The Welter-Weight MTB tube is Maxxiss do-it-all mountain tube optimized for trail riding and XC but a great option for racing if you need the added insurance of 0.9 mm walls. 0.9 mm-thick walls. 26 x 1.92.125 or 29 x 1.92.35. Presta or Schrader valve. 161 g for 26. 200 g for 29.