which has bigger contact area?

Contact area is a function of tire pressure and vehicle weight, period. The tire size is not a factor, in that the area of the contact patch will be the same for any tire size, given the same pressure and loading. On a tall, narrow tire the patch will be longer front to back, and on a shorter, wider tire it will be longer side to side, but the square inch area of the patch will be exactly the same. That's just science. That said, other factors come into play, such as sidewall stiffness and tread thickness, mainly at very high or very low pressures. But the point is, drag racers get a larger contact patch by lowering tire pressure, but that applies to any size of tire equally.