Gnil:
I don't see how non N rated tires can have anything to do with a warranty problem, unless it is directly linked to the tires. For sure that will not hold in a court of law.
I was waiting for the N rated, but after seeing so many people have the non-rated on their 997, ranging from the Carrera S , to the Turbo S , GT3 and even GT2 , on the track or on the street, and nobody not being happy with them, I will also go this route by next summer when I'll need new tires.
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997.2 C2S, PDK, -20mm
The extended warranty is actually an insurance policy.
The insurer dictates the terms of that policy - in this case N-rated tyres.
If you don't comply with the terms of the policy then the insurer legally has the right to refuse cover.
Whether the insurer would refuse a claim for say the engine if the tyres weren't N-rated remains to be seen, but legally they would be within their rights to do so.
Why take the risk?