For 17" wheels it's 36psi all round.

16" & 18" are 36psi at the front and 44psi on the rear.

Some owners prefer to run the rear tyres at a slightly lower pressure than this to improve ride quality.

For a narrow bodied car the limit is probably something like 10J with an offset of 47mm.

For a wide bodied car there is a little more clearance so 11J should be usable. For really extreme requirements a wide bodied car using narrow body trailing arms should be able to fit 12J wheels on the rear.

It depends on the make of the tyre.

Many tyre manufacturers recommend a minimum 7.5J wheels for a 225/45 tyre, others only a 7J. Many owners have confirmed that they use 225 tyres on a 7J rim with great success but we would recommend conforming to the advice of the tyre manufacturer.

Because of the unusual weight distribution of the 911 range of cars, Porsche go to extremes to ensure that the tyres that are approved for fitment comply with the strictest demands of construction and manufacturing in order to give the car the ultimate in grip, traction and wear rate whilst making the handling as safe as possible. Tyres are submitted by manufacturers on a regular basis for Porsche to approve and often significant changes are demanded to standard production tyres in order to comply with Porsche's requirements.

Additionally the owner is expected to comply with fitment and replacement criteria regarding axle matching and tread depth.

It is ultimately up to the owner whether to fit N-rated tyres but, if you choose not to, we would recommend that you check with your Insurance Company to ensure that a potential claim would not be rejected because of your choice.

During 2008 the Porsche engineers at Weissach conducted a series of tests on N-rated tyres and their suitability for many of the Classic models, including the 964. The results of those tests were published by Porsche and the 964-specific results can be found here.