuel it costs you is cheaper than the paint the flaps protect!

-mickey
 
M

mickey

Guest
On the rare occasions when I venture into the netherworld of the Economy section I'm always reminded of one thing: You people are nuts!


-mickey
 

car54

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Location
Woodbridge VA
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man... someone once told me there is no such thing as a stupid question. this one takes the cake as the closest question to being stupid. God forbid you let your elbow extend out the window when driving with the windows down, or do you keep them up for fear of aerodynamic drag? how about the roads you drive on? do you choose smooth ones for less rolling resistance and more economy? Logic tells me taking a road 5 miles out of my way thats smooth to avoid 1 mile of bumpy road would be good for my mileage. keep up the economical thinking.
 

jhedrich

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I'm going to compile a list of obsessive compulsive TDI club members. I was going to make Skypup the leader, but I think I've found a new person to fit the bill!!

PS. I put mud flaps on my car and I'm lucky to get 20 mpg now. In fact, they produce so much drag that I can't get the car rolling if there is a slight headwind.
 

Kyanoti

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See, you're just thinking negative. Consider the 'sail effect.' When you've got a good tailwind, whip out those so-called splash guards and get even better MPG!

On a more realistic note, considering that a teardrop shape, with a round, bulbous end forward and a point to the rear, is the most aerodynamic shape, a splash guard could encourage the overall air flow to go past the wheel well and slide along the body of the car, only encouraging larger, heavier, possibly paint-damaging menaces into the wheel well. They would have to be installed close enough to the wheel itself to not actually interfere with the air flow, though...

Just one more example that reasoning can get you anywhere. PS: what sort of TDI do you have? You know that the Jetta has the lowest drag coefficient?

PPS: Did you know a Formula 1 car generates enough downforce with its aerodynamics that, at 100 MPH, there's more downforce from the wind than the weight of the car--theoretically, those things could drive on the ceiling of a tunnel, upside down! Now, if only we could apply those principles to minimizing drag on our cars...
 

RabbitGTI

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An average Formula One setup yields a drag coefficient of about 1.0 The average roadcar is about .3 to .35 The wings of a formula car can generate a ton of downforce at each end of the car, but in doing so they generate a tremendous amount of turbulence. Generating big aerodynamic downforce on a roadcar would result in a big fuel mileage penalty.
 

Ric Woodruff

BANNED, Ric went to Coventry.
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No. Mud flaps won't affect MPG one iota. Your tire block airflow to the mudflaps anyways, so ther won't be an additional air drag by them.
 

Driv'n EZ

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I tend to agree with Mickey and somewhat with Ric on this one. The paint that I protect with my four mudflaps is much more valuable to me than the extra spoonful of fuel per tank I MAY consume. Of course, I'm the guy who has no problem towing a 5x8 enclosed trailer with my Jetta TDI and am satisfied with 23 mpg at 72 mph.

As far as increased drag or turbulence, I'm sure there will be SOME increase, but not significant enough for me to detect a difference in my actual MPG figures. After all, the wind is already broken by the wheel. It's not like they are sticking out with no other front wind break.

Without the trailer and with mudflaps, I still achieved over 50 on my trip to Chicago this summer. So, in reality, I would say, "No" They do not affect fuel economy.

[ July 31, 2001: Message edited by: Driv'n EZ ]
 

GGFIII

Active member
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May 26, 2001
Location
Seattle, WA
Maybe the next "war" will be about what brand of car wax provides the lowest drag, and allows that extra 1/10 of a mpg.

I guess I will have to ignore my family and job, so I can get really involved in these important issues.
 

godlike242

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Aug 10, 2000
Location
Bellevue, Wa
well,

i have had mudflaps on for a while now, and the only change is that i have to wash the sides of the car less often than before.

the drag coeffient of a jetta is... .30, a golf is .31 and a bug is... .34 if i remember correctly.. they are all pretty decent i guess for their size and shape.

i suspect at anything less than triple digit speeds, the difference a mudflap makes is negligible. it is really not worth worrying about as quality resprays on cars will pay for a good year or two of fuel for TDI's.

The only problem i see with them is the asthetics.. if you have a light colored car, get 'em sprayed to match or they look really lame.
 

jorpet

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This reminds me of the old question (in the early '70's) on where to mount a water bottle on a bicycle. It was determined that mounting it on the seat tube increased the drag of the bike by 10%
and on the down tube by less than 1% (since it is in the turbulance of the front wheel).

Funny all bikes now mount them on the down tube...
 

fordfalcon

New member
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Jul 28, 2001
Location
NC
Maybe you should consider cross drilling and slotting the mud flaps. Not only will that reduce the drag, but also cut down on mass. You must take into account the added weight.
 

tommy37

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Nov 19, 2000
Location
Rockville, Maryland USA
Whatcha wanna do is, get a set of mudflap hinges. The VW part is made of genuine ABS plastic which won't crack unless something hits it. I forget the VW part number. The hinges allow the flaps to deflect upward out of the airflow as speed increases.

The EPA reported that these things have no effect. But it was a staionary test conducted in their own lab so it doesn't prove anything.
 

jetmann

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<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by tommy37:
Whatcha wanna do is, get a set of mudflap hinges. The VW part is made of genuine ABS plastic which won't crack unless something hits it. I forget the VW part number. The hinges allow the flaps to deflect upward out of the airflow as speed increases.

The EPA reported that these things have no effect. But it was a staionary test conducted in their own lab so it doesn't prove anything.
<HR></BLOCKQUOTE>ROFL!

Sign me up for four pairs! I'll put em on my bicycle and the wheelbarrow, too


Seroiusly, there would, of course, be an increase in drag, and corresponding decrease in mileage at speed if the mudflaps were traditional in shape and mount (perhaps as much a CDx of .02 and mileage differential of .002! These are serious numbers, folks!)

If however, the flaps were radiused along their major axis, and mounted in such a manner that the deflection were out, away from the car, instead of down, there would be several huge benefits!<UL TYPE=SQUARE><LI>1. Air would be vented away from the car, at speed, allowing enterprising modders to create another exit point for foul or hot atmosphere<LI>2. Downforce would not be compromised by the airfoil effect of the mudflaps<LI>3. Straightline stabilization would increase, due to the tremendous amount of atmosphere being vented outward from the sides of the vehicle<LI>4. Instead of dousing old lady and little kid pedestrians within 20 feet of that puddle, this mod will extend your target range to 90+ feet<LI>5. Indeed, you really needn't wait for a rain, gravel and other roadside debris becomes usable as projectiles, year around[/list]

Along with all these benefits, CDx would be lowered and potential fuel mileage raised, because atmosphere blasting out from within the car would create a partial vacuum next to the skin of the car, the degree of which would increase with vehicle speed, and through which the vehicle would be moving. The net effect of this would be to lower the density of the air through which the vehicle was moving, forcing a net decrease in CD, and increase in MPG.

BTW, does anybody in this forum possess a BSometer?


[ August 06, 2001: Message edited by: jetmann ]
 

Old Navy

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Location
Ozark Hill's in Missouri, USA
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None now, .
On my '00 NB the mud flaps are getting rather ragged from being draged over speed bumps and rain hup in my driveway at the street edge. I will have to go out tomottow morning and hit the bottom edges again to smooth them out. I'll bet in a years time I have scraped of at least a 1/2 inch of plastic.

bone stock white NB, running 42 PSI front & rear tires, and 8oz of Diesel Kleen with Amoco PowerBlend. Also have 15D throttle stompers for improved fuel consumption.
 
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