Marathon Industries 00003 13-Inch Diameter Flat-Free Residential Wheelbarrow Tire, Eliminate downtime! Marathon flatfree 3.50/2.50-8-inch tire is the most commonly found on residential wheelbarrow. This tire is also known as a 4.00-6-Inch tire (13 inches in diameter). Airless tires have the same bounce, feel, cushioning, and performance as a regular air-filled or pneumatic tire. They are also non-marking and will not be affected by ozone or UV rays. Airless tires are made of lightweight, solid polyurethane foam and are guaranteed to never go flat. Mounted on an 8-Inch steel rim with a 6-Inch centered hub and 5/8-Inch ball bearings. Includes grease zerk.