FF1101B Rexway Bib 20x4.00 AV40 This 20 inch inner tube with a 40 mm Schrader (car) valve from Rexway is specially designed for the Fatbike, with an ETRTO size of 102-406. This Fatbike inner tube is made of butyl material, which means it maintains the correct tire pressure for a long time and is super elastic. Thanks to this elastic property, the inner tube can be used for multiple tire widths, namely from size 20 x 4.00 to 40 x 4.80. Shrink film packaging.