The advantages of bias-ply tires are: 1) Most authentic, period-correct look for a vintage car. 2) Less expense generally. 3) In most cases, wider whitewalls and more choices of brands and whitewall sizes and appearances. 4) The most notable appearance features are the straight up and down or vertical side walls, the attractive "pie-crust" edges of the tires that resemble scallops and the period-correct looking tread patterns. The disadvantages of bias-ply tires are that they do not ride as nice as steel belted radials will nor perform as well on cornering or in wet conditions.
The advantages of steel-belted radial tires are: 1) Superior ride and performance. 2) Attractive design. 3) Period-correct appearance and whitewall stripes for more modern cars. 4) Longer tread-life and 5) Speed rated for higher speed driving. The disadvantages are: 1) Higher cost. 2) Can cause cracking or harm to antiquated wheels. 3) May detract from a vintage presentation on an older car. 4) In tight quarters, a steel belted radial may be wider than needed and could rub or make contact with a fender skirt or body panel.