Best Type Rear Spoiler

[MICAH1]

I was reading on aerodynamics and began to think what would be the best or most favorable type spoiler for my GT. On my first GT back in the late 70's, I installed the duck tail style by moving the gas cap and neck up about six inches, then laying fiberglass over the opening and blending the edges of the spoiler to the body. Not wanting to take that long route again so I am thinking some type of bolt on like a whales tail, small aluminum wing (49 inch). Question is once I get through the chapter on installing my motor replacement, the rear spoiler will be my last mod prior to body work and another paint job before Carlisle next year, so with the GT weighting a tad over 2,000 pounds, just how much stability will the rear spoiler add to our GT @ 70 mph +?? I have a front airdam, so now to balance it off. I am leaning towards a aluminum wing, painted black like the rest of the car of course.


The photo below shows the front airdam now on my GT.

[Redskinsjbs]

Thomas,

From what I know about aerodynamics, the name of the game with spoilers is to generate downforce. But in order to obtain that downforce, there is normally comes a price which is a larger drag coefficient and therefore a less slippery body which means worse fuel economy.

Now if you ignore the fuel economy bit, a F1 car has a drag coeffiicient of around .7, more that twice that of a normal car. This is because the cars are designed to generate more that twice the weight of the car in downforce alone!

I see two ways to go about generating downforce, either by altering the direction of the air or by fiddleing with pressure zones.

Low speed cars tend to use 'directional spoilers' because they are reletively straight forward and are very effective if you aren't after the ability to go fast. (Think about it, a flat board pointed towards the ground increasingly becomes like a wall the faster a car goes through the air). - - - This is like a duck tail spoiler.

Cars which tend to go faster use 'pressure spoilers' because they have a lower drag coefficient than directional spoilers but can still generate a substantial amount of down force if you are moving fast enough. Think about these types of spoilers as wings simply turned upside down, so instead of generating lift they create downforce.

So, using my even MORE limited knowledge of the GT, I think that you would have to use a front spoiler in conjunction with a rear spoiler if you would like to add any stability. The rear fishtailing at high speeds because of a loss of down force is one thing, but I think that you first need to force the front wheels down before you work on the rear.

I hope my basic understanding of the subject can help. This is essentially all that I *know*, so anyone who is willing and able to correct or expand on my answer, by all means please do.

[thescifiguy]

Unless you take turns at 90mph, it's unlikely any car would NEED a spoiler. When have you ever heard of someone's back wheels fish tailing or loosing traction going in a straight line? If there was even the slightest need for one, you'd see EVERY car out there with one. As far as drag caused by a wing, I think the vortex formed by the chopped off rear ends of our GT's makes that worry pretty slight. In fact, a wing might actually IMPROVE that problem back there by breaking up the air flow.

That said, I LOVE WINGS!!! The bigger the better and jacked up as high as the roof line! I've put'em on all 5 of my GT's.

That was mine with the Lenk wing from OGTS. As their catalog states:"...proven by the German TUV to give sufficient downforce to provide stability at speeds over 100mph". It's something like 12" front to rear. I've also had the wing from the Mirage body kit and it also was about 12". Basically, you need a "deep" wing to provide enough surface area to do anything. Skinny wings or whale tales probably don't do anything.

The bottom line is: Wings make your car look cool as heck, but that's about it.

[ungermm]

Originally Posted by thescifiguy Unless you take turns at 90mph, it's unlikely any car would NEED a spoiler...The bottom line is: Wings make your car look cool as heck, but that's about it.

That's my understanding too.

I like wings and use them depending on how I want my car to look. I am using an older modified Toyota Supra on my current project.

72 OpelGT 047.jpg

However, I think my preference would usually be for a smaller fiberglass one on a GT.

Jerry

[wrench459]

Rear wings are cool as beep!
Side skirts.
I would look at the area under the car first for added stability at speed.

[myopels]

Thomas, I had a dodge challenger that I customized years ago, and put a spoiler and the big superbird wing on the buck witha big rubber spoiler on the front. The fromt kept air out from under the car, creating a vacumn under the car and pulling it down. The wing was an upside down air foil, and I read that when racing in nascar on the daytonas that it put out 900 pounds of downforce at speed. Most of the wings that you see today are only good for a towel rack or a push bar, they do not have the correct design,or are too low where no clean air flowes over it. The other duck tail that I molded to the trunk was to reduce the drag/vacumn on the car. The angle of the spoiler was about 45 degrees from the deck. Any taller, and you create a lot of downforce with a ton of drag. Going the other way, will drop the draqg, but lose on the downforce side. If you see drag cars, they have a very flat, but 2-3 foot long spoiler on the back. This causes the vacum of the air coming off the car to make a vortex way behind the car where it has little effect. The difference on my challenger was amazing. When I first bought it and hit the freeway at 70 or so, it would start to lift . After the mods, the car socked down to the road andran like a slot car at speeds way over 100. I like to install stuff that really works AND looks cool.

[MICAH1]

I have pretty much decided to go with this style rear spolier with measurements of 49 inches across, 10.5 inches high. Would like to hear from RallyBob, and some of the racers on this topic.

[baronbors]

I like the brake light in mine for added visability- thats about all its good for.

[hrcollinsjr]

Thomas,

I think there are mainly two reasons to put a rear spoiler on a street car; either to balance out the looks because there's one on the front or for looks. Both of those reasons are about looks.

From everything I've read, the front spoilers if designed correctly work. The more air you can keep out from under the car the better. I would probably choose a rear spoiler that looked right on my car and actually changed the airflow the least. Why? How much downforce do we actually need and if it isn't balanced with the front downforce then we may loose high speed stability. Remember when the NASCAR guys use to 'accidently' flatten the rear spoilers to increase top speed at some lose to stability.

If you put a big wing style spoiler on, I'd try to pick one that is adjustable.

JM2CW,
Harold

[RallyBob]

Originally Posted by MICAH1 I have pretty much decided to go with this style rear spolier with measurements of 49 inches across, 10.5 inches high. Would like to hear from RallyBob, and some of the racers on this topic.

I've worked with a lot of racecars that are allowed aerodynamic aids. Unless you are track testing non-stop, or have access to a wind tunnel, there's just no way to know if you are doing something that is better for handling or worse. The best rear spoiler in the world on brand 'X' car might work like total crap on brand 'Y'. Wing location (height and depth), angle of attack, and wing profile need to be proven on your particular body style in either real world testing or wind tunnel evaluation.

Most of the German kits have been tested in a wind tunnel to gain TUV approval. They need not provide significant downforce, but they must provide front/rear aerodynamic balance, and must not increase lift (a lot of aftermarket parts are for looks only and make things worse!).

Bob

[Redskinsjbs]

Originally Posted by RallyBob I've worked with a lot of racecars that are allowed aerodynamic aids. Unless you are track testing non-stop, or have access to a wind tunnel, there's just no way to know if you are doing something that is better for handling or worse. The best rear spoiler in the world on brand 'X' car might work like total crap on brand 'Y'. Wing location (height and depth), angle of attack, and wing profile need to be proven on your particular body style in either real world testing or wind tunnel evaluation. Most of the German kits have been tested in a wind tunnel to gain TUV approval. They need not provide significant downforce, but they must provide front/rear aerodynamic balance, and must not increase lift (a lot of aftermarket parts are for looks only and make things worse!). Bob

Anybody have a toy model GT that they are willing to contribute to some 'real world wind tunnel testing'? This could be fun.

Even better idea, if you have a kid who is in Middle or High school, convince them to do a science project on the aerodynamic characteristics of the GT, and then 'borrow' their wind tunnel setup to test and tune a wing and air dam design!