ozbot87

I was reading through the November issue of Men's Health and on page 72 I found an interesting little paragraph on spoilers:

"...a few high-performance sports cars feature tiny underbody spoilers. ..designed to create downforce. at high speeds, which improves areodynamics, stability, and fuel economy ."

The article goes on:

"But ar under 60 miles an hour, they're ornaments-in fact, big aftermarkey wings can reduce fuel economy by increasing weight..."

Anybody care to comment on this issue as to whether the spoiler either helps or harms the 8's (or other high performance car's) economy?

CraziFuzzy

I can't see how any wing could possible improve fuel economy... What it does is translate extra air resistance into downforce (or for most wings, which aren't shaped for any downforce anyways, just looks) just add more air resistance. The only way the underbody spoilers can improve economy is by smoothing out the air path, creating less restrictive turbulance. (A large cavity in the underbody will produce a rolling Ettie, that will actually resist some flow of air under the car)

RXGr8

Those dorky kids who put airplane wings on the backs of their civics are definitely getting less gas mileage. Those cars can't even get up to the speed they need to actually benefit from them, and if they do, it's probably the equivalent of driving 120 mph with 200 extra pounds in the trunk. My impression with spoilers on consumer vehicles in general is that for the most part they are ornamental. It gives cars that "sporty" look. But if the designer, be it oem or aftermarket, is taking aerodynamics into consideration when adding spoilers to cars, there might be some slight gains, however trivial, to performance. But the type of gains are probably more in the area of reducing the drag on the rear of the car from the vacuum caused by the abrupt drop in the rear. I read somewhere that the RX-8 spoiler will reduce the drag coeffienct by 0.01, which isn't all that great.

My initial desire was to have an RX-8 without a spoiler, I finally settled for one after I saw it on my blue 8. It really adds form to the rear of the car that I decided I really liked. In short, I think the RX-8 spoiler option is a really nice treat if you can afford to add it as an option.

ozbot87

Well, I think that the spoiler tends to reduce the drag caused by the car at high speeds. I have heard by many people that drag induced on the car causes the vehicle's economy to go down.

I drive my car with both windows down at speeds or 90 mph on the freeway and I observe about 26 MPG, which is about the same economy when I have them all rolled up. (The differnence is negligible)

matt

Cars with venturi tunnels (channels under the car) do increase fuel economy and aid in down force. Cars like the new Enzo and 360 Modena are flat bottom cars. They have covers that help the air flow under the car. Open bottom cars like the rx-8 has moderate amounts of drag coming from the air turbulence from the drive train, engine, and transmission. Drag = poor economy. When the air is channeled from the front of a flat bottom car into the internal venturi, the air flow is smoothed and forced from the low front bottom to the mid rear high creating the down force and releasing the air

Gord96BRG

Some wings can and do reduce drag, thereby improving fuel economy. MOST wings, especially the aftermarket ricey wings, just increase drag, which costs hp, which decreases fuel economy. They might add downforce, but who needs it? Racers know that downforce = extra drag (unless you have real ground effects via venturi tunnels and diffusers - but those are designed in at the factory, and those stupid body kits that some people refer to as "ground effects" are nothing more than a joke), and extra drag just requires more hp to haul around, making you slower except in corners. Of course, all the cars sporting the huge wings only run in straight lines anyway.

On the RX-8, the Mazda European small lip spoiler reduces the Cd from 0.31 to 0.30 - which would indeed provide a very slight increase in mileage, and probably a slight reduction in rear lift. I'd bet that the Mazda wing increases the Cd (ie increases drag), though.

Regards,
Gordon

wakeech

first and ABSOLUTELY foremost, why the f*ck would you trust Men's Health for information on cars?? for christ's sake man, their "how-to" sex articles are crap next to what i can tell you!! no, i'm not kidding in the slightest...

they say "it can be good for stuff" and then turn around and say "it can be bad for stuff"... no specifics, basic conditions... no information at all, really.

hey gord, i've never heard of any wing ever being the best option for drag reduction.

the long and short of it is what Crazi (hi again) said: what a wing does is take energy from the forward moving vehicle, displaces air around it to create a net pressure difference across its surface, and with that pressure difference multiplied by the area that difference is acting on, you get a force, either up, or down, or sideways, or whatever. this does not help you go quicker in a straight line. the end story is: even with a wing that has 100% efficiency (ie: ALL of the energy which it draws from the car goes into displacing air, and none into heat, sound, etc etc) a wing will slow your car down in a straight line.

spoilers on the other hand can generate a streamlining effect by disrupting the airflow BEHIND them, creating an area of turbulence which streamlines the shape of the car, giving the laminar flow coming over the back end of the car a far more gradual path back to rest: it's a comprimise between a very high area of drag (immediately behind the spoiler) and reducing the drag from all other flows around it. because it reduces the force of the air returning to rest behind your car, and is implemented for the flow coming over the top of your car, they do reduce drag by reducing that ever important pressure difference over the back of your car as it returns to rest.

as far as real ground effects (diffusers and channels) they will never be the most efficient way of moving air around your car; it can be true that a vehicle with expensively optimized venturis and diffusers has a lower Cd than a car with a naked underbelly, but a nearly-flat bottomed, streamlined and lowered vehicle which produces close to zero force (up or down) is far FAR more efficient moving through the air.

for what its worth Gord, a -0.01 difference in your Cd is pretty damned good, although there's always room for improvement

MrWigggles

A cd change of .01 will make no difference around the city, but if you are going fast enough, say 100 MPH+ where the car is doing much more work on the air than on the road, a 3% improvement in drag can create nearly a 3% improvement in fuel economy.

At 100 MPH+ you are going to be at 10 MPG or less anyways. So would someone even notice a 10 MPG to 10.3 MPG jump?

-Mr. Wigggles

r0tor

iTrader: (1)

The wing on the back of an EVO is a good example of a wing that was actually made in a wind tunnel. It helps to shed the wake thats behind the rear window which reduces drag and improves downforce slightly (since a wake is an area of low pressure that will suck the car up).

Indycar wings - produce huge downforce by angling the wing up at like 30 degrees on roadcourses and huge drag because of it

ricer wings - completely non wind tunnel designed and just produce drag.

stock RX8 wing - I doubt it makes a difference since its probably sitting in the rear window wake.

downshift

I spent almost all night reading this website. It's not an authority in explaining how aerodymanics works but it's an interesting read nonetheless. This site has a lot of other interesting articles as well, such as polar momentum, FF vs FR vs MR vs AWD handling, suspension types, variable valve timing, etc. Check it out:

http://autozine.kyul.net/technical_s..._aero.htm#Wing

ozbot87

Hey, easy there buddy. Calm down. I like Men's Health because it gives me good health advice. Not sex advice, not advice on buying a car, not anything else. I just found the snippet and thought I would share this with my fellow RX-8ers (and wannabe RX-8ers like me).