Hothonda

Because of the Turbo AWD drivetrain, is there a go...no-go ratio that must be maintained so nothing gets screwed up?

Example in 21" vs OEM 20"

F 255-30 21"
R 305-25 21"

Most run 325's in the rear, but in this case the mounted tires are 305

THX

Hothonda

Bump...where are all the wheel / tire advertisers when you need them?

ace37

Hopefully a tire vendor can tell you of cases they know have worked (ideally for 50k+ miles but doubt that’s available) to give you a bit of empirical data.

Rules of thumb are out there if that’s not already known to you. General guidance is to both have the ratio of front tire Outer Diameter (OD) to rear OD at ~ <2% difference compared to stock (to keep the AWD system diffs and related systems happy) and to have all tires within ~ <3% difference in OD from OEM (to keep the ABS and related systems happy). Problem is, only Porsche really knows as the details behind the design and failsafes will dictate when things start to wear aggressively or not work properly.

Jean

Both front and rear are 27" you will be fine.

Downside is your rear tire has a 17% shorter sidewall than stock --> bumpy ride and more vulnerable wheels/tires to damage on poor roads.