The rubber is extremely resistant to damage from impacts (three work disks were severely damaged), and it has a tensile strength of at least x. Before that, I skated the season on a PS3 equipped with 225/45/17 bearings. After that, I purchased a new PS4 equipped with 225/40/18 bearings, and this review will focus primarily on 18 radius. Skated for one season and enjoyed it to the utmost; have no regrets about my decision! I advise