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ccm302 01-02-2013 11:13 AM

Improved Aero by Lowering
 
So, I've read and heard where people who lower there cars get improved gas mileage...especially bricks like Jeeps and whatnot. And I know this has probably been beat to death...but I'm curious as to whether or not lowering my DD ('02 SVT Focus) would yeild any improvements in gas mileage. I know the Focus isn't exactly a brick like some vehicles, but I figure going a little lower and maybe a rear diffuser (and maybe a belly pan) would help out some. but i'm not sure the cost and amount of effort is worth the ROI. I would say my cutoff for it being worth my time would be a consistant 1.5mpg+ increase. But, I may would accept a little less.

So, anybody done this to their '00-'04 Foci and seen improvements?

Cobb 01-02-2013 12:47 PM

I lower all the vehicles I own. Its mainly for performance in regards to cornering, but the mpg is an added bonus. :thumbup:

ccm302 01-02-2013 01:47 PM

Quote:

Originally Posted by Cobb (Post 348258)
I lower all the vehicles I own. Its mainly for performance in regards to cornering, but the mpg is an added bonus. :thumbup:

How much do you usually gain with lowering your vehicles?

mcrews 01-02-2013 01:49 PM

Concider a body kit first.
The sacrifice in ride quality is not really worth it.

NeilBlanchard 01-02-2013 01:51 PM

I doubt that lowering a car will have any noticeable effect on the FE. You can do several things to reduce aero drag, but lowering really won't matter.

ccm302 01-02-2013 02:13 PM

Quote:

Originally Posted by NeilBlanchard (Post 348283)
I doubt that lowering a car will have any noticeable effect on the FE. You can do several things to reduce aero drag, but lowering really won't matter.

In a past life (college), I was mechanical engineer with a sort of minor in aerodynamics. Unfortunately, all of my days were limited to the theoretical as opposed to actual :( Hence my original question...since I never really got to do any research on such things. I used the jeep (SRT8 in particualr) as an example because several people reported that getting that floating brick out of the air with a couple inches of drop actually increased FE by as much as 2mpgs. Seems ridiculous, but numbers don't lie.

CigaR007 01-02-2013 02:21 PM

Well, theoretically, lowering the car will reduce frontal area and improve the fineness ratio of the vehicle. The resulting effect on fuel economy will depend on the vehicle and its design. An SUV/Pickup will benefit more whereas smaller, more streamlined cars will net lower gains.

A good set of progressive springs coupled with a good set of shocks can also minimize the decrease in ride quality.

Sven7 01-02-2013 02:52 PM

I'll go out on a limb and say 2mpg from lowering a Jeep (any Jeep) is nonsense. That's a 13% increase in FE (from 15mpg) which would mean you'd need a 26% aero improvement at 55mph. A couple inches of tire are not going to be the difference in frontal area or Cd to pull the FE up that much.

If you want to lower your car, buy some high quality coilovers. It'll be much more fun to drive than stock and it'll look better. But suspension parts are expensive so don't expect a ROI.

LeanBurn 01-02-2013 02:59 PM

I lowered my Corolla, not a lot but by less than 2 inches with TRD factory backed springs. I didn't see any really noticeable improvement in the FE department. Perhaps it did in some small way, but my car has already decent Cd. It did improve highway stability, city handling as well as cross wind manageability which for me increased driver comfort.

Cobb 01-02-2013 03:46 PM

Well, to each his own. You can cut your springs for free to test it out. If you dont like it get some from the bone yard.

The past few vehicles ive lowered it was up to 5 mpg. I lowered my sidekick and also went up 3 tire sizes, luckly I am at the same mpg in the end. :thumbup:

I use either eibach or tanabe springs. The nfs are good for lowering and firmness, df will let the car bottom out and ride the bump stops.

As for best bang for your buck for instant mpg increase, just block off your radiator. :thumbup:

wungun 01-02-2013 06:27 PM

SVT Focus...nice. I have one of those!
But I converted it over to the Euro only RS Focus model...and with the bulging fenders and gaping grill, and 225 tires, it's probably a step in the wrong direction as far as aero is concerned (I know for a fact the drag is higher than a regular Focus hatchback).

But having the engine tuned (for performance) Also gave noticeable gains in mileage.
There are a couple of really good tuners you can talk to on the popular focus forums which would be happy to sell you a flasher with a custom tune...One of which, offers free upgrade tunes if you happen to change somethings like throttle body, exhaust, filter, etc.

NeilBlanchard 01-02-2013 10:58 PM

Lowering a vehicle will only decrease the frontal area a tiny bit - only the area of the wheels gets reduce by the reduction in height. If you drop the car an inch, then the width of two tires; say 8" X 1" X 2 = 16 sq in. The Cd is not likely to change one iota; or it might even increase the Cd because it compresses the air under the car somewhat.

If the vehicle frontal area is 25 sq ft and it has a Cd of 0.35 then the CdA is 8.75 sq ft. Take away the 16 sq in and the CdA is 8.71 sq ft - a net improvement of 5.76 sq in.

If you install video mirrors in place of both side mirrors, you reduce the frontal area by about 80 sq in *and* you reduce the Cd by say 0.03 or so. The resulting CdA is 8.482 sq ft - net improvement of 38.56 sq in which is 6.6X better than the lowering.

With a good grill block, smooth wheel covers, rear wheel skirts, a smooth bellypan, a partial Kamm back, and the video mirror swap, you could drop the Cd to 0.31 or so? That would be a CdA of 7.58 sq ft - a net improvement of 168.8 sq in which is 29.3X better.

wungun 01-02-2013 11:02 PM

You're not taking into account the lesser amount of air going underneath the car...
Similar effect to having a dam.

GRU 01-02-2013 11:19 PM

I gotta say, less air going under the car doesn't make it any better when it comes to fuel economy...turbulance is turbulance, weather it's 5" or 3" it's not much of a difference...there is a bigger benefit if you can "clean up" the turbulance because when you look at the best, most aerodynamic cars ever made, arn't slammed to the ground

NeilBlanchard 01-02-2013 11:24 PM

I am "taking that into account". Lowering a car too much actually increases the Cd because there simply isn't room for the air to move around, and with a typical rough and lumpy and crevassed underside, this can cause some additional drag. You want the air to flow easily and smoothly, and moving vehicle is "squishing" the air around and the lower the vehicle, the less space there is for this to happen.

With a smooth underside then air is not as turbulent and the reduction in Cd is way greater than the reduction in area from lowering. Ideally, the rear of the underside is a slightly rising slope, and the ideal minimum is about 6-8" of clearance. Less clearance compresses the air more and causes lift - which is drag. A air dam adds frontal area and increases drag; though it reduces lift or even adds downforce - which is also drag. A smooth underside negates the need for an air dam and it reduces turbulence.

A smooth belly pan will be a much bigger improvement than lowering the car.

Edit: to emphasize GRU's point, look at the Schlörwagen. In the Hucho book, they have a chart showing the Cd at various heights - the *higher* it was the Cd went down (but this adds to the frontal area, and there was exponentially diminishing returns above a certain height). Lowering the car added Cd - more so with a rough underside. The best compromise with a smooth underside was with about 6" of minimum clearance.

wungun 01-02-2013 11:37 PM

You're just being argumentative...
And only speaking half truths.

Isn't enough room for the air to move around?
We are trying to prevent air from going under the car by lowering!

Squishing the air? Really?
We are lowering the car, not just lowering the rear and creating a wedge shape under the car...

A smooth underside that raises towards the rear causes low pressure, pulling the car down, and of course, increasing drag...

I'm sure each car is going to be different in the results, but generally, lowering helps.

Check this out...apparently it's been posted a few times! Lol....

Car Aerodynamics - Hot Rod Magazine

NeilBlanchard 01-03-2013 12:01 AM

Have you looked at the Hucho book? Would lumps and bumps on the sides or top be good for drag? Would shielding lumps and bumps on the sides or top help anything? The ground and the spinning wheels makes the underside into a special case, and turbulence there is amplified by the proximity to the ground.

If there is adequate ground clearance and the underside is sloped up, then this allows the air to flow back under the car, and the pressure at the back bumper can be a closer match to the sides and the top. This greatly reduces turbulence in the back - which is the single greatest cause of drag.

An air dam that is lower than any part of the underside greatly increases drag. An air dam is a kludge solution for lift and/or a rough underside.

I'll take the Schlörwagen any day over a Camaro, by the way.

wmjinman 01-03-2013 12:23 AM

During the few years I was making my pathetic attempts at Bonneville Salt Flats, I had the extreme pleasure of becoming friends with Tom Burkland, former piston powered, wheel driven land speed record holder at Bonneville (417 mph in a twin engined, 4 wheel drive streamliner, reaching 450 mph in one pass - an all time, piston powered, wheel-driven record speed). When discussing my poor pathetic efforts with him, his advice was to chose:

either slam the car down as close to the ground as you can (with a front air dam that also almost drags the ground) - the idea being to try to keep as close to ALL the air out from under it as you can,

or;

streamline the underneath with a belly pan just as smooth and aero as the top & sides.

Now, at Bonneville, there are rules out the ying-yang, and as I soon discovered, all the stuff that would REALLY help was also illegal! :mad: The car I was driving (actually, the CLASS I was in) did not allow belly pan streamlining. Therefore, the consensus was to get it as low to the ground as I could. HOWEVER, Tom's streamliner was allowed to have streamlining anywhere and everywhere, so he did the belly pan. (and it was pretty low, too). As I recall, if you have a choice, do the belly pan. Lowering is just the best you can do if you're not allowed a belly pan.

So after all that, I think I would have to concur with those who say "do the steamlined belly pan & you'll get more". Lowering should help too, but it's a weak, second-place choice. (The car in the Hot Rod article was in a class similar to mine, where belly pans were NOT allowed, too)

wmjinman 01-03-2013 12:45 AM

This same Tom Burkland I just mentioned (who also happens to be an aeronautical engineer in his "day job"), designed and built a "competition coupe" before he got into the streamliner project. Interestingly enough, this old competition coupe was bought by a guy here in Carson City who still races it. When I learned the aerodynamic design of it (and I was allowed to lay down next to it and look at the bottom), it just blew my mind. Tom designed it as an upside down wing!! It's higher from the ground at the tip of the nose, then slopes down closer in an airfoil curve to a minimum somewhere underneath, then back up towards the tail. Tom's theory; downforce without drag (or any more drag than a wing).

I just couldn't believe it. "What about the air you're compressing underneath?!?!?! You've GOTTA be causing LIFT!" Not so. The air accelerates under the car just like it would over a wing, producing a low pressure area under there. "But what about the air 'trapped' between the car and the ground?" I asked. The answer: no air is "trapped" - it's flowing under there, and the ground is just the opposite side of the venturi throat. It has to accelerate, causing the pressure to DROP. At about that time, my poor little brain began to smoke and I had to stop thinking!!!!

But it worked. Dan (Dan Webster, the car's current owner) routinely holds multiple land speed records with that car powered by vintage flathead Fords. I think he's right at 200 mph. And when Tom Burkland was racing it, he was hitting 300 mph with small block Chrysler engines. Weird, huh?

So the lesson I learned: Aerodynamics is a lot more complex than I thought it was!! LOL!!

serialk11r 01-03-2013 01:17 AM

Quote:

Originally Posted by wmjinman (Post 348501)
This same Tom Burkland I just mentioned (who also happens to be an aeronautical engineer in his "day job"), designed and built a "competition coupe" before he got into the streamliner project. Interestingly enough, this old competition coupe was bought by a guy here in Carson City who still races it. When I learned the aerodynamic design of it (and I was allowed to lay down next to it and look at the bottom), it just blew my mind. Tom designed it as an upside down wing!! It's higher from the ground at the tip of the nose, then slopes down closer in an airfoil curve to a minimum somewhere underneath, then back up towards the tail. Tom's theory; downforce without drag (or any more drag than a wing).

I just couldn't believe it. "What about the air you're compressing underneath?!?!?! You've GOTTA be causing LIFT!" Not so. The air accelerates under the car just like it would over a wing, producing a low pressure area under there. "But what about the air 'trapped' between the car and the ground?" I asked. The answer: no air is "trapped" - it's flowing under there, and the ground is just the opposite side of the venturi throat. It has to accelerate, causing the pressure to DROP. At about that time, my poor little brain began to smoke and I had to stop thinking!!!!

But it worked. Dan (Dan Webster, the car's current owner) routinely holds multiple land speed records with that car powered by vintage flathead Fords. I think he's right at 200 mph. And when Tom Burkland was racing it, he was hitting 300 mph with small block Chrysler engines. Weird, huh?

So the lesson I learned: Aerodynamics is a lot more complex than I thought it was!! LOL!!

lol, that's called ground effects. The effect is more pronounced because the "bump" gets very close to the ground, and the air doesn't have anywhere to go, whereas on a wing there's the rest of the sky in place of the rigid ground.

ccm302 01-03-2013 12:47 PM

Quote:

Originally Posted by wungun (Post 348366)
SVT Focus...nice. I have one of those!
But I converted it over to the Euro only RS Focus model...

But having the engine tuned (for performance) Also gave noticeable gains in mileage.
There are a couple of really good tuners you can talk to on the popular focus forums which would be happy to sell you a flasher with a custom tune...One of which, offers free upgrade tunes if you happen to change somethings like throttle body, exhaust, filter, etc.

I've seen you lurking around the forums and have seen your car. Looks good btw. Also, I have a tune from the inidividual you are talking about :thumbup:

Quote:

Originally Posted by wmjinman (Post 348501)
I just couldn't believe it. "What about the air you're compressing underneath?!?!?! You've GOTTA be causing LIFT!" Not so. The air accelerates under the car just like it would over a wing, producing a low pressure area under there. "But what about the air 'trapped' between the car and the ground?" I asked. The answer: no air is "trapped" - it's flowing under there, and the ground is just the opposite side of the venturi throat. It has to accelerate, causing the pressure to DROP.

I remembered most of this from my aero classes which is why I was thinking/mentioning belly pans. There are a couple of the high end exotics that use them and can actually create a vacuum high enough to keep the car glued to the road, even if the road were to abruptly turn upside down.

some_other_dave 01-03-2013 02:02 PM

One of the benefits for fuel economy of lowering a car is that, in general, you don't have to slow down as much for corners. So you don't have to spend fuel to get back up to speed again.

In theory, you can get better or worse MPG from lowering your car. It seems that most of us see no benefit or a very small benefit, while some see worse FE, and a few see a lot better (relatively) FE.

Doing A/B testing is a bit more involved for lowering. Even if you have adjustable spring perches ("coil overs") it still takes some fussing to precisely set the ride height.

-soD

YeahPete 01-03-2013 02:29 PM

Belly pan.

freebeard 01-05-2013 06:33 PM

One of Luigi Colani's Bonneville cars was inspired [allegedly] by the water strider. I haven't found a good illustration of it; this is the best I've seen so far:
http://i.imgur.com/Pthpt.jpg
It was completely flat on the top; e.g., a very high stagnation point. It looks like it should have very good cross-wind performance.


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