Best mod to reduce "float"/oversteer in early car

[David E. Clark]

Hello to all!

I am seeking opinions on the best modification I can make to my '73 911E to reduce the "floating" feeling that I get at about 70+mph and the underlying oversteer at all speeds. While I am new to the breed, I do realize that one of the characteristics of a rear engined car is a very light front end. I'm not convinced, however, that this "floating" feeling can not be reduced. My car does not have the "S" style front air dam, so I was wondering if this would be a worthwhile investment considering the cost. The air dam bumper itself is not all that expensive, but to have it painted to match the rest of the car would be. Would new shocks, Konis or Bilsteins, help? It appears that my current Boge shocks have significant mileage on them. (They do not bounce, however, and seem pretty functional). How about turbo tie rods? Lowering the car and installing a bump steer kit? I do not plan to race the car, I am only looking to have more fun on my weekend drives.

I am also considering removing the two old style batteries, which are about shot, and replacing them with one Optima or Stinger as suggested in other threads. This would save me about 25 lbs but since the savings would all come from the front, would this make my "float" feeling worse? As always, thanks in advance for the advice.

David Clark
'73 911E Targa

[silverc4s]

David,
Things to consider would be:
1. Get the ride height set properly (24" front, 24.5" rear on std flares)
2. Add the front spoiler, reducing lift by a LOT at speeds >70 mph
3. High Performance tires, turbo tie rods, bump steer kit all will help a bit, but not as much as 1 & 2 will.
4. Lower the car even more, in 1/2" increments, revisit #3.
5. Once you have the front firmly plannted at speed, it may be time to look into the "ducktail"...;-)

[Early_S_Man]

David,

New shocks and strut inserts F&R would probably solve the 'floating' ... Koni's are my preference, but Bilstein Sports are good, too.

Does your car have the factory anti-roll bars F&R? Weltmeister bushings would help, too. The old bushings are probably worn and loose-fitting by now.

But, eventually you will want to do everything else Bill suggested, too ...

[masraum]

24 front 24.5 rear sounds too low and also the wrong measurements. To get the proper slope of the body front to rear the front measurement should be a half inch higher due to the wheel arches being different front to rear. The norm is 25.5 front 25 rear. Either way, lowering will help.

Good shocks and struts will make a huge difference if the origin of yours are unknown or if it is known, but they are really old.

A front S style dam and a ducktail should make a considerable difference at highway speeds.

I think first things to tackle would be the shocks, lowering if needed, and alignment, and then if all else is in line then go for the spoilers.

The front and rear spoilers at 150 reduce lift over the front and rear axles by about 400 lbs, and according to a Car & Driver Article from '74 they start working as slow as 30 mph

One thing to remember though is that the factory designed the spoilers together to reduce the rear lift more than the front lift (not overall, but the ratio of before and after) to design in high speed understeer rather than high speed oversteer.

[RallyJon]

The norm is 25.5 front 25 rear.

With ~25" diameter tires. If your tires are smaller, ideal ride height is proportionately lower.

[Joe Bob]

Shocks, bushings, turbo tie rods, bigger T-bars, sway bars, lower profile tires on wider wheels, front lip spoiler, rear wing.......

See, you are done....

[304065]

David Clark (no relation to the noise-attenuating headset people?),

You are correct, if you reduce the polar moment by going to a single battery, you increase the tendency to oversteer. You are, in fact, doing the opposite of what the factory did in first putting cast iron inserts in the bumper, then putting dual batteries out at the corners.

I have reduced the polar moment pretty significantly in my race car, by going to a lightweight battery, fuel cell, fiberglass "s" spoiler, and this lightening DOES make the car more inclined to rotate/swap ends, BUT when the tail steps out, the very light weight in the front makes it possible to quickly correct, make the front radius match the rear.

Presumably this is not what you desire for street driving-- a new set of Bilstein's and a lower and align should fix you up.

[jluetjen]

If the car "floats" at high speed, it has nothing to do with shocks, springs or swaybars. Those things only make a difference while the wheels are firmly on the pavement. If the air-flow is picking the car up, mechanical changes will have little if any impact. It's an aerodynamic issue and the fix is aerodynamic. Put a front spoiler on the car.

As far as "underlying oversteer at all speeds", could you elaborate a little bit? Also what is your current set-up? Tire pressures? Swaybars? Torsion bars? Alignment?

[Randy W]

I think you are mistaken John. Shocks will make a difference. A "floating" feeling of instability at speed is often a symptom of worn out shocks. New shocks will make the car feel more planted at speed.

[Mike M]

In short...do all of those things!! I had the same problem with my 69S.
I replaced the rear spring plate bushings,installed larger torsion bars,turbo tie rods and rack spacers.After an alignment,the car FINALLY drives and steers the way it should.Ultimately,I think it was the rear bushings that made the most difference. Good Luck...

[Early_S_Man]

Condition of the shocks and anti-roll bar bushings is much more important for rear-engined cars than most people are aware! As MikeM pointed out, the control arm bushings are also important in terms of handling quality issues ... but, not typically regarding the 'floating' issue being discussed here.

Pre-74 911's don't have any serious aerodynamic issues unless there is an upset ride height at one corner, typically. Yes, the front 'S' spoiler is helpful on early cars, especially regarding stability in crosswinds, but certainly not critical for straight-line stability! I tested a '67 911S once with over 110K on the clock and dead stock, including original Konis and stiock-sized Michelin XAS 165VR-15 tires on the 4.5 x 15 Fuchs ... and it was rock steady and all speeds up to 135 mph [as high as I got on the local roads here] on the highway! No front spoiler, and none needed from the feel of that car!

That is not to say the 'S' spoiler and ducktail aren't a good idea ... just that they aren't as important for handling as tires, shocks, anti-roll bars and suspension bushings. Neatrix rear and 'street' hardness poly-graphite front bushings are a good idea, ultimately, but not as critical as the condition of the shocks!

[island911]

Originally posted by Early_S_Man
. . .. Pre-74 911's don't have any serious aerodynamic issues . . .

are you saying post-74 have serious aerodynamic issues?

[turbo dave]

I'm with Warren and Randy on this one- I've done most of the things mentioned in the last year and a half, and its quite a difference- amazing, actually. I'm anxious to get out on the track for the first time since I did all the work (next weekend), but even on local twisties, night & day. And, the nose on my car is higher than it was pre-updates (it does have an S spoiler).

[silverc4s]

In all cases I will defer to the experience and knowledge of Warren...
In the particular case of my 1969 Targa, no spoiler on the front, even after a thorough front end rebuild, Bilstien shocks, some lowering and the bump steer shims, it was still heavily understeering at anything over about 80 to 90 mph. Downright scary at 110. I never put a spoiler on the front, always attributed the understeer to large qtys of air builtup under the nose.

[Neilk]

If you want to reduce oversteer, replace the rear spring plate bushings with Neatrix ones. It made a HUGE difference in my car. The car would oversteer in a 25mph corner, now it's firmly planted to the ground.

If you have never had the bushings replaced, you will be amazed at how bad they are after 30 years, at least mine were.

[Early_S_Man]

Island ... no, I simply referenced 'early' cars, since that was the model being discussed! Of course, the late cars, with all of their greater 'road-hugging weight' ...

Bill,

I neglected to mention the possibility of a 'nose-high' attitude ... possibly due to sagging rear torsion bars! I have seen a few cases, but not driven them extensively that way, since I usually adjusted the rear ride height in the course of dealing with general issues.

[island911]

Originally posted by Early_S_Man
Island ... no, I simply referenced 'early' cars, since that was the model being discussed! Of course, the late cars, with all of their greater 'road-hugging weight' ...

Heh-heh thanks Warren.
Now don't the early cars have some chunk of cast-iron in the bumper for 'road-hugging weight' ?

[silverc4s]

Warren,
I don't think the nose was high. Most people commented the opposite, that the rear was a bit on the high side..

[jluetjen]

Randy;
Granted, new shocks will dampen the car and might help. But given David's description and desire for the "Best modification" (rather then modificationS), I'd still stand with the front spoiler.

Since the "floating" feeling would suggest the low speed dampening on the shocks is shot, maybe David could do the old "step on and off the bumper" and see how many times the car bounces. If it bounces, I'd say that you're right Randy and the shocks should be fixed or replaced. If it doesn't bounce but rather just settles back to the ride height, then I'd say the shock are most likely not the issue and the money would be better spent on a front spoiler.

BTW David, how does the car feel when driving over wrinkled pavement? Does the feeling change at all with car speed?

[David E. Clark]

WOW! Thanks for the great responses. I've only owned this car since Dec 2002. I did quite a bit of research (on this site and others) prior to purchase and decided that I wanted a 72-73 E, Targa. My two highest priorities were NO RUST and good compression. Since my budget was limited ($10,000-$12,000) there were some things I had to compromise on. In my case it was ANY history of the car. Well, after two years of searching I got what I wanted. Not a spec of rust, a car that is very presentable, and an original MFI engine with excellent compression that pulls very strong to 7,000rpm. On the other hand, I have no idea how old the shocks are (or anything else for that matter); nor do I have a single service record prior to my ownership. Since the price was right, I thought it was worth the risk. Anyway, no sense fretting about that now since I already bought the car and so far so good! No major complaints.

I have done the "bounce" test and have concluded that there is room for improvement (2-3 bounces depending on how hard I jump). Tire pressure is 28 front, 31 rear. Tires are mid-grade radials with good tread left (room for improvement there also). I have also inspected the bushings and concluded that the rear bushings (which are clean and bright orange plastic) are probable reasonably new and the front bushings (which are black, rubber and show signs of cracking) are probably original. Since money is still limited, I think that I will go with new shocks all around, new bushings up front and a four wheel alignment. I guess I probably should do the turbo tie-rods at the same time since I'll have to align again after putting those on -- right? If that doesn't do the trick, I'll try the front spoiler. Any other suggestions as always will be appreciated.

David
'73 911E Targa