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HI Aalim, As @cyborg points out, bigger wheels will give you a bit of extra ground clearance, but that is it. Fitting bigger wheels does not make a car stronger, or give it more pulling power. In fact, there is no relationship between wheel diameter and torque, since wheels are driven from their centres, meaning that the definition of torque, "Force Multiplied By Distance", does not apply. However, the diameter of the driving wheels is only one factor in the equation that determines how fast a car moves at any given engine speed in a given gear. Therefore, if a car moves at speed X at 2000 RPM in first gear, the road speed and RPM will both change if the driving wheels are bigger than standard. This is because a bigger wheel covers a greater distance in one rotation than the standard wheels do. Since the bigger wheels cover more ground than the standard wheels, the engine does not have to run at 2000 RPM in first gear to propel the car at speed "X". In practice, this means that if a cars' most economical speed was say, 120km/h at 3000 RPM in fifth gear with standard wheels, bigger wheels (depending on the size difference) can make the engine run at say, 2700 RPM to maintain 120 km/h. In some cases this is good, since it uses less fuel, but if the wheels are much larger, and especially on smaller cars, it could mean that the engine is running below its maximum torque in any given gear, which is bad, because the final gearing may have changed to the point where bigger throttle openings than normal may be required to overcome the effects of the changed gearing. Changing to slightly bigger wheels is usually not much of a problem, but changing too much larger wheels can have all sorts problems, including making a car use more fuel than before, and causing shifting issues on automatics, since the engine speed now no longer matches the road speed in any given gear- which is one of the conditions that has to be met before a transmission will shift. Finally, the only reason big trucks use big wheels is because big wheels are designed to carry the weight of the truck and its load. The final pulling power of a vehicle is determined by the engine and gearing in the transmission and differential(s), and has nothing to do with the size of the wheels.