Flat-Free Polyurethane Foam Wheel,8-5/8" 38ER67. MARASTAR 00090. Flat-free polyurethane foam wheels absorb shock and vibration for a cushioned ride and will not go flat if punctured. Flat-free wheels are heavier than pneumatic or semipneumatic wheels, and they provide more shock absorption than semipneumatic wheels.Pneumatic, semipneumatic, and flat-free wheels have air-filled, foam-filled, or solid-rubber tires that absorb more shock and vibration and produce less noise than standard wheels.
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