Loose steering at high speeds

[Guest]

I know I shoundn't be driving this fast and don't very often, but hey it is a Porsche and sometimes you just can't resist. I have a 996 C4 and the faster the better it drives, it loves to run and drive better at around 100-120 than at 60 mph, however. When I get up around 130-150 My steering seems to be slopy or have extra play in it. It feels like I would expect any other car to feel at sppeds over 100 mph. I am just wondering what the fix is to get tighter steering. I would be afraid to push much beyond 150 with the existing set-up. Should I be happy as is or is thier some linkage that should be adjusted or what do you folks think.

[JimB]

Your car feels like it's floating because it is. The lift created by air passing under and over your car is causing lift. Remember studying how a wing works? The way to fix it is to reduce the amount of air passing under the car. You can do this by lowering the car or adding a splitter of some type or both.

Either way you are right that you should not be driving that fast on the street. There are plenty of opportunities to track your car where the only person you are likely to kill is yourself.

Jim

[Orient Express]

I have a 996 C4 and the faster the better it drives, but. when I get up around 130-150 My steering seems to be slopy or have extra play in it. I'm afraid to go faster than 150. What should I do?

This sounds like the story:

"Doctor, it hurts when I poke myself here. What should I do?"

Doctor says, "Easy, don't poke yourself there."

In your case, if your car's very-high-speed handling scares you, then don't go that fast.

My C2 actually gets very heavy at 130+, and feels very comfortable (and noisy) going at those speeds. But not on public roads here in the US. (I take that back, there are 3 roads in 3 western states that I find very enjoyable). In Germany is OK as well.

[nick49]

Any excessive play or lash in suspension or steering components will become more apparent or magnified at speed. Tight and close tolerences as well as tire balance and correct pressure become proportionately more important as speed rises. You probably have also noticed that a little steering wheel movement makes a bigger difference when traveling faster. If you are going to travel fast, the machine should be tuned accordingly. I learned that high speed driving is either something you can either really enjoy or something that you don't like at all. I personally like it and have spent quite a bit of time at or over 150 mph mainly roadracing motorcycles over an 8 year period and racing on the Salt Flats. I cannot recommend speeding on public roads as there are too many unknowns unlike a closed coarse track.

[toddel68]

This topic has been covered quite a few times and I think the common understanding was that it's quite normal for the 996 (earlier even more) with standard aerodynamics to FEEL a little unstable at high speeds. :drive: That doesn't necessarily mean it is. The fact that the steering is very direct adds to that. I get the same feeling in my C4 but until now I never went airborne at speeds 170+. Even not with gusty headwinds. No comparison with my buddy's Vanquish though :P

If you are in doubt you should have your steering checked of course, but again the Porsche is no high speed cruiser like a Benz S-class or BMW 7 series.

BTW: Funny how everybody thinks it's much more safer to go fast on the german autobahn than on a deserted Nevada highway just because you're allowed to. A car changing onto your lane at 100 km/h while you are at 280 is not funny. Apart from that I'd say 70% of our autobahn have a speed limit between 100 and 120 km/h anyway.

Thorsten

[wingless]

(I take that back, there are 3 roads in 3 western states that I find very enjoyable).

And those are?

[1999Porsche911]

I agree that not have a front splitter will make a significant difference in the floating of the front end. I removed mine a few years ago because of damage and I could not believe how much more unstable the car was at 130+. Put it back on and the front end stayed down.

Also make sure the body of the car is sitting as designed. If you have non standard size tires/wheels on the car, make sure the difference between the front body height and the back, is as specified.

[Orient Express]

(I take that back, there are 3 roads in 3 western states that I find very enjoyable).

And those are?

Here are my favorite 3:

Nevada -US 95 between Amargosa Valley and Tonopah - pavement is noisy, but straight, with excellent visibility.

California - I 40 Between Barstow and Needles. The best and smoothest asphalt anywhere, and slightly downhill grade the whole route. On the weekends it is patrolled by air.

Nebraska - I 80 between Lincoln and Ogallala. This is such a boring road, you want to drive as fast as you can just to get past it.

These roads are all lightly travelled during the week, straight, flat, in the middle of nowhere, and good for 180 easy.

And the last one is maybe CA190 from Towne Pass (el 4956) to Stove Pipe Wells (el 5) (31 miles all downhill with a couple of negative-G washes on the west entrance to Death Valley :jump: ) This one is good for 80-90 during the week.

[Guest]

I live in Alabama and thier are many empty roads, especially on Sundays while all the Bible thumpers are praising the Lord . You can drive and not see another car for very long intervals. I don't drive at these speeds unless the road is empty. Even then for short stents only.

I am planing on going to Barber motoer sports for some track time, Posche driving school is thier and I got two days of schooling as a Chrismas present.

As for the possibility of hitting someone else it is thier responsibility to get out of my way :clapping: , If I hit somebody at that speed I don't have to worry about it.

[wwest]

I live in Alabama and thier are many empty roads, especially on Sundays while all the Bible thumpers are praising the Lord . You can drive and not see another car for very long intervals. I don't drive at these speeds unless the road is empty. Even then for short stents only.

I am planing on going to Barber motoer sports for some track time, Posche driving school is thier and I got two days of schooling as a Chrismas present.

As for the possibility of hitting someone else it is thier responsibility to get out of my way :clapping: , If I hit somebody at that speed I don't have to worry about it.

I picked up my 2001 C4 at the factory and it was quite stable well above 130 mph. It has been driven cross country twice, summer of 2001 from POE, and 2005 returning from Daytona, and in MT WY and TX it was as stable as one would wish. On the track at Pacific Raceways and Daytona it was as if on rails even at or about 130 mph judging from knowing I was often at the top end of 5th.

But then my 2001 C4 does have the full factory aerokit.

And by the way, on the AutoBahn drivers are required by law to yield the left lane right of way. In the US. Nevada included, many drivers think they OWN the left lane. And if not that some of them will actually move into the left lane to block you from "speeding".

But then in MT I have had ranchers intentionally drive a herd of cattle out in front of me, across the highway. Apparently in hopes my insurance would reward them for all the calves the cows I killed didn't have. Luckily I was a better driver than they thought. And for Godsakes do not drive I15 in Northern NV or southern Utah at night at any speed, slaughter alley for deer, is that.

[Guest]

I have been playing with the tire air pressure and driving without the psm on. The car really drives or should I say the steering is much tighter at 130+ without the PSM engaged. Anybody know if PSM is used when tracking or do most remove or cut off the psm to race?

[Orient Express]

I have been playing with the tire air pressure and driving without the psm on. The car really drives or should I say the steering is much tighter at 130+ without the PSM engaged.

Air Pressure is probably the reason for the steering response feeling better. PSM has nothing to do with the steering system.

If you have to ask about tracking a car with PSM on or off, then it is probably best for you to drive on the track with it engaged.

[eastriver]

I have been playing with the tire air pressure and driving without the psm on. The car really drives or should I say the steering is much tighter at 130+ without the PSM engaged.

Air Pressure is probably the reason for the steering response feeling better. PSM has nothing to do with the steering system.

If you have to ask about tracking a car with PSM on or off, then it is probably best for you to drive on the track with it engaged.

i don't have PSM on my car, oh boy it gets tricky/ugly sometimes. :eek:

[lrapoport]

If you are running the base/stock suspension, this is normal. It is the front end getting light with speed. I noticed the same thing at 130+ when I first got my 02' C2. Talking to many others, this is normal. It has to do with the US soft suspension, tall ride height and the way air flows above and below the front end. Stiffer springs and dampening will help. You may also notice that the ROW standard (US Sport) and ROW sport have a ride height that is 10mm shorter in front than in the rear. This is to pitch the nose slight and change the airflow above and below the vehicle. When I swapped to a ROW M030 suspension it completely tightened up. It is now very direct and more stable at 160.

You can add big wings and front splitters if your goal is to go slower. In order to create downforce you add drag. The cosmetic changes in 02' changed the cars to eliminate any lift front or rear.

[lrapoport]

i don't have PSM on my car, oh boy it gets tricky/ugly sometimes. :eek:

There must be something wrong with your car. You should probably check your alignment or tires if this is the case. I intentionally bought a car without PSM because of how stable these cars are and wanting to explore the limits without the computer interfering. From having driven one on and over the limits without the use of PSM or 4WD, I fail to see why these were ever offered as options. There are simply no ill tendencies in these cars inherant from the factory. This is not the old 911 of yore. I have a 79' 911 that was basically scarry trying to have anything other than throttle in a corner. Adding additional rubber to the rear was the only way to tame it. That car really needs 4WD or PSM. The 79' is always going to have a delicate balance at the limit. My 996 is completely the opposite. It has plenty of grip, good balance and communicates its intentions always smoothly. I have taken hard turns off throttle in the rain under compelete control. Even on the track when mistakenly entering a corner about 20 mph too fast and even braking through the entire corner, I never felt a single hint of lightness in the back end. The 996 is more of a revolution than an evolution since Porsche has definitely tamed the beast.

Edited March 26, 2006 by 02 Carrera

[JP66]

A few months ago I got my C4S to 137mph, on a bridge. It was fairly stable with a slight crosswind. Last week I went 150mph on a lightly travelled highway, and the car was very stable, with no loose steering or car wable. I could have easily gone faster with confidence, but ran out of straight highway. I don't know what my tire pressure was, but I do have the P-SS9 suspension, with a lower ride height. Prior to PSS-9's I had the stock suspension and at 125mph, it felt a little "floaty".

[RascalRuss]

Just do add a note,

Be carefull just adding a splitter, this is not always the best result and may may make matter worse.

Aerodynamics is a tricky subject and you need good knowledge to understand what add-on will and wont work, CFD is a optimum tool, but doubt you have access to this, although if any of you have a CAD model of a porsche I will run a CFD analysis on it.

Ok, using a splitter, great development, and it works if set right and working with other aerodymanic devices on the car. The splitter, as mentioned diverts the air flow from under to over it. This creates a low pressure region under that car therefore sucking it to the ground. However, sometimes this can be counter acted by the fact that more air is flowing over the top of the car, therefore (mass continuity equation!!) the air flow will need to increase in air flow speed. The higher the velocity, the lower the pressure, and this resultant force wants to pull the car from the road (counter acting force).

If the splitter is design correctly, from aerodynamic analysis, and not some muppet just adding a flat plate to the bottom of a bumper, then they can be tweaked to work "WITH" the car. Such details as diverting the flow to the sides of the car, to the brakes (cooling) and even the angles (resulting in votices being generated, flat plate aerodynamics!!) can alter the other all aerodynamic characteristics of the car.

If you want to get serious, then may be look at having a rear diffuser designed for you, that can sweep up from the floor to the top of the rear bumper (fire proof as it will be past the exhaust) this would work very efficently both with or with out the spliter.

Also a rear wing will help, depending if it has been design correctly to work with the seperation points of the rear.

If you want to hold well over 150MPH than you will need to put money in to it, not just buy add-ons from halfords!!

One more thing, be careful driving at them speeds on the road dude, I know it a rush, but it only take one error and you aint getting out alive at that speed. If you want a rush, spend the money on a track day, that way you learn the vehicles characteristics in a safer enviroment.

Russ H

[geolab]

oo

Edited June 13, 2008 by geolab

[WeekendWonder]

Question for cab owners - at what speed do you get that 'floaty' effect with the top up + with it down?

[PeterC4]

Question for cab owners - at what speed do you get that 'floaty' effect with the top up + with it down?

Interesting question. I think it depends on the year and model. I had a 2000 C4 6spd Coupe that did feel light at the front at high speeds. My 2004 C4S Tip, is heavier, has different aerodynamics and it feels rock steady at high speeds. I have not had it up to racetrack speeds, but even at 80 mph, the C4S feels much more stable, top up or down. The 2002 and later 996 models have more ridgid bodies and I think front end lift was reduced due to certain design changes.

Edited August 27, 2007 by PeterC4

[WeekendWonder]

Is it possible that the GT3 Aero kit spoiler is pushing the back down too much and consequently raising the front?

Even with the hood closed I don't feel enthusiastic about going over 110/120 in this car!

On P Zero Rossos with one new tyre /7mm - other 3 tyres on around 5mm. Running 32 psi rear and 30 psi front.

Rims have a few scuffs from before I bought the car

Some vibration starting from 80mph +.

Recently went over a slight bump/ramp on a 5% upward sloping road at about 100 and the front definitely took off for a millisecond! Felt the car being pulled back on course when the tyres made contact again!

Floaty steering from 110mph +

My mindset is now that something isn't right at high speeds - and when it's put right there will be a huge difference!

Going to get the wheels refurbed and balanced first, then if the vibrations aren't better should I look at alignment - I don't think the car pulls but the road noise is pretty bad. Any other avenues to explore? Do I need to do something to keep the front end down?

Very interesting thread! :renntech:

[PeterC4]

Is it possible that the GT3 Aero kit spoiler is pushing the back down too much and consequently raising the front?

Even with the hood closed I don't feel enthusiastic about going over 110/120 in this car!

On P Zero Rossos with one new tyre /7mm - other 3 tyres on around 5mm. Running 32 psi rear and 30 psi front.

Rims have a few scuffs from before I bought the car

Some vibration starting from 80mph +.

Recently went over a slight bump/ramp on a 5% upward sloping road at about 100 and the front definitely took off for a millisecond! Felt the car being pulled back on course when the tyres made contact again!

Floaty steering from 110mph +

My mindset is now that something isn't right at high speeds - and when it's put right there will be a huge difference!

Going to get the wheels refurbed and balanced first, then if the vibrations aren't better should I look at alignment - I don't think the car pulls but the road noise is pretty bad. Any other avenues to explore? Do I need to do something to keep the front end down?

Very interesting thread! :renntech:

I would have thought a properly installed aero kit, front end included, would help reduce lift in the front, not induce it. As to vibrations over 80 I think you have to get your tires balanced, but don't rule out an out-of-round tire. The other thing worth exploring would be to lower the car slightly, with a different suspension set-up, unless you have already done so. I do think you should research what changes were made to the 2002 models to address this issue and see if you can implement some, but I would have thought with your GT3 kit, it would go along way to doing that.

[WeekendWonder]

Is it possible that the GT3 Aero kit spoiler is pushing the back down too much and consequently raising the front?

Even with the hood closed I don't feel enthusiastic about going over 110/120 in this car!

On P Zero Rossos with one new tyre /7mm - other 3 tyres on around 5mm. Running 32 psi rear and 30 psi front.

Rims have a few scuffs from before I bought the car

Some vibration starting from 80mph +.

Recently went over a slight bump/ramp on a 5% upward sloping road at about 100 and the front definitely took off for a millisecond! Felt the car being pulled back on course when the tyres made contact again!

Floaty steering from 110mph +

My mindset is now that something isn't right at high speeds - and when it's put right there will be a huge difference!

Going to get the wheels refurbed and balanced first, then if the vibrations aren't better should I look at alignment - I don't think the car pulls but the road noise is pretty bad. Any other avenues to explore? Do I need to do something to keep the front end down?

Very interesting thread! :renntech:

I would have thought a properly installed aero kit, front end included, would help reduce lift in the front, not induce it. As to vibrations over 80 I think you have to get your tires balanced, but don't rule out an out-of-round tire. The other thing worth exploring would be to lower the car slightly, with a different suspension set-up, unless you have already done so. I do think you should research what changes were made to the 2002 models to address this issue and see if you can implement some, but I would have thought with your GT3 kit, it would go along way to doing that.

Going to get tires balanced, check for tyre problems and wheel buckle this weekend.

Any pointers for a starting point/good source on the 2002 improvements? Sounds like a good path to go down.

[skipp]

get an X74 suspension.....my US stock suspension floated alot above 100 mph...recently got the X74....much better...I've only been to 120mph since the install, but it was very stable.

[WeekendWonder]

get an X74 suspension.....my US stock suspension floated alot above 100 mph...recently got the X74....much better...I've only been to 120mph since the install, but it was very stable.

Thanks I will read up on it. My understanding is that the ROW stock suspension is stiffer. Has anyone got experience of X74 vs the ROW suspension which is on my car?

Edit - Sorry should have done a search before asking.

Edited August 30, 2007 by WeekendWonder