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  • David Blades

A guide to choosing the right tire size for your bike

If you’re in the market for some new tires for your bike, you will be spoiled for choice given the vast menu of choices on the market from various manufacturers. Alas, it’s not always so simple to pick the right tire. This a short guide on how to go about picking the right tire size for your bike.

Replacing existing tires

This guide assumes that you don’t already have tires that you’d like to replace with similar or identical ones. If this is indeed the case, then all you’d have to do is look at the information on your existing tire's sidewalls. You should see two numbers.

The first number is the diameter of the tire. The four most common diameters are 29in, 27.5in and 26in for mountain bikes and 700C for road bikes. Gravel bikes can come with either 700C or 650b (same as 27.5in) size tires.

Matching the diameter of the tire to that of the rim is only half the required information. The second piece of the puzzle is the tire width, which is denoted by the second number.

Tire width is critical, because of two main reasons: the maximum tire width that your frame can accommodate (tire clearance) and the recommended tire width for your rim widths. We explain this further below.

Frame clearance and tire width

If you attempt to fit tires wider than your frame’s maximum tire clearance, there is a big chance they might rub on the frame and cause damage, which often happens much quicker than it can be noticed. Even if the wider tires fit with minimal room to spare, the maximum tire width recommendations are set to also allow for adequate clearance when tires pick up road debris or if riding in muddy conditions on mountain bikes.

While road bikes usually have tires in the popular 25mm width, many modern road bikes now accommodate wider 28mm-32mm tires. While narrower tires are lighter and more aerodynamic, advantages of wider tires include improved traction and comfort on rough roads, and better pinch flat resistance due to the larger air volume.

For mountain bikes, the advantages of higher volume tires are undeniable given the type of terrain these bikes are ridden on.

Matching rim width and tire width

When we talk about rim width, we are specifically referring to the internal width of the rim, which is the inside distance between the rim walls. Rim manufacturers will often have this information printed on the rim decals.

Rim width matters because if you upgrade to tires that are too wide for your rim’s internal width, the tire will have less support when subject to braking and cornering forces. The tire might be susceptible to rolling off the rim, especially with the tendency to run high-volume tires at lower pressures.

Below are some general recommendations for ideal tire width to internal rim width matching:

  • For road bikes with internal rim width between 19-21, choose tires between 25-28mm.

  • For gravel bikes with internal rim width between 21-25mm, choose tires in the 32-45mm range

  • For cross country and trail mountain bikes with internal rim widths between 24-30mm, choose tires in the 2.1in-2.35in range

Keep in mind that these are only recommendations, and that there are no rules set in stone for matching your tire widths to rim width. One reason is that actual tire widths vary between different tire manufacturers.

Choosing the right tire tread

  • Road bikes: Road bike tires prioritize low rolling resistance and speed on smooth tarmac. Hence, the best road tires will be slick with no protruding knobs, sometimes with little channels or grooves to make for better traction in wet conditions

  • Mountain bikes: Mountain bikes come in various types, and tire volume and tread choice will depend on the kind of mountain biking you do. While, generally speaking, off-road tires will have more aggressive tread patterns with protruding knobs to bite into the ground, tread pattern choice should be matched to the kind of terrain you ride on. It is often a good idea to check the tire specification charts that manufacturers have on their websites to pick the right tire for your terrain. With modern mountain bikes becoming incredibly capable machines in the roughest of trails, you will want to ensure that your tire can handle the additional stresses of off-road riding.

  • Gravel bikes: gravel bikes are an “in between” category of bikes, and they’re often used on mixed terrain rides. Gravel tire tread patterns vary, but most often combine characteristics of road and mountain bike tires. If your rides take you on equal measures of tarmac and dirt roads, pick a tire with a smooth center tread and raised cornering knobs. It will be a compromise, but one that’s well suited for this type of riding.

Folding vs wire beads

A tire “bead” is the outer edge at the tire’s sidewall that sits against the rim. A wire bead is often made of steel and it cannot be folded (without potentially damaging the tire). Wire bead tires are usually cheaper, heavier and not suited to tubeless setups.

Conversely, a folding bead tire is one that uses a softer material, most often Kevlar, instead of steel wire. Kevlar is often the chosen material for folding bead tires because it is simultaneously very strong and very flexible. Folding tires can, as the name implies, be folded for storage or transportation and they are lighter than wire bead tires. If you intend to run your tires tubeless, your search will be limited to folding bead tires which are “tubeless-ready”

Rubber compounds

Tire manufacturers compete in comping up with new rubber compounds for various riding applications. In some cases, they will use more than one compound in the same tire. Some compounds are made to increase traction, some for less rolling resistance, others for better longevity. Which compound to choose? It all comes down to the intended use and your own riding scenarios

Okay, all of this information just confused me further. There are so many tire choices!

Don’t get caught up in paralysis by analysis. There are so many great tires to choose from, just focus on picking the right size based on the information we have provided in this article, and go ride your bike!

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