Tire pressures

[wildbilly32]

2005 996 C4S 52k miles. Owned for two years. Stock suspension, as far as I know. One year old Bridgestone Potenza S-02A N3 225-40 front, 295-30 rear on stock 18" wheels with approx. 1500 miles since new. While airing up for new season remembered rough ride and that I had reduced pressure a few #'s to soften ride. Is this a bad thing? I drive the car mostly in town like a normal car. While I will occasionally zip from a stop or take a corner or two quicker than wife appreciates! No track, no DE, no pylon racing. Just a grocery getter! Manual calls for 36#'s front and 44#'s rear. I know it has a sport suspension but the ride on less than perfectly maintained Nebraska roads is at the minimum taunt and maximum punishing. Am I just getting old or should I look further into things that control this like suspension bits ?

[Ahsai]

I run 34# front and #40 rear. My understating is the 36# and 44# is for a fully loaded car (full of passengers and luggage).

I found 36/44 to be really too harsh even on the stock suspension. I have x74 so 34/40 is a must for me.

[wildbilly32]

Ahsai: Thanks. I'll try 34 & 40. Have you noticed any funky tire wear after reducing pressures?

[Ahsai]

Nope. Tire wear is normal. The Rear tires will always wear faster on the inner side.

[wildbilly32]

Yeah inside rear tire wear is why I put new tires on after I bought it. Previous owner was oblivious to that fact. Just looked at the outer tread while checking air pressure. Should have seen his face when PPI mech. had it on lift and said "come here and take a look at this!" Good negotiating point plus the "it will need an alignment check"(which turned out good).

[techengr]

2004 996 Carrera Cab 56K miles. I have owned this car for about a year and LOVE the way it drives, handles, everything about it....except rear tire wear. Pirelli that came on it on the rear blew. Replaced with the only tires I could find in Eastern Texas on a Sunday afternoon, 275/35R18 Firestone Firehawks. Good tires. I had no complaints except I only got 5000 miles out of them. Replaced with the same size Michelin Pilot SPT AS 3+ 95Y in January of this year. I mixed with 224/40R18 BF Goodrich G-Force C2 A/S. I know this is not recommended but thank the good Lord that I had tread on the front tires to keep me on the road in the rain on the highway. The Michelins have gotten 5000 miles since installed in January! I should have paid more attention to the tire pressure that was added during installation as all 4 tires had 32 lbs added. I checked depth across the back tires and they have worn to 2/32nds on the outsides but still have 4/32nds on the insides. All else constant, is this the behavior I would see with low tire pressure? Could the slightly different tire size from stock in the back cause excessive wear? The car has not been wrecked, per the dealer and I see no evidence to say that it has been. Thanks in advance for your help.

[wizard]

Excessive wear on the outer edges of the tread Is the classic sign of under inflation. It's wiser, safer and far more economical to regularly check tyre pressures and to stick to the tyre sizes recommended by Porsche.

Checking alignment might be an idea also.

Edited April 22, 2018 by wizard
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[Ahsai]

32psi is way too low. Factory recommends 36psi front and 44psi rear when car is fully loaded. With driver alone, I run 34 front and 40 rear.

[techengr]

Many Thanks! So, any idea if I will have problems with Michelin honoring the mileage warranty? The tires are warranted for 65,000 miles but since they can't be rotated on this car, the warranted mileage is cut in half per the warranty. At 4660 miles, that is still way below the 32,500 miles that I should be getting but I need to know if my missing that the installer screwed up the tire pressure makes me liable for the accelerated wear.

[wizard]

Driving on under-inflated tyres, as evidenced by wear, would most certainly void the warranty. As the owner of the car, you are responsible for its maintenance.

[creekman]

Wizard, nicely said... 

Air pressure for the tires is as important as oil and water to the engine...

[techengr]

Thanks guys. Yep, I figured as much. Not making excuses. Just hoping for a legal loophole. Live and learn.

I still think the rear tires are wearing much too fast, though. The car is so much fun to drive, it is hard to drive conservatively but I don't drive dangerously or overly aggressively and never been on a track. I have inflated the tires to the proper pressures and plan to drive it like I stole it to even the tire wear before the warranty time expires.