A friend of mine had the same problem and wanted me to ask someone at the Toledo show DuBro booth about a solution. I learned that there is a fitting that was available in their new catalog and the gentleman suggested that my friend buy a basketball pump and use a hose to connect to the fitting. He also stated that it was important to suspend the model, in my friend's case a Cub, off of the wheels and inflate to the tire's dimension. That would ensure the tire had the scale baloon look. Hope this helps.