So you or your kids have a flat tire, it’s not only annoying but what sized tube do you actually need? Looking at all the numbers on the side of the tire can be baffling, which number is the one I need?
This post should give you a guide to the in’s and out’s of bike inner tubes, how they work, valve types and finding the right size for you or your children’s bikes!
What is a Bike Inner Tube?
Inside a normal bicycle tire, you will find the air-filled rubber tube that gives the tire it’s shape and ability to hold pressure and give a firm but stable ride. Think of it as an inflatable balloon inside your tire, it doesn’t pop because the tire stops it over-expanding in size and you can keep inflating to the desired pressure since air compresses in a closed space.
The tubes themselves are mainly made from rubber, they come rolled up in a small box and require a slight inflation to allow the shape to be recognizable and how it fits inside the tire.
It’s likely you or your kid’s bikes are running on inner tubes (unless you have converted them to tubeless) and the cushion the tube provides allows the tire to conform to the ground giving better grip and comfort.
Tubes are commonly made from Butyl Rubber, this is relatively cheap and lasts a long time. There is a difference between standard tubes and light-weight tubes, this is the lightweight tubes uses a thinner walled tubed to cut weight, a trade-off is they are more susceptible to punctures.
Latex is the other material, used more in road racing bikes, the latex needs frequent topping up and is difficult to patch, but they have better-rolling efficiency.
Do they stay up? My Bikes have been sitting in storage and the tires went flat?
The rubber that tubes are made from is actually porous and allows a small amount of air to be released over a longer period of time. It’s very common for tires to gradually weep air and go soft over 3 to 6 weeks, even more, if the climate is particularly warm.
If you have a bike that’s been in storage and the tires have gone down, it’s highly likely the tubes are still fine, it’s just they have lost their air over a long time sitting. Before swapping them out, just pump them up and check them the next morning, still up your good to go. Flat? either patch or replace.
Bicycle Valve Types
There are two main types of valves you will come across, the Schrader (Car Valve) and the Presta (skinny looking) valve.
They both do exactly the same job but are different in size so a car valve will not just fit straight into the Presta valve hole.
This is by far the most common valve type, it’s used widely in the automotive industry and is easy to use and quick to pump up. These valves are generally less fiddly than the Presta valves and are found on lots of kids bikes through to town and commuting bikes, or bikes using lower pressure tires.
Pumping up is simply a matter of attaching a pump and away you go, no screws or need to push the valve down first to un-seal it.
This is the skinny looking valve you may have seen on road racing bikes or some mountain bikes. The diameter of the valve itself is smaller, while at the top there is a locking screw that unlocks the valve allowing the air to enter and exit. Also there usually a lockring that screws down over the outer body of the valve stem and sits against the rim.
The Presta valve is usually specced on road bikes since the rims are narrower, hence needing a smaller diameter valve. Also on mountain bikes which use tubeless sealant, these are used for their easily removable valve core and simple cleaning.
To pump up a tire using a Presta valve, unscrew the top locknut, give the valve a press to unseat the seal and carefully pump your tire, you will have to keep the pump square to the valve to stop the top bending making it difficult to close the valve and fit a valve cap.
Which valve is better?
Both systems have their pro’s and con’s but for general ease of use, and especially on kids bikes, a Schrader valve is probably going to be the easiest to use.
Presta valves need a bit more care when pumping up, it’s easy to bend the undone center valve core and sometimes it even snaps off, which may mean a new tube of the valve core is not replaceable.
My bike has skinny valves, can I fit a car valve instead?
In most cases, Yes! unless you have extremely narrow road bike rims, you should be okay (check with your local bike shop first if you do have really narrow rims)
For rims with the skinny Presta valve, the conversion is quite simple. By using an 8.5mm drill bit (11/32″) you can drill the hole larger to accommodate the bigger valve, this is safe on most alloy rims, but if you’re unsure, just check with your bike shop first.
Is a Valve Cap necessary?
For Schrader valves, the inside moving parts of the valve is exposed and having dirt and mud get into the valve can make it jam up and just generally be annoying to use, so if you have a cap use one on this valve.
For Presta’s, it’s not necessary since there are no exposed moving parts and it’s easy to clean but again if you have one you may as well chuck it on.
Are Bike Tires and tubes the same size?
Most tires on kids and adults bikes are known by their “inch” size. For example, a 16″ bike uses a 16″ tire, and a 26″ inch bike uses a 26″ tire.
The other main measurement is the width of the tire. There are many widths of tires out there and you will have to check to make sure your tubes not only the right wheel diameter but also the right width.
If your tubes to big, it will scrunch up inside the tires, being very difficult to fit and likely to rub itself inside the tire and puncture, while if it’s too small in width it will get thinner as it’s inflated to fill the inside of the tire and will likely cause more punctures or fail.
Picking the right tube for your tire
There are only two numbers that you really need to find the right tube for your bike, the size of the wheel and how big the tire is, or how wide it is.
Looking at the numbers
For anything that uses an air-filled tire, be it strollers, buggies, kids and adults bikes, and even golf trundlers the first step is to find the bunch of numbers located on the sidewall of the tire. They will usually be in a bunch, below are a few examples.
This is a tire off a stroller. Nowhere else was there any numbers written on it so this is what we have to go off.
16 X 1.75 When we see the first number X the next number, the first number is the wheel or tire diameter (wheel size), in this case, it’s 16 so it’s a 16-inch tire. The second number after the X is always the width, in this case, it’s 1.75 which is 1.75 inches. So we need to buy a 16″ X 1.75″ inner tube.
Tube Size Ranges
Because there are different widths of tires, tubes come in different widths as well.
You might see this written on the outside of the box when looking for this 16″ tube.
16″ X 1.25, 1.5, 1.75″ This is a 16″ tube that will fit well in a 1.25″ tire but can stretch out to fit a 1.75″ tire
16″ X 1.5 – 1.75″ This tube is best suited for a 1.5 – 1.75″ tire
16″ X 1.75 – 2.1″ This tube is best suited for a bigger 1.75 – 2.1″ tire
The varying sizes indicate the width best suited for that particular tube. If the tubes a 2.1″ wide and you try to fit it in a really narrow tire it will scrunch up, be hard to fit and likely puncture quickly.
Here’s a kids bike tire, there’s a bunch of numbers here, which one’s right? look for the number X number, in this case, it’s 12 1/2 X 2 1/4. Just like before, this reads like a 12″ tire that’s 2 1/4 inches wide. Don’t worry about the other numbers.
This one is off a hybrid-style bike. Again the number X number shows up, here it’s 700 X 40c, don’t worry about the other numbers, the 700 is the diameter of the wheel while 40c is the width (40 millimeters) Might sound confusing but just look for the tube box that 40 goes width. This box reads 700 X 40/45c. The tube will best fit a tire 40 – 45mm wide.
I hope this has helped clear any confusion about how inner tubes work and what to do when you need one, punctures are never fun, but if you know what you need to look for when buying it takes a lot of the hassle away!
If you’re keen to learn more about how to patch a bike tube, see our guide to fixing a bike puncture.