How does the wind effect an early Porsche?

[H.G.P.]

Wondering the effects that may be noticed both 1. on the road, and 2. on a track, in an early 911? Weight effects?

Thanks

[john70t]

It is a teardrop shape with the point in front and the weight in back:

So I guess that makes the rear traction more predictable/planted and has the attention of the driver focus, while the front is lighter in weight to change direction quickly.

All this is negated by the back weight wanting to bypass the front under turning and braking, and the front(without a spoiler) being too light and twitchy on a fast strait-away.

It's a unique combination, kind of like designed instability in a jet fighter, that rewards the skilled and punishes the inattentive.

[juanbenae]

it can cause chaffing if the windows or sunroof is open...

[A Quiet Boom]

It's basically a backwards airplane wing, at speed there is a great deal of lift exerted on the car which is why the factory went to front and rear spoilers. I have an IROC front and ducktail rear on my car, at around 70mph the car starts to fell more planted than between 50-70 where it feels a little loose.

[Randy Webb]

It is a bad design for wind effects. Side wind will affect a 911 be destabilizing it. And there is a side component to most winds, if you think about it. I think Frere's book discusses this.

[Grady Clay]

The critical issue is the center of wind pressure from the side is different from the center of gravity (in the vertical plane). That causes a torque around a vertical axis. Not a comfortable feeling.
I recall there was a technical article about this in Christophorus several years ago.

Aerodynamic aids (shape, wings, spoilers, etc.) can help mask the problem. Christian is right, aerodynamic down force (or lack of lift) will make it more stable with wind side forces. A 935 is a totally different animal at 215 MPH with perhaps 2 G additional down force compared to 75 MPH and minimal down force.

Best,
Grady

[nigel911]

1) Blows it all over the road

2) Blows it all over the track

; )

[azasadny]

We drove through a tornado in Hell, Michigan last summer and the car did great! Held to the road and took corners well. I think the new Dunlop Sport 9000's helped, but the 911 performed admirably and got us to our destination safely (Porsches to Pinckney event).

[H.G.P.]

I had a side wind today on the highway. And I'm thinking I need a wind driving lesson.

[Zeke]

Originally posted by H.G.P.
I had a side wind today on the highway. And I'm thinking I need a wind driving lesson.

The first time a stock car driver gets to run the Talladega or Daytona tracks, they tend to overdrive or oversteer the car. The buffeting makes the car jump all around, literally well over 2 feet side to side total. The mrore experienced drivers just drive the average centerline of the jumpy tracking. The wind is not smooth and has pockets, or low pressure and high pressure zones. This is when they are all alone on the track. It just gets worse when several cars are on the track at the same time. It's a tough lesson to learn, to trust the car.

I had a Barber formula driver tell me that the way they set up the cars, he always felt that the front end was off the ground going down the straight. This was more of a function of the air pushing down on the rear wing. The steering got real light like he was hydroplaning. He never got used to it and therefore, didn't trust the engineers. They have several cars to set up for the series and know each track. The engineers know what they are doing.

Getting light is not a bad thing in itself, but the force lifting the car is also slowing it down. Same is true with downforce. The trick is to get the car neutral and then add downforce as needed for quicker lap times. Add more downforce for higher corner speeds. On the same track, on the same day, one car might be running less downforce for higher straight speeds while another is going thru the corners faster with more downforce.

How does all this answer your question or your statement about a lesson for driving in the wind? Simply, you don't drive the wind. The car does. You just point it. If you don't like the way your car 'drives' the wind, add downforce.

First, lower the car. Less air under, less lift. Add a duck or whale and add a dam or splitter on the front valance. Try to keep the car balanced. If one end is creating more downforce than the other, the other is actually getting lighter in proportion.

Many of us slow our cars down overall because we don't know what we are doing. But it looks good and it feels better in terms of grip. We like grip, it's our security blanket.

[H.G.P.]

Originally posted by Zeke
The first time a stock car driver gets to run the Talladega or Daytona tracks, they tend to overdrive or oversteer the car. The buffeting makes the car jump all around, literally well over 2 feet side to side total. ....
Many of us slow our cars down overall because we don't know what we are doing. But it looks good and it feels better in terms of grip. We like grip, it's our security blanket.

Thank you for the detail. "Hydroplane" vs. "grip". Yes, I slowed down.

[Pettybird]

>>>>>The first time a stock car driver gets to run the Talladega or Daytona tracks, they tend to overdrive or oversteer the car.

that banking messes with your head, too. it's a smoother transition at the tracks, but i got to drive around the chrysler 5 mile oval test track in chelsea, MI in the superbird. 6 lanes wide, 33 degrees of banking in the top lane. i tried to get into the top lane at around 80 and the car was uncontrollable. went back up at around 110, and it was a lot better. got it up to about top speed (130ish- 3.54 gears, stock 630cfm carb on a 440... honestly now), and it was a lot smoother. between the banking and the aero parts it felt like i was riding in a high speed elevator.

a second lap would have been nicer, though

the sc gets blown around pretty badly compared to the dailys, probably because it's small and light. the 'birds don't get blown much, possibly due to the nose and wing, but probably a lot more because it weighs as much as a tank with another tank bolted to it.

doug

[Randy Webb]

Grady's comment re Cp and CG is right on -- that is the problem and no other production car really has it.

[911SCfanatic]

Great, thread--very informative. I was driving a few days ago when wind gust were up to 15 mph and I wondered for a moment if something was wrong with my suspension because it felt so loose. Drove it the next day in no wind and it felt great again. I was surprised how much more the wind impacted steering on the Pcar v. other cars.

[Zeke]

Originally posted by Zeke



Many of us slow our cars down overall because we don't know what we are doing. But it looks good and it feels better in terms of grip. We like grip, it's our security blanket.

I need to clarify that. I didn't mean we don't drive as fast. I meant some are putting a sail on their car and adding drag which is hindering top speed and rate of acceleration at high speeds.