There are two ways a tire can be treaded that restrict mounting. One is a
directional tire. Directional tires are made that way to evict water better. The Goodyear Aquatred was a big commercial hit that familiarized people with the concept.
These tires can be mounted on the rim either way: but you need two each way. Once mounted, they only rotate the correct direction on one side of the car. To even out wear across the tread on directional (or plain-jane) tires, you have to "flip" them on the rims, so they can run on the other side of the car. That's what Jim was doing, and it maintains directionality.
The other kind is an asymmetric tire. These usually have less void on one side, to give more rubber on the highly-loaded outer edge. The very popular (for ST solo) Azenis 615 is one of these.
These must be mounted one way on the wheel, so that the outside is, well, outside. They may then be rotated freely around the car: unless they are also directional!
Some tires are both asymmetric and directional. This means you have to get left and right tires, and they're stuck on that side of the car. You can rotate them, but then you have the tire running with the tread "backwards" from it's design: not in rotation, (there's no reason to do that) but in cornering.
