CST 406 20 x 1.90/2.125 Inner Tube A/V Schrader
Size: 20 x 1.90 / 2. 125 SV
Weight: 125 grams
Note : The rim valve hole diameter for Schrader is approximately 8mm and 6mm for Presta. So you cannot fit a tube with Schrader valve in a wheel that was made for Presta valve. Unless you want to widen the hole with a drill - some bike shops will do this for you
How to choose your inner tube?
The inner tube markings is supposed to fit the tyre. So check the tyre markings
Its says 20 x 1.35, meaning the wheel diameter is 20" and the width of the tyre is 1.35 inches
And sometimes you can also see the ETRTO (ISO) marking. In the above case, its 32-406. Meaning the witdh of the tyre is 32 mm and the rim diameter of the wheel is 406 mm. In fact the diameter to be precise is measured between the bead seat (BSD)
Note: Important to note that 406 and 451 are both marked as 20" but they are different and not interchangeable. 451 is slighly bigger in circumfrence. Also 20 x 1 1/8 does not translate to 20 x 1.125 !
The most accurate way to overcome this confusion is to lookup the table for the right ETRTO marking. Any tube with the same ETRTO marking as the tyre should be good fit