To be clear and for the sake of comparison, the Sportcrafter rollers including the Overdrive resistance drum are 3.25 inches. The High Inertia drum for spinning is 3.75 inches.

The photo below shows the setup with the Overdrive resistance drum (red end cap) installed in the rear. The Overdrive drum is removed and replaced with the High Inertia drum depending on the desired workout.



-Tim-