Can you "feel" your Rear Spoiler's Downforce?

[PNewitt]

With the thousands and thousands of cumulative CS driving miles between owners, I was wondering if you've ever felt the downforce of the rear spoiler while driving.

It's like a tugging feeling--and you can feel the rear of the car move down a bit. A similar spoiler was tested at Bonneville for a magazine in 1969, and it pretty much didn't kick in until about 110 mph--noticed by the test equipment.

However...if you're going 70 into a 30mph headwind, you could feel it with the net wind force of 100mph..

Your personal experiences--at higher speeds--would be appreciated.

Have any of you driven a stock '67 or '68 Mustang coupe, and then can tell the difference with a GT/CS--by the spoiler?? Do you get any sense of greater stability through the spoiler while driving?

thanks--Paul N.

 

[Midnight Special]

Hmm... I'm not sure if I can say I noticed a difference, but all my cars have been beyond "triple digits" and the CSs (especially FEs) have been remarkably stable. I had a '66 and another '69 (351W) that were a real handful!... A 30 kt headwind is rare around here & would be hazardous re; tree limbs and debris, so the airport runway (or valley on a day w/o helicopters) is preferable.

I have also had the stock '68 up around 90, but was afraid to push it w/160K+ miles on the original 289... It too seemed stable.

The fastest I've been in a CS was the white J-code, pegged... Very smooth

 

[Mosesatm]

With the thousands and thousands of cumulative CS driving miles between owners, I was wondering if you've ever felt the downforce of the rear spoiler while driving.

It's like a tugging feeling--and you can feel the rear of the car move down a bit. A similar spoiler was tested at Bonneville for a magazine in 1969, and it pretty much didn't kick in until about 110 mph--noticed by the test equipment.

However...if you're going 70 into a 30mph headwind, you could feel it with the net wind force of 100mph..

Your personal experiences--at higher speeds--would be appreciated.

Have any of you driven a stock '67 or '68 Mustang coupe, and then can tell the difference with a GT/CS--by the spoiler?? Do you get any sense of greater stability through the spoiler while driving?

thanks--Paul N.

When drving in the snow it seems to me that the air does not hit the spoiler at high speeds. Since the snow builds up on the rear window, trunk lid, and spoiler I think the air going over the roof creates a low pressure area, almost a vacuum. That is a very unscientific observation from 30 years ago so please take it for what it's worth (diddly squat)

Anyone have access to a wind tunnel?

 

[rvrtrash]

When drving in the snow it seems to me that the air does not hit the spoiler at high speeds. Since the snow builds up on the rear window, trunk lid, and spoiler I think the air going over the roof creates a low pressure area, almost a vacuum. That is a very unscientific observation from 30 years ago so please take it for what it's worth (diddly squat)

Anyone have access to a wind tunnel?

My limited knowledge of aerodynamics would lead me to believe that Arlie is correct. Because of the shape of a coupe, there would be a low pressure zone at the rear window and the spoiler would increase that by moving the exit point for air flow higher. I would imagine you would have to have significant air speed to compress the air over the trunk and provide downforce. At the same time, those speeds would create lift at the front end since there is no front spoiler, making it seem the rear spoiler is doing more than it really is, and making the car more unstable due to decreased tire contact pressure for the steering. Just my opinion. My degree is in electronics, not fluid dynamics.

Steve (My head hurts now. I'm going skiing! :wink: )

 

[PNewitt]

Steve--your comments are fairly close to what the (1969) magazine's test was like, and they do recommend a front spoiler.... And--as a coupe, and not a fastback, the spoiler still works very well.

But I'd just like to know--from a driver's perspective, if the rear spoiler works for you --at speed.

Tim's comment is right--it creates stability. That is exactly what Shelby wanted for the fastbacks--and it worked just like that. It was from his years of racing how that spoiler was developed. It's not just for show.

(A side note...then engineer Fred Goodell sat in the back seat of a '67 Shelby out at Bonneville, lit a gigar, and watched the smoke be extracted right out of the interior at over 100mph. Those upper side scoops really worked!
Ah! 1960's exact-science at work!)

Paul N.

 

[GTCSMustang]

I doubt you're going to see much "real" downforce from the spoiler at normal driving speed. I did some quick calculations and at 60-mph the spoiler would produce about 10-lbs of downforce. At 100-mph the downforce increases to 26-lbs. The spoiler produces as much drag as downforce. The combination of both drag and downforce could produce a slight stabilizing affect, but I'm not sure how much the driver would really feel.

Scott

 

[Midnight Special]

...I made a similar attempt in the late-70s with my first S-code that had an after market front spoiler... It departed at around 80 & I promptly ran over it (thought about adding a change of pants to the tool kit in the trunk after that ;-)

But seriously; I can see it working on the fastbacks @ speed, tho have never seen or read any significant data. Seems to me cars that are produced for high speeds pay as much attention to the front aerodynamics as to the rear. I do remember some data on the Boss 302s and a noticeable difference in their rear wing (adjusted full tilt) at about 130 mph... but it was slight.

I agree with Arlie in that it was designed more for appearance than function based on the Shelby success and may have a little to do with why Shelby wasn't interested in producing performance coupes.

I also believe high speed stability in our cars have as much to do with the condition of front tires, suspension and steering in keeping control when the front wants to lift... The ones I found scary over 100 had alot of backlash in those areas.

Speculative IMO

 

[PNewitt]

I doubt you're going to see much "real" downforce from the spoiler at normal driving speed. I did some quick calculations and at 60-mph the spoiler would produce about 10-lbs of downforce. At 100-mph the downforce increases to 26-lbs. The spoiler produces as much drag as downforce. The combination of both drag and downforce could produce a slight stabilizing affect, but I'm not sure how much the driver would really feel.

Scott

That's the whole thing....is the feeling of the spoiler just imagined--or is is a real sensation while driving? I know that there are so many variables in this (engine, tires, how far the car is off the ground, etc..), but I thought that some owners would know.

So far, Tim can confirm this experience. I'm not asking everyone to go out and drive in excess of 100mph (LOL), but hundreds of owners times 50K+ miles is a lot of driving experience. Does anyone with a '67-'68 coupe know how it feels WITHOUT a spoiler?

I wonder what David A. knows about this--at the drag strip? Hmmm....I wonder what his CS would do with a front spoiler? Anyone out there use a front spoiler? Does it help?

I know that there is zero air pressure at the back, where the taillights are, because on a college trip to Yellowstone (circa 1978), my rear trans seal went out, and there was this perfect sheen of trans fluid on the whole back of the car.

Paul N.

 

[GTCSMustang]

A little of topic...but I swear my car runs better after it's washed.

 

[Diesel Donna]

A little off topic...but I swear my car runs better after it's washed.

Now that's a fact!
As for the spoiler issue? uh...I'd just say no.

 

[Midnight Special]

That's the whole thing....is the feeling of the spoiler just imagined--or is is a real sensation while driving? Personally, I would believe you would need to go alot faster for it to be a "real sensation".

So far, Tim can confirm this experience....
Yes Paul, but I stop short of attributing that to the trunk spoiler. The true GTs with the 390s were extremely comfortable at those speeds compared to the others likely due the weight vs aerodynamics.

I wonder what David A. knows about this--at the drag strip? Hmmm....I wonder what his CS would do with a front spoiler? Anyone out there use a front spoiler? Does it help? Joe would be another valued opinion based on his trips to Grass Valley (that Yeager would envy! ...and he didn't even need to be launched from a B-29! ;-) Six hours for a trip that usually takes 8 should provide some data.

I know that there is zero air pressure at the back, where the taillights are, because on a college trip to Yellowstone (circa 1978), my rear trans seal went out, and there was this perfect sheen of trans fluid on the whole back of the car. This is very true (also on 69 & 70 FBs)

Paul N.

...Whatever the outcome; it is a fine looking design that promotes classy expectation without need to prove it to the onlookers (with today's no-tolerance speed consequences ) based on Shelby's history, Fred & Lee's insight and FoMoCo's marketing ;-)

 

[PNewitt]

Yes, as far as spoilers go, it IS a more radical look--than even on today's cars. I've seen wings and stuff on Hondas and other cars, and they don't do much more than cause more drag...

Somehow, for the book, I'd like to get a photo of the side of the car with a smoke stream running over the top, and up the spoiler.

More than once, in a rainstorm, I've seen water flying up and off the rear while going about 60-70.

There is something we all share...it's seeing the top of that sassy spoiler in our rear view mirrors. Pretty cool, and pretty rare.

Paul N.

(BTW-- I've noticed more radical wings on the NASCAR racers now, with side winglets--like the Knight Rider KR)

 

[Diesel Donna]

Those little wings and so called spoilers on the Honda's and other small cars always make me immediately think it looks like a handle and I want to pick them up and carry them around. Most are silly looking. Just my opinion of course.

 

[Midnight Special]

Those little wings and so called spoilers on the Honda's and other small cars always make me immediately think it looks like a handle and I want to pick them up and carry them around. Most are silly looking. Just my opinion of course.

...add an exhaust driven fan to the bottom & they'd make great lawn mowers...

 

[heliaster]

I used to have a 67 C-code coupe that I "tested" a few times. When it began to top out at 100+ the predominate squirrelly-ness came from the front end and not from the rear. It had a pretty stock front and rear suspension, although it had been lowered 1" and poly bushings were used. If I was going to put $ down on where stability (downforce) could be needed, it would be with the front end of the car - but I love the rear spoiler.

Now it is important to note that I haven't driven my GT/CS yet, so I'm not saying the rear spoiler doesn't do anything, just that I noticed some front-end instability on a normal coupe.

Just my two cents.
-Zac

 

[rvrtrash]

Steve--your comments are fairly close to what the (1969) magazine's test was like, and they do recommend a front spoiler.... And--as a coupe, and not a fastback, the spoiler still works very well.

But I'd just like to know--from a driver's perspective, if the rear spoiler works for you --at speed.


Paul N.

Not exact, but further input. When I had my '72 Mach 1 (fastback of course, with front and rear spoilers--rear was a wing) it did feel like the whole car would settle down at around 100-110, but when it got up around 140 or so, if I hit an "undulation" in the pavement (not a bump, but a level change that would make the suspension load and unload), it felt like the whole car was going to go airborne. Just for info----and I'll deny going over 70 when #1 daughter is around. :wink:

Steve (Dad to some)

 

[CALIF GIRL]

around 100-110, but when it got up around 140 or so, and I'll deny going over 70 when #1 daughter is around. :wink:

Steve (Dad to some)

Now I know where my "Big Bro Joe" gets his lead foot from:wink:

 

[Scott]

Spoiler at 120+

Hello,

Just new to GTCS and a virgin poster in the forum but this thread has tempted me as soon after I bought the car I took it to the stops on the speedo and felt what I believe to be the spoiler's effect....

Acceleration in first gear gets too scary to hold any longer at about 45 and then as traction breaks momentarily (the locking diff thankfully keeping it to a twitch) into second I had originally thought there was a sensation of the spoiler's effect.

After reading the earlier posts I am sure that rather than the rear getting heavier it is more due to the torque/power balance from the motor as it revs throught this range. I base this on the elementary aerodynamics mentioned earlier and also the fact that the weight is still very well forward.

After 70 when top is selected the trip to 110 is sudden with 120 coming a little slower, although this is almost certainly more due to my courage waning than the engine's ability failing. However, and this is the point of the thread, the weight of the car does seem to become more balanced and even through bends.

Having said the weight shifts, I should clarify that it is a shift to what is in my opinion a more balanced and poised position. Braking from these speeds is even and the transition from spoiler being operational to having no effect is unnoticed. There has never been any "floating" sensation far less any desire to become airborne.

ss.

 

[robert campbell]

In 1977 I had my 68 Shelby GT-500 KR up to 130 miles an hour coming from Tacoma to Bremerton. 5,100 RPM on the tach at this speed. 3 plus me in the car. My future wife in the car. 2 lane highway then, but a nice long straight stretch. Amazing the acceleration of this car. I brought it up to 120 without mashing it fully. From 120 to 130 I mashed the throttle. You could feel it accelerate!

What idiot sold this car in 1978… That would be me….. $4k….

Car was very stable at his speed!! Rob was not!!! Never went that fast again. Whether the spoiler had anything to do with it was lost quickly after I stopped shaking!

I know my cars are faster after a wash!! Really fast after a wax job! Blinding fast after a two stage McGuires polish and wax!!

As for wings on Honda’s. the lawn mower picture says it all. They double as a leaf blower with a huge rubber hose on those giant useless exhaust tips!! And they get good mileage downing it!!! Little stinkee in the garage as most of then have had the doody run out of them and they burn as much oil as gas. “check the gas, and fill “er” up with oil”!!

Rob

 

[case12]

When I was 16, I ran 138mph in my 72 Dodge Charger (the fastest I have ever been in a car). No shaking, no weaving, smooth ride.... and just pure speed adreneline. And it had no wing/spoiler - I guess it didnt need it. I was embarrassed though when the Roadrunner with the 426 Hemi blew past me.

I know this doesnt help the CS discussion - but the full design, weight and aerodynamics of the particular car style probably have a lot to do with the usefullness of a spoiler - and the speeds would have to be pretty high.

I will say that the spoiler on my CS makes it look faster at zero mph.

Casey