Front spoiler / rear wing relationships

[944pilot]

I am currently looking at a car to buy which has a Carrera rear wing but no front spoiler below the valance. I have read that this may cause "instability" at speed.
I am curious, because I will drive the car on the highway for a couple days to get it home (after the PPI, purchase, etc...)
So... 2 questions.
1. What does "instability" mean? All over the road like driving on ice?
2. What is "speed" ? Do I have to worry about anything at normal highway speeds (75-85?)

I plan on putting a stock front lip spoiler on the car, or a RUF style front bumper/valance once the car is home.

Thanks for any comments.

Brian

[defcon65]

I think you'll be OK for the trip back but keep it under 120. Then either remove the wing or add the spoiler in front.

[Rick V]

When I bought my SC it had no spoilers of any kind. I found the front end got realy light around 80, I added the front chin spoiler. After that it was fine during highway driving up to around 100. I found it somewhat unstable on the country roads (I drive them the most) around 80. I added a ducktail and all is now well.
You should be good to drive the speed limit (without the front spoiler) But when you install one you will wonder how anybody can drive without it!
Don't forget to post pics!

[bmgmd]

from what I've read, that set-up would cause some front lift at high speed. What is "high", I don't know. Guess that depends on what's in you trunk, how much gas is in the tank, wind/road conditions...

IMO, it should be fine for speed limit and below driving.

[911S Targa]

What if you dont have a ducktail, or a wing on the back, but you install a front chin spoiler. How will that effect the lift at high speeds ? How does it effect the rear ?

[charleskieffner]

you will enter low lunar orbit at high speeds! just like wil ferch! LOL! as per weissach wind tunnel tests...........having front spoiler and any type tail is noticed at high speeds. on mine at 85mph and above you will really notice crosswinds w/out either. w/both front and rear spoiler/tail combo will track wonderful!

[944pilot]

My .02 after driving my car back from Texas (about 1000 miles), Carrera tail with no front lip is:
It does get a bit "light" about 95. There were some pretty strong crosswinds at times, and if I had a crosswind and was passing someone at the same time (maybe 95ish), it certainly wasn't as planted as I would like. I'm gonna find that front lip ASAP.
Brian

[911S Targa]

Bump.

Still searching for the answer to my question.

[Jack Olsen]

The car will be a little looser at very high speeds. It's probably not something that would be hazardous in road driving, but likely noticeable on a track.

[tonythetarga]

911sTarga
with some downforce on the front and not in the back, the back end will be loose on cornering at higher speeds. Ever seen an F1 car lose the wing before the corner in the braking zone?? Kinda like that but not as dramatic

[911S Targa]

Thanks guys.

[rs6er]

I've been driving my 81 SC for 25 years with just the front spoiler. Even done some PCA track days at Lime Rock. I've had it up to 142 MPH and the steering def. feels scary light at that speed. However, I hate what the rear spoiler does to the 911's lines and the front looks naked without it. So, all expert advice aside, I'm keeping it that way.

[charleskieffner]

i tend to look at it this way. A) porsche would not have dropped mega bucks on weissach wind tunnel w/out a reason(racing). B) porsche does not put anything on their cars w/out a reason C) and WIL FERCH was beside himself when i finally e-mailed him and offered to sell mine, due to me going to RUF spoiler w/cooler. D) WIL FERCH did not want to go into LOW LUNAR ORBIT when hauling A$$. E) WIL FERCH is a engineer and if he has one............IT HAS BEEN SCIENTIFICALLY CALCULATED THAT IT WORKS BETTER than not having one!

thats my story and i'm sticking to it!

[RaceProEngineer]

Just a couple added thoughts:

The stock Carrera, especially at "USA ride height", generates lots of lift (and drag, but that's for another thread.) At the front, the lift is caused primarily by air being forced UNDER the car, resulting in John's "definitely feels scary light at that speed".

At the rear, much of the lift is caused by the 911's "airplane wing cord" body shape - air passing over the roof and tail faster than that traveling underneath the car. Thus, Tony G.'s "the back end will be loose on cornering at higher speeds".

If this is true so far, think for a moment about the effect of drastically reducing lift AT ONLY ONE END. Fix the front, the rear "becomes" worse! Fix the rear, and the front becomes undrivable at high speed.
At least before, the Carrera had lift at both ends - now it is totally UNBALANCED.

The solution: Limit air being jammed under the front of the car, AND interrupt the smooth flow of air over the roof and down the engine lid. PRESTO! Less lift all around, more "stability" as Brian aptly described it, and that nice, balanced feel that Ricky V's car has achieved.

Now, if you really want to get fancy (and achieve unbelieveable stability at speed), the next step is to apply aero downforce in the same distribution as the car's physical weight bias front to rear. Or maybe just use a chin spoiler and a duck tail.

Ed LoPresti

[paulgtr]

I have a 75 911s with no spoiler below the valance in front and I put a duck tail on the back.
front ride height is 3/4 of an inch lower than the rear ride height and i have no stability problems up to 135mph.

will be back dating the car and going to an s front spoiler and ducktail combo.
more than likely the ride height will be evened out more as well.

[juanbenae]

i was a skeptic on the chin spoiler stability thing, until i installed one. makes a HUGE difference at speeds even over 90mph. i have the 964 auto-gig on my car so the tail spoiler is not what some of the huge one's will do, but the chinny was one of the best upgrades ive done for car handling. i guess i mean "bang-for-the-buck" upgrades.

thanks shawn!