RayBest

Today whilst driving at speed (236km/h) my 997 Carrera S started to feel unstable. Thereafter I went to a garage to check my tyre pressures and found that the pressures were too high all around. The car has recently had suspension and drive shafts replaced (rear). Could this be (hopefully) due to the high tyre pressure or perhaps due to the suspension repair? All work was done by Porsche. Any comments would be greatly appreciated.

Renzsport

I haven't been that fast in mine
Was the suspension properly aligned after the work? Are your tyres properly balanced?

yvesvidal

How about the wind?

Yves

Macster

Tire pressures must be right cold. If you checked them right after a high speed run they could be "too high" but obviously due to the increase in pressure from the heat.

It is up to you if you want to check and set the tire pressures cold and for the payload weight of the car and then make another test. Whether you make the run or not be sure the tires are properly inflated.

The suspension and drive shaft replacement should I believe have been followed by an alignment. Was this done?

alexb76

At those speeds, wind might play a role if it was windy. Otherwise, for tire pressure, set them cold 33/39. Didn't you have TPMS to check your tire pressures?

Rocco07

I really wish Porsche had an indicator to, well, indicate when the spoiler was deployed. I can only verify it's deployed when passing another car and looking for the reflection.
I'd say put your spoiler up manually, and try it again. See if there's a difference. Or, somehow verify it's deploying when required @ 75 mph, I believe.

wc11

Never been but are the roads good for that speed?
I assume you've driven the same stretch of road at similar speeds prior to your repair for comparison?

myw

its not to be set cold at 39/44?

ps. 235 km/h!!?? wow

yemenmocha

alignment could be off too.

However, with the light front end, in my experience with a 997 the front end is a little light and doesn't give the same sort of planted, heavy feel that other cars may give, i.e. my BMW ///M cars do feel more planted and safe at high speed (they weigh more and are near 50/50 balance).

Edgy01

I keep my 06 S partially loaded at 39 and 34. (R-F). Stable, and smooth. What pressures specifically were you using?

Little Green

First off going near 145MPH is going to make our cars feels "unstable" which is a subjective issue anyway. I have always thought my car to be very light footed up front at anything over 125MPH. I put a front lip spoiler on it as well as a fixed rear wing( I know I am not a Porsche engineer) and it seems to have helped but again subjective. Different track, different wind conditions may have made a difference in how the car "felt". I would get an alignment done if you have not already. On a perfectly smooth road these cars are great, albeit light up front. On a mediocre road that lightness up front feels like you are about to take off if you hit the slightest bump and our amazing steering at regular speeds becomes amplified at high speeds.

RayBest

Alignment was done by Porsche. I believe that the tyre pressures were actually correct because I measured them hot after the drive (thanks guys for the info regarding this). The spoiler was up, I noticed it. There was virtually no wind, however the road conditions weren't bad at all, but not of 'Autobahn' or highway standard' - slightly, ever so slightly ridged. One thing, though, that I forgot to mention, is that I had the suspension on 'soft' and not on the sport setting. Perhaps this was the reason for the 'light-nose' feeling? Fuel was low and total est. occupant weight of 140kg. The front tyres were at 3bar and rear 3.3bar when measured after the drive. Balancing and alignment was done after the suspension replacement, and done by Porsche. I have driven the same stretch of road before with my Cayman S and know that a similar feeling occurred, but thought at that time that it was also tyre pressure - but being too low at that time with the Cayman which I also checked thereafter. I now realise, though, that the Cayman S was also on the softer (and not the 'sport') suspension setting. Do you think this was the problem, or me just going too fast? Thanks for the replies btw, greatly appreciated.

vern1

I have been close to that speed on the track (yikes but never on a "street") and i usually run 39/35 hot (dont remember the bar eq). I have a c4s so maybe the added weight in the front helps but didnt find it unstable. My guess is its just the lift

Misdirection

I personally think at those speeds a little lightness in the front is to be expected with stock aero, and any little puff of wind or surface irregularity will contribute. I had that experience myself on the long straight at COTA.

PasPar2

I was close to 130mph on the track yesterday after finally figured out my cold tire pressures (997.2c2s 25/31 cold), but even when they were wrong ( way too high, end of session was 50 psi *yikes*) , I never felt unstable at any speed. Look elsewhere, its not the pressures, Im pretty sure.