Why Road Bikes Lose Air & What you Can Do

Nothing is more frustrating than getting ready to head out on a ride on your road bike to discover your tires are unusually flat. This is made more confusing when the bike hasn’t been used recently. You might begin to wonder why exactly the road bike tires have lost so much air.

Why do road bikes lose air?  Road bike tires lose air for two main reasons: because rubber tires are porous and naturally allow air out through tiny pores, and because there’s an object in the tire or some other kind of wear that has made the tire susceptible to air loss.

While tires can hold air for quite some time, they cannot hold air for an infinite amount of time. Tires leak air naturally and do so at different rates, depending on how the tires are made. Over time, bike tires will go flat when not used. Not because anything is wrong with your tires but simply because science takes over.

Reason 1: Science

The first reason road bike tires lose air is pure chemistry. Air will inevitably escape tires. Rubber, which is the material bike tires are made of, is porous. This means that air can pass through the tires. It escapes gradually over time and does so through the microscopic openings within the tube or tubeless tire. The thinner the rubber, the quicker air escapes. The thicker the rubber, the longer it takes for air to escape.

Not all gasses possess the same amounts of molecules. Some gasses, like oxygen, are made up of a higher number of molecules.  On the other hand, gasses like helium consist of fewer molecules.

If you filled your road bike tires up with helium, your bike tire would be flat as the pavement within 24 hours. Why? Because helium has a lower molecule count.  In other words, there are fewer molecules so that helium can pass through the pores of rubber more easily than oxygen or carbon dioxide. 

The Gas Law

This scientific occurrence is referred to as the gas law (PV = nRT). The gas law governs the relationship of pressure, temperature, volume, and amount of gas. There are three primary gas laws: Charles’ law, Boyle’s Law and Avogadro’s Law (which, when combined, equal The Ideal Gas Law).

  • Boyle’s Law – says the volume of gas increases as the pressure decreases
  • Charles’ Law – says the volume of gas increases as the temperature increases
  • Avogadro’s Law – says the volume of gas increases as the amount of gas increases.

What does all this gas law chemistry mean for your road bike tires?

It means that high pressure inside or around your road bike tire will allow air to escape more easily. It also means temperature greatly affects your road bike tires.  If you live in a cold climate, you likely already know this because you put air in your tires more often in the winter.

Bicyclists Prioritize Speed over Tire Health

Many road bicyclists prefer less weight on their bikes to increase speed and tend to purchase thinner tires. While this will make the performance of the bike improve in speed and ride quality, it does, unfortunately, mean a shorter oxygen life for the tire. This means filling the tires with air far more frequently as in, every day.

Conversely, if a bicyclist runs thick thorn resistant tubes instead of a cheaper tube, they will likely not have to add air as often.

Reason 2: Faulty Tire Syndrome

The second reason road bikes lose air is due to faulty tires. A tire becomes faulty when an object has penetrated the tire, allowing for air to escape at a more rapid rate. A faulty tire can collapses in on itself. This would also be an obvious reason for air loss in a road bike tire.

What You Can Do

Reading articles like this and understanding the actual chemistry that is occurring inside your road bike tires is the first step to tackling the ever-frustrating escaped air problem of road bike tires. However, as we now know, air will escape your tires.

You can take measures to increase the amount of time air remains in your road bike tires by doing the following things.

Proper Tire Pressure

As we’ve learned from The Gas Law, gas and pressure go hand in hand. One of the first things you should do to ensure your road bike tires don’t lose air at an abnormal rate is to ensure you are always riding with the proper tire pressure.

Every tire has an ideal air-pressure range, measured in psi (pounds per square inch.) This ideal range is stated on the tire sidewall. A road bike tire should generally run between 100 to 140 psi.

  • Under-inflation – under inflating your road bike tires can lead to ‘pinched flats.’ This occurs when an under-inflated tire hits a bump, causing the weak tire to compress itself against the rim, which can create two small holes that look almost like a snake bite.
  • Over-inflation – conversely, when you over-inflate your road bike tires, it can lead to potential tire blowouts if the tube is pushed to its max (this is in extreme cases).

Learn Basic Tire Maintenance

Check your tire thoroughly for any objects protruding from your bike’s tire or tube, especially after completing a ride that was on a route with considerable debris.  While a tiny pebble or sliver of glass may not seem like a cause for alarm, it can slowly wiggle its way into the rubber of the tire leading to an ill-timed flat.

When you find any debris, no matter how small or seemingly benign, remove it with your fingernail or a small dull tool. It’s also paramount to check your tire sidewalls to see if there’s any excessive wear or noticeable dry cracks. These symptoms increase your risk of a flat tire. If you aren’t sure how to check for these symptoms, here is a great video that walks you step by step on how to compare a healthy road bike tire with an at-risk tire.

Use Tube Sealants 

Tube sealants are excellent to have on hand because they allow you to repair existing flat tires, while also being useful as a preventative tool to avoid prospective flats.

Squeeze the tube sealant through the valve stem. This will coat the inside of the tube. If your road bike tire has a small abrasion, you can use the tube sealant to plug the leak quickly.

Depending on the type of road bike tire you have, will depend on the type of sealant you purchase. If you ride Schrader-type tube tires, you’ll likely want to purchase the slime sealant. If you are riding Presta-type tube tires, you will likely want to buy the latex sealants.

Fair warning: sealants can be messy, and they cannot protect your tube from substantial gashes or holes.

Use Tire Liners

Tire liners fit between the tire and the tube. They are little strips of plastic that give an added layer of protection to your ride.

Liners have become increasingly more popular and have a good success rate. However, they do add 6 oz. or more sometimes to the weight of your tires, which will contribute a larger amount of rolling resistance in high-performance tires. For some, this may deter them from adding liners.

Liners are recommended mostly for riders who frequently ride routes with lots of debris and thorny objects. If the extra weight means preventing punctured tires, it may be worth it!

Invest in Puncture- Resistant Equipment

Puncture-resistant tires have a band of aramid fibers that resist punctures. As you might expect, these tires will not give you the same smooth, speedy ride. However, they seriously decrease the prevalence of flat tires, which is a major win.

Use Talcum Powder

To prevent the tire and tube from sticking one another, you can administer talcum powder before installation to make the tire’s surface slicker.

The Key Take Away?

The best way to maintain the proper air in your road bike tires is to be preventative instead of having to fix things after the fact. Always be sure to keep the tire pressure at the correct psi for your specific road bike tires, invest in puncture-proof tires or similar materials if you regularly ride debris-filled roads, and watch for noticeable wear and tear to prevent un-wanted flats.

While losing tire air, in general, is unpreventable, proper tire maintenance and procuring more durable tires can help to extend the tire’s air supply for longer.

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