There should be ZERO feeling of bouncing (out of balance) when driving on smooth roads. Anything you feel should be related to the road only. As long as you're anywhere within limits tire pressure won't matter either. But a wheel does not need to be dinged much at all for you to really feel it. Because of the way wheels are made the inner rim is easiest to ding, but of course hardest to see. Also if you dropped a weight, you might not see it on your relatively new wheels. Time to visit the tire shop to check balance, check runout.

 

it could be a flat spot on the tire or just normal tire behaviour, I had PS2s on my 997.2 and they are somewhat bouncy compared to other tire. In case of flat spot, it can be corrected/ reduced with help of a professional. Good luck

 

Was the car parked long enough to develop a permanent flat spot? This is a winter set that was stored. Stacked, no problem. Stored sitting on a concrete floor though….

 

Something wrong with the wheel / tire (flat spot, wheel weight, dented rim) probably wouldn't create a bounce, but more of a vibration. At highway speeds, that wheel is spinning 15 times in a second, probably not what you are describing.

I drive 95 in north jersey all the time, that road sucks. The road itself has a slight inflection in the concrete sections, which causes the rear end to bob up and down. My guess is it's just that. How is it on other roads?

 

Highway expansion joints can become pronounced after rain. The joints are supposed to be cleaned out periodically and never are. When they are filled with debris the edges can pucker up.

 

^^ borrowed ^^

Had to do it.

 

I had the rear wheels balanced today and it seems to be better. They said that they were slightly out of balance - not something they would expect to cause vibration on most cars, but given all the weight in the back of the 911, it could have been the cause

 

Are you bouncing on smooth asphalt roads? When did it start? Usually a tire balance problem can be driven through pass the vibration point by going faster. Did you check run out?

 

There's a stretch of freeway here in the Bay Area (on 280) that is concrete and the joints seemed to be perfectly spaced in comparison to the 991's wheelbase that you literally feel like you are bouncing along the freeway (in a stiff not floaty way). Even with the sport button off.

When I picked up my car and drove up there for the first time I actually pulled off the road and check all four tires!

Probably not your issue if it's present all the time, but scared the heck out of me.

 

Seven. At 15/sec you'd be doing 128.