Increasing downforce while reducing drag? - Fuel Economy, Hypermiling, EcoModding News and Forum

Hermie · 08-07-2009, 08:33 PM

I know there's got to be some ways to reduce lift and give downforce while reducing drag.

Tire spats are one of them, and I've installed a pair on the rear end of my '91 Ford Tempo using material from my front license plate holder (which actually cover the whole width of the tire!)

I've seen data showing that vortex generators allow air to stay on the surface of the rear of the car better, and improving the effectiveness of spoilers (as shown by studies on the Mitsubishi Lancer Evolution VIII).. But what if you don't have a wing?

Discuss lift-reducing and downforce-making aero tricks!

To save reading through spam posts, here's a list so far:

1. Roof-mounted vortex generators when a rear wing/spoiler is present

2. Tire spats

3. Rear diffuser

4. Front Air Dam

SVOboy · 08-07-2009, 11:46 PM

How fast are you driving that you actually need downforce?

PS: I'm not sure I know the answer

Christ · 08-07-2009, 11:52 PM

Well, Ben, it could be a function of vehicle weight and tire contact patch. If I were driving on bicycle tires, with a fairly hefty vehicle, I'd want some downforce as well.

I'd probably not be concerned about it if I were driving the average vehicle though, since more downforce at speed equals more power necessary to continue propulsion. (It's the same thing as adding weight at speed.)

RobertSmalls · 08-08-2009, 12:11 AM

Lift creates drag, and so does downforce. Some aerodynamic improvements (such as a kammback over your trunk) will reduce drag and lift at the same time, others (such as deleting cosmetic wings) will reduce downforce and drag.

Downforce and lift are mostly a distraction here. A few lbs added to or lifted from the tires will have a tiny effect on mpg. Pursue drag reduction whether it removes lift or removes downforce.

Hermie · 08-08-2009, 01:04 AM

I'm actually more concerned about stability at highway speeds. Next month, I'm going to be taking a 600 mile trip on I5 into Oregon, and I want to know I'm not going to lose control because of traction loss from aerodynamic lift. Downforce and lift may be just a distraction in the city or around town, but on a freeway where average speeds are around 80 MPH, it plays a vital role.

You could have a car with a super-low Cd, but if it lifts at speed, you're not going to have any control if you need to suddently stop or swerve into another lane to avoid an accident.

Browsing the threads, I've seen a bunch of great data on Cd, but almost nothing on how they affect lift or downforce.

For example, tire spats force air away from turbulent rotating tires. Without them, air would be pushed under the treads, creating a super-high pressure zone at the base of the tires. With the spats in place, that high-pressure zone is reduced, thus reducing lift.

Vortex generators can reduce drag (6 points on the Evo VIII), and increase downforce when a non-cosmetic spoiler is present. If it generates lift or downforce without one, I haven't a clue.

This thread is for ideas that both cut drag and cut lift. Know any good tricks?

gone-ot · 08-08-2009, 01:19 AM

tire spats - interestingly, our '09 Vibe has a pair located just in front of the front wheels...barely the width of the tire itself...little airdams for each wheel.

Hermie · 08-08-2009, 01:24 AM

Ah, a fellow Tempo owner. ^^ Mine's a 2nd Gen, though.

Obviously, cars can't "take off", because their power source is connected to the ground. But I beg to differ- Lift does make a difference. I'm seeing a little bit too much of an MPG obsession here when control at speed needs to be taken into account.

Look at the Audi TT- Even a seasoned rally driver died on the autobahn from loss of control due to lift.

Hermie · 08-08-2009, 01:51 AM

True enough.

So, do you have any data on the Cd of the 4-door Tempo? I haven't a clue what it is.

Christ · 08-08-2009, 02:23 AM

escort transaxles fit as well, and may have longer gears/final.

Christ · 08-08-2009, 02:31 AM

You, Sir, are correct. You need the mounts, transaxle, pedals, shifter and linkage, and the clutch kit/flywheel. It's about a $250 conversion from u-pull-it yards.

A 3.0/3.2 transmission will also bolt up to the block, but might not fit in the car's chassis, even though they came with optional 3.0's. I think the 2.3 is a bit longer than the 3.0, but I might be wrong. I do know that when putting the 3.0 into an Escort, you're shoe-horning everything to make it fit, and the Topaz isn't THAT much bigger under the hood, that I remember.