#Wheel size comparison iso#
The ISO comparison list at the bottom of this page covers all sizes which we know to be in production as of 2016. The tables below give a partial listing of traditional tire sizes, with their ISO bead-seat equivalents. If its too wide for the rim, there's an increase risk of sidewall wear from brake shoes, and a greater risk of loss of control in the event of a sudden flat. If your tire is too narrow for the rim, there's an increased risk of tire/rim damage from road hazards. If you pull the beads apart and measure the total width from bead to bead, it should be approximately 2.5 x the ISO width. The width difference between these sizes would make them less-than ideal replacements for one another, but any rim that could fit one of them would work after a fashion with the other.Ī general guideline is that the tire width should be between 1.45/2.0 x the inner rim width. Generally, if this number matches, the tire involved will fit onto the rim if it doesn't match, the tire won't fit.įor example, a 700 x 20 C road tire would be a 20-622 a 700 x 38 hybrid tire would be a 38-622. The second ISO number is the critical one: it is the diameter of the bead seat of the rim, in mm ("B.S.D."). This will vary a bit depending on the width of the rim. For the rim, this is the inner width between the flanges, as shown in the diagram for the tire, it is the inflated width. (This system was formerly known as the "E.T.R.T.O." system, developed by the European Tyre and Rim Technical Organisation.) ISO, the International Organization for Standardization, has developed a universal tire and rim sizing system that eliminates confusion.
#Wheel size comparison code#
Due to the appetite of the market, you can get tires as narrow as 25 mm to fit these rims, so you wind up with a "26 inch" tire that is more like 24 7/8" in actual diameter!Ī second number or letter code would indicate the width of the tire. This same rim size was adopted by the early pioneers of west-coast "klunkers", and became the standard for mountain bikes. Although they are still called "26 inch", these tires are actually 25 5/8", not 26". The industry responded by making "middleweight" tires marked 26 x 1.75 to fit the same rims.
Some riders, however, were dissatisfied with these tires, and wanted something a bit lighter and faster. This size tire is very close to 26 inches in actual diameter. Here's how it works: Let's start with the 26 x 2.125 size that became popular on heavyweight "balloon tire" bikes in the late '30's and still remains common on "beach cruiser" bikes. Unfortunately, evolution of tires and rims has made these measurements lose contact with reality. This would usually be measured in inches (26", 27", etc.) or millimeters (650, 700, etc.). The traditional sizing systems are based on a measurement of the outside diameter of a tire. A larger rim goes with a skinnier tire, and vice versa. If the bicycle has hub brakes (drum, disk, coaster), different rim sizes are possible as long as the tire is fits the frame. Nominal tire width is marked on the tire actual width can be measured if the tire is installed on a rim.
#Wheel size comparison plus#
Measure at the radius of the widest part of the tire, usually the rim radius plus half the tire width -except that the widest part may be at the tread of an off-road tire.
The space between the fork blades or stays must be wide enough to clear the tire, with a few mm extra on each side in case the wheel goes slightly out of true. On a bicycle with horizontal dropouts, additional clearance to the chainstay bridge is desirable so the wheel can be removed without deflating the tire. A tire must have typically 1 cm clearance, 2 cm if a fender will be installed, but do not use a wheel that is much smaller, or a pedal is too likely to strike the ground in cornering. Tire outside radius is nominally the rim radius plus the tire width, and as much as 1 cm greater for a tire with a deep tread. Take measurements from the axle position to the fork crown, chainstay bridge and seatstay bridge.
The front tire must not reach the fork crown the rear tire must not reach the seatstay bridge or chainstay bridge. A different rim size may be possible with different brakes, though longer brake reach generally results in poorer brake performance. Then look up the rim radius in the ISO table on this page. So, first measure the distance from where the center of the hub axle would be in a dropout to the center of a brake shoe. If the bicycle has rim brakes, the rim must line up with the brake shoes and so only one rim size or a small range of sizes will work. To determine which tire size will fit, perform measurements on the bicycle's fork and frame.
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