The Sairs Fluid Trainers provides a quiet and consistent ride due to its fluid resistance unit and precision balanced flywheel. The Fluid unit allows resistance levels to vary with cadence or gear shifts. Features: Fluid resistance unit provides a quiet and consistent ride Progressive resistance offers the widest resistance range and road-like feel Wheel-on bike trainer with Clutch Knob for perfect roller-to-tire pressure each ride Noise level at 20 mph is super quiet 64-68 decibels Self-cooling mechanisms including a patented fan design keeps the unit performing better, longer Compatible with quick release hubs; 120mm, 130mm and 135mm. Optional thru-axle adapter available for 12 x 142mm and 12 x 148mm spacing Specifications: Resistance: Fluid Adjustable Resistance: No Minimum Wheel Diameter: 20" w/ adaptor (Sold Separate)