A light car will have a smaller contact patch for the tires than a larger car, so the pressure per area on the tread of a light car is roughly the same as that for a heavier car. It's one of the design considerations that manufacturers use to choose the tire for a vehicle, and which consumers can use to alter depending on the needs of the tire. For instance, having a greater force per area is useful for winter tires, to allow the tread elements to dig into the snow, so that's one reason why narrower tires work better in those conditions.
Tire wear is mostly due to shear forces acting on a tire at a microscopic level, so any time acceleration or braking happens, or the tire is rolling but pointed in a different direction than the vehicle is moving, wear will be accelerated. Because the smart is so power limited, wear is probably occuring mostly when turning, and in those instances will be governed by the dynamic alignment of the tires at that moment. These dynamic changes to the static alignment settings occur due to compliance in bushings and changes in the suspension geometry as the wheel moves in its range of travel. An easy example to visualize would be where you've seen all of those lowered vehicle with the tires canted inward. This is because in the vast majority of vehicles, tires get canted inward (develop greater negative camber) as the suspension compresses. If you are turning hard when this happens, the majority of the pressure on the tread occurs on the inward edges, and you get extra wear at that location.
For most passenger vehicles driven on public roads, toe is the main killer of tire life. Toe in or toe out means the tire is not pointed straight ahead, and the tire will scrub even if the car is rolling along in a straight line. For example, the front toe specification on a 451 is for 0.2 degrees of toe in. In 10000 miles, the static direction the tires are pointing versus the direction the vehicle is pointing, is 34.9 miles. That means that that the front tire must squirm or slide sideways 34.9 miles for each 10000 miles driven. Toe changes occur during driving, and most manufacturers recommend a small amount of toe in, around 0.05 degrees, because rolling resistance causes dynamic toe out in the front, resulting in a near zero dynamic toe when driving. In the rear, power application also causes dynamic toe out, and braking causes dynamic toe-in. Also, as a wheel moves up and down through its suspension travel, toe changes occur due to the suspension design.
It's all a complex system and makes it hard to know what factors are causing tire wear, and what may happen with larger or smaller tires. In general, using a wider tire will result in a wider but shorter contact patch, which will make wear worse for toe issues, camber issues, or in a vehicle which tends to lean quite a bit when cornering. It should wear less under braking and acceleration because the variation in pressure and squirm under the contact patch is minimized longitudinally (fore-aft) with a wider tire, but you might also have a bit less grip as well unless you use a grippier tire compound.
