When thinking about idler diameter, we usually think smaller is better. But smaller is not always best. Bearing drag and rotating inertia combine during transients to upset the web's tension. In lines with large accumulators and many idlers, this can result in missed splices, and long times to steady state production. The right diameter can minimize their affects. This paper shows how to "right size" idler diameter and discusses factors that must be considered when selecting idler diameter.