996 Cab

[antonio_spain]

Hi Loren,

First of all congratulations for the forum. Very helpfull and grat site. This is my question: I used to have a Boxster S with sport suspension for a couple of years. Since the last 13th of June a have a beautifull 03 C2 Cabrio with PSE and Sport Suspension, and I have done already 2000 miles.

The engine is really GREAT, but I find the handling of the car is very very diferent. I think I am geting to the new weight distribution but, lets be honest I miss the Boxster chassis.

The very first day I founded the front very very loose, so I looked at the tire preassure and they were rocket high in cold something like 38/45 psi. I went down to 34/42 cold, but here in Spain is really hot now, and last week after an intensive ride I found that I was having hot preasures at 40/49...

So again I took out some preasure to leave them cold at 32/36. I have been reading a LOT of information in various boards but I am a bit confused.

Question: What shoul be the cold preasure gap ? 8 psi as factory recomends ? Less ?

Thanks,

Antonio.

[Unitah]

I have a 2002 C4 Cab running the X74 suspension kit and Pilot Sport Cup tires. I find a cold pressure of 28f/32r very good and balanced for the street. With the cup tires, you want to achieve about 34 to 36 hot. On the track, I have to start way down about 22/24 cold. Now, this was just to give you an idea, I don't know which tires you are running, let me know...

[Loren]

Thanks!

Changing from a mid-engined car to a rear engine car is a bit different. The Boxster (like the 914 before it) are great handling cars and... because of their great balance very forgiving to drive. Now, your new Carrera is a little tougher since it has a weight bias over the rear wheels. To compensate for the weight bias Porsche has fitted the Carrera with a tire/wheel combination that promotes understeer -- mainly for safety. Tire pressure changes on a Carrera will have a greater affect on how the car handles and feels than it did on the Boxster. I believe that tire pressures need to be dependent on your driving style. So, there is not a tire pressure that works for everyone. The factory says front 36 and rear 44. I found that to not be the optimum pressure for my driving (I drive pretty hard and aggressive). I found the car too loose at those high pressures. After I experimented with lowering the pressures I have settled on 32 front and 36 rear (cold). Again, your pressures may vary but I would try to keep a 4 psi difference between the front-rear to keep the car in balance. I would not go much below these pressures and certainly not below 30.

I guess the bottom line is try a few different pressures and record you results (an autocross or closed track session is good for this) and then settle on the pressure that you feel most comfortable with (and gives the fastest times!).

[Guest Guest_antonio_spain]

Thanks Loren. Tomorrow I will go again for a drive and let you know. :)

[Brian in MA]

Hello Antonio!!

I picked up my '03 C2 Cab on Friday the 13th of June too. It also replaced a Boxster. I'm only halfway through the break-in period, so I can't give much of a comparison to the Boxster yet. I'll be doing an autocross next month which should give me a good reference point on it's handling.

[RJFabCab]

Antonio,

I track my cab (Euro M030) with 18" OEM Pirelli Rossos. Stock pressures of 36/44 (cold) are just simply too high. I have found that my car has nice grip, balance, and handling with hot pressures of 36/44.

At rest, this translates into cold pressures of 32/39 for me. I know many people who run several psi lower in the rear (cold).

You're going to love the 996's handling... once you master it! The US stock setup was plowing with too much body roll at the track... hence, the M030. It's a nice compromise for street/track use.

Experiment with your tire pressures and see what you like... just be safe. :)

[Carlos from Spain]

Loren,

Antonio uses 18" 225/285 size tires if I remember correctly (RoWM030), would you want a bigger gap between the rear and front pressures with those compared to the 225/265 rear setup for a less understeering handling?

I'm wondering cause my prefference is 33/41 PSI with my 18" 225/265's (RoWM030) which is already a big gap between front and rear, I feel the car is fairly neutral with the RoWM030 and these pressures and the understeer is dialed out. If I drop the my rear pressures to 36 or so would I get more understeer?

OT: Unitah,

I see that you have the X74 :thumbup: and I'm very interested in how you find it for everyday street use. I have the RoWM030, how would it compare in terms of ride confort for street use? Is the ground claerance too limiting?

[Carlos from Spain]

Oh, and, glad I finnally found your forum BTW Loren, you are an inexhaustible source of valuable info :clapping:

... and also glad to recognise some of my favorite posters (like Don) here too along with the "down to bussiness" and very relaxed ambience here :cheers:

[Loren]

Carlos,

Welcome! :cheers:

Again, tire pressures are (IMHO) very much dependent on how you drive. I grew up with the tail happy (oversteer) Porsches of the 70's so I tend to want a certain amount of throttle oversteer in my 911 (996). I have found that with the 996 though it is not the same... If the rear tire pressures are too high the back end seems to break loose too much (more than I like)... so throttle steering becomes more of a "regain control " condition. So I have tried to balance the cars understeer and oversteer to a level where I feel like I can push the car knowing what is going to happen. My personal experience was that if the front to rear ratio gets to large (or small for that matter) the car becomes less "predictable".

Again, this just maybe my driving style and your mileage may vary... So, that's why I tell folks to balance the car to their liking (not mine) and just make sure you are not breaking any fundamental laws of physics (i.e. tire pressures under 30 psi, ratios too high or too low).

[Carlos from Spain]

Understood thanks :)

I'm going to experiment with lower rear pressures and see how it works for me. Come to think about it, the rear is a bit "jumpy" or "skipppy" when you catch some surface irregularity while in a turn, lowering the rears more with respect to the front will probably help.

[Unitah]

X74 is wonderful. I think there are no issues with its use as an everyday suspension, however, it is not made for that. The car (after about a month of settling), dropped about 60 to 70mm, a lot. The lowest part of the car is now only about 2 to 2.5" above the ground, however, in 3 months of driving with the suspension, I have not bottomed out nor hit anything yet. As for performance, hahahaha, there is no comparison. It still isn't nice like a cup car, but, that would be too too much for the street. This is indeed the best compromise. The car is no longer a soft, mushy Cadillac, it is now what it is supposed to be: a race car. In terms of alignment, I am running -1° front and -2.5° back. A friend runs -2°front and -3° back and the car feels even better. Turnin is instant, the car is sticks and sticks and sticks. I love it!!!

[Carlos from Spain]

Thanks Unitah, I wish I could get by around here with that ground clearance, but I would be hitting the front on everything around here ;)

[Guest Guest_Antonio_Spain]

Loren

After some making another 300 hundred miles this weekend I am going to keep 32/36 cold, that gives me 36/44 hot, at least here in a very very hot Spain during those days. The car is not loose in the front as it was before but as said before very diferent from the Boxster.

For instance with the Boxster it was not easy to do throttle steering, but with the 996 in slow turns I have started to enjoy lifting a bit the gas and the rear slides turning the car into the turn in a very smooth way.

Another thing that hapened today in a slow turn ( I was pushing a bit hard ) was that first I had understeer I lift on the gas and had a bit of tail happy you now, not the controlled thing I was taking before.

Some more feelings are that even with the RoW 030 setup my car is still soft, at least for me. The boxster was much more hard, more direct turn in, which I guess is what you get with X74...but if I am not wrong you can´t get that as factory option in a Cab ?

Well I think is going to take some thousand miles more to start understanding and feeling the car... Maybe it should be nice Carlos to contact some other guys in Spain and rent a circuit for a day or so to push the car in safe place...

[Carlos from Spain]

That would be a great idea Antonio :thumbup:

We can rent the Jarama for a day, but better yet I think, is that if you get a group of people they will set up a DE for the group which not only track time but first lessons with instructors around the track with test cars :D

My brother was at a Mercedes Benz DE there and loved it, and he told me you can also do your own DE if you gather a group of people.

[Loren]

Antonio,

If your car is a MY02 or newer you can retro-fit the X74 suspension. Jonathan(Unitah here) has done this. He can give you all the details.

[alter_schwede]

hey Loren,

you using 32/36 psi cold, and what do you get in warm (not tracked)?

and what tires size and brand?

cheers,

Tony

[Loren]

I don't think I have measured them warm -- but hot is about 38/40.

I am using Bridgestone Pole Position S03's. I am running 225/40 in front on 8 x 18 wheels. On the rear I am running 285/30 on 10 x 18 wheels.

[Greg]

My 2001 996 cab with 18 inch wheels also returned from service with 36/44 cold pressures. Is there any known drawbacks to lowering the pressures? I assume there is increased rolling resistance causing increased heat buildup and increased fuel consumption with lower pressures. A relatively free handling upgrade does sound great.

[Loren]

My 2001 996 cab with 18 inch wheels also returned from service with 36/44 cold pressures.  Is there any known drawbacks to lowering the pressures?  I assume there is increased rolling resistance causing increased heat buildup and increased fuel consumption with lower pressures.  A relatively free handling upgrade does sound great.

Yes, if you go too low you can overheat the sidewalls and cause tire damage.