Replacing bike tyres is something most riders will go through at least once in their life. While it may seem like a straightforward aspect of maintaining your bike, there are a lot of small details to pay attention to. Tyres marked 28-inches are in fact less than 27-inches in diameter, and tyres marked 28×1.5 and 29 1/2 are two different sizes. So how do you know which tyres are best suited for your bike? Buying exact replacements can be the simplest thing to do, but sometimes, those aren’t readily available. Or, you might want something different.

If that’s the case, and you’re looking to buy bike tyres that will outperform the ones you had previously, you’ll need to learn how to read the markings and specifications of tyres. One of the best ways to get the right sized tyres is by measuring your previous tyres’ outer diameter and their maximum width. However, this can still be misleading. Fortunately, most tyres on the market nowadays are marked according to the ISO, which are two numbers separated by a dash. You’ll want to pay extra attention to the number after the dash, as that’s the bead diameter at which the tyre will fit the rim. The first number is the tyre section, which indicates the tyre’s width. The width is typically less, but it can vary based on tyre design and the width of the rim.

Tyre and Rim Compatibility

If two tyres have the same ISO markings, they’re interchangeable. Some rims are also marked with ISO markings. However, some manufacturers provide the overall width instead of the bead diameter and internal section. If that’s the case, remove 6mm from the overall width to get an estimate of the rim section, or just measure the distance between the flanges. The ideal relationship between the rim section and the tyre is 1.8 to 1. However, any tyre from 1.4 to 2.2 should fit, provided that the bead diameter corresponds.

Nowadays, most rims feature hooked flanges that hang onto tyres that are 3 times their width. This is to ensure a more comfortable ride from the tyre, even if you fit them to narrower rims. However, it may increase the stress on the sidewall of the tyres. Mountain bike tyres are typically designed to handle this extra stress, while road tyres aren’t. Exceeding the 2.2 limit on road tyres can make them deflect sideways, negatively impacting your road holding and control. On the flip side, fitting tyres of less than 1.4 times the rim section size will make for a harsher ride and create more rolling drag.

Tubular Tyres

Tubular tyres are mainly used for racing. They must be fixated to the right rim using cement, adhesive or glue. Most tubular tyres today are referred to as 700c, 28-inch or 27-inch tyres, as they fit a brake track diameter of 700c clincher rims. These all fit the same rim size. Moreover, tubular tyres need to be fitted skillfully, so if you’re unsure or don’t consider yourself savvy, consider a trained cycle mechanic. Tubular tyres are also available in 26-inch sizes, but those are particularly rare.

Tubeless Tyres

Tubeless tyres, as their name implies, don’t feature an inner tube. So, they completely rely on the shape and tightness of the tyre bead to make sure it doesn’t blow off the rim at higher inflation pressures. In traditional clincher tyres, the inner tubes keep the bead securely located just under the rim’s hook. These tyres should be used with specialised tubeless rims, or a conversion system that uses tape to seal the rim bed. Tubeless tyres are marked as tubeless-compatible, tubeless-easy, or tubeless-ready, and feature stretch-resistant folding beads made of carbon fibre.

American, Imperial and Metric Markings

If you can’t find ISO sizes on the tyre, you’ll need to understand the old-school markings. Even though they’re quite similar, they can be confusing. Tyres of the same size can come with various markings. You might even find similar markings on different tyre sizes. You can find charts online where you can compare the old-school markings with ISO markings.

Tyre Pressure

All tyres are marked with a number that represents the maximum pressure that shouldn’t be exceeded. Off-road tyres, however, are marked with a pressure range that ranges from the minimum to support the weight of the rider to the maximum. Never exceed the maximum pressure range. Riding a bike with properly pressured tyres allows for a more comfortable and safer ride, so it’s not something that should be overlooked, especially if you’re riding down mountain trails.

Conclusion

As the only point of contact between your bike and the surface, your tyres play a crucial role in how your bike performs, and how enjoyable your rides are. Choosing the right tyres can be difficult if you’ve never bought any before, as tyres can be marked using different numbers. Same-sized tyres can be marked differently, and differently-sized tyres can be marked similarly. Refer to the ISO markers to make sure you buy bike tyres of the right size for your rims.