I want to replace my fat bike tires 20x4 inch size with normal 20x2.5 inch MTB tires but could not afford to replace the wide rims with narrow rims. Few of the spare parts shop onwers told me that you can do it easily and told me that they have replaced several fat bike tires with normal MTB tires without replacing the rims on their customer bikes. Is it possible to install narrow tires on wider rims.