fwiw, the "20_in
2 of contact" example was used for example to help understand a basic ... like those massless ropes and frictionless pulleys used in physics studies. Speaking of frictionless pulleys,
you say "A tire doesn't have friction. It has grip." What about the point when a tire goes beyond it's point of static friction and starts to slide? Will the
Molecular Adhesion prevent this? . . .is friction never part of "grip"? . ..or is grip never part of friction?
-just raz'n ya.
Seriously,
by far the largest force our tires have with the road is
friction. -usually/mostly static friction. ...the Molecular Adhesion of a hot tire certainly
can help hold the tire from sliding, but the problem is, as the adhesive forces start to go up, the
Cohesive forces (of the rubber) go down. That is, "wet glue" is slippery. Oh, and "mechanical interlocking" is exactly where friction lives.(there are exceptions) usually at a micro level. ..whereas tire designs strive to maximize the "interlocking" on both micro and macro levels.
For a fun extreme, let's say you have such high adhesive forces that friction is not needed... what happens to the needed rolling torque to pull the adhesively stuck contact patch free? ..with adhesion forces higher than the friction coef=1 implies that 70-something percent of the weight of the car would have to be pulled lose, in overcoming adhesive force ...that would be the same as driving up a 100+% grade. (45°+ hill) TO add to your high adhesion problems, MUCH of the road would be permanently stuck to your tire. THEN you are rolling around with asphalt tires (in a larger radius).. . how much force would be required to turn the steering wheel? ...could turns be made?
Anyway, Are you sure that you want to say
"A tire doesn't have friction." ?
...I would be okay with; "Beyond friction,
some tires provide
some adhesion."
