These are the Kreitler 4 ½" PVC rollers with a nonslip finish, 15" wide drums and precision shield/sealed bearings. The frame adjusts from 39" to 44" without changing the belt.
The key benefits of rollers are:
Smooth Pedal Stroke-Forces you to pedal in even circles to eliminate dead spots.
Balance and Form- Teaches you to ride straight and keeps your upper body relaxed.
Core Activation- Requires minor, constant adjustments that work your stabilizing muscles.
High Cadence- Makes it easy to spin fast gears cleanly during warmups or recovery.