The only 20-inch tube here — and check 406 against 451 first
YunSCM 20" butyl, Schrader 32 mm (1.26 in), 2-pack
Two 20-inch butyl tubes with 32 mm (1.26 in) Schrader valves for children’s bikes, BMX, folding and small-wheel commuters.
What you are getting
Two 20-inch butyl tubes for 20 × 1.75 to 2.125 tires, with a 32 mm (1.26 in) Schrader valve. 320 g (11.3 oz) the pair, about 160 g (5.6 oz) a tube. $9.99.
It is the only 20-inch tube in this group
Every other tube in the American survey for this shelf is 26-inch, 700C or 14-inch. Twenty inches is the wheel of a child’s bike, a BMX, a folding bike and a small-wheel commuter, and it is the size most often needed in a hurry.
“Universal fit for kids, mountain, road, BMX, and city bikes… junior mountain bikes, children’s bikes, BMX freestyle, city commuters, and folding bikes.”
160 g (5.6 oz) a tube, which is the right weight for the job
For comparison on this page: Continental road 100 g (3.5 oz), Bell 26-inch 136 g, YunSCM 20-inch 160 g, Ultraverse 26-inch 236 g, Slime 322 g (11.4 oz) a tube.
A 20-inch tube is physically shorter than a 26-inch one, so 160 g (5.6 oz) on a small wheel is a relatively thick wall. On a child’s bike ridden over curbs that is useful; it is the pinch flat, not the thorn, that ends those rides.
And its last bullet is the best advice on this page
“Before installing the inner tube, please put the inner tube into the water for inspection — if there are bubbles, it means that it has been damaged. Check the valve position to ensure that the installation direction is correct.”
Two genuinely useful instructions that no other listing in this group gives. Testing a new tube in water before fitting it sounds excessive until you have fitted a tire twice; and a valve that enters the rim at an angle tears at the base, which is the failure the Ultraverse listings describe guarding against with a reinforced base.
“Please follow inflation guide when airing a tire from a complete flat” is the third: a tube inflated flat out of the box can fold and pinch under the bead.
Butyl, with a list of properties
“Better sealing performance, ozone resistant, anti-aging, shock absorption and electrical insulation.”
Ozone resistance and anti-aging are real properties of butyl and the reason it replaced natural rubber in tubes. Electrical insulation is true and irrelevant on a bicycle.
No ETRTO, which on a 20-inch wheel matters more than usual
Twenty inches is not one standard. The common one is 406 mm (16 in), and there is also 451 mm (17.8 in), used on some folding bikes and junior road bikes. A tube for a 406 rim will not fit a 451 rim.
This listing gives inch sizes and no ETRTO pair, so it cannot be checked. The buying advice on this page — photograph the sidewall — is the only protection, and here it protects against a mismatch the listing does not even acknowledge exists. Ask the seller for the rim diameter if the bike is a folder.
What is not published
No ETRTO, no rim diameter (406 or 451), no wall thickness, no weight per tube, and no pressure range.
Availability
Read on the day this page was built: $10 at the American Amazon shop.
Read from Keepa on the day this page was last revised; stock and price both move without notice.
Prices quoted in this text were read on 2026-10-06. The live price is at the top of the page.
