carson2

Bought the PS4S EOM-sized NA0s available on tirerack a couple wks ago. Received an email a couple days later saying "my Michelin rep is quoting a 4-6 week lead time on the rears, do you still want to keep this order?" I am aways from hitting the wear bars and expected a wait, so I said no problem on waiting. Another email came yesterday - now Michelin has no quoted lead time/no promises... "do you want to go with the Mercedes spec in the same 305/30zr21?" The answer will be 'yes', knowing that I'll most likely be on another set of (NA0) rears before trading in. I don't see an issue with this, especially with a C2S (non-AWD) drivetrain, and can't imagine the AMG GT tires could be significantly different than 911's spec. Pros of Merc rears in the OEM size (to me) outweigh the Cons of Pzeros or Goodyears, and can't imagine warranty, insurance coverage, or any other stumbling blocks. Can't wait to drive them...

Il CP

Don't!
The comfort will be the least of your worries.

The ESC and ABS system was never set up for this combo. You might end up with ESC issues.

When you change the diameter by that much on one axle, you also change the balance of the car, significantly in fact. On top of that, the aero changes quite a bit, and you build a lot more air pressure under the car at speed. Porsche does quite a good job of making sure the ground effects of the car are set right. Just look at how small adjustments you add to a front wing of a GT3 between minimum downforce and max downforce. When you change the angle that much, you run the risk of going from a slight downforce on a car that is not an aggressive downforce car, to actual lift.

Lastly it will look like crap. The rear wheel arch gap will increase,a lot compared to the front. And if you try to offset the negative effects of the smaller diameter rear by lowering the front, this wheel arch gap inconsistency will be even uglier.

Just don't. It's an all around bad idea.

Il CP

Have driven that Merc shoe on an FF and it is different. Just like the MPS4S on the wifes GTR, Mercedes is one of the manufactures who make quite a few changes to the OEM tyres. They run built in camber in the form of different tyre wall stiffness between outside and inside. They also change compound, tread width and design. That said, it might not be a bad thing. Just be aware that your car might handle different. It might have more oversteer or more understeer. Just go easy to begin with, so that you know the effects. Also make sure you inçrease,pressure in them. Mercedes developed those,tyres for a car with the weight on the front axle, whereas your 911 has a lot of weight on the rear.