Chris,

Your posting has a typo in the year part of the car id. It says 75 which can't be right since production of the 1800 series ended in 73 with the ES. Assuming you have a 1965 1800S like mine, you would have the original 5 on 4.5 bolt pattern 15 inch wheels with 4.5 inch rims. You are right, the original tires on those cars were 165 SR 15. Mine came from the factory with Pirelli Cinturato tires in that size. I recently decided to upgrade my wheels & tires and wanted to preserve the original appearance without spending a fortune in the process. I ordered 4 new wheels from American Racing Equipment (ARE) in their classics rally series (#775-5604) for about $60 each. They come in either 6" or 7" rims and have the correct bolt pattern and a roughly correct positive offset. They are slotted and look similar to the original wheels (although they are chromed as opposed to painted and have plain hub covers without the V on them). I combined these with a set of four Pirelli 6000 "Sport Veloce" tires in 195/55 HR 15 size which gives me a much wider footprint but about the same height as the original tires. I am very pleased with the result. The car feels like it is glued to the road either straight ahead or in corners and the ride comfort and steering effort have not changed. The entire upgrade (tires, wheels, balancing & mounting) cost around $600 and was well worth it. I haven't had the new setup for long enough to report on wear, but see no reason to suspect that with such a modest change there will be problems with suspension, steering or the like.