"Factory-installed kick-out wheel has two 3.5in. casters that provide 4-wheel support. Works best on smooth surfaces - for rough terrain, see Item# 144373. 850-lb. capacity. Must be purchased at the same time as Item# 144323 to be factory installed. U.S.A. Tire Size in. 3 1/2, Product Type Accessory, Tire Type Caster."