Yours is a very interesting observation, Akima.
Your reasoning is accurate:
https://www.ninjette.org/forums/show...5&postcount=32
Pure friction (attraction forces at molecular level) depends only on the nature of the surfaces in contact and on the force that is normal or perpendicular to the surfaces; nothing to do with area of contact.
Traction of a tire over pavement deviates a little from that concept because the rubber tends to fill up the cavities of the pavement's surface, creating an additional mechanical interlock that resists skids and slides.
That additional grip depends on the softness of the rubber and the pressure of inflation of the tire.
That traction is also dynamic; hence, irregularities or undulations of the surface, as well as camber of the road, combined with the speed of the bike and the response of the suspension mechanism is constantly changing both, the normal force and the area of contact.
The combination of flexible rubber, deformable carcass, rotating tire and lateral forces create a crabbing effect; therefore, the tire cannot follow the path that a rigid wheel would follow.
That is an additional twisting effect on the contact patch that makes it less complying with the roughness of the surface: less available traction when that is happening.
The rear contact patch can:
1) Have X area of contact while it supports its share of weight distribution (50~60% solo or 70~85% luggage-passenger) during non-accelerated conditions (just riding at constant speed on a straight street).
2) Have 120% of X area of contact while it supports the total weight of bike plus rider during a wheelie (even more load if a leaned wheelie like the picture above).
3) Have zero area of contact while it is in the air during a stoppie or hard breaking.
Accelerating during a turn artificially loads and hardens the rear suspension (bad for rear traction), but it lifts the points of the bike that could drag over the road or track (good for more clearance) and unloads and makes more complying the front suspension (easier for the tire to follow road undulations = front contact patch keep contact with surface and suffers less dramatic changes of shape = good for front traction).
It also moves the whole dynamics away from the influence of the nervous steering (sudden changes of trajectory and induced lateral forces/deformations) of the front tire and closer to the more stable condition of a coin describing a circular trajectory while leaned (unicycle or motorcycle during a leaned wheelie).
