retroz

Hi everyone new 987 owner so i got lots of question lol

The car is running 19" porsche crab claw alloys with 235/35/19 Pirelli pzeros on the front AND 265/35/19 crap brand ditch finders on the rear all have good tread the car handles great in corners bags of grip but feels unstable over rough road surfaces and at speed.

Sometimes it feels like it's on ice lol i'm thinking the rear ditch finders are the reason for the problem but just wanted to ask if it could be another issue like antiroll bar bushes or something suspension related.

No knocks or noises from the suspension and great cornering grip too

Would wheel misalignment cause this issue ?

Brian C in Az

Mismatched tires are most likely the cause.
Loose/worn bushing are common on older cars. All rubber deteriorates with age. All rubber suspension parts should be replaced every 7 years unless the car is driven hard or on the track, it those cases replace sooner.
Wheel alignement can cause the described problem also.

The first step in a wheel alignment is to start with matched tires with good tread at the proper tire pressure.
Second step in an alignment is to check and replace any and all suspect rubber parts.
Third step is the actual aligning of the tires to the chassis.

LexVan

Start with new matching rear tires.

All tires have a specific harmonic balance and vibration. You're seeing the effects of a very poor mismatch. The mid engine platform of the Boxster further exacerbates the situation.

Alan C.

Agree, matching front and rear. If you think they are crap go with your gut feeling.

terbiumactivated

Would be more helpful to know exactly what the rear tires are that earned them the nickname ditch finders. As others have noted, I wouldn't mismatch. I won't even do it on my DD, winter rats only for that. If the fronts are not worn out but the rears were replaced and with garbage you might want to have a look at the over rev report on it, knowledge is power.

CAlexio

Hold on, before you go changing tires.. why has no one asked about the obvious, tire pressures?

Dealer often over-inflates, THAT would make car feel like this too.

LexVan

The second post stated proper tire pressures. But you're right. Regardless, the OP says the rear tires are crap.

CAlexio

Damn, I just became captain obvious, must have missed that bit

Marine Blue

I would also have the alignment checke when you replace the tires.