20 x valve insert balancing powder type 504 Hofmann power weight, valve insert tyres. The special valve insert prevents the penetration of balancing bodies into the valve. When should tyre valves made of metal be changed? Best with every tyre change. The metal valves are enormously stressed during their service life and are exposed to many different environmental influences. These include different levels of ozone levels, sunlight and the use of chemicals. It does not matter whether it is a tyre valve car, truck or bicycle or what material (rubber or metal) it is. Therefore, with every tyre change in the workshop, in addition to the tyres, rims, the valves should be inspected and tested. Only with regular control of the rim valves can a safe driving experience be guaranteed. Potential tyre pressure loss can be caused by