Bike Tires 101
Bike tires are like shoes. Most people just aren’t going to get very far without them. A bad tire can ruin a good bike ride or keep it from even starting, while good bike tires can improve your performance and make riding more enjoyable. As with many parts in the world of bicycles, they can also be a bit confusing if you don’t know what to look for. And that’s why we’ve put together this handy little guide.
Bike Tire Sizing
The main thing that dictates the size of the wheels (and thereby the tires) is the size of the bike. Over the years, there have been many different sizes of bike wheels produced. These days, most wheels are one of four common sizes.
The most common bike tire sizes:
700c: Most common size for road and cyclocross bikes.
26 inches: Common size for older mountain bikes and old city bikes.
27.5 inches: Most common size for newer mountain bikes.
29 inches: Another common size for newer mountain bikes.
Some other sizes you’ll see:
12/16/20 inches: These are common sizes for kids’ bikes.
24 inches: Often found on youth mountain bikes.
650c: This size is sometimes found on road bikes with small frames.
As a general rule, when you want to get a new tire, just look at the old tire and get the same size. With that said, there are some things you should know.
Common sizing vs. ISO
One fact that is essential to understanding bike tire sizing is this: the common size is not the exact size.
First of all, if you have any experience in bikes, you’ll know that it’s just a strange, mixed-up world of metric measurements and inches. Tires are no different. The 700 (which is really 700mm) and the 26/27.5/29 (in inches) supposedly refer to the outside diameter of a tire when inflated. But in reality, it’s an approximation. This can be especially troublesome when you’re looking at 26-inch tires for bikes that are more than 30 years old.
Most of the time you’ll be okay following the common size, but if you want to make sure you’re really getting the right tire, you need to look for the ISO (International Standards Organization) size. This standard adopted the European Tire and Rim Technical Organization sizing format, so whether you see it listed as ISO or ETRTO, know you’re on the right track.
The ISO bike tire measurement is in millimeters and has two parts: the diameter and the width. It is typically written with two numbers separated by a hyphen. The larger number is the diameter at the bead (the inside diameter of the tire). The smaller number is the tire width. For instance, a road tire with the common measurement of 700 x 23c will have an ISO of 622-23. A mountain tire with the common measurement of 27.5 x 2.0" will have an ISO of 51-584.
Tire width is important
It’s obvious that if you get a tire with the wrong diameter, it won’t fit your bike’s wheel. But it’s also important to pay attention to the width of the tire. While most rims can handle a range of tire widths, if you get a tire that is too wide, there’s a chance it may not fit in your fork or frame.
Where does the "C" in 700C come from?
We've established that 700C is actually a millimeter measurement. So why the C? It hearkens back to an old French standard where A, B, or C were used to describe the width of a tire, with A being the widest and C the narrowest. Somehow the C stuck. We hope A and B aren't too offended.
Bike Tire Tread
Bicycle tire tread can basically be divided into three different categories: slick, knobby, and inverted.
Slick tire tread is used on road bike tires where speed is the goal and smooth pavement is the riding surface. With little-to-no actual tread, these tires are designed to reduce rolling resistance.
With a pattern of raised bumps along the surface of the tire, knobby tread is typically seen on mountain bike tires. The tread helps you grip the trail so you don't slide out on loose dirt or gravel.
You'll see some tires that are knobby on the edges and almost slick in the middle. These are designed for cross-country bikes or hybrid bikes to limit rolling resistance for straightaways without compromising control on the turns.
For bikes ridden on rough city roads or in the countryside, inverted tread is common. The lack of knobs helps you ride faster, while the inverted tread gives you some traction and durability when you meet loose gravel or crumbling pavement.
There are three basic bike tire/rim interface designs. If you get the wrong one, your tire will be useless.
The most common tires are clinchers. Clincher tires have a distinct, open bead where the tire seals to the lip of the rim when air pressure is applied. Most clincher tires require an inner tube to hold the air.
Tubeless tires are technically clincher tires, but the main difference is in the name: they don't need tubes. These can be ridden at a lower air pressure for a smoother ride with a smaller chance of pinch flats. While the advantages are great, tubeless tires are more difficult to set up and to patch when you get a hole. You can carry a tube throw it in if you get a flat, but it might get a bit messy with the sealant required for tubeless setups. Your rims must also be tubeless-ready, and there are conversion kits available. Tubeless tires have become very popular for mountain bikes in recent years, and their popularity is slowly increasing in road cycling.
Especially popular with triathletes and time trialists, tubular tires are essentially the tire and tube in one. Without a bead, the tire has to be glued to the rim. This can be done with brush-on cement or glue tape. Racers like tubular tires because they can be ridden at a higher air pressure. And even though the rim adhesion may sound like a pain when you get a flat, a tubular can be easier to replace than a tight clincher where tire levers and a lot of elbow grease are required. Additionally, since the rim doesn't have the additional material required for the hook bead of a standard clincher, tubular wheels typically weigh less than comparable clincher wheels. However, tubular tires are usually more expensive than clinchers.
Additional features to look for in bike tires
Folding bead vs. wire bead
You'll notice tires labeled as "wire bead" or "folding." The wire bead is what keeps a tire in its circular shape when it's off the rim. A folding bead has a soft bead made of Kevlar or a similar material, so it can fold up when not installed. Folding beads have become more popular in recent years because they are easier to ship and store, and they often weigh a little less than their wire-bead counterparts.
Many tires come in both wire- or folding-bead version. While the wire-bead tires tend to cost a little less, the actual construction of the tire is usually the same in both versions, so it's more a matter of personal preference.
The rubber on a bike tire is attached to a casing, which is usually a sheet of woven nylon between the two beads. The quality of the casing is measured in "threads per inch," or TPI. Similar to the thread count in bed sheets, a higher TPI means a higher quality casing. That means the threads are finer, reducing weight and giving your tire a more supple ride. In some cases that also means the tire won't be as durable, so consider the conditions you'll be riding in when comparing two models with different TPIs.
Some tires offer puncture protection as a feature. This usually means there is a belt of Kevlar or a similar material that runs underneath the tread, providing a layer of protection against thorns and other sharp objects that want to put an end to your ride. Puncture protection is especially good for commuters and mountain bikers, but it does add weight to the tire.
Other features you may want:
Studded tires for riding in snowy and icy conditions.
Dual-compound rubber for optimal grip and low rolling resistance.
Colorful tread or sidewalls.