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

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

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"...;-)

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 ...

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.

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

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.... :eek:

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.

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?

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.

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...

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!

:confused: are you saying post-74 have serious aerodynamic issues?

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).

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.

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.

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.

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

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

http://forums.pelicanparts.com/uploads/69 targa.jpg

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?

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

Actually the early cars did have better aerodynamics than the bellows bumper cars until you get to the 964 which was designed with aerodynamics in mind.

That settles it. I'm with Randy now -- your shocks are shot. Before I typed my previous post I went and did the same test on my car in the garage and it didn't bounce at all. If you're getting 2-3 bounces, they're junk.

Are you going to install them yourself or have a shop do it? If you're going to do the job yourself, I'd recommend that you also check the ride-height and corner weights (if you can borrow the scales or a checker). Those two jobs are somewhat labor intensive, but can be done at home before you do the alignment. Do a search on "corner weight" or "do it yourself alignment" on this BBS and you'll find lots of reading.

Welcome to the world of 911's and Pelican's BBS! SmileWavy

I KNOW ITS BEEN A WHILE SINCE A POST ON THIS TOPIC BUT MY CAR FRONT END FLOATS FROM 90+ WHATS GIVES? I HAVE THE FOLLOWING DONE 77 S

BILSTEIN RSR FRONT REAR
22/ 28 TB
BRONZE BUSHING FRONT AND NEATRIX REAR WITH SOME NEW FACTORY STUFF ALSO
SMART RACING REAR SWAY BAR
FACTORY TURBO UNDER THE BODY SWAY BAR
FRONT RSR BUMPER W/ 2" LIP
STRUT TOWER BRACE
RACK SPACERS
GETTY REAR WING 3.8 FOR SC
RIDE HEIGHT 25.5 FT 25 REAR
996/BOXTER 17" TWIST RIMS
1.5" FRONT AND .75" SPACER IN REAR
215/40/17 FT
245/35/17 REAR


CAR WAS ALIGNED WITH STOCK FRONT BUMPER IT FLOATED
RSR FRONT BUMPER IT FLOATED
REAR SWAY BAR IT FLOATED
NEW TOYO T1S IT FLOATED
FLOATES ON OR OFF THE GAS

SHOULD RSR FRONT STRUTS RIDE LOWER THAN REGULAR BILSTEIN?

WHAT GIVES???

Do you have that rubber lip that the later cars can use to get some front spoiler effect?

And... has it always done this?

One other thing to consider is to verify that your car is properly corner balanced. Some of the float may be attributable to improper corner balance.

the rsr bumper has a 2" lip and help it a tad. the problem seems to be the the suspension setup. i have not corner balanced it yet. just a 4 wheel aligment.

Replacing worn out stuff is not upgrading is it? Assuming shocks, bushings and alignment are all in order, that should be what the factory spec'd and provided. It's fairly easy to "upgrade" when the old part is NG, but in my book that's called repair. That's why X brand spark plug wires are such an improvement compared with wires that have broken conductors and cracked insulation. Replace the worn out stuff, then try it again.

If you still need assistance, I'd say, minimally, lower the front slightly for a slight rake, then add a front spoiler. If you have the budget, add everything else that's been suggested. It all helps, in other areas as well.

Sherwood

I would reiterate the suggestion that you also replace the rear spring plate bushings. I would prioritise this ahead of the front bushings. The reason IMHO is that the rear toe and camber adjustments both come from the spring plate. If the spring plate is not held firmly by bushings in a good state of repair, you get toe and camber change under load. Particularly unhelpful is that you get toe out under load. If you have ever seen 30 year old spring plate bushings you will know that they change from being round to being quite oval - if they have not been replaced, they will certainly need it. Most people use Neatrix rubber bushings to replace OE bushings as the OE ones are vulcanised onto the spring plate and an OE replacement involves buying new springplates at much greater cost. The Neatrix bushings (available from Pelican) are very close to OE in the key ride/handling characteristics.

The bad news is that this is not the easiest job in the world and reqires removal of the rear torsion bars and normally requires re-indexing of the rear torsion bars. If you are getting the ride height adjusted and a corner balance completed this removal/re-indexing may be necessary anyway - so its a good to do these altogether.

I promise you that new rear spring plate bushings will make a big difference to the way the rear of your car feels. I also agree with the consensus that the floating feeling is primarily shock related, although you should remember that the light front end of the 911 will always feel a little more floaty (or at least lighter) than "normal" cars.

HTH
Richard

I'm assuming that this is a track car so I'm responding within that context. I'm also assuming that the mechanicals for your car in reasonably fresh shape. I believe that you are describing an aero problem.

Can you post a picture of your rear wing (GETTY REAR WING 3.8 FOR SC). I wonder if it is still too agressive and overwhelming the RSR front bumper/spoiler. Are you running any sort of adjustable lip/gurney on it? Have you tried (just for kicks) to replace it with a standard whale tail or duck tail? How about adding an adjustable front splitter?

If you absolutely can't change the aero package, I believe that a combination of spring and shock changes might help (but not solve the problem), but to be honest it would be a crutch and not a solution to the problem.

We now have two different owners (and cars) looking for a solution on this thread, but not necessarily the same answer. Let's keep them straight.

Sherwood

i dont have an adjustable splitter. the getty wing is a tad samller than a standard 3.8 to look better with sc flares. i think the front ride height and coner balance is off. perhaps the rsr raised spindles require a lower ride height.

Alfizzo, the RSR raised spindles by definition require a lower ride height by about 3/4 an inch -- basically the 18 mm that I believe that the spindle is raised. If you are running at something close to stock ride height with RSR spindels, the affect would be the same as raising the front ride height with stock spindles. Does that make sense?

replace the 6 cylinder in the rear with a 4 cylinder WRX engine. the WRX engine weighs 250 lbs less, and the radiator in front gives the car more nose...

50/50 weight disty, makes for way less oversteer and a much happier driver.

sjd
ducking and running.

john,

iam running euro ride height 25.5 front 25 rear. so your saying to drop it an additional .75"?

thanks
fracno

Your rear spoiler may be too agressive over powering the affects of the front spoiler. In these cars changing the spoiler can affect the car like a see-saw. If you put a big spoiler on the back it can cause the front to get lighter, so if your rear spoiler is too effective then it can cause your front end to get light despite a front lip/spoiler.

fracno, Yes, I'd lower both ends by 18 mm (.71 inches). While you're doing that of course I'd check the alignment, bushing condition and corner weights to make sure that they are where you want them to be.

sjd; :rolleyes:

When I first purchased my 73 S, it was scarey as hell to drive fast. I implemented all the recommended changes on the first page of this thread except the Neatrix, and also had the car aligned and corner balanced and the difference was phenominal. The car is confidence inspiring, agile, and predicable. When you get enough funds to do the whole thing - follow these guys advice - they know of what they speak. Until then get a front spoiler and invest in new shocks and an alignment.

A good first step may be an alignment which seems like the logical approach when confronted with basic handling issues and would be a good baseline for further major suspension modifications.

Believe it or not, too much toe can make your car feel floaty at speed and oversteer like crazy.

Always good to start with the basics.

Cheers,

Joe