Oh you mean wheel diameter. If you hold a 26" bicycle wheel/tire up to a 14" car/tire you'll find they aren't very far off in terms of size (for instance my road bikes tires/wheels are only a few inches taller than the 13" tires/wheels on my car, and a bit smaller than the 15" tires/wheels on my truck), since car tires have way more sidewall compared to bike tires. The change in angle wrt the outer diameter isn't very different. In fact, other confounds, like lack of a suspension in many bikes, leads to small bike tires having a lot of give to them, so it's not exactly a tomato tomatoe deal compared to cars, where the suspension dissapates energy from rough riding.

regarding 1 vs. 2: You make a good point. I do think they are different. Treadflex on smooth ground may prove to be more a function of the tire's design, whereas a tire's ability to roll over irregularities seems to be a direct function of diameter. Look at exaggerations: which would be more difficult to roll over a curb, a 3" wheel, or a 60" wheel? The road just seems to be a series of irregularities.

Ah I gotcha, the designated inflation pressure can be different for different tires which impacts treadflex, but diameter/mass is directly related to the polar moment and the ability to roll over much rougher obstacles. I see... Thanks for the info!