you can purchase the best quality & priced plastic centered 400x8 wheels for land sailors or simular equipment from any richmond castors store in Australia, They have stores in all states www.richmondau.com . The rims are manafactured from high grade UV stable polymer material,The tires are 4ply motor cycle grade rubber. The standard off the shelf wheels are fitted with the tradition flange type bearings .Their is a optional upgrade bearing kit which includes a rubber sealed precision bearing in either 20mm or 25mm bore. These simply press back into the bearing pocket once the exisisting bearings are removed, I have attached a picture. The product codes are as follows. Wheel PN1603-1PL $48.88 ea + g.s.t Up grade bearing kit BUSH20MMBRG or BUSH25MMBRG $4.79 ea + g.s.t Total price $58.46 ea + g.s.t Richmond Castors will also give you a 25% discount of the above price which equalls a fantastic deal for wheels.