If you pick up your bike after months of not using it, it is almost guaranteed that the tires will have gone flat. You kind of expect that. But when you pick up cycling as a new hobby, you may be surprised to find out that your tire has lost pressure over time despite the bike being in use and may wonder if this is normal.
It is normal for a bicycle tire to lose 1-40 psi (0.06 – 2.7 bar) pressure per week even without punctures or damages to the tire or the tube. Narrow tires lose air at a faster rate than wide ones. The type and quality of the inner tube, the tire and gas type all play part in how fast pressure is lost.
Normal pressure loss in tires
Unless you have tubeless tires, the air isn’t contained in the tire chamber itself, but in the inner tube inside the tire. There are two main inner tubes for cycling: butyl and latex.
Butyl tubes are the more common type. They are readily available in any bike shop and wherever inner tubes are sold, and you know that you have one if you have a black tube.
Butyl tubes are perfectly capable of keeping large molecules contained, such as water, but oxygen can diffuse through their structure. This happens at a slow rate depending on the quality of the tire and the tire pressure.
|Road bike||Hybrid bike||Trekking bike||Mountain bike|
|Typical tire width||23-28 mm||28-38 mm||35 – 45 mm||40+ mm|
|Avg recommended pressure range||100+ psi (7+ bar)||80-100 psi (5.5 – 7 bar)||35 – 80 psi (2.5 – 5.5 bar)||20 – 35 psi (1.4 – 25. bar)|
|Pressure lost per week||5 – 40 psi (0.3 – 2.7 bar)||3 – 30 (0.2 – 2 bar)||2 – 25 psi (0.1 – 1.7 bar)||1 – 15 psi (0.05 – 1 bar)|
|How often to check pressure||Every few days||Every two weeks||Every two – three weeks||Every three – four weeks|
If you use a CO2 canister instead of a regular pump, the rate of diffusion is faster because CO2 acts as a solvent of butyl, slowly degrading its structure and leaking at a faster pace.
Some inner tubes are made of latex. These are quite common among racers, because they allow the tire to roll more efficiently, saving up to a few watts. They can be recognized by their reddish or greenish color.
Their main drawback is that latex tubes are very thin and lose pressure at a much quicker rate than their butyl counterparts. Since they are mostly used for road racing, they only come in narrow versions (maximum 30 mm). These should be topped up daily, or before every ride.
Pressure loss through the valve
Besides diffusion through the structure of the inner tube, tires can also lose some air through the valve. The valve is designed to offer an easy passage for the pressurized air into the tube, and to prevent it from easily escaping, but with oxygen being a tiny molecule, it may find its way out.
In Presta valves (road tire), it is quite common to have some pressure loss because the nut on the valve core isn’t tightened properly after inflation. As soon as something touches the pin, air can escape if the nut is loose.
Over-tightening the nut can also lead to air leakage. The nut serves the purpose of preventing the pin from being pushed down,
In Schrader valves (same as on cars) the lock is built into the valve pin, which is pressed down by the nozzle, so these are less likely to lose air due to negligence.
You should always keep the cap on the valve, which prevents debris from potentially damaging the valve and leading to pressure loss.
Quality inner tubes
Low quality inner tubes may lose pressure at a higher rate despite consisting of the same material. This is mainly due to quality control issues around the valve and the seams.
Good quality inner tubes, like the Continental tubes, aren’t very expensive, but you know that you have quality tubes that will hold air pretty well.
Do patched inner tubes lose air faster?
Inner tube patches are very resistant, and the glue used to apply them solves the rubber in a way that when the patch is applied, it heals together with the rubber.
A properly patched inner tube will hold air pressure just as well as a new one.
If you find that your inner tube loses air at a quicker rate than before, the patch may have been applied incorrectly. In this case you may want to check if there’s another hole due to a snakebite, or if air may leak through a tiny hole where you didn’t apply enough glue.
How often should you check tire pressure?
Now that you know that your tire pressure decreases over time, you need to remember to check your tire pressure regularly.
You should check your tire pressure on average once a week. On road bikes check it every other day, on hybrids and on mountain bikes week or every other week. The narrower the tire, the higher the recommended pressure and the heavier you are, the more often you should check the tire pressure.
This floor pump is compatible both with Presta and Schrader valves, which means that you can use it with MTB tires as well as road bike tires.
Always make sure to stay within the manufacturer recommended pressure range, which is tire specific and not tube specific, and can be found on the tire sidewall.
Invest in a decent floor pump with a gauge, which gives you an accurate reading of the pressure and make it a habit to check it regularly.
If your tire loses pressure faster than normal
There are a few nasty problems that can cause your tire to lose air at a faster rate than normal.
Bicycle slow punctures are hard to detect tiny holes on the tube, which let out air gradually. A fully inflated tire can be completely flat in the morning. They are impossible to spot with the naked eye, but they can be found quite quickly with a bucket of water.
Remove your tube and inflate it. Then, place it in a bucket of water and keep it under water. You will see air bubbles coming up to the surface from the hole.
Remove the tube from the bucket keeping your thumb on the hole. You can patch the hole with your puncture repair kit.
A damaged rim either from the outside or from the inside can lead to quicker loss of pressure. Check your rim and make sure that there are no dents visible damage to it. You may also find that the rim tape has moved or been poked through by one of the spokes.
If anything rubs against your inner tube while riding, it will cause a puncture on the tire sooner or later.
Damage to the valve
If you find that air escapes through the valve itself when doing the bucket test, it means that your valve has been damaged either in its core or at the seam where it meets the rubber.
In this case you have to replace the tube altogether.
Brand new inner tube losing air fast
You may find that a brand new tire goes flat after being installed in your tire. There are two main reasons:
The tube got punctured during the installation process as it got pinched between the tire and the rim or the tire lever. This is quite common, especially if you don’t have much practice replacing inner tubes and fitting on tires.
The other reason is that you forgot to check for sharp objects and debris in your tire after a puncture. Goatheads, thorns, glass can all sneakily hide away inside the tire chamber going unnoticed to the naked eye, but quite easily detectable to your fingertips.
Check your tire and rim after each puncture before installing the new tube in order to avoid this.
Is it possible to ride with low tire pressure?
It is possible to ride your bike if it has low tire pressure, but keep in mind that it increases the chances of a pinch flat.
If there’s no pressure in the tire at all, and you have no kit with you, you should push your bike in order to avoid damage to the rim and to your tire.