I remember seeing a picture of what you are talking about Jerry.
It was a third tire mounted on a swivel with springs and it took some of the tongue weight off the bumper hitch when towing.
Back in the day, passenger cars were mostly used to tow camper trailers and did not like much tongue weight.

Don

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!