Qualnhick

Today I finnally managed to take my C2 to full speed (290 km/h) and it was with surprise that above 220 km/h I notice the front of the car all over the place (expecially with side wind). Is this normal ? All of my other cars donīt have this problem, neither my older cars (Maserati 3200, BMW Z3 M ...). Is this normal ? It really fels unsecure ...

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2004 Porsche Cayenne Turbo
2003 Porsche 996 C2 Cabrio
1999 Jaguar Xk8 Cabrio

djantlive

It's probly bc of the rear weight bias. Are the wheels/tires in good condition? Any looseness in steering? I doubt it's due to convertible since the cab is pretty aerodynamic.

Qualnhick

The wheels and tires are in perfect conditions and yes, I think itīs because of the rear weight bias. Insteed of a back spoiler Porsche should put a front automatic spoiler (donīt ask me how, iīm not engeneer :-)
BTW, the rear spoiler doesnīt help, it makes things worse, because it lowers the back of the car and makes the front more loose.

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2004 Porsche Cayenne Turbo
2003 Porsche 996 C2 Cabrio
1999 Jaguar Xk8 Cabrio

1999Porsche911

There are so many things that will cause the front end to get light at high speeds. What size tires are you running? Stock suspension? Any lip on the front bumper? Spare tre in the trunk? Top up or down?

Qualnhick

19 wheels, 225/40 front and 285/30 rear, stock suspension, no lip at front bumper, spare tire at the trunk and top up (I donīt think itīs a good idea to drive with the top down at 290 km/h :-)

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2004 Porsche Cayenne Turbo
2003 Porsche 996 C2 Cabrio
1999 Jaguar Xk8 Cabrio

1999Porsche911

Well, the slightly lower back end due to tire sizes is not that big, but a front spoiler would sure help keep the air from going under and lifting the front end.

Qualnhick

Upps, itīs not 19 wheels itīs 18, sorry for that.
I just think that if the car needs a front spoiler in order to be safe at high speeds, Porsche should set that as standard in 996.

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2004 Porsche Cayenne Turbo
2003 Porsche 996 C2 Cabrio
1999 Jaguar Xk8 Cabrio

1999Porsche911

Your back end is more than 1/4 inch lower than it would be with the 265/35/18 tires. Doesn't seem like alot, but at speed, it makes alot of difference because of the change in angle between the bottom of the car and the road surface. Changing the fronts (when you replace the tires) to a 235/35/18 will bring the front end down about 1/4 inch. I agree with putting a skirt or lip on the bottom of the front bumper.

Qualnhick

Yes, you are right, but Porsche installation size approved are the following:
- 225/40 and 285/30
- 225/40 and 295/30
Next time Iīll change my back tires to 295/30 (it will be lower than front, but less than it is now)
Here in Portugal if you use different tires dimension that the car was approved, youīre in big trouble next time your car goes to inspection (2 in 2 years). Stupid laws ...

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2004 Porsche Cayenne Turbo
2003 Porsche 996 C2 Cabrio
1999 Jaguar Xk8 Cabrio

newport996

I have a C4 cab and I know that the car got MUCH more stable at high speeds when I installed PSS9 coilovers and lowered the car....I also have the Turbo front bumper so I am thinking there is much more downforce on the front end than the stock front at stock height.

washington dc porsche

290 klicks is how many MPH?

Sids911

Assuming "290 klicks" = "290 km/hr" it'd be 180 mph. If not, then 290 kilo-licks must be something nasty ...

washington dc porsche

Wow, 180 with the top down, that's fast!

evo_333

our cars can reach 180????

djantlive

must be getting tail wind.