What Size Bike Tires Do I Need – Bike Tire Guide

Tires for bicycles come in an overwhelming variety of sizes.  Does choosing the exact size really matter? What size bike tires do you need? In this article, we’ll try to answer your important questions about different bike tire sizes.

Choosing the right tire size for a bicycle isn’t as straightforward as many of us would think. In some instances, manufacturers have their own tire size descriptions. That’s why it’s best to talk to people from a good bike shop to get expert advice.

As what we’ve promised, we’ll go in-depth on how to choose the right bike tire size in the sections below.

Do Bicycle Tire Size Really Matter?

If you want the short answer, it’s yes.

But since you have so many choices for tire sizes—not to mention, wheel sizes—it’s easy to get confused and overwhelmed. Therefore, it’s important to understand tire sizes because they’ll greatly affect the performance of your bike.

In most cases, you only need to look at the sidewall of your bike’s current tires to know the correct size you should buy. Aside from the diameter (determined by your wheel size), a bike tire’s width is another important dimension that you’ll need to think about more.

Bike tires can have slight variations in their width. For instance, you could get wider replacement tires if good ground traction and a cushier ride are important to you.

Simply put, the wider your bike tire, the  more road surface area it covers. As a result, it improves your bike’s handling and maneuverability.

The correct or optimal bike tire width will depend on your riding style. If you usually ride on loose dirt trails, you’ll need wider tires for increased cornering grip and better shock absorption.

On the other hand, if you mostly ride on hard-packed dirt roads or concrete roads, narrower tires are better options. Narrow tires also give you more speed because they offer less air resistance.

To sum it up, getting the correct tire size for your bike is important. With that said, the next thing we’ll discuss is how to read the numbers on a bicycle tire and other sizing information.

How Do Bike Tire Sizes Work?

The sidewall of bike tires contain plenty of information, like the numbers that indicate their size. There are several ways manufacturers express these size markings. Therefore, there are different ways to read them.

The size of tires are usually measured in either inches (in.) or millimeters (mm). In general, bike tire sizes are made up of two groups of numbers:

         The larger number (the first number) indicates the outside diameter.

         The smaller number (the second number) indicates the width.

For instance, 700x25c means the bike tire has a 700-millimeter outer diameter and a 25-millimeter width. Or, if it says 26×1.75 on the sidewall, it means that the outer diameter is 26 inches and the width is 1.75 inches.

Now, the dilemma: There are different sizing standards that exist in different countries. This led to a lot of mix-ups—bike tires with the same size were differently noted or different-sized bike tires were given similar dimension note.

That’s why two major international organizations formulated and introduced the standard notation for bike tire size that’s in use today:

The ISO

ISO stands for International Organization for Standardization, a Switzerland-based, nongovernmental organization. It develops a variety of commercial, industrial, and proprietary international standards, including the standard for bicycle tire sizes.

You don’t mainly depend on the common size of bike tires because they could have different variations. For instance, a 26-inch bike tire could be available in three different sizes. To make sure you got the right one, you use the ISO size or the rim measurement.

The ISO size, also called as the true size, consists of two groups of numbers:

         The width of a fully inflated tire in millimeters

         The diameter of the inner circle of a tire that sits on the rim (tire bead) in millimeters

Note: The second and third groups of numbers could be different, depending on the country where you buy the tires. It’s important for the tire bead to precisely fit to the rim.

The ETRTO

ETRTO stands for the European Tyre and Rim Technical Organisation. The ETRTO measurement is under the ISO system. In fact, it has the name ISO 5775. Thanks to this measurement system, you no longer need to wonder which of the six types of 26-inch bike tires are right for your needs.

Unlike the ISO standard, however, ETRTO sizing measurement lists the width first then the diameter. Also, the measurement of the rim diameter is different with under the ETRTO system. For instance, a 700x18c tire is the same size as a 18-622 (ETRTO) tire. Or, an MTB tire size 26×2.35 is equivalent to the  58-559 ETRTO size.

The French

The French system, which is still in use today, provide the approximate measurement of a bike tire’s outer diameter. For instance, A 700x40c size indicates that a bike tire has an outer diameter of 700 millimeters and a width of 40 millimeters.

If you’ve noticed, the French standard for bike tire sizing uses the letters a, c, and d. The “c” indicates the actual rim type, while the “a” means a thin tire that needs a larger rim. The “d” indicates a smaller rim and wide tire.

Note: Not all bike tires use the French size markings. For example, tires for mountain bikes don’t use these markings.

Common Tire Sizes for Each Bicycle Type

When it comes to tire sizing, the (outer) diameter is a more important consideration than the width. The diameter of every bike tire is different, but it mainly depends on the tread pattern. Most of the modern bikes you see on the road or in stores will have the following tire diameter sizes.

26″ (ISO: 559 mm)

This tire size is widely used on modern mountain bikes and hybrid bikes. This came to be because the features of the earlier versions of the mountain bike were based on beach cruiser bikes, which were fitted with 26-inch tires.

The width of 26-inch bike tires typically range from 1.75 to 2.2 inches. However, they could also be as narrow as 1 to 1.5 inches. Bikes for downhill mountain cycling and snow cycling are fitted with 26-inch tires that have a width of about 2.5 inches and 4 inches, respectively.

There are no fewer than 5 types of 26-inch tire sizes that are available today. Aside from an ISO size of 571 mm, some 26-inch tires could have an ISO rim size of 571 mm, 584 mm, 590 mm, and 597 mm.

27″ (ISO: 630 mm)

This tire size was used for road bikes built in the ‘70s and ‘80s. If you need a new tire for your vintage road bike or racing bike, you can ask your local bike shop to order a 27-inch (ISO: 630 mm) tire for you. Tire manufacturers still produce this size because there are still plenty of these wheels hanging around all over the country.

Most modern 27-inch (ISO: 630 mm) bike tires work on hooked rims (or “crochet type” rims). But, they could also work on rims with straight sides. The only downside is they won’t be able to handle higher pressures compared to if you use the hook rim version.

27.5″ (ISO: 584 mm)

27.5″ (ISO: 584 mm) and 650B are actually the same. They describe the same rim diameter. That’s why they’re often used interchangeably.

A 27.5-inch tire is mostly found on downhill mountain bikes and triathlon bikes. It’s a good choice for people who aren’t blessed with height and can’t comfortably fit on a 29er mountain bike.

The main advantage of a bike with 27.5-inch tires is it’s the next best alternative if you can’t choose between a 26-inch bike and 29-inch bike. It combines the best features of both bikes—the forgiveness and speed of a 29er and the responsiveness of a 26-inch bike.

29″ (ISO: 622 mm)

29-inch tires, also called as 29ers, are widely used on mountain bikes. They’re similar to 700c tires when it comes to their diameter. One of their differences is the 700c tire is intended to be used on a 700c rim. Since a 29er tire is wider, it won’t fit a 700c road rim.

Like 26-inch mountain bike tires, 29-inch bike tires have a width that ranges from 1.95 to 2.3 inches. And because of their larger wheel size, these tires have a better overall traction.

650B (ISO: 584 mm)

The 650B (ISO: 584 mm) is one of the most common types of tire sizes. It’s  typically used for commuting bikes, hybrids, mountain bikes, randonneur bikes, and older French tandem, touring, and utility bicycles.

Now, you might’ve heard of  the “27 five” (or “point five”). This is a fourth designation for the 584 mm tire size, which a few misguided marketers popularized to mean that the 584 mm tire size is a middle ground for the MTB 26-inch and 29-inch tire sizes.

650C (ISO: 571 mm)

Sometimes, a 650c is described as a 26-inch tire size. Tires of this size are meant for smaller bikes for triathlon and paved roads. Some people use 650c tires with smaller widths for time-trial bicycles (racing bicycles designed for riding against the clock), while the heavier and wider ones are used on older Schwinn cruiser bikes.

Note: There are no medium-width tires in this size. There are only narrow and wide tires.

700C (ISO: 622 mm)

700c is the standard size for most modern road bikes, cyclocross bikes, and touring bikes. The “700” refers to the outer diameter measurement (in millimeters) of the tire, while the “c” indicates the bead seat diameter.

On a 700c wheel, you can fit tires that vary in their widths. For the past few years, 700c tires that are 22 mm or 23 mm wide have been the standard for most road bikes. If you have a 700x35c cyclocross tire, you can swap it for a 700c tire that’s not narrower than the outside width of your rim.

You might be wondering: Are 700 and 700c tires the same? Yes, they are similar. 700 refers to the average outside diameter of the rim, while the 700c refers to the typical standard tire size for road bikes.

How do I choose the right size bike tire?

Needless to say, tire sizing is important. Overall, there are no hard and fast rules that you need to follow to the letter. And that means you’re free to experiment to find that tire size that’s perfect for your setup.

Now, let’s go through some of the important considerations when choosing the right tire size for your bike.

Check the Sidewall

As what we’ve mentioned before, you don’t always need to ask experts to know the correct tire size. Simply check the tire sidewall to get this information.

It doesn’t matter whether there are one, two, or three sets of sizing numbers on your bike’s tire. The more important thing is the size of the replacement tire (or tires) matches any of those sets of sizing numbers.

If the rim is too narrow, your new tire is going to be loose through the corners. Or, if your new tire’s size and internal width are closely matched, the side knobs of the tire might become useless because of an overstretched tire tread.

Measure Your Bicycle Tire’s Diameter

This is the part where experimentation just won’t work well. Unlike the width, which you can slightly change, the diameter of your new tires should be compatible with your current rims.

Remember:The larger the diameter, the easier it is to navigate through bumps and obstacles and maintain a certain level of speed. The downside is it’s going to be difficult to change direction.

The smaller the diameter, the easier it is to change direction at all speeds. It’s also easier to slow down and speed up. The downside is rolling over obstacles is more difficult.

Here’s how to measure the bike tire diameter:

1.         Position the end of your measuring tape against the middle of your bike’s wheel.

2.         Extend your measuring tape in a straight line. Make sure it goes all the way to the outer edge of the tire.

3.         For traditional sizing: Double the inches in order to get the tire diameter.

4.         To get the ISO diameter: Use millimeters to measure from the middle of the wheel up to the tire’s inner edge. Then, double the measurement value.

To give you a rough guide, we’ll give you a few examples of the approximate diameter for common tire sizes for every bicycle type.

1. Mountain bike tires: The approximate outer diameter of mountain bike tires could be 26 inches, 27.5 inches, or 29 inches.

2. Cross-country bike tires: Most cross-country bikes have a default tire/wheel size of 29 inches, which have an outside diameter of more than 29 inches or around 740 millimeters.

3. Road bike tires: Most road bike tires have an outside diameter of 700 millimeters.

4. Cyclocross tires: Similar to road bikes, cyclocross bikes have a standard tire size of 700c, which indicates a diameter of around 700 millimeters.

5. 29ers: 29ers, also called two-niners, refer to hybrid bikes and mountain bikes that are designed to use 700c (ISO: 622 mm) wheels, specifically 29-inch wheels. 29er wheels have a diameter of approximately 622 millimeters (24.5 inches).

6. Kid’s bike tires: Tires for kid’s bikes would typically have a diameter of 20 inches and 24 inches. Bikes for smaller children would have a tire diameter of 20 inches and below.

7. BMX tires: The average BMX tire diameter is 20 inches.

Get the Bead Seat Diameter

What’s a bead? The beads are found on the farthermost edges of the rim all the way around on each side. They help keep an inflated tire in place by gripping the rim.

Meanwhile, the term bead seat diameter (BSD) refers to the diameter of the outermost part of the rim, where it connects to the tire. It’s measured in millimeters. Some manufacturers call it as the ISO/ETRTO rim size.

There’s really no way of knowing what tire width each person is going to choose. This is where the BSD comes to the rescue. It allows you to compare different wheel sizes and narrow down your options for tires for a rim size.

It’s also used to determine other fit characteristics, such as:

         Standover height (the distance between the top of the top tube and the ground)

         “Tire to Pedal Spindle Distance” (the closest distance from the pedal spindle to the front area of the tire)

         Trail and bottom bracket height

The ISO sizing of bike tires are a more accurate measurement of the bead seat diameter, so you don’t need to be overly worried about it when buying new bike tires. But if you feel like calculating it yourself, here’s how to do it:

1.         Get a straight edge (a tool for drawing straight lines)—or a measuring tape or ruler, if that’s what you have available—and place it across the inboard and outboard flanges of the wheel.

2.         After measuring the distance between the two points opposite each other, multiply it by two. (Make sure to get the largest measurement.) Then, subtract the product from the outer diameter measurement to get the diameter of the bead seat.

Examples of bead seat diameters for some of the common wheel sizes:

         622 mm BSD: 700c, 29-inch, or 28-inch

         584 mm BSD: 650b or 27.5-inch

         559 mm BSD: 26-inch

Important: Avoid combining tires and wheels that have different beat seat diameters. Sometimes, countries use different size markings or marketing nomenclatures for their tires. This makes it frustrating to select the tire that properly fits your wheel.

Know Your Choices in Tire Widths

While a tire’s diameter should match your bike’s wheel, the same isn’t true with the width of a tire. You have the option to use a tire with a slightly different width, without buying new rims or wheels.

Some riders at times put narrower tires to reduce weight or make acceleration and turning easier. Others prefer to have tires that are wider than their previous tires to provide them with more traction and more comfortable rides.

The important thing is the difference isn’t significant. For instance, if you install new tires that are too wide compared to the width of your bike’s rims, they’ll most likely wear through the sidewalls or not clear your fork crown.

Here’s how to measure the width of a tire:

1.         Locate the flat area across the tread of your tire.

2.         Get the measurement from one side of the tire to the other. The value you get is the width of your tire.

3.         If you’re using the traditional tire measurement, the width should be in inches. If it’s the ISO measurement, it should be in millimeters.

4.         Arrange the measurements for the diameter and width of the tire. In traditional bike tire sizing, the diameter should be first then followed by the width. In ISO sizing, the width is listed first then the diameter.

Other things to consider when buying bike tires:

         Tread patterns: No matter how subtle, tread patterns matter. The best tread pattern will depend on your riding style and road conditions you usually traverse.

         Threads per inch (TPI): The TPI value of a tire carcass will determine its durability, flexibility, and weight. The rule of thumb is the higher the TPI (120-320), the lighter, quicker, and more flexible the tire becomes. The lower the TPI (60 and below), the heavier and sturdier the tire becomes.

         Puncture resistance: If you want to experience fewer (unexpected) flats, it pays to upgrade to puncture-resistant tires. Most of these tires consist of one or more layers of woven artificial fibers. Some tires are reinforced by polymer fibers to protect them from slashing.

         Folding versus wire tire beads: Folding bead tires are portable and offer better performance, but the downside is they’re usually more expensive. On the other hand, wire tire beads are more long-lasting than folding bead tires.

         Tubed versus tubeless tires: If you want a better feel of the trail, choose tubeless tires. If you’re looking for speed and easier installation, choose tubed tires.

Conclusion

Choosing the correct tire size for your rims is probably one of the more confusing parts of owning a bike. It’s not as straightforward as one might think because of the different considerations and the lack of standardization in the description of tire sizes.

We hope this guide has helped shed some light on this topic. Remember: If you’re in doubt, consult an expert from your local bike shop.