ejlif

I got a flat on one of my rears and it was unrepairable. I had to get it towed to the tire shop and since the rears had about 30% left I got both replaced. It feels very active now in the back like the tires have a squirmy feel, kind of almost an oversteer feeling in the back or floating around a bit. It's kind of sketching me out at higher speeds. The PSI is set at 48. Any ideas? I recall getting some new rears on a dually ford work truck and it had the same feeling like the back was floating around on me.

Al.Fresco

48 psi….. yikes. What psi did you have in the old set? I run 34 front 37 rear with car gauge set to comfort partial load.

ejlif

It was around 40 all around. Good to know I'll drop it and see what happens. I thought lower might make it feel even worse.

Porsche_nuts

New tires have a film on them. You need to drive cautiously until the film wears off. My new Michelins did the same thing when first mounted.

sy1616

Which brand and model? Are they mounted correct side to the outside?

BSO

Every time I leave a tire shop or dealer I find my tires inflated to max pressure or close to it.

As others said that pressure is too high, particularly if those are cold readings. Make sure you’ve got the recommended pressures.

991.2 Carrera S comfort pressure 29/33 partial load is what I run, feels like a good balance.

asellus

+1 on the "holy crap that's high pressure"

drop those tire pressures and things will feel a lot better, especially if you're in the USA where it's getting colder.

nstar8

What tire and size did you go with?
Had the exact same experience when I purchased new rear tires only. I was running the Conti extreme sports, and they seemed great...until I only replaced the rears, with the exact same tire (non spec). The stability control would come on when spirited driving on off ramps, or when not under acceleration. .Needless to say, the rears finally began to behave much better after over half of the tread was worn, although I can still get the stability control to come on...which is bs...but whatever...
Fast forward a year later and hours of tire research...I just ordered a set of Michelin PS4S N0 spec. Although there is much skepticism regarding the N0 spec tires vs standard PS4S, the N0 (or 1, or whatever) are what the Porsche engineers laid out for Michelin to spec to the 991.1 vehicle, and those tires are indeed different than a non spec standard PS4S, the tire compound is different across the face of the tire as well as subtle differences within the tread pattern...
I am anticipating a much more precise feel to the road and no bs tail wagging or stability control warnings...

Southbranch

Besides being overinflated for normal driving, your new tires are slippery because new, and they have 70% more tread than the old ones.

911dude41

I've driven a 991 on brand new rear Conti's. It was terrifying.

N spec is a huge deal.

ktnielsen

I run 32psi on the fronts and 35psi on the rears and they generally heat up to 35psi and 38psi after driving a few miles.

manifold danger

Tire Rack will tell you that all tires require a break in for 500 miles- https://www.tirerack.com/tires/tiret....jsp?techid=5&

CSK 911 C4S

Yep. ^^^^ This ^^^^

And it will go away in a few miles. I took mine on about a 60 mile twisty back road journey after replacing and they were fine when I got home.

BTW lower that pressure.

Jack F

The Rennlist brain trust has provided excellent information and recommendations:
1-outer coating needs to wear off with regular driving.
2-psi. Much too high. In the MFD go to the tire pressure screen and scroll and choose either winter or summer and 19” or 20” and full load or partial. That will tell you what to set to. You can use that screen to lower pressures until you are at a zero difference from the goal psi. If this doesn’t make sense, then read up a bit and learn to use it. It’s helpful when driving around.

asellus

Even more this ^^^^^^

The idea that mold release compound corrupts the outer 1/32" of tire or something is a thing of the past (if it ever was a thing, I'm too young for these myths). Driving your car from where you got the tires mounted+balanced to home is enough to scrub in new street tires.