photo credit: Wouter de Bruijn via photopin (license)

Why do bicycle tyres lose air?

It’s a sad fact of life – if you’ve got inflatable tyres, they’re going to lose pressure over time. While modern cars come with low-pressure indicators, your bicycle doesn’t have that level of on-board tech, so it’s up to you to keep an eye on the tyres and make sure you’re ready to roll at any time.

The modern bicycle tyre hasn’t changed a great deal over the last few decades. Your wheels are made up of an inner tube, which is a bit like a sausage, and a separate tough outer rubber layer, which is what comes into contact with the ground. 

In terms of why bicycle tyres lose air, there doesn’t seem to be a definite answer, so we’ve collected a few different ideas, which might explain your unexpectedly flat tyres.

1. Slow puncture 

The tiniest sharp item can make a hole through your tyre and into your inner tube. Imagine this like making a tiny hole in a balloon. Air will get out through the hole, no matter how small it is.

2. Tyre deformation 

Some engineers think that when you “park” your bike for more than a few days, either in your house or garage, the weight of the bike naturally carries through into the area of tyre which is touching the ground, and this causes tiny pores in the natural rubber to open up, allowing gas to escape. Using the bike regularly and changing the point on the tyre which comes into contact with the ground minimises this.

3. Rubber’s composition

Rubber is a natural substance, which is made up of long, stretchy fibres. There are miniscule gaps between the fibres, which allow air to escape and the tyre to deflate, in the same way that a rubber balloon does. Think about how a rubber helium balloon loses its gas faster than a foil helium balloon.

The best way to tackle flat tyres is to be as hands-on as you can by keeping those tyres pumped up. Your Presta (Or Schrader) valve needs regular monitoring to ensure it hasn’t got stuck. Push fit bicycle pumps are now commonplace and they’re really easy to push on top of the valve and inflate your tyres. They won’t last forever, though, because they’re reliant on their own rubber seal to form a tight grip on the valve. Once the rubber fails, the seal is gone and they won’t allow air in as efficiently as they once did.

When you’re pumping air into the tyres, make sure you push the handle of the pump all the way down. The early part of the push compresses the air, ready to deliver it into the tyre. The pump doesn’t push the air into the tyre until you push all the way down.

Now you’re armed with the knowledge, there’s no need to wonder why bicycle tyres lose air anymore. Check your tyres regularly for punctures or slow leaks, and keep them properly pumped up, then there’s no reason for your bike not to be ready for you as soon as you want a two-wheeled adventure. Check what else you can do to maintain your bicycle in good order. 

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