What "wrong" size were you running before? The 235/35 and 315/25 is the correct size to be running if you go wider, having 25.5" and 25.2" diameters respectively. From the factory the difference is only .1", but they also use the larger fronts. I've tried a number of different size combos and anything other than fronts that are slightly larger than the rears causes issues with the PSM.

I recently went back to running a set of old 18" wheels with PS2 on them due to a flat in the rear that required ordering new tires, and it was amazing how much better the car felt with the 18" wheels. I hadn't run 18" street wheels in 4 years and had been running my 19". If I didn't love how the 19" HREs I have look, and didn't have 18" track wheels, I'd definitely go back to 18" for the summer street tires too!

So when you went from the wrong size combo to the right size combo, and made no other changes, the handling got worse? If so, that's really weird (and interesting!).

What alignment settings are you using? Porsche OEM, or did you go to the performance settings that a lot of us use? I'm assuming you didn't change the dogbones or anything other than the coilovers and sways, so your front camber adjustment is going to be very limited (maybe negative .3-.4 degrees). Given your setup and what you use the car for, I'd recommend going with a 1/16" toe in each front (1/8" total), 1/16" toe out each rear (1/8" total), as much negative camber as you can get front (probably -.3 to -.4), and somewhere in the negative 1-1.8 range i the rear. Keep in mind the further you go from zero on any of these, the worse your tires will wear / the shorter they'll last.

I don't believe that's correct. Can you point to where you're getting that from? Porsche runs 315 tires on 12" rims from the factory on the 996 GT2, so you're basically saying Porsche ignored the tire manufacturer's recommendations?

The car is supposed to have toe out in the rear, and most people that modify these cars run them that way with great results...

This is a good suggestion. Myself and a lot of others find the recommended tire pressures to be a bit high and run 2-3 pounds lower to get better handling and feel.

 

My car had darty feel when she had more agressive track alignment settings and I hated that when going high speed. Changed it to a less agressive settings and work much better for me.

 

Could it be possible that when you ran incorrect tyre sizes you may have damaged your front diff? After that, everything you have done has made little or no difference. It seems to me that it is obvious that this was the turning point and so must be when the damage happened. I cant think why you would swap every suspension component without first finding out what is the likely outcome when running uneven tyre sizes front to rear. Just a thought, check your diff

 

look at any tire manufacturer specs. use discount tire , tire rack , pirelli, michelin, toyo, mickey thompson so on. every tire manufacturer that builds a 315/30-18 tire has a width max at 11.5" i have searched this over and over and they are all they same.
if porsche recommends a 12" rim then yes they have chosen to ignore the specs form the tire manufacturers.

heres the michelin ps2 spec sheet direct from michelin
http://www.michelinman.com/tire-sele...techspec_table

heres the toyo r888 spec sheet from toyo
http://toyotires.com/tire/pattern/pr...petition-tires
now let me be clear im going to run a 315/30-18 on a 12" rim just like everyone else is doing. im not saying it wont work obviously it does. i just find it odd that porsche goes against the grain according to tire specs

 

You know, when I first got my car. Stock suspension and all, it felt horrible at high speed.

After 8 months or so, now it just feels normal. I think some of my discomfort was just not being comfortable with the weird light front end, which you can't fix with suspension.

Defeintely try all the tech stuff, but it might be more worth it to ride in another 911 and see if you feel the same way on a "dialed in" one.

Good luck.

 

these cars are bred on the autobahn. they get better as the speeds pile on. if its not, something is wrong. usually alignment or tires....

 

that was great stuff. wow. love this bar.

i gotta say, of all the things they got right on this car, oem wheel sizes ( esp gt2 ) sizes are best. 18's are best, hands down. i honestly believe that anyone that really drives the car with discernment will quickly feel the same. add that extra inch on the rear to 12", and you're almost there.

i know nothing, but still, 19's only lasted on my last car a year.

36/40 max. excellent advice!

 

it cracks me up all the 19" and even 20"s I see on this board. Pretty much like chicken strips on a M/C. You can instantly tell who is for show or for go.

Tires make a big difference as well. I tried some Kumhos which made the car frighteningly unpredictable at speed. IMO the PS2 and sportcontact are the best oem tires. I settled on the Sumi htrz3 as they are a great compromise between cost, performance and tire life.

 

most common failure at sports cars is you renew only rear tyres and hold the old front tyres....so your car will be unstable and need at minimum 2000Miles to become the good driveability return