Regardless what your tires are filled with, just go by the recommended air pressure on the tire. Be sure sure valve stem at the 12 position and take weight off the tire ( jack tractor up). You MAY still get some BJ out. If your rims still have the rubber valve stem, be careful stem core does not come out when removing cap. There have been issues with the factory rubber valve stems when using BJ. I know of one, mine. Supposedly the stems were to be replaced with metal stems when loading with BJ. Check out other post on this subject.