What You Need Before You Start

Replacing a bike tube takes about 15 minutes once you have the right tools. You will need a new tube that matches your wheel size (check the sidewall of your current tire for the size — it looks like "700x25c" or "26x2.0"), two tire levers, and a pump. Tire levers are plastic or metal tools that pry the tire bead away from the rim; they cost $3 to $8 and come in packs of two. You may already have them in a toolbox or bike bag.

Before you buy a replacement tube, write down your wheel size and tire width. Tubes are sized by wheel diameter and width range, not by exact tire width, so a tube marked "700x23-28c" will work in a 700x25c tire. If you buy the wrong size, the tube will either not fit or will bunch up inside the tire and pinch itself flat. Most bike shops will sell you the correct tube if you bring your wheel or tell them the size.

You do not need to remove the wheel from the bike to replace the tube, though it is easier if you do. If your bike has rim brakes, you can leave the wheel on. If it has disc brakes, removing the wheel prevents you from accidentally squeezing the brake lever and locking the rotor.

Key Takeaways

  • Buy a replacement tube that matches your wheel size and tire width range, which you can find printed on the tire sidewall.
  • Use tire levers to pry one side of the tire bead off the rim, then pull out the old tube completely before inserting the new one.
  • Inflate the new tube partially by hand or pump before seating the tire bead, then inflate fully once the tire is seated evenly on the rim.
  • Check that the tire bead sits in the same groove all the way around the rim; if it bulges on one side, deflate and reseat it.
  • A tube that goes flat again within a few days usually means the tire bead is not seated correctly or the old tube left debris inside the tire.

Remove the Tire and Old Tube

Start by deflating the tire completely. If the valve has a small metal cap, unscrew it. Press the valve stem (the metal or plastic post sticking out of the rim) to release all air. You should hear a hiss; keep pressing until it stops.

Insert a tire lever under the tire bead — the edge of the tire that sits on the rim — about 6 inches away from the valve. Pry the bead up and over the rim edge. You may need to use both levers, one on each side, to break the bead free. Once one section is loose, you can usually work your way around by hand, peeling the tire bead away from the rim with your fingers.

Once one side of the tire is completely off the rim, reach in and pull out the old tube. It will come out in one piece. Set it aside — you do not need it anymore, though you can recycle it at a bike shop or tire retailer.

Insert the New Tube

Before you put the new tube in, look inside the tire for thorns, glass, or sharp edges. Run your fingers slowly along the inside of the tire and the rim tape (the strip covering the spoke holes). If you feel anything sharp, remove it. If you skip this step and the sharp object is still there, the new tube will puncture in the same spot.

Inflate the new tube just enough so it holds its shape — about 20 percent full. You should be able to squeeze it but it should not be flat. This makes it easier to position inside the tire without twisting or pinching it.

Insert the valve stem through the rim hole first. Then work the tube around the inside of the tire, making sure it sits evenly and does not bunch up anywhere. The tube should form a smooth ring inside the tire with no twists or folds.

Seat the Tire Bead

Start at the valve and work your way around the rim, pushing the tire bead back onto the rim with your thumbs. The bead should click or snap into place as it seats. Work slowly and use both hands to keep the bead even on both sides of the rim.

Once the tire is mostly on, you may find the last section — usually opposite the valve — is tight and hard to push on. This is normal. Push the valve up into the rim to create slack, then push the final section of bead onto the rim. You should hear a pop as it seats.

Before you inflate, check that the tire bead is sitting in the same groove all the way around the rim. Look at the rim from the side and trace your eye around the wheel. The bead should be at the same height everywhere. If it bulges outward on one side, the bead is not seated correctly. Deflate, work that section off, and reseat it.

Inflate the Tube

Once the bead is seated, inflate the tube to about half pressure. Stop and check the bead again — it should still be sitting evenly in the groove. If it has shifted, deflate and reseat that section before continuing.

Inflate to full pressure. The pressure you need is printed on the tire sidewall as a range, like "80–100 psi". Start at the lower end if you are not sure. You can always add more air later. Use a floor pump with a pressure gauge so you can see when you have reached the target.

Once the tire is fully inflated, spin the wheel and watch the bead from the side. It should stay in the same groove and not bulge or shift. If it does, deflate and reseat again. This usually means the bead was not fully seated before you inflated.

Common Mistakes That Cause Flats

The most common reason a new tube goes flat within a few days is that the tire bead is not seated correctly. If the bead is not fully seated, the tube gets pinched between the bead and the rim, and it will develop a slow leak or blow out suddenly. Check the bead visually every time you inflate — it should be a smooth, even line all the way around.

The second most common mistake is leaving debris inside the tire. A thorn, piece of glass, or sharp edge of the rim tape will puncture the new tube in the same spot as the old one. Always inspect the inside of the tire before you insert the new tube, and run your fingers along the rim tape to feel for rough spots or holes.

A third mistake is using the wrong tube size. A tube that is too small will be stretched tight and will fail under pressure. A tube that is too large will bunch up inside the tire and pinch itself. Check the size printed on the tire sidewall and match it to the tube label before you buy.

When to Call a Bike Shop

If you have tried to seat the bead three times and it still will not stay in the groove, the rim may be damaged or the tire may be worn out. A bike shop can inspect both and tell you whether the rim is salvageable or the tire needs to be replaced.

If the new tube goes flat again within a few days, bring the wheel to a shop. They can inspect the inside of the tire with a light and find debris you may have missed, or check whether the rim tape is torn and exposing spoke holes.

Frequently Asked Questions

Do I have to remove the wheel to replace the tube?

No. You can replace the tube with the wheel still on the bike if you have rim brakes. With disc brakes, it is safer to remove the wheel so you do not accidentally squeeze the brake lever. Removing the wheel makes the job easier either way, but it is not required.

What if the tire bead will not go back on the rim?

The bead is stuck because the tube is in the way. Deflate the tube completely and push it away from the section you are trying to seat. You can also try inflating the tube slightly — just enough to give it shape — which sometimes helps it slip into place. If the bead still will not seat after several tries, the rim or tire may be damaged.

Can I patch the old tube instead of replacing it?

Yes, if the hole is small and you have a patch kit. However, if you do not know what caused the flat, patching may be a waste of time — the tube will go flat again if the thorn or glass is still in the tire. Replace the tube first, inspect the tire carefully, and patch the old tube later if you want a spare.

How do I know what pressure to inflate to?

The correct pressure range is printed on the tire sidewall. It usually looks like "80–100 psi" or "3–4 bar". Use a floor pump with a built-in gauge so you can see the pressure as you inflate. Start at the lower end of the range if you are unsure; you can add more air later.

Why does my new tube keep going flat?

The most common cause is that the tire bead is not fully seated on the rim, which pinches the tube. Check the bead visually — it should be a smooth line all the way around. The second most common cause is debris left inside the tire from the old puncture. Inspect the inside of the tire carefully before you insert the new tube.