Here's a collection of four rings with different tire tread designs. Two basically generic treads, and two treads based (loosely) on the 2013 Pirelli intermediate and full wet Formula 1 race treads.
The rings all have an inside diameter of .67" and an outside diameter of 1.07" and are all .45" wide.
I'll put some pictures up as soon as the rings are done printing.
The printer we are lucky enough to have at Kishwaukee College in Illinois is a Dimension uPrint SE Plus. We use the .stl manipulation and print management software that comes with the printer called CatalystEX, and we are currently running version 4.3 of that. These rings were all printed with a resolution of .010", solid infill, and with support material generation set to "smart".