I recently upgraded from the stock 18" turbo wheel setup with Pirelli PZeros to 19" wheels with Michelin PS2s. Fronts are 225/35R19s on 19X8.5" rims and rears are 315/25R19 on 19X11.5" rims.

They handle / stick way better than the Pirelli's in hard cornering, but the car feels squirrely / twitchy at speed and under acceleration on a slight curve like on an on-ramp. It's like the front end rocks a bit and the steering is very fast and light. I had none of this with the original set up - which was easier to drive.

The car is also lowered abut 1/2 inch and has Bilstein PSS10s and has 3-way adjustable sway bars front and rear. I'm not sure what they're set to. Thoughts?

 

too many variables to tell but 19"'s on a 996 are not necessarily an "upgrade" as far as handling goes...you should also check the circumferences with 35 profile in front and only 25 frofile in the rear as that could be the source of your problem...of course the lowering, shocks and sways confuse the issue completely...assuming you had a proper corner balance and alignment after the install...

 

When I think twitchy steering, I think alignment.

 

Perhaps you are too low for the damper to work properly... PSS9's for sure do not mix with 19" wheels and GT2 height... not sure about PSS10's but it could be the same story.

 

Maybe you should try with 235 in front when you have 315 in the rear?

 

I think the car is too low and bouncing off the gump stops. That looks lowered 2.5" not .5"

A great alignment with proper height adjust and a corner balance can make the biggest difference

 

twitching is generally a sign of improper alignment, which from lowering can add a whole slew of alignment problems and hitting the bump stops as ARI said.

 

I hear you...other than the wheels all that other stuff was done before I bought it. I was thinking alignment as well. GMP in Charlotte did the work so I'll likely have them give it a thorough once-over.

I also checked the setting on the Bilsteins since I posted and I think one side was set a little softer than the other up front (maybe a Nascar mechanic was thinking I only make left turns LOL) so that could have contributed.

 

This was a very good post for me as I am thinking of going to a 19" wheel and PS10's. And of course, lowering it. Now you have me thinking

 

I was considering that but the 235 had a taller diameter. The 225/35 and the 315/25 have identical diameters, so I went that route, which was also the same rolling diameter as the stock 18" setup.

Thanks guys you've given me some things to chew on...but I think starting with a fresh alignment would be the best bet.

 

Let me ask a stupid question...what mods are typically done when you lower your car? Is this an adjustment that can be made to bring it back up, say halfway?

Second question, given your comment on the damper travel and height, would you soften or tighten the adjustments? I'm currently running them pretty stiff adjusted at 8 out of 10.

 

Springs or coil overs?
Normally when people go with springs they upgrade their shocks/struts as well.
Am I right about this?

 

It's got coil overs. I have to admit suspension is not my strong suit on these cars...most of my gearead experience is in Detroit muscle...I'm a recent convert to the 911 world. I had a 944T back in the 90s but that had torsion bars which I don't think is applicable here.

 

A few tuners have had alot of trouble setting up pss9 and pss10 shocks at GT2 ride height handled not so well and ran on the bump stops so if you want a real good drop do your research find someone who can set it up the right way the first time

 

Are the wheels new as well? if they are new wheels and tires the car needs alignment> the 19s change the whole geometry of the cars suspension. I did the same, changed to JIC then new wheels 19 x 9.5 in front and 19 x 13 in rear. 245 in front and 315 in rear. As you can imagine the suspension was totally "confused" to say the least.
First, get an alignment. The ride height will need to be adjusted though! Dont go too low or the handling will suffer because there is no travel.

Good luck!