People are too obsessed with matching 'N' rated tyres all round (apart from warranty issues)
I'd love to see someone do a blind test and see if they can tell the difference.
Porsche allow for mixing between axles
Here's an extract from Porsche's manufacturer's Certificate list of approved summer tyres for the 996 GT3.
Information: Approval status: July 2009
WARNING
Driving with different tires (mixed tires)
"¢ Uncontrollable vehicle handling
Only use tires of the same make and type, with the same speed index and the same specification code
(N0, N1, N2, ...) on a vehicle.
Contrary to the rule mentioned above, which specifies that only tires with the same specification code
(N0, N1, N2, ...) must be used on a vehicle, the following mixed tires can be used on each axle.
Michelin Pilot Sport 2 N2 on front axle/Michelin Pilot Sport 2 N4 on rear axle and Michelin Pilot Sport 2
N4 on front axle/Michelin Pilot Sport 2 N2 on rear axle.
2 The Pirelli P-Zero Rosso N5 tire can also be used either by itself or together with the Pirelli P-Zero
Rosso N4 tire.
It would be interesting to know what mixes Porsche allow for the 997 range -and then maybe people wouldn't have to waste money swapping all four tyres when not necessary.