It is not a good idea. There are significant differences between passenger car tires and “Special Trailer” (ST) tires. A passenger car tire is not designed to carry heavy loads for extended periods of time while an ST tire is built for such purposes as well as low rolling resistance, long-life, and stability while towing. It should be noted that an LT or light truck type tire will work as an alternative to an ST tire. An ST tire is engineered to carry ten percent more load than a similar-sized passenger car tire. As a result, the tire may have different steel belts, plies, beads, thickness, and diameter as compared to a passenger car tire. The treads are also created to minimize the tires squirming around. The tires also contain different materials that allow the tires to stand-up better to the elements while in storage. One big concern when running a passenger car on a trailer is that the side walls are not as strong as an ST tire and can aggravate trailer swaying. The flexible sidewalls of a passenger tire could cause the trailer to sway badly enough that the driver could lose control. We wouldn’t want to risk injury to life or limb or to your special vintage trailer by using the wrong type of tire.