Aerodynamic lift- A real problem

[MetroMPG]

Originally Posted by Hermie

I'm talking about speeds of 65-80 MPH, the common speed of highways and freeways, which I drive on daily.

So far, the examples of lift being a problem have been at speeds much higher than that... 100, 110, 120.

[Nerys]

"If there is sufficient lift to affect traction then it would also reduce rolling resistance and improve gas mileage."

I doubt that. There are 2 rolling resistance numbers primarily in effect here. Bearing drag (virtually NILL for our purposes) and Rubber Patch drag. Theoretically if you lift the car up the contact patch becomes smaller reducing drag.

but by generating lift you create more aero drag. since the law of the universe is entrophy I am betting the aero drag you create is greater in impact on your mileage than the miniscule rolling resistance you decrease. I fully admit I don't really have a clue what the figures would look like but I did goto school for AE (ended up not liking where it would take me) and my butt check says the above is probably a good bet. Especially since parasitic drag is a FAR FAR smaller factor than Frontal/Base drag. (I mention this because adding a boat tail increases one but decreases the other but the other base drag has a far greater impact than parasitic drag so you get a net gain)

Frank is a royal pain in the ass and is sometimes pretty harsh or blunt (borderline rude and trollish) but he does have a lot of GOOD info and experience by the sounds of things.

there are cars that have LIFT ISSUES at normal speeds 45-60mph. The beetle was one example which is why they added the little spoiler to them IIRC.

get a nice 50+mph cross wind and the things would slide right off the road :-)

[MetroMPG]

A quick look at vw.com shows the New Beetle -- top speed 125 mph -- comes new (2010) without a rear spoiler, at least in standard trim.

Edit: I belive the turbo has one. But the majority sold are non-turbos. (I'm not even sure they sell the turbo any more.)

http://vw.com/newbeetle/gallery/en/us/#/exterior/0/

[Nerys]

I imagine current beetles are designed NOT to produce this lift or maybe it was not a beetle. It was a light bubble shaped sporty car is what I remember (just assumed it was the beetle)

[Christ]

Originally Posted by Hermie

If Frank would stop being so immature and jumping to insults, we wouldn't have this problem. But apparently, he has nothing intellegent to say, so he resorts to the only thing he knows.

I merely act as a mirror and return what is given. Remember the golden rule?

I'm sorry, I have to address this, then I'm done and ignoring this thread, as it has turned into something less than useful already, and I can't imagine it getting anywhere from here.

Have you heard the phrase: "An eye for an eye, and the world is blind."?

How about "Sticks and Stones may break my bones, but words will never hurt me."?

The latter seems to be closer to your reference of the "golden rule", which, if I remember correctly, is "I'm rubber, you're glue... whatever you say bounces off me, and sticks to you!", which I might remind you, we all learned between kindergarten and second grade.

It just might be time to grow up a bit, eh?

Here's another one: "Turn the other cheek.". This doesn't mean turn tail and run, it doesn't mean you have to take **** from everyone and anyone, it means that if you don't acknowledge ignorance, it deviates from you.

If you honestly believed that Frank was being ignorant, and you weren't (caveat of the analysis), you'd have already understood this.

I guess the fact that it continues to be a pissing match over quibbling words makes us blinded to any data that may be provided here, no?

Please, carry on. Hopefully, you'll find something finite and informative in your research, and I can only hope that when and if you find what it is you're looking for, you'll be somewhat more diplomatic when you prove us all wrong.

[Frank Lee]

Frank is a royal pain in the ass and is sometimes pretty harsh or blunt (borderline rude and trollish)

I apologize for only being borderline rude and trollish! I would do a better more thorough job but the mods won't let me. : pouting :

Spoilers are glommed on to "sports" versions of cars more as a visual aid that says "Hey! I'm the sports version!" than for any real performance aspect. The truth is most of those spoilers degrade performance but hey they look cool. Don't look to tarted-up performance versions for any aero holy grail. Some of the brand new stuff, though, is getting more believeable i.e. more likely to have real functional improvements to go along with the looks.

Pressure varies with the car's speed squared, so downforce increases quickly as the speed increases. Generally, the effects are felt at speeds over 75mph.

This is from Modified Mags article that Michael linked... did you get that far into it Mikey?

With an autotragic transmission-equipped Tempo the first place to look for better econo is via lower speeds, NOT just cuz of aero concerns but because the stupid things lack both overdrive ratios AND locking converters. Anything over 60 mph puts the 2.3 Tempo engine outside of it's best operating speed at least as far as optimal piston speeds go. BSFC curve? Anyone? I can almost watch the fuel gauge drop at speeds above 60. So if efficiency is any factor at all in this pursuit of lunacy you can forget about going 80 mph.

NOW what is still needed to put this **** to bed is some actual values for lift i.e. how many pounds at what speed on what or both ends of the car; and then of course some sort of judgement as to the effects of that. I'm not home with my Tempo data or my Hucho book so online it is, and there is nothing online specific to Tempo so then what? And even so, my accumilated Tempo data includes Cd, Cda, Cg, etc., etc., but I'm sure I never found Cl anyway.

So here's what: All values were recorded at 200 kmh (124 mph)

BMW 335i: 42kg of lift at the front / 28kg of lift at the rear
Drag Coefficient: .28
Rating - 7/10


SLK55 AMG: 23kg of lift at the front / 31kg of lift at the rear -
Rating - 7/10

SL65 AMG: 29kg of lift at the front/ 33kg of lift at the rear
Drag Coefficient: .31
Rating - 7/10

CLK DTM: 37kg of lift at the front / 12kg of downforce at the rear
Drag Coefficient: .34
Rating - 8/10

997 GT3: Even Balance at the front -0- / Even balance at the rear -0-
Drag Coefficient: .29
Rating - 10/10

997 Carrera S: 20kg of lift at the front / 7kg of lift at the rear
Drag Coefficient: .27
Rating - 9/10

M6: 15kg of lift at the front / 26kg of lift at the rear
Drag Coefficient: .31
Rating - 8/10

Z4 3.0CSi: 28kg of lift at the front / 43kg of lift at the rear
Drag Coefficient: .33
Rating - 5/10

Roadster S: 2kg of downforce at the front / 40kg of lift at the rear
Drag Coefficient: .36
Rating - 7/10

Corvette C6: 54kg of lift at the front / 28kg of life at the rear
Drag Coefficient: .29
Rating - 6/10

B7 RS4: 34kg of lift at the front / 15kg of lift at the rear
Drag Coefficient: .31
Rating - 7/10

GranSport: 50kg of lift at the front / 29kg of lift at the rear
Drag Coefficient: .34
Rating - 6/10

V8 Vantage: 48kg of lift at the front / 13kg of lift at the rear
Drag Coefficient: .33
Rating - 7/10

V8 Topster: 65kg of lift at the front / 30kg of lift at the rear
Drag Coefficient: .40
Rating - 5/10

Zonda F: 1kg of downforce at the front / 25kg of downforce at the rear
Drag Coefficient: .36
Rating - 10/10

CCR: 13kg of downforce at the front / 11kg of lift at the rear
Drag Coefficient: .35
Rating - 9/10

GT: 44kg of downforce at the front / 2kg of lift at the rear
Drag Coefficient: .35
Rating - 9/10

C55 AMG: 2kg of downforce at the front / 33kg of lift at the rear
Drag Coefficient: .29
Rating - 8/10

E46 M3: 5kg of lift at the front / 18kg of lift at the rear
Drag Coefficient: .32
Rating - 8/10

E60 M5: 13kg of lift at the front / 19kg of lift at the front
Drag Coefficient: .30
Rating - 8/10

360CS: 10kg of downforce at the front / 21kg of lift at the rear
Drag Coefficient: .31
Rating - 9/10

Viper SRT-10: 15kg of downforce at the front / 18kg of lift at the rear
Drag Coefficient: .38
Rating - 8/10

SLR McLaren: 19kg of downforce at the front / 35kg of downforce at the rear
Drag Coefficient: .37
Rating: 10/10

Carrera GT: 49kg of downforce at the front / 40kg of downforce at the rear
Drag Coefficient: .37
Rating - 10/10

Zonda S: 8kg of downforce at the front / 53kg of downforce at the rear
Drag Coefficient: .40
Rating: 10/10

Murcielago 6.2: 34kg of downforce at the front / 1kg of downforce at the rear
Drag Coefficient: .33
Rating: 10/10

Does any of that stuff have a 3-box shape like a Tempo? Well.... several of the BMWs and MBs are the closest of the lot and they show anywhere from downforce, to the worst of the lot at 42 kg (92 lbs) front/28 kg (62 lbs) rear lift. Hmm. 92 + 62 = 154 total lbs of lift. At 124 mph. For the worst car in this sample. Hmm. Assume the Tempo is the aero equal to this worst car, Cl wise. 2000 lbs on the front end... no, wait, don't be a dumb jackass!!! -make that 1750 lbs on the front end minus 92 = only 1658 lbs left to keep that sow on the ground! Put another way, effective front end weight decreased about 5%!

Do I need to go further?

[Hermie]

Originally Posted by Frank Lee

Michael has been all over the internets with this **** for at least 4 months now... not finding too many buyers either.

So... where's the data? Where's the figures? Where's anything that adds up to anything- in your posts that is?

Actually, I haven't been putting too much time into looking up stuff. I do have a life, and a college career to attend to.

Besides, it's common sense that lift degrades performance. Why would people that actually work designing cars spend time and money publishing papers stating the blatantly obvious?

[Christ]

Data... finally.

Ok, yeah... I'm out. Have fun, guys.

[Hermie]

Happen to notice that those are all high-end, ultra-expensive cars, where engineers spend hours REDUCING lift to IMPROVE performance?

Thanks for proving my point that people that actually know things about aerodynamics know that lift isn't good.


Also, the new Beetle Turbo has an active spoiler. It rises at highway speeds to reduce lift and increase control. Caught a glimpse of that this morning.


Oh, and Frank. You're still not factoring in the fact that mass doesn't just magically dissapear. Anyone knows that's a basic law of physics. Inertia still holds, so that weight that's no longer on the tires from lift holds your car from turning, or keeps it turning, with less available traction to work against inertia.

Once again, thank you for proving me right, "dumb ***".

[JackMcCornack]

As an equal opportunity offender, I'm not going to quote anybody, I'm plucking out comments sans credits.

> I didn't join here because I want to squeeze every drop of gas I can.

:-) That's exactly why I joined! I already do all the communicating I need to on car DIY in general, and aero performance mods in particular. I hang out here for information and discussion about automotive efficiency.

> Along with drag, anyone that drives on the highways and freeways should also be concerned about aerodynamic lift.

I'm not sold. My mom drives on highways and freeways and doesn't think twice about lift, and I'm not going to educate her because I don't think it would be an improvement. If she finds herself in an oversteer situation (unlikely with her driving habits) I want her to remember to steer into the skid, I don't want her distracted by her conscience yelling at her in its Jimminy Cricket voice, "See, I told you you should have bought a spoiler."

I sure think anybody doing competition driving (even autocross, a motorsport where average speed is lower than freeway speed) should be concerned about aerodynamic lift...well, kinda; in road racing we're concerned with increasing downforce rather than decreasing lift, and have been since about 1964, but that's gotten some people in trouble. Ground effect cars that lose ground effect (over a bump for example) can do a sudden transition to the land of lift, best shown by the flying Mercedes at Le Mans. Anybody going over 200 mph on salt needs to be concerned about aerodynamic lift--if you're putting 400 horsepower onto a slippery surface through your rear wheels, a small loss of load can spin you, and at 200+ darn near any car is going to produce lift if you put it sideways--a sideways car has about quadruple the aspect ratio of a frontways car and if it has left-right symmetry then sideways it's a symmetrical airfoil--it'll be inefficient but it'll be high lift and I think you could fly a school bus if you got it sideways over 200 mph. I even think you should be concerned if you're hooning around at 120 and cornering hard enough to make the tires squeal. But the question before us is, is aerodynamic lift a real problem to ecomodders.

> When air pressure builds up and generates lift, it reduces your tires' available traction...

I will stipulate that lift reduces traction. I have a bit of trouble with the "air pressure builds up and generates lift" part, but as to lift resulting in loss of traction, I nod my head in agreement.

> Since to some people it seems to be completely foreign, I thought they would like to know it's common knowledge to those in the real world.

We have lots of different takes on what's significant--and even on what is common knowledge to those in the real world. I read these posts and see complete agreement that lift reduces traction, but questions re it being a real problem in the context of ecomodding. I'm on the fence myself. It's not that the concept is completely foreign, I just wonder if it's significant.

For example, in pursuit of high mileage, I'm looking into low rolling resistance tires. These tires reduce traction compared to many other tires. Were I the sort to drive at a given G force (say, half a G) regardless of my environment, high mileage tires would increase the likelihood of me spinning out of control. Yet nobody has started a thread of "High mileage tires--a real problem" even though they'd be a real problem in the 200 mph club at Bonneville. Is the lift issue of similar significance at ecomodding speeds and ecomodding driving style?

I'm genuinely interested in finding out. I'm considering a low drag body inspired by pre-war racers, when speeds were low enough that drag was much more important than downforce.