Why do bigger wheels roll faster?

If we are discussing larger wheels moving a vehicle ahead faster: The diameter of a larger wheel means that its circumference is larger. A 15″ wheel is a little over 47″ in circumference. So every revolution moves the vehicle 47″ forward. read more

However, larger wheels theoretically provide slightly better rolling resistance (the effect of this is incredibly small). On rough terrain, a larger wheel will roll more easily over obstacles/holes - imagine this - a tractor wheel will easily roll over a curb, but a rollerskate wheel would just bump into it. read more

Larger are better because they can roll over stuff better (like gravel or sticks), but have more inertia and so require more force to start or stop. Also the larger wheel requires less friction to roll because the ratio of wheel diameter to axle diameter is larger. read more