The early 123's called for 175-14 or 185-14. These are, of course, sizes that are no longer available.

The ideal size for the 123 is 195/70's or 196/75's. In about 3/4 million miles in these cars, I have come to prefer quality 195/75's. They are generally higher mileage tires AND they cost less. These are not sports cars and the skid pad capabilities are limited, so the advantage of running wid profile tires is somewhere between minimal and non-existent.

the 225/75's are way too big for this car. Whatever tire you buy MAKE SURE that they are dynamically balance with weights on the inboard AND outboard lips of the wheel. Many tire stores will put them only on the inboard. On this car, that is a guarantee that you will have vibration. I got so tired of fighting with the tire store zero's that I bought a used computer balancer so I could balance them properly. This is the epitome of the old saying, "if you want it done right, do it yourself."

Good luck,