Hi Jeff, I have been experimenting with these wheels because I have hundreds of wheels here with broken/no inserts. I have about half filled the wheels with styrene balls (bean bag) then put in a layer of concrete mix about 10mm thick and then put a 2mm layer of ridge pointing adhesive. Without the adhesive the concrete cracked on the front right hand wheel. I just put the ridge coating on the wheels last week and haven't tried to see how they last. I have to find some jungle type yard/grass to give them a good bashing around to see how they stand up to it
