This is what piston skirts are actually designed for: Jalopnik

It’s easy to assume that a piston skirt is simply extra material left over to guide the piston as it moves through the bore. But it actually performs a much more important job, namely controlling forces that, if not taken care of, can adversely affect ring sealing and stability. Combustion pressure and rod angle combine to continually push a piston sideways as it moves through the four-stroke cycle.

Especially during the power stroke, the piston is pressed into the cylinder wall by gas pressure and mechanical leverage on the main pressure side. This is the moment when the load is highest. In the absence of a skirt, the only remaining contact point would be the ring pack and the piston would rock back and forth. This would cause the piston to pop, which you should definitely worry about, and also cause the seal to fail in no time.

What a skirt does is it distributes the side load over a larger surface area and creates two contact zones that keep the piston stable as it moves in the cylinder. Just as importantly, the skirt must do all this while causing as little friction as possible.

Although a piston skirt appears cylindrical, it is deliberately machined oval and barrel-shaped. What these shapes do is compensate for the uneven expansion of the piston (which is also why the end gaps of the piston rings matter more than you think). The underskirt does not get as warm as the crown and ring belt, where most of the combustion heat accumulates. At the same time, some parts of the piston are stiffened by the pin cams and internal ribs, while others remain more flexible. The piston deforms as soon as the crown is pushed down by the gas pressure, and the skirt spreads outward in a non-uniform manner.

To address vertical behavior, barrel contouring is used. A point is calculated below the ring pack where the skirt is held at its largest, and there is a gradual taper both above and below this point. What this does is define a controlled contact patch to stabilize the piston while keeping most of the skirt away from the bore. Horizontal loads, on the other hand, are absorbed by the ovality. To ensure that the material is concentrated where side loads are highest, the skirt is kept wider across the pressing surfaces and narrower along the pin axis.

Early pistons relied on full round skirts to survive heavy loads, but the added mass and friction limited engine speed and efficiency. As engines evolved to higher speeds and shorter strokes, skirt designs changed along with them. Slipper skirts removed unnecessary material while maintaining enough surface area to control thrust. This reduced reciprocating weight and allowed pistons to clear crankshaft counterweights in compact engine designs.

Further gains came from refining the way the remaining skirt material was used. Asymmetrical skirts recognize that the large thrust side carries much more load than the small side. By maintaining a robust, carefully shaped edge on the large pressure side and reducing material on the small side, designers have reduced friction and weight without sacrificing stability. Balance is maintained by pin offset and lighter wrist pins, not just symmetry. Coatings add another layer of control. Skirt coatings are intended to protect against cold starts and brief contact events, which in turn can cause scratches to the cylinder wall.