BMX & Kids Bike Tires
20” (ISO 406) is the most common size of BMX tire. Though, it’s not uncommon for BMX bikes to have both larger and smaller sizes of rims. With BMX and kid’s bikes, pay attention to decimal vs. fractional sizes – decimal sizes are more common, but fractional sizes are not rare. Tire clearance on kid’s bikes is often limited so it is usually best to replace with a similar width tire to what was originally used.
Mountain bike rims mostly come in three standard sizes – 26” (559 ISO) , 27.5” (584 ISO), and 29” (622 ISO). All three are very common so it is important to double-check which size you have. Additionally, kids mountain bikes have smaller rim sizes such as 20” (406 ISO) and 24” (507 ISO). Mountain bike tire widths tend to be based around the type of riding the bike is designed for. Cross country (XC) bikes and older mountain bikes often have limited clearance, especially for the rear tire, and may only be able fit tires around 2.1” and narrower. On modern trail bikes, 2.3” to 2.6” tires are the norm. And on downhill bikes, ‘plus-sized’ tires can be as large as 3.0”. Going wider than that moves into the realm of fat bikes, which are specially designed to handle extra-wide tires.
Many tires are available in multiple widths. In general, narrower tires are faster and wider tires provide more comfort and traction. On most bikes, the frame presents a physical limit to how wide your tires can be. The inner width of your rims only needs to be close to the right width for the tire. For example, a 19mm inner width road bike rim will work with nearly all road tires and even some gravel tires, but will not be suitable for wider mountain bike tires. Likewise, a 30mm inner width mountain bike rim will not work for road tires.
It should also be noted that the width designated by a tire manufacturer is usually an estimate based on a common rim width. Depending on the rim, these measurements could be off by as much as a few millimeters.
The single most important tire measurement is the rim diameter. On road bikes, this is usually named using the old French system (700c, 650b, 650c) and, on mountain bikes, rim size is almost always named in inch measurements (29”, 27.5”, 26”). Unfortunately, these naming conventions are, at best, arbitrary and other times very confusing (for example, there are at least four different sizes of 26” rims). To combat this confusion, tire sizes can also be referred to by their ISO size.
ISO, the International Organization for Standardization, developed a universal sizing system which provides a reliable metric for measuring tire and wheel diameters. These numbers represent the diameter measurement of the tire bead and are a surefire way to size-match a tire. On many tires, ISO numbers can be found on the sidewall similar to where you might find tire pressure recommendations. At Performance Bicycle, our tire specs include ISO information, so it’s easy to confirm that you’ve found the right match.
