If you have ever geared up to ride your bike only to find that your tires have mysteriously gone flat since the last time you rode it, then you know how frustrating that can be. Not only does it put a damper on your ride, but you may also wonder why the tires didn’t hold air in the first place.
Bike tires can go flat from sitting unused even if there has been no damage to either the tube or tire. There are several things that can cause this to happen, including cold temperatures, dry rot, or simply the porous rubber with which bicycle tubes are manufactured.
If you’re having problems with your bike tires deflating, and you can’t figure out why it keeps happening, then you’re in the right place. In this article, we are going to dive a little deeper into the following topics:
4 Reasons Bike Tires Go Flat When Not In Use
There are several things that might cause a tire to go flat from sitting unused. The 4 primary reasons are:
- The Porosity of the Rubber in the Tubes and Tires
- Undetected Damage to the Tube or Tire
- Dry Rot
- Cold Air
Let’s take a closer look at these different scenarios:
1. The Porosity of the Rubber in the Tubes and Tires
Rubber bike tubes and tires naturally leak air over time. This is because the rubber that they are made from is naturally porous.
At the microscopic level, you can think of the rubber as a sponge. There are tiny holes and gaps throughout its structure. Over time, the air molecules contained inside of the tubes and tires find their way out of these tiny holes, leading to air loss.
Tire companies have put significant resources into developing different rubber compounds with lower porosities in order to increase longevity and durability of bike tires. However, regardless of the type of tire or tube, some air loss is still inevitable.
2. Undetected Damage to the Tube or Tire
Even if your bike tire held air the last time you rode on it, it could have still been slowly leaking air. Damage to the valve stems, rim strips, or tiny abrasions to the tube or tire can cause the tire to lose air slower than a puncture.
There are several ways to check your tire and tube for damage. Try adding air and listening for a “hissing” sound of air escaping. You can also take a soapy sponge and give the tire a good soaking, keeping a close eye for bubbles forming. This is a good method for finding the source of a tiny leak that may be the flat-tire culprit.
If you’re unable to find a detectable source of air leakage, but your tires still keep going flat when not in use, consider replacing the rim strips, tubes, and tires.
3. Dry Rot
Like many materials, rubber has a limited life-span. If left unused, the rubber in tires and tubes will begin to break down and degrade over time. As this happens, your tires may begin to “dry rot”. Tires that are exposed to severe temperature changes, humidity, and direct sunlight for extended periods of time are more likely to become dry rotted.
You can tell if your bike’s tires have begun to dry rot by looking at them closely, particularly around any knobs or seams. If you notice the rubber has developed cracks or seems dry and flaky, that’s a sign that your tire has begun to dry rot.
Tires that have dry rotted are no longer safe to ride and should be disposed of.
4. Cold Air
During the colder months, you may find that your bike’s tires seem to become soft more frequently than in the summer months. Without hitting you over the head with a ton of science, (we’re here to talk bikes, afterall), the reason can be summarized as this:
As the temperature drops, air molecules move more slowly and condense. This overall decrease in molecular movement causes a loss in air pressure. That includes the air pressure contained inside of your bike’s tires.
If you’re riding your bike on a colder day, check your tire’s pressure and add some air if necessary.
How Quickly Do Unused Bike Tires Deflate?
Unused bike tires will lose air relatively slowly. A hybrid bicycle with a tire pressure of around 40 psi might not have a noticeable loss in air pressure, even if left sitting for 1-2 months.
A mountain bike with tires set to 20-30 psi might hold its air even longer, and may only require a minimal amount of “topping off” every few weeks or so.
How quickly your bike’s tires lose air will ultimately depend on a number of factors, including where it’s stored, the tire’s size, air pressure, and age. It’s good practice to check air pressure every few rides, even if the tires aren’t complete pancakes.
Road Bike Tires Lose Air Faster
Because road bikes tend to have the narrowest tires and require the highest air pressure, they tend to lose air faster than all other types of bicycles. Road bikes may even lose noticeable amounts of air just sitting in the garage for a few days.
Take for example this Cannondale SuperSix EVO road bike: Notice it’s narrow 25mm tires. This bike’s specifications call for a tire pressure between 100-120 psi.
This high pressure means that their air inside is pushing hard against the walls of the tubes and tires, which will ultimately lead to more air escaping. This bike would likely require the addition of air every few days, even if left unridden.
On the opposite side of the spectrum, this Surly Ice Cream Truck fat bike has 4.8 inch tires which can run a much lower tire pressure than the Super6. Although this bike’s tires will have less air to begin with compared to the road bike, they also won’t lose their air nearly as quickly.
3 Ways To Keep Tires From Going Flat
So now that we’ve spent a little time talking about why your bike’s tires might lose air from sitting unused, now let’s talk a bit about how to keep it from happening.
The following three methods will help prevent your tires from losing air:
- Using Baby Powder When installing Tubes
- Avoiding High Tire Pressure
- Storing Your Bike Somewhere Dry And Out Of Direct Sunlight
Let’s find out how these methods can help stem (like a valve stem, get it?) the loss of air from your tires.
1. Using Baby Powder When Installing Tubes
When installing your tube, take a small palm full of baby powder and lightly coat the entire tube. This will reduce the friction between the tube and the inner surface of the tire, decreasing the chance of small abrasions forming in the tube.
This tried and true method will help maintain the lifespan of your bike tubes, so that they’ll hold air longer.
2. Avoiding High Tire Pressure
If you’ve ever read the writing on the side of your tire, then you’ve probably noticed that there is a specified recommended air pressure. It is a common misconception that the larger number is the higher recommended tire pressure, when in fact, it is actually the tire’s maximum air pressure.
Instead of pumping your tires up to this maximum, consider running your tires somewhere within the middle of the specified range. Not only will you avoid an inadvertent blow-out, but you’ll reduce the amount of air that escapes on its own.
You can check out this article if you want to learn more about recommended tire pressure for various types of bicycle.
3. Storing Your Bike Somewhere Dry And Out Of Direct Sunlight
A good protective measure you can take against flats, is to make sure your bike is kept someplace with relatively low humidity and out of direct sunlight. This will maintain the integrity of your bikes tires, tubes, and other rubber components, so that you get the maximum lifespan out of them.
Do Tubeless Bike Tires Lose Air?
Traditionally, bike tires use an inflated inner tube that gives the tire its structure and rigidity. However, tubeless bike tires are a bit different, in that they don’t use tubes to inflate the tire. Instead, the air is contained by the tire and rim itself, and uses a special sealant to keep everything airtight.
Tubeless tires are most likely to lose the most air soon after they are initially set up, or when the sealant has not been replaced after several months.
4 Ways to Keep Tubeless Tires from Leaking Air
There are several ways you can keep air leakage from tubeless tires to a minimum. These are:
- Using Tubeless-ready Tires and Rims
- Using Soapy Water During Initial Set-up
- Regularly Replacing and Topping-off Sealant
- Replacing and Cleaning Valve-cores Regularly
Here are some details on the “how’s” and “why’s” of these methods:
1. Using Tubeless-ready Tires and Rims
In the early days of tubeless tires, you had to use a tubeless conversion kit if you wanted to ditch the tubes. As tubeless became an increasingly popular method (especially with the mountain and gravel-bike crowds), component manufacturers began making wheels and tires that could be set up tubeless without a conversion kit.
A definite advantage of using tubeless-ready tires and rims, is that they will not only set up easier, but hold air longer.
2. Using Soapy Water During Initial Set-Up
How you initially set up your tubeless wheels will affect how well they hold air over time. A common bike shop-approved tactic is to soak the bead of your tires in soapy water before installing them on the rim. This will allow the bead of the tire to slide into the lip of the rim better, helping create an extra air-tight seal when you are ready to inflate it.
3. Regularly Replacing and Topping-Off Sealant
Sealant that is old or has been sitting stationary within a tubeless tire may not hold air as well as it did when first installed. It is a good idea to regularly add sealant, especially if you notice significant air loss from your tires.
Tubeless sealant should be cleaned out and replaced every 4-6 months at a minimum.
4. Replacing and Cleaning Valve Cores Regularly
One of the most common reasons tubeless tires leak air is because of dirty or broken valve cores. These small removable pieces can become “gummed up” with old sealant. They may also become bent and broken after continued use.
If you have a valve-core removal tool, it’s not a bad idea to pull them out and clean them when you replace your sealant. If you notice that it appears bent, or that the tip of the valve does not tighten down smoothly, then you should consider replacing the valve core with a new one.
Wrapping It Up
As you can see, there are a number of reasons your bicycle’s tires may go flat, even when the bike has not been ridden. Knowing why this happens, and what you can do about it, will keep you and your bike ready to hit the road or trails.