In this context the wheel is attached to the axle so they move together as single piece around a shaft or bearing. The relative mechanical advantage of a wheel is proportional to its radius. If the radius is doubled, the rim force reaching the centre of the shaft is doubled.

The simplest example for us us the spanner. The rest of the wheel is absent but essentially we are manipulating one of the spokes to turn the fulcrum at the centre.

The other context for this principle is the winch, where the shaft has rope or cable wrapped around it. In this case the length of the lever is calculated as the difference between the shaft diameter and the diameter of the wheel driving the shaft. It's worth noting that as the cylinder fills with cable the shaft diameter increases, shortening the lever and reducing mechanical advantage.