What size tire on a 15x4 inch rim ?

The original metric size was 165-15 which replaced the 600-15 original sizing. These were the oe tire size for the VW Super Beetle. They came out in 1971, equiped with the new McPherson strut front suspension.
The standard bug wore 560-15 or 155-15 sized tires. The max load rating was a little over 1,000 punds per tire @ 32psi. This was about 400 pounds per tire less than the cars original tire size.
The early tire sizing system did not generally give aspect ratio numbers, just the section width and rim diameter. The average aspect ratio on the early tires was 75-83%. Later replaced by 75, 70, 60, 50 % ratios in the late 60's, 70's.
Very little contact patch area, so very dangerous when hard braking. As well as overloading the tire.
The true race cars of that period used the old 855-15 sized tires on the front of the stock, super stock cars as they also had very little contact patch area but were much large in diameter to give more roll out at the start and had a lot more load carrying capacity as they were the load equivalent of the H sized tires used in large sedans.