Increasing downforce while reducing drag?

[Christ]

Thank you, Neil, for properly expressing what I referred to as "cross flows". I couldn't think of what I wanted to say to that effect last night.

[Hermie]

Now to get back to the original topic- Reducing drag while simultaneously reducing lift.

[NeilBlanchard]

Hi Hermie,

I think what we need to worry about is drag -- we do not have enough lift at normal speeds to really worry about, IMO.

An upper grill block will reduce drag, and probably reduce lift; as I said before.

You should try to find the Hucho book at a university library -- I borrowed a copy from MIT (via my wife who is a librarian). It'll knock your socks off with the sheer volume of detailed info about vehicle aerodynamics.

[Hermie]

I'll look for it, thanks! ^^

I'm also thinking about taking my car to the track on weekends once in a while, so I'm looking to make my car the best of both worlds- fuel efficient through less drag, but handles at speed through reduced lift/increased downforce. I don't want mods that'll increase lift, because performance at speed will be dramatically reduced.

I probably should have made myself clearer from the start to avoid the rudeness some people have posted...

If I can get Stickers to run 30mpg highway from lowered drag, but have zero lift or net downforce, I'd be more than happy.

[Bicycle Bob]

The trade-offs for street use usually leave a bit of lift. If you want to race occasionally, bolt on a big wing at the track. A really smooth belly pan, and an arrangement to lower the front might be another fine combination.

[winkosmosis]

We Take Audi's Tamed TT for a Spin - First Drive Review - Auto Reviews - Car and Driver

More obviously, all TTs get a small rear spoiler mounted to the decklid in a move aimed at reducing lift on the rear axle at high speeds. The TT has 148 pounds of lift at the rear axle at 125 mph without the spoiler, but only a 53-pound lift when the spoiler is fitted. By comparison, the BMW Z3 coupe generates 64 pounds of lift at 125 mph; the Mercedes-Benz SLK, 104 pounds of lift; and the Porsche Boxster, 68 pounds of lift. The chassis engineers claim they could have solved the problem without the spoiler, but this would have meant a significant increase in understeer at normal speeds, a trait they wanted to avoid. All TTs also get a version of VW's switchable Electronic Stability Program (ESP).

So it turns out a car for which lift actually was a problem at high speeds was only experiencing 148lbs before they added the spoiler. I'm surprised that's even though to make a big difference in handling though.

So what kind of lift would you get a 65mph? About 1/4 as much as 125mph?

[evolutionmovement]

The Audi TT in question was notorious for high speed lift-off snap oversteer due to the style-over-function design. After that incident (not the only one), the optional rear spoiler was installed on all of them by the factory.

My 1983 Subaru GL sedan was a similar style car to the Tempo with a likely comparable drag coefficient. I had few stability issues until it was topped out at "P" (the P in MPH at the bottom of the 85 mph speedometer), which worked out to be around 110 going by the tachometer. At that point, it would move around a little in crosswinds, but could still keep in a lane sawing the wheel like a '50's movie racecar driver. Where it bothered me was on on-ramps at speeds over 80, with significant understeer, so I added a front airdam. Got slightly better mileage which was probably within a margin of error, but it did add straightline stability and cured the understeer (at least the lift-induced understeer). What it also did (besides scrape the occasional driveway when I forgot to enter at an angle) was increase oversteer to a level that was fun in the dry and a little hairy in the wet. A tree fell on it while I was driving down the street, so I never got to put an adjustable rear spoiler on the trunk.

[Hermie]

Wow, I'm glad you're okay.

I'm definitely adding an air dam then. Tomorrow I'm going to look for material.

I'm going to balance it with a rear lip spoiler, with vortex generators to aid airflow onto the rear deck, which should improve the spoiler's properties and reduce drag at the same time.

*points up*
These are the exact mods I'm talking about. XD

So, anyone have any wind tunnel data on the ecomods here, by any chance?

[wdb]

Front undertray. My '08 Honda Fit was squirrelly around the big rigs on the freeway. Then I put a Beatrush front undertray on the car. It is now much, much more stable at speed, in crosswinds and so forth, plus it handles the offramps better.

Oh yeah -- 1 to 2 MPG improvement in fuel economy.

[lunarhighway]

i'd vote for an undertray to. it's a little more involving than an airdam, but it has so much advantages. even my first relative small one made out of a sheet of coroplast made such a difference in the way the car felt, it seemed more stable and quite. i once drove a day or two with my current dam removed the car felt wobbly and unstable... and while my car has a terible ammount of oversteer, the dam actually gives is the stability that allows my to toss it around a sharp corner or roundabout. it will still oversteer at some point but i've never found this to be a problem with in normal driving, even at high speeds

it also protects your engine from debris and dirt

what i most certainly recommend you do is to evaluate your mods.

you could do several things. first of all record your milage and work out if there's any change, but don't draw conclusions to soon... the best thing to do is do A-B-A testing over the same track, as weather and traffic all influence your results. if you have a fuelcomputer that tells you your milage instanly thay's even better.

you could also do some diy tuft testing especially on the vortex generators that should tell you one or two things
this aoutospeed article has some nice info on how to tuft test