The basic of this topic is the basic Pressure definition which states pressure is Force per unit Area.
That is, P=F/A. In more simple language, it means more is the surface area, less is pressure. This is the reason why heavy load trucks have four rear tires, so as to increase Area and reduce pressure.
Having larger diameter will give more distance covered at less Rpm too. So this concludes two cars can have different speeds even at same RPM. If two cars are at same RPM for an instance, the car with larger tire circumference or diameter will have a higher speed.
Because of this there is also change in odometer and trip meter.