RayBest

Thanks PasPar2 I tend to agree with you. Honestly - if I thought that it was tire pressure, I probably wouldn't be stressing about this in the first place. Hopefully Misdirection is right and it is road surface irregularity. I did mention earlier that my suspension setting was on 'PASM - soft'. Nobody commented on this. Is there a 'given' that above a certain speed, the setting should be, or is expected that the Porsche owners are aware that we must push the button to firm up? I am a 'newish' Porsche driver so not sure about this. PS - I was on a quiet stretch of road with no other vehicles, so wasn't being that irresponsible. Also, I have quite a few trophies for bike racing, so am accustomed to a bit of speed. The Carrera has just had a suspension replacement by Porsche. Little bit worried about the instability. Honestly - 236km/h is not that fast for a Carrera S.

alexb76

Do you have TPMS? To monitor your tire pressure? How come you couldn't tell while driving?

RayBest

Don't have TPMS.

PasPar2

I had sport plus and PASM on at the track, but the road surface was perfect. On the way to the track I hit the PASM button on to see if I can tell the difference and OH man can you feel it. The car follows EVERY little ripple in the surface and the ride became very harsh and uncomfortable... Maybe retry your experiment on a better, smoother highway? I dont think you need to go quite as fast as you did. I had an alignment issue on my 996 and it was very obvious at 85mph and higher.

RayBest

OK, I'll try that. Perhaps I should speak to Porsche and ask for a re-alignment, or at least their opinion.

RayBest

I took the Carrera S for a drive today (for the first time since) and she felt solid and stable all the way. Properly. It must have been the road condition last Sunday that made things feel unstable. I drove the same road the other day with my pickup and did notice rutting was actually worse than I originally thought. However, I still do think that the tire pressures had a role to play because I checked them today cold and they were spot-on which means that they were way too high that day (I had to release a substantial amount of air that day after the drive). Also, I suppose it is understandable to be a bit over-critical with assessment when you get your car back from a repair, especially when the car is so very much loved.

ralt12

Do you have 18's or 19's? Cold pressure seems low relative to 997.2 CS recommendations...

RayBest

19's. My pressures (in psi) were 45 front and 50 rear. Here in South Africa, we use bar, so were 3.1 front and 3.5 rear. I've reduce to 39psi rear and 48 front. Would that be the right pressures to use?

Macster

There should be a tag on the inside of the gas cap lid, or on a door jam or perhaps on the inside of the glove box lid that gives the inflation pressures for your car.

Be careful. In some cases the pressures are for a fuly loaded car: 4 "adult" passengers; luggage. Inflated to the recommended pressures for this load would be too much pressure for just you and a passenger and a moderate amount of kit..

Lvt19672

I have a base C2 with 19" sport designs as a factory option and looking at my door jam it reads that the tire pressure for unloaded vehicle is 34psi front and 40psi rear others have reported 33psi front and 39psi rear is this correct?

RayBest

Sorry 39 front and 48 rear. Perhaps still too high. The tab says 2.7 bar front and 3.0 bar rear for 19 inch. Maybe 34 and 40 is better? 2 up max - I never have rear seat passengers. Also I try to keep the fuel tank full for weight on the front. Is this over-kill?

CAVU

Door Jam is a starting point. You will also want to take a look at your owner's manual as it will have more information when it comes to tire inflation pressures. In my 2009 manual I need to look at 3 sections to gather what I need:

- Tires/Wheels
- Loading Information
- Technical data

I only change the tire psi if I am making a big change in the load. Simple as that.

Jamesr6967

Porsche has traditionally set the pressures a little high in the rear to induce understeer, which would be noticeable at those speeds. You could try dropping the rear a lb and possibly increasing the front pressure, do one end at a time tho.

Macster

Overkill.

The only time the fuel tank level is important is when the car is in for alignment. The alignment guidelines call for a full fuel tank. (At least for the pre-997 models.)

Just keep the fuel level somewhere between full and empty (Generally I like to fill up at a quarter a tank but sometimes I'll continue to drive the car after the low fuel warning light is on.)

GT Silver

I just think that its the light front end of the Porsche. Did a run this past weekend in my 997.2TT and yes, I experienced some "instability" at speeds above 230km/h when my other car, BMW F10 M5 twin turbo felt very planted. My tyre pressures were chacked before I started off, and my rear spolier was deployed too. This drive was done over the same highway which I did 10 plus high speed runs with the M5 earlier.