help please - SWB unstable in a cross-wind, any solution?

[haycait911]

in my stock-bodied SWB any cross-wind makes the car dart and drift, not much fun. I recently had an alignment done and we put on a little extra toe-in to help stabilty. in calm weather it tracks beautifully straight and stable, but even a light cross-wind changes the whole ball game. I've got plastic bushings thoughout the suspension and I've gone over it, everything's tight.

hoping someone out there with more experience could suggest something. I do have a glass S bumper and a ducktail, if that would help but really like the stock body look. the car weighs a little over 2000 lbs fully wet without driver, and the problem really only shows up in the 100 - 120+ mph range.

any help/input much appreciated. Don.

[john walker's workshop]

when you push the front or rear of the car sideways, repetedly, do the tires move between the wheel and the ground? soft sidewalls are a common handling problem. no spoilers @100mph is another.

[Christien]

Interesting - I get a bit of that even at regular highway speeds (120 km/h) - the wind can just push me all over. The only time I get speeds like you're talking about is at the track, and there I don't have any stability issues at all, which is notable, because the highest speed point at Mosport is often very windy - in other cars I've driven there (at much higher speeds than my car can reach) I've noticed instability. I only get about 160-170 km/h at the end of the straight in my 911, but in a 996 turbo or Z06 Corvette you can easily see 230, and both those cars don't feel planted if there's any wind at all.

I've always assumed that the difference is tires - my street tires (Pirelli P6000s) are old and crappy. They've got a huge sidewall (60 profile) and always feel greasy. But the track tires (RA1s) are completely different. Both sets of tires are shot, so I'll be replacing soon (if I don't sell the car) and will just go with RA1s or R888s for street and track.

[Christien]

Originally Posted by john walker's workshop

when you push the front or rear of the car sideways, repetedly, do the tires move between the wheel and the ground? soft sidewalls are a common handling problem. no spoilers @100mph is another.

John, I'm curious, how can you tell if the sidewall is moving or flexing? What does it feel like?

[Drisump]

Originally Posted by haycait911

in my stock-bodied SWB any cross-wind makes the car dart and drift, not much fun. I recently had an alignment done and we put on a little extra toe-in to help stabilty. in calm weather it tracks beautifully straight and stable, but even a light cross-wind changes the whole ball game. I've got plastic bushings thoughout the suspension and I've gone over it, everything's tight.

hoping someone out there with more experience could suggest something. I do have a glass S bumper and a ducktail, if that would help but really like the stock body look. the car weighs a little over 2000 lbs fully wet without driver, and the problem really only shows up in the 100 - 120+ mph range.

any help/input much appreciated. Don.

My car is fine at that speed.....maybe you should ADD 700lbs or so.....LOL

[john walker's workshop]

Originally Posted by Christien

John, I'm curious, how can you tell if the sidewall is moving or flexing? What does it feel like?

you can easily see the movement as you push the car sideways, by hand. you don't see much with a shorter, stiffer sidewall. 15" tires are usually pretty soft, with their taller sidewalls. try that with a 17 or 18" wheel and you get very minimal movement.

[1QuickS]

You might like to get a copy of Porsche 911 Story by Paul Frere. He provides lift and drag coefficients for the 911s during the development of the duck tail. Turns out that the "S" front spoiler must be used in conjunction with the duck tail for 87 lb of lift @ the front wheels and 161 lb of lift @ the rear wheels @ 143 mph while these numbers were more like 183 lb and 255 lb for a standard body. It was noted that the fenders being higher than the sloped hood created a rapid air pressure decrease over the front axle with cross wind.

I have opined that a car running at higher speeds would benefit of an alignment performed at a ride height equivalent to the lifted vehicle height at the higher speeds intended.

You might want to convert to monoballs at the inner rear pivots, the rubber bushings allow for toe-steer. You might also be aware that the trailing arms provide significant toe change with vertical motion as in lifting at speed.


On a different topic...Targas are good donor cars for coupes.

Paul Abbott
www.PerformanceOriented.com

[Jeff Higgins]

Early 911's with no aero aids are notorious for this. Paul Frere covers this topic very thoroughly in his book Porsche 911 Story. There really isn't much you can do to eliminate it, except for following Porsche's examples of ever more sophisticated aero aids as the cars increased in power and speed. These cars actually generate a good deal of lift at speed, and a side wind makes it even worse. As a matter of fact, even the later aero aids (front spoiler and whale tale) produce no downforce - they merely reduce, but don't eliminate, lift.

Any of these later aero developments would be out of place on a SWB. An S front spoiler will help tremendously, though, and not look too out of place. A ducktail would offer even more stability, but even that kind of crosses over into being a bit off for an early SWB. Try an S front spoiler. I have one on my 3.0 liter '72. The car is pretty darn planted up into the 120's down the front stretch at Pacific Raceways. Much over 130-ish, and I gain some insight as to why RS's had ducktails...

Edit: 1QuickS is quick - he beat me to the Paul Frere recommendation. Great book that belongs in every enthusiast's library.

[kenikh]

Par for the course. Same as both my 911 and my VW fastback. The only things that help are lowering the center of gravity, adding weight or adding aerodynamic accoutrements (that are inappropriate on an SWB).

Lower, stiffer suspension is the way to go.

[s5uewf]

perhaps installing heavier torsion bars or sway bars would at least reduce the body sway a bit, though it would not affect lift.

[teenerted1]

i have tried to chase jeff up to 120...my stock bumpers and engine lid dont help. i start to float around anything north of 100...110-120 i have a hardtime keeping it in my lane due to the lift the early cars have.

get that s bumper on there to say the least...not sure how sidewinds are effected by the bumpers...dont really notice much up to 90 but i really dont like to spend that much time at those speeds...i like the twisties these cars are great on, not long straights.

[haycait911]

Originally Posted by john walker's workshop

when you push the front or rear of the car sideways, repetedly, do the tires move between the wheel and the ground? soft sidewalls are a common handling problem. no spoilers @100mph is another.

I did the wiggle test, there's a LOT of sidewall flex in those tires. a little more tire pressure would probably help.

I want to keep the stock-ish SWB look so a ducktail is out. any thoughts on running just the S front bumper? I did this on my '73 and it seemed fine, quite stable at 130 plus.

[john walker's workshop]

a friend had a 78 vw bus that was a lane changer when cross winds hit it. i was driving it down around kelso wa one day and i had to pull over it was so bad. a stater would have thought i was drunk. ordered up a set of beefy front and rear swaybars, heavy duty gabriel shocks and 6 ply truck tires and it was night and day.

[1QuickS]

The early 911's used an alignment trick to help adjust for steering compliance and the resulting toe-steering effects; a 35(?) pound compression load was applied between the front tires during alignment. If you have rubber in your steering links I suggest you replace them with the "Turbo tie-rods" to help eliminate this compliance. Also, if your car has been lowered without making bump-steer adjustments to the front suspension then you might have exaggerated steering effect with slight vertical body motion. Another item of compliance is the upper front strut mounts, they may be old and you would benefit by their replacement.

Paul Abbott
http://www.performanceoriented.com/

[haycait911]

I seem to have solved my problem. I found another ducktail that I liked better than my glass one.

help please to ID this ducktail?

and put on as 'S' type front bumper. very stable now at speed, even with a fair crosswind. I don't particularily like the look, but it's growing on me. functionality comes first. went on a porsche run this weekend and even at speeds over 120 mph things were very stable and steady. I'll look for a plastic air dam type lip to go on the bottom of the bumper, but even now things are quite acceptable.

[billybek]

Which ferry crossing is that, Don?
Maybe it just doesn't look right to me because of the lack of a long summer line up of traffic!
Car looks great.

[JT912]

I've got a bra that isn't the type that hugs the hood. The dam between the headlights seems to help push the front end down and does seem to help the light-end feeling at higher speeds.

[tcar]

Get the front 'S' spoiler, aftermarket has some. They were an option, I believe in 66.

The ducktail doesn't help without it. No duck would be better.

I believe a '66 still had the weights in the corners of the front bumpers. Are they still there? They'll help.

What battery (ies) do you have?

Put an extra 4-5 lb. in the tires also.

16"-17" wheels would look bizarre on a SWB.

[Christien]

Originally Posted by haycait911

I don't particularily like the look, but it's growing on me. functionality comes first.

I think it looks a bit unusual because we're so used to seeing flares in combination with the ducktail and front S spoiler, so to see them on a narrow body car looks a bit different. That said, I still think it looks pretty damn good!

[haycait911]

Originally Posted by tcar

Get the front 'S' spoiler, aftermarket has some. They were an option, I believe in 66.

The ducktail doesn't help without it. No duck would be better.

I believe a '66 still had the weights in the corners of the front bumpers. Are they still there? They'll help.

What battery (ies) do you have?

Put an extra 4-5 lb. in the tires also.

16"-17" wheels would look bizarre on a SWB.

thanks tcar. it has the 'S' spoiler, bumper weights are gone and won't be back. they would certainly help but way too heavy.

billybek, it's the ferry heading east at needles. wasn't busy at all.