What??? That is like the maximum tire pressure for each tire. That is not what you do. Try 32-36 for fronts and 38-42 for rears if they are 18 inch tires.

 

Op that’s a dangerous tire pressure as you drive the tire heat increase’s tire temperature this cause tire pressure inside to go up as well exceeding tire max
you are one pothole away from disaster

 

50 PSI is whacked out.

I would run about 34 F and 36-38R.

 

Yep, I'm right about there on my tire pressure as well.

 

That could be it (tire pressure). I have tried all sorts of different pressures, but I’ve found the stock Porsche pressures work perfectly for my 99 Cab: 36/44 front/rear

 

I thought it was a bit high as well. When I told the shop to use those pressures ranges, they strongly advised against it. They referred to the Sumitomo website and I just assumed they knew better given their clientele. Yesterday I lowered it to 35psi front, 40psi rear and the problem has been HUGELY minimized. It's still there though a little, but I suspect that tire pressure was a large bit of the issue and I think the remaining "floaty braking" it's having can probably be solved with the alignment scheduled on the 7th.

Thanks for all the help!

 

This shop does not know what they are doing if their pressure recommendation default is to use the tire MFG MAX approved pressure.

 

OP - Toe adjustment, if it’s out of parameters now, will help with any residual skittishness. 35/40 is a good mid ground. Find a spot where you can threshold brake safely a few times and assess the handling as the car decelerates. Do this before/after visit to Protech. Now that your pressures are right, you can give the guys a better description of how the car is currently handling. See how and when ABS kicks in and how front and rear behave a few stops. Please post pre- and post-alignment numbers. This is a good post for others in the future to refer.

 

Completely agree! WTF!

 

Yes. Unacceptable.

 

Agree 100%. Of all the things a shop should know about, this is so basic and critical that I wonder if a neighbor who is ‘good with tools’ would be better and safer than this mechanic.

 

Sounds like you don't have enough "toe-in". ....Toe-in is whats keeps the car stable and tracking straight.

The 996 should have a lot of rear toe-in, this keeps the tail from wagging during hard braking. With the stock rubber bushings you loose some rear toe-in during hard braking, so if you don't have enough to begin with you can end up being at 0 toe-in or worse, toe-out......MUST have the proper specs.

Same for the front, except a 0 toe-in or even a slight toe-out will make a faster "turn-in" into a corner at the expense of less straight line stability.

 

+1
What a bunch of incompetent and ignorant people at that shop.
The chart on the sumitomo site mentions no specific vehicle type pressures only the max. pressure which is always 50 psi for any passenger tyre (and it's 'written' on the side wall).
It does make you wonder though why that pressure is listed if it is wrong for 99% of all vehicles and misleads most consumers...
Doesn't mean it is the correct tyre pressure and the guys in the shop must know that.
Every tyre manufacturer will always refer/direct to the pressures given by the vehicle manufacturer.
I'd give the shop manager a right lecture that he should have his mechanics trained on the matter.
OP, check out the tyre pressure sticker inside the frunk, it's all there (and in the car's operating manual too) so you know for yourself what the recommended pressures are.

 

That was the local Porsche dealer, fwiw...outside of pointing me to whatever literature they showed me the max being 51psi, they mentioned something along the lines of how low profile the tire was, anything below that was a hazard to the rim, etc...

You would expect a service advisor who sees these cars regularly to know such things, especially since the PO took it there regularly, so I blindly took their word for it...needless to say, that wasn't the first bad experience I had there, but this one will definitely be the last....

 

Inexperience and incompetence know no bounds, even at a Porsche dealer. Kind of scary actually. I would stay away from them.