How to Choose a BMX Inner Tube: Sizes, Valves and Fitting
Need an inner tube for a 20 × 2.40″ BMX tyre? A box marked “20-inch” is only part of the answer. Check the size on your tyre, the tube’s supported width range and the valve fitted to your rim before ordering.
BMX inner tube sizes: start with the tyre markings
The tyre sidewall usually shows an inch size, such as 20 × 2.40″. You may also find an ETRTO marking, such as 60-406. The first number is the tyre’s nominal width in millimetres. The second is its bead seat diameter: the diameter where the tyre sits on the rim.
That 406 mm figure is not the outside diameter of the wheel.
Most 20-inch freestyle BMX wheels use a 406 mm bead seat diameter. Some BMX race wheels use 451 mm instead. Both are sold as “20-inch”, but their tyres fit different rims, so the inch size alone is not enough.
Choose a tube approved for your tyre size. If the packaging lists several sizes, check the full compatibility range rather than relying on the largest number printed on the front.
Which inner tube fits a 20 × 2.40″ BMX tyre?
The tube’s width range must include 2.40″, and it must suit the tyre’s bead seat diameter. For example, a tube marked 20 × 2.10–2.45″ covers a 2.40″ tyre. You still need to check the wheel standard and valve type.
There is no need to match the width to a single decimal figure. A tube can fit both 2.30″ and 2.40″ tyres if its manufacturer includes those widths in the supported range.
A tube that is too small can stretch excessively. One that is too large can fold inside the tyre and get damaged during fitting. Stay within the stated size range.
For 16-inch and 18-inch BMX bikes, use the same checks: read the tyre markings and compare them with the tube specifications. A 20-inch tube is not a substitute just because its width range looks right.
Schrader, Presta or Dunlop: which valve do you need?
Look at the valve on your current tube. If it was correctly matched to the rim, replacing it with the same type is the simplest option.
- Schrader / AV — the wider valve commonly found on BMX bikes and car tyres. It has a small pin in the centre.
- Presta / SV / FV — a narrower valve, also called Sclaverand or French. Unscrew the small nut at the tip before inflating.
- Dunlop / DV — a traditional bicycle valve with an insert held by a retaining nut. It is less common on BMX bikes.
The valve must suit the hole in the rim. Do not force a Schrader valve into a Presta-sized hole or drill the rim yourself. A narrow Presta valve in a larger hole is not automatically a suitable fit either: the edge of the hole can damage the tube around the valve. Check the rim manufacturer’s instructions before changing valve types.
Valve length matters too. Enough of the stem must extend beyond the rim for your pump head to attach securely. A short valve can be difficult to reach on a deep rim.
Is a thicker BMX tube worth buying?
Compare the intended use, weight and stated puncture resistance of the tube, rather than choosing by thickness alone. If you keep getting punctures, check the tyre and rim before changing to a heavier tube.
TPU tubes have their own fitting and repair instructions. If you choose one instead of a conventional butyl tube, check how much it can be inflated outside the tyre and which patches are suitable.
Why does your BMX tube keep puncturing?
Find the cause before fitting another tube. Inspect the tyre inside and out, then check the rim tape. It should cover every spoke hole. Look for sharp edges and damage around the valve hole as well.
Do not run bare fingers around a tyre that may contain glass or wire. Inspect it visually first, then use a cloth carefully to check for anything you missed.
The position and shape of the damage can help:
- A small hole on the tread side — check the tyre for a sharp object still embedded in it.
- Two cuts close together, or a snake bite — usually a pinch flat caused by an impact that compresses the tyre against the rim. Low pressure makes this more likely.
- A hole on the rim side — check the rim tape, spoke holes and sharp edges.
- Damage at the valve — check that the valve sits straight and suits the rim hole.
Replace a tyre with a torn casing, damaged sidewall or exposed casing threads. Fitting a fresh tube will not repair that damage.
How to fit a BMX inner tube
- Check the tyre, rim and rim tape. Remove the cause of the previous puncture.
- Fit one tyre bead onto the rim. Add just enough air for the tube to hold its shape. For TPU tubes, follow the manufacturer’s limit for inflation outside the tyre.
- Pass the valve through the rim hole and place the tube evenly inside the tyre, without twists or folds.
- Fit the second bead, starting opposite the valve. Do not use a screwdriver or other sharp tool. If you need tyre levers, take care not to catch the tube underneath them.
- Check both sides of the wheel all the way around. Make sure the tube is not trapped between the tyre bead and rim, and that the valve sits straight.
- Inflate gradually and check that the tyre seats evenly. If it bulges or starts lifting off the rim, stop and release the air.
Never inflate a loose tube to riding pressure.
What pressure should you use after replacing the tube?
Follow the tyre, rim and tube manufacturers’ instructions. If the rim has a lower maximum pressure than the tyre, use the lower limit. The maximum printed on the sidewall is not a target for every rider.
Within the permitted range, adjust pressure for your weight, the surface and how you ride. Use a pressure gauge to check it, especially if you have been getting pinch flats.
BMX inner tubes: common questions
Will a 20 × 1.75″ tube fit a 20 × 2.40″ tyre?
Check the tube’s full size range. If it ends at 1.75″, choose a wider tube for a 2.40″ tyre. The supported range must include your tyre width and bead seat diameter.
Does the tube need to be the same brand as the tyre?
No. Check size compatibility, valve type and any requirements specified by the manufacturers of your tyre, rim and tube.
Should you patch a punctured tube or replace it?
A small puncture can often be repaired with a patch suitable for the tube material. Replace a tube with a large tear or damage where the valve joins it. For TPU tubes, use a repair kit approved by the manufacturer.
Once you know your tyre size and valve type, browse BMX tyres and inner tubes at RMDBike and check the size range of the tube before buying.
