What you need before you start

A 20-inch wheel uses a smaller tube than adult bikes, so you need a replacement tube sized for 20-inch wheels — check the sidewall of your old tube or the rim to confirm the size. You will also need tire levers (plastic or metal tools that pry the tire away from the rim), a pump, and ideally a bowl of water to find the puncture in the old tube so you know what caused it.

If you do not have tire levers, you can use a flathead screwdriver, though it is easier to damage the rim or pinch the new tube without proper levers. A new tube costs between $8 and $15 for a 20-inch size at most bike shops or online retailers.

Key Takeaways

  • Remove the wheel from the bike by opening the quick-release lever or unscrewing the axle nuts, depending on your bike's design.
  • Use tire levers to pry one side of the tire away from the rim, then pull out the old tube completely.
  • Inspect the inside of the tire for thorns, glass, or sharp objects that punctured the tube in the first place.
  • Partially inflate the new tube before installing it so it holds its shape and does not twist inside the tire.
  • Reinstall the tire bead (edge) into the rim by hand first, then use the pump to finish inflating and seat the tire properly.

Removing the wheel from the frame

If your bike has a quick-release lever on the axle, open it by flipping the lever outward — you may need to unscrew the opposite nut slightly first if the lever is very tight. If your bike has bolt-on axles instead, use an appropriately sized wrench (usually 9mm or 10mm) to unscrew both nuts, keeping track of any washers or spacers that come off.

Once the axle is loose, lift the wheel out of the frame. If it is the rear wheel, you may need to pull the derailleur back or shift to the smallest cog to create slack in the chain. Set the wheel on a clean surface so the tire does not pick up dirt.

Getting the tire off the rim

Insert a tire lever under the tire bead (the edge of the tire that sits in the rim) about 6 inches from the valve. Pry gently until that section of tire pops out over the rim edge. Move around the wheel and repeat every 12 inches or so until one full side of the tire is out.

Once one side is free, reach in and pull out the old tube. Start at the valve and work your way around, being careful not to pinch the rim with your fingers. The second side of the tire usually stays seated in the rim — you do not need to remove it to change the tube.

Checking the tire for damage

Run your fingers slowly along the inside surface of the tire, feeling for thorns, glass shards, or sharp objects. If you find something, remove it. This step prevents the new tube from puncturing in the same spot.

If the old tube has a visible hole or tear, look at where it is located on the tube and check that same area inside the tire. Pinch flats (two small holes close together) mean the tube was pinched between the rim and tire, usually because the tire pressure was too low or the rim tape was damaged. Check that the rim tape (the strip covering the spoke holes) is intact and not torn.

Installing the new tube

Inflate the new tube partially — just enough so it holds its shape and is not completely flat. This makes it much easier to position inside the tire without twisting or pinching. Screw the valve through the rim hole first, then tuck the rest of the tube evenly around the inside of the tire.

Starting opposite the valve, use your hands to push the tire bead back into the rim, working your way around in both directions. The tire should seat fairly easily by hand for most of the circumference. Once the tire is mostly seated, use the pump to inflate it the rest of the way.

Seating the tire and checking your work

As you pump, watch both sides of the rim to make sure the tire bead is seating evenly — you should see a thin line where the tire meets the rim all the way around. If one section bulges outward or looks uneven, stop, let air out, and reseat that section by hand before pumping again.

Inflate to the pressure marked on the tire sidewall (usually between 40 and 65 psi for 20-inch wheels, depending on the tire). Spin the wheel and watch for any wobbles or bulges. Reinstall the wheel on the frame, tightening the quick-release or axle nuts firmly, and test the brakes before riding.

Frequently Asked Questions

What size tube do I need for a 20-inch wheel?

Check the sidewall of your old tube or the rim itself — it will say "20 x" followed by a width measurement, such as 20 x 1.75 or 20 x 2.0. Buy a replacement tube marked for that exact size. Tubes are inexpensive, so buying the wrong size once is not a major loss, but the right size makes installation much easier.

Can I patch the old tube instead of replacing it?

Yes, if the hole is small and not near the valve. Patch kits cost $2 to $5 and work well for emergency repairs. However, if the tube has multiple holes, a large tear, or damage near the valve, replacement is faster and more reliable. Many riders keep a patch kit as backup but replace the tube as their first choice.

What if the tire keeps going flat after I install the new tube?

The most common cause is a sharp object still inside the tire — run your fingers around the inside again, paying special attention to the area where the first puncture occurred. The second most common cause is the rim tape is torn or missing, allowing the tube to contact the spoke holes. If neither is the problem, the rim itself may be bent or damaged.

Do I need to remove both sides of the tire?

No. You only need to pry one side out to access the tube. Leaving the other side seated saves time and reduces the risk of damaging the tire or rim. Only remove the second side if you need to inspect or repair the tire itself.

How tight should the quick-release lever be?

Tight enough that you need firm pressure to flip it open, but not so tight that you cannot open it by hand. If it is too loose, the wheel can shift during riding. If it is too tight, you will struggle to remove the wheel. The nut on the opposite side should be snug but not over-tightened — you should be able to turn it with your fingers, though it takes some force.