I'm driving a 997s with 19" wheels. I've read similar posts but I was hoping someone has a more direct answer to my situation. I often drive with myself
200 lbs, my wife 120 lbs :-) , and my two small girls totaling about 65lbs.

I've been running around 31psi in the fronts and 39psi in the rears.

does this sound reasonable or should increase it a little since that's closer to a
"Full Load" in the manual. I don't want to be rolling around on rocks but I don't want to compromise safety either.

 

Low load pressures are:

- 997.1 - 33/39 PSI

- 997.2 - 34/40 PSI

You are low at front. If you carry 2 adults + 2 kids I would go 34/40 if I were you.

It is quite dangerous to run under-inflated.

 

That's not significantly closer to full load. Not unless Porsche has a very sexist view of "two occupants." In aircraft we figure an average male is 170 lbs and only a damn fool pilot uses that average instead of looking over his prospective passengers carefully. That number comes from the early twentieth century and people grow a lot bigger these days.

Even if you figure at 170 lbs, two men would be a load of 340 lbs. You're only carrying 385. Not a big deal intuitively, but tire wear will tell the story.

Personally, we just bought our 997.2S, so I'm trying the pressures in the manual first: 34/40 for that partial load. They seem quite comfortable, but of course I'm biased by two things. First, the dealer's guy just read the plaque on the driver's door, which is the full load pressures, and then he got a little generous to boot. When you drive home on rough freeways at 39/45, changing to good roads and 34/40 seems like a limo. On top of that, we have PASM, which is more comfortable in normal driving than the passive suspension.

Now... about safety. I haven't checked the references and done the arithmetic yet, but I seriously doubt the pressures were chosen to stay inside the load limit for these premium tires. The Porsche is not a motor home. It's not even slightly heavy as sports cars go these days. So the pressures are almost certainly chosen for handling and braking considerations.

If you run 31/39 you're not going to roll these tires off the rim, so unless I'm missing something that longer-term owners can tell us about, the only effect may be uneven tire wear. And not even that necessarily. Different brands of tire with different driving habits want different pressures. It's always trial and error finding the right pressures when you first buy a car or change brands of tire. (Assuming you have the background to judge or have knowledgable friends. Tell anybody else to read the manual and do whatever it says.)

Since your pressure furthest from recommended is the fronts, in extreme conditions you might increase the understeer somewhat. Skipping a long (and long standing) argument, more understeer is generally safer than the other direction. Safer than letting the pressures get too low in back that is. You're only ten percent below recommended in front, so you will find the steering is slightly less responsive, but we're talking about a car whose response is needle sharp already. You're not going to be taking your little girls along while you kiss the wall at a race track.

I can't see a safety issue myself, but different cars react in different ways to changing tire pressures, so it's smart to ask. For me too. What do more experienced owners think?

 

Great... Thanks again adias.

I'll go put some more air in when I get dinner tonight

 

Tony is one of those more experienced owners I was talking about. I would take his advice.

 

Sorry I missed your post initially.

No tracks days with girls yet but hopefully someday.

 

I follow PAG recommendations as I know Weissach knows best. In my 996 days the recommended tire pressure for 18" rims was 36/44. For a bit of comfort to cushion the common expansion joints I rode for a while on 33/40. I then found out that my rears were wearing faster in the center... Counter-intuitive right? I was expecting inside wear due to the negative camber 911 rears have. It turns out that these low profile tires have very stiff sidewalls and when at speed (and under-inflated) the tire expands the tire circumference between the stiff walls due to the centrifugal force in the center, thereby reducing the contact patch (less grip) and center wear. I learned my lesson. And it's not wear only, it's safety. When under-inflated the centrifugal pull at high-speed can trash the tire to bits, and I've seen that happening with 911 drivers running under-inflated.

Std high profile tires is different - they wear outside when under-inflated. Also, I suspect that our low-profile tires, if also grossly over-inflated, would wear in the centers too, so there's that correct value when the tire is full, expansion is controlled, and wear is right - mostly on the inside.

Note: lowering front pressure may lead to over-steering, not under-steering.

 

The sensor on the front drivers side is funky. The others adjusted after about 30 seconds of adding air. The front drvers didn't move at all until I gave up and drive away. Then it took another five minutes. Is this normal or do I need to replace something.

 

Someone will tell us both I'm sure, but I wouldn't be surprised if that is normal. I think I read something about it in the owners manual, but it makes sense anyway for a couple of technical reasons to boring to bear telling.

 

TPMS sensors are slow on 997.1 cars. You need to drive a few miles to sync them. In any case, you should adjust tires cold w/ an accurate gauge like an Accutire.

 

I do 36/44 in southern Florida-smoothe roads and mostly only me in the car......................

 

Is this both you? Why do you have two accounts?

 

Just curious... what would you recommend for 20" pressures?

 

interesting? that would explain why some email replies are going to the wrong address.

Let me look into that.

 

I have an '08S my DD and 90% of the time only me in the car I have the 19" Bridgestones, and find 31/37 cold to be ideal. they warm up to around 33/40 after some fun driving, and that is perfect. On my pirellis, I noticed that 34/40 was best. Seems like the bridgestones have a nice stiffer sidewall, so at 34/40, the car felt more bouncy I ay play with it in the ranges indicated until you find what you like. Regardless, none of the indicated pressures are going to be "Dangerous" You just won't be maximizing the handling IMHO