Why Do Bike Tires Lose Air? – How To Fix It

A flat mountain bike tire out on the trail with a red capped presta valve

Naturally, due to the porosity of the tube material, your tires lose some air and their pressure over time decreases, so checking their pressure and re-inflating them regularly is a regular habit.

However, if it becomes too regular, if you have the impression that air escapes as soon as you try to inflate your tires or very soon after, there may be a puncture, a small hole that is not far away, several solutions are then possible.

In this article, I have put together all the important information for you so that you know how to react in case of an abnormal deflation so that you don’t lose time or money.

First, we will see exactly why bicycle tires deflate and what to do in case of abnormal deflation.

Let’s get started.

Why do bicycle tires lose air?

Tires are generally made of butyl rubber, an elastic and resilient material that can expand and withstand air pressure. However, butyl inner tubes, although they hold air better than their latex friends, the porosity of the material means that over time, the air will leak out and the tire pressure will decrease.

However, beyond this ‘natural’ loss, it is possible that your tires may drop in pressure unusually fast. Where does this come from?

There are several possible answers, depending on the type of tire you’re running.

I will cover both cases: tubeless and tube tires.

Tubeless bike tires

Tubeless tires are supposed to be reliable tires that are no longer (or much less) susceptible to punctures than their tube friends, however, it can happen that you run out of sealant and it is dry, it is possible that the vagaries of the road damage your tires and that the sealant no longer fills the small holes and leaks.

Secondly, a valve problem is a common concern, there may be a micro leak in the valve causing a small amount of air to escape, too small to be detected directly, but causing the tire to lose air over time or during your rides. The rim tape could be the issue. 

A bent wheel could also be a problem. Indeed, in the case of a tubeless tire, a bent wheel would prevent the tire from being positioned correctly on the rim and thus could cause a slight air leak at a point where the tire would not be in the right position.

Finally, if your tires are getting old, it is possible that the general wear and tear of the tire is causing a leak somewhere, allowing air to escape slowly.

In summary, the reasons for air loss on tubeless tires would be :

  • A lack of sealant
  • A leak around the valve/rim tape issue
  • A bent wheel
  • A tire that is a little too old and worn

Bike tires with inner tube

flat bike tire

For tubes, it’s a bit of the same fight.

An old tube will deflate easily because of wear.

A damaged rim tape will not protect the tube properly from the spokes that may be able to puncture any new tube you think of trying to put on.

A ‘thorn’ stuck in a tire, whether it’s a small metal rod or a small piece of glass, if you have anything too sharp or pointy stuck in the tire, you can bet you’re going to damage your tube every time.

So overall, you have these points to check:

  • Tire/Tube wear
  • Damaged rim tape
  • Thorn stuck in your tire

What to do to prevent tires from deflating

If you find that you have a problem with your tires, the first thing to do is to find the location of the leak.

Tubeless tire method

For a tubeless tire, use soapy water and spray your tires with it, bubbles will form where the air is escaping. Once identified, check if it’s time to reload your tire with sealant, to do this shake the wheel and listen if you hear the sealant still present in quantity. If there is nothing, it is probably dry and you need a refill.

If you had enough, there may be a problem with the rime tape. Remove the tire to ensure that everything is in good condition. If the tape is indeed damaged, it should be replaced, being careful not to damage it again when you put your tire back on the rim.

A little tip: if the leak is located around the valve and you still have some sealant in the tire, a classic mistake is to tighten the valve ring even more in the hope that it will seal everything. Spoiler alert: it doesn’t work. In fact, the solution is counter-intuitive:

  • Gently loosen the valve so that it can move slightly
  • Shake your tire in all directions while moving the valve stem gently with your finger
  • After a few moments, tighten the valve ring (be careful, the correct tightening is done by hand, do not use any tools or pliers that will absolutely ruin everything).

By doing this, you have allowed the sealant to slip into the base of the valve and seal the hole by preventing air from escaping again.

Cyclist inflating tire of his bicycle

Tube tires method

For an inner tube, dip it under water and watch carefully for the formation of air bubbles that could escape as well.

Mark the spot and look at which part of the tube the leak is located on. Is it on the rim side or the tire side?

If the leak is located on the rim side, it is time to check the condition of your rim tape, it is probably damaged and no longer protects your tube properly. If indeed the rim tape is worn, change it yourself if you know how to do it, or ask your bike shop.

If you do it yourself, be careful when you put the tire back on the rim, it is quite common to shift the rim tape during the maneuver and expose the tube again without wanting to, at the risk of being pierced by the spokes.

If the leak is on the tire side, check the inside of the tire to make sure that no sharp elements are stuck and can damage your tube. Be careful, do not put your hand directly on the tire or you could cut yourself.

Unfortunately, bike tires do not last forever. If you feel that one of your tires/tubes is objectively getting old, it is time to change it. When in doubt, never hesitate to ask a professional.

What’s next?

Now that you know it’s normal for tires to lose air over time, make sure you check their condition regularly so you can use them as long as possible. Check the pressure before each ride and if you notice that your tires have deflated since the last time you rode them, pump them up to the correct pressure.

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