Mechanical Monday: Five Most Common Ways of Flatting with an Inner Tube
There is a growing trend of going tubeless, and with good cause: tubeless systems are becoming increasing reliable, they provide a good feel both on the road and off-road, and if you happen to flat on a ride, you can replace a tubeless valve with a standard inner-tube. However, the vast majority of cyclists still use inner tubes, which are still the most inexpensive way of getting around on two wheels.
Unlike a tubeless system, it can be pretty daunting to figure out what caused a flat with an inner tube. Even worse, you can repair on the side of the road only to find that your brand new inner tube is also leaking air. Below are the five most common ways to flat an inner tube, and pictures to show the differences between them.
1) Pinch Flat
These are also called a "snakebite" flat, but when I used this term as a mechanic, 1 out of 20 customers took it literally and thought a snake bit their tire (there is no scientific evidence that snakes are that attracted to rubber that your local shop mechanic could calmly identify such a puncture).
A pinch flat is caused when a tire pinches between the tire bead and a rim, and in the vast majority of cases, it happens on both sides. The result is what you see above, two holes that look like a snake bit the tube. This is very common for cyclocross racers who use inner tubes, but it is also common with road cyclists who don't pump their tires to the recommended pressure before every ride.
These can be a pain to patch up, often requiring two patches, and a replacement inner tube is a better bet. Unless this happens in the same day that a new tube was installed, you likely shouldn't blame the installer for this one.
2) Puncture and 3) Vandalism
Punctures are one of the most common types of flat tires, especially in heavy traffic areas without clean, dedicated bike paths. They are also the hardest to identify. The photo above shows how difficult it can be, with a minuscule puncture right above the thumb. The best way to figure these out is by using a portable pump to put air in the tire, and running the tire an inch away from your lips (you will look silly, but your lips are far better at detecting a leak than your hands).
The photo above shows a common puncture, usually caused by thin debris like wire on the road. Ideally, you should try to match the location of this flat to your tire, because likely the pin or wire is still in your tire, and installing a new tube will only puncture the new tire. Small punctures like this are the easiest to patch, but if you are on a group ride, save the patching for when you get home and install a fresh tube instead. No one wants to wait for a patch project on a group ride.
However, some punctures are way too large for a patch, like the photo above. Often this is caused by glass. Check the tire as well, since you may need to remove the glass (with a multitool, not your hand). If the hole in the tire is longer than the width of your pinky, you likely will need a tire boot (also known as a dollar bill) in order to prevent a blow out of a new tire (you will eventually need to replace this tire once you get to a shop).
If you leave your bike locked outside, and walk out one morning to find your inner tube looking like this without glass, you might be a victim of someone who decided they would have some fun with a razor. You'll likely have to replace your tube and tire, sadly. This is more likely the case if the cut is very clean and occurs on the sidewall of the tire.
In both of these cases, you really shouldn't be blaming your installer for this one. The very rare case where you can is if you have an identical puncture due to the installer not removing the wire/glass/object from the tire, but again, this is pretty rare for most mechanics to miss.
4) Blow Out
We introduced blow outs in the last section. 29 out of 30 times, you'll know you have a flat tire because the rider will be in the area/riding the bike when you hear a loud booming noise.
One of two likely things happened. First, you had a pre-existing large hole in a punctured tire that wasn't properly booted, and the tube was trying to escape through this hole and burst.
Secondly, the tire bead was not properly seated, and the inner tube was able to sneak up the side of the rim. Most of the time for road bikes, the burst will happen while an installer is pumping the tire to 110-120psi, and they should sheepishly replace that tube with another new one while you scold them with a proper head shake.
Only the most penny-wise and pound-foolish of riders will attempt to patch this up. The photo above shows all the obvious signs of a blow out. You are better off not wasting your time (and likely the value of a patch) trying to re-use such a tube.
5) Twisted Pinch
While this is technically a pinch flat, the causes of this one are far different than a normal pinch flat (the tire is more likely to give under normal pressure rather than too low pressure). Much like a small punctured tube, this one is better felt than seen. In this case, you might be able to make out spiral formations in the tube, and when you run your lips close to a pressured tube, you can feel a long line of slow leaking air.
When a tube is installed with a twist in it, sometimes the tube blows out, but far more often, it pinches as described above. Usually before the tire flats, a rider can see or feel an odd bulge in the tire even on smooth roads.
While this is completely the fault of the installer, this flat is hard to discern unless the twist and holes are blatantly obvious, and you can see the twist when you pump the inner tube back up (which isn't easy to prove when the tube is outside the tire). If your installer owns up to accidentally installing a twisted tube, and gives you a free inner tube and installation, don't be too hard on him or her. You might not have the most dialed in mechanic alive, but at least you have an honest one.
You may as well replace your inner tube since this is even more difficult to patch than a standard pinch flat, especially as you'll likely miss a few of the very slow leaking holes.
In the Mid-Atlantic, and want to learn about fixing flats and perform a safety check on your bike? Von Hof is having a free roadside repair clinic on March 21st (a Monday night). If you haven't already, be sure to fill this survey out with your email address, or better yet, sign up for our newsletter to stay up to date with all the Von Hof rides, clinics, and events.