Why does my bicycle tire keep going flat? (It may be more than a thorn in your tire)

The other day I went for a ride over the bridge and out to Stinson Beach. It’s a nice ride and once you get past four corners and through Mt. Tam, the relatively steep percent grade uphill matched with the technical downhill is very fun to get to the coast. The one damper was that I got two different flats during the ride which was exhausting to replace the tube. So it made me wonder why does my bicycle tire keep going flat and why is my bike tire losing air?

In this post, I will tell you the four ways your tire (and the reason why my tire) can go flat repeatedly when you don’t see the most obvious sign of a bicycle tire going flat. We will discuss slow leaks, pinch flats, rim tape issues and general inflation issues.

If you happen to be in the process of pumping your tire and it still won’t inflate, press here because this will be the most helpful post for you.

Why does my bicycle tire keep going flat?

Here are the reasons your bicycle tire is deflating. For more details click on the link in the bullet points or scroll down for more detail on each. Keep in mind that it is completely normal for a bicycle tire to slowly lose air over time.

• Slow Puncture
• Pinch Flat
• Rim Tape
• Tire Inflation Issues

How to keep my bicycle tire from going flat

Before moving forward, consider investing in ride. I’m a Mr. Tuffy user and anyone that rides where burrs, thorns or car glass tends to be found on the road and can lead to a flat should consider Mr. Tuffy tire liners. They will extend the life of your tires and your tubes.

These are great for road bikes, though cause some complications with mountain bikes. My auntie recommended the liners to me from when she rode – and if the brand has been around for 3 generations, I trusted it enough to at least try it out.

As it stands, I have not gotten a single flat this season after I put them on and I ride through the city, and across the bridge where I deal with both burrs, thorns, and glass from cars on the side of the roads (the culprit of one of my first flats was being blown by a gust of wind into a small pile of glass without tire liners.)

Slow Puncture

These are tricky. Whenever you get a flat, typically you want to look at both the tire and the innertube to see what is causing the flat. More important, take your tire off, and flit it inside out to see if there is a very small item inside of your tire.

After my two flat within 60 mile ride, I got home and saw that I had a micro-burr causing a very slow leak in my tube.

It is important to find the cause of the micro leak which is typically in the tire by running your thumb along he inside. Second, it is important to find the leak in the tube.

You can inflate the tube fully and run your hand along the side of the tube and wait for a stream of very cold air.

Your second option is to submerge the tube in your sink to find the micro leak. This is easier accomplished at home than on the road.

Pinch Flat

A pinch flat happens when the tube gets caught in between the tire and the rim. It will typically happen when you are replacing your tube.

The easiest way to avoid this is to pump the tube halfway (~40 pounds per square inch for a roadbike), release all of the air, and then pump it up all the way afterwards). This also ensures that the tube is seated well in the tire rather than bunching in one place around the wheel.

When a pinch flat happens, and you are blowing up your tire with anything stronger than a handpump it is usually dramatic and loud. However, if you are using a handpump, a pinch flat can happen quietly, and you can slowly lose air throughout a ride.

It can be frustrating, and the tube will need to be patched or replaced.

Did you (or your mechanic) put on the Rim Tape?

Five years ago when I was on my first bike, I had a shop mechanic show me how to replace a tube and put on a tire.

Unfortunately, he was not the greatest teacher because my rim tape was not put on and the spokes were not tightened correctly. When you do not put on your rim tape, the tube will rub against the rim and the spokes and cause flats throughout the tube. It will lead to a flat in as little as a day.

Did you under or overinflate the tube?

If you under inflate the tube, the tube and tire will be more susceptible to penetration from foreign objects like thorns and other items on the ground.

If you overinflate the tube, you will begin losing air at a faster rate than if it were at its standard air pressure rate. I like having an electronic tire wand at home to make sure that I am always at the correct air pressure without needing to do much thinking.

This one has lasted me a couple of years so far. I would hesitate to go any lower than this price point because one at a lower price point that I tried; the motor simply stopped working after one month twice after replacement. If you are having trouble deflating your tires to a reasonable pressure, press here for a guide on deflating all 3 types of valves for cyclists.

Natural Air release

Presta Valves, road bikes and other high-pressure bikes from the 80-120 PSI range will typically lose 10-20 PSI per ride. This is natural and not a problem.

It is a good point to remember to add this as a list of items to do check up on your bike before each ride and include it in your general maintenance routine.

Other Low Probability Edge Cases

The above 4 reasons will be the reason why 95% of your bike tires will go flat. If you are still having trouble with your innertube, here are other reasons why it may be going flat.

However, these are edge cases and will be less that 5% of the reasons why your innertube is flat. There are some other edge cases that may be caused when coupled with incorrect bicycle tube and tire installation, lower value parts, and other complications that would only make these issues while riding your bike viable.

However, they are worth a mention in case the previous four reasons were not why your bicycle tube and tire keep going flat.

Wheel True-ness

When a bicycle wheel is not completely true, it means that the bicycle is not a perfect circle when looking at it from the side. There may be some flat edges of the circle.

If it is particularly bad, you will feel a bump when you ride (or the tire will rub against the brakes). This distortion in the rim for too much time can cause bunching in the tire space which is able to lead to a pinch flat when the innertube is not perfectly aligned to a trued rim.

If your bicycle wheel has been out of true for some time, then take your bicycle to a shop and have your bicycle wheel trued ($20) and then replace the tube afterwards.

Damaged Valve

In 2023, the typical quality of valves in tubes that you come across are pretty high standard. (I do not recommend buying the lowest price [less than $10 each] tubes online, as in my experience they can struggle to hold air).

However, from time to time you can come across a valve that gets damaged. You are able to replace the valve specifically on Presta and some Shrader valves, though the amount of time to find a valve and go through the repair may be better served by simply replacing the tube.

Pinching in Tube

Do you ride your bike flat very often? When you ride your bike with a flat tire, and you brake on the tire (with rim brakes or caliper brakes, the rim itself will stop moving, though the tire and the tube will shift a very small amount along the wheel.

This shifting can cause the tube to pinch, pop and lose air. Further, the shifting can drag on the valve as it tries to hold the tube in place.

The valve leaning at an angle can pinch the tube and it can go flat, or there can be damage to the valve which will keep the tube from filling with air.

Riding in the heat

Some lower value tires and tubes can be affected by the heat. The air can expand in the tube and cause the tube to pop if the rubber is old or if it is unaccustomed to these temperatures.

If you have changed to a different location and a vastly different climate, then consider changing the tube and the tire. The rubber may not be accustomed to that specific climate that the bicycle is now placed in.

Conclusion

From this post you should have a good understanding of why your bicycle tire keeps going flat. From my years of experience I now know why does my bicycle tire keep going flat and why is my bike tire losing air.

I am happy to pass my learning experiences on to you. If you want to manually deflate the tire to check for a flat, then follow this guide here to learn how for any valve system that you have.