How Are Bike Tires Measured (Quick Answer & My Recommendations)

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Quick Answer:

To find the measurement of your bike tire simply look along the sidewall of your tire until you see a series of numbers printed. These will look like “700x32c” or “26×1.95” or “20-559”. This is the size of your tire.

Read on for more details and my recommended tires for the most common tire sizes.

How to read bike tire size

You know the ‘hilarious’ quip which goes, “You don’t have to be a rocket scientist to understand this, but…”? Well, I can tell you from my own personal experience that you need to be way, way more qualified than a ‘mere’ rocket scientist to get your head around the arcane sizing of bicycle tires.

First up, let’s take a look at finding your tire size in a little more detail.

Start by squatting or kneeling next to your bicycle so you’re looking at the sidewall of a tire. The sidewall is the bit of the tire that you’ll find adjacent to the metal wheel rim. It tends to be smooth, unlike the rubber tread area, which is the bit that connects with the ground and generally has knobbles or grips running along it. You may find that the sidewall is also a different color to the rest of the tire. For example, beach cruiser bikes often have tires with a colored sidewall. This doesn’t affect the performance of the tire but will make it look especially cool as you’re heading down to the beach with your surfboard under one arm and cooler of chilled drinks strapped to the rear rack.

Bringing our thoughts back from the sun, surf, and sand in our sandwiches. Take a look at the sidewall of the tire and you’ll see a series of letters and digits embossed into the rubber. You’ll most probably see a brand name there, such as ‘Continental’. You’ll also see the tire code, which will look like one of the following:

  • 700 x 28c – Metric system
  • 26 x 2.0 – Imperial system
  • 20-559 – ISO/ETRTO system

Metric system (e.g. 700 x 28c)

The first number, e.g. 700, is the nominal tire diameter in millimeters. The second number, e.g. 28, is the nominal tire width in millimeters. The letter ‘c’ is a hangover (literally) from the old French system which classified tires according to their width. ‘a’ was the narrowest tire, up to ‘d’ which was the widest tire.

Imperial system (e.g. 26 x 2.0)

Similar to the metric system, although without the confusing French ‘c’ thankfully. The first number, e.g. 26, is the nominal tire diameter in inches. The second number, e.g. 2.0, is the tire width in inches.

One tricky aspect to this is that the tire code might appear as say 29 x 1.5 or 29 x 1 ½. To you and I, these appear to be the same size: 29 inches diameter by one and a half inches width. Unfortunately, tire manufacturers are up to their tricks again with this and these two tires will be a different size. To be safe, if your tire code has a fraction, pick a replacement tire measured with a fraction and vice versa.

ISO/ETRTO system (e.g. 20-559)

This is an attempt to bring some order to the world of bike tires. The ISO system (which was formerly called the ETRTO system) measured tires in millimeters with the first number (e.g. 20) being the tire width and the second number (e.g. 559) being the bead seat diameter.

This is great news, however, there doesn’t seem to have been a full ‘switch over’ to the ISO system, with most tires still having either metric or imperial tire codes printed on them.

Don’t make the mistake of thinking that you can convert from millimeters to inches when it comes to bike tires. The numbers that you’ll see in the tire codes are ‘nominal’ and that means that, over time, they’ve drifted a long way from the actual tire measurements. The reasons why are too long and, frankly, boring to go into. Suffice to say that the underlying reason is tire manufacturers trying to ‘pull a fast one’. Either shaving weight off road bike tires or making mountain bike tires sound beefier.

The simplest route is to get a replacement tire that is an exact match to the tire code on your existing one. That way you can be confident that it’ll be a good fit.

Now we know our tire size, let’s take a look at my recommended tire for each.

My recommended bike tires

Now comes the easy part! You’ve got your tire size and all you need do is compare that to the chart that I’ve created below.

Find your tire size and you’ll see a link next to it. Click on this and you’ll go directly to the Amazon page with my recommended tire.

For bikes with slimmer tires, I’ve suggested slicks. These bikes tend to spend most of their time zipping along smooth pavement and you’re best with smooth tires for that, otherwise you’ll get a load of unwanted arm vibration. Bikes with wider tires, such as mountain bikes, cruisers and hybrids, tend to go on a wider range of surfaces. So they need a more knobbly profile to give confident cornering on looser gravel or dirt paths and I’ve suggested tires that match this requirement.

I’ve picked all these tires on the basis of (1) great buyer feedback and (2) their key features so you can be sure you’re getting an awesome replacement tire for your bike.

Let’s dive in!

16in tire diameter? CLICK HERE

20in tire diameter? CLICK HERE

Recommended inner tubes

If you’re replacing your bike tire then it’s worthwhile taking a close look at the inner tube as well. You may well find that your tube is looking a little dog-eared and, if that’s the case, then it’s a good idea to swap that for a new one at the same time.

Once you have your tire code, then picking a new tube is a surprisingly easy process. I’ve written an article about it that includes links to my recommended inner tubes for all the commonest tire sizes. You can find it here:

Bicycle Inner Tube Size Conversion Chart (Plus Recommendations)

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