Reading the cryptic language on your tire’s sidewall
I have always inflated my tires to the “max. inflate to ___ psi” molded in the side wall of bicycle tires. I have received a new set of Continental Top Touring 2000 tires that have “max. inflate to 70 psi – 5.0 bar” molded in the side wall, but the tire also has a hang tag that says “Rec. Pres.: 60 psi, Max. Pres.: 75 psi.” I have another set of tires that have “Keep Inflated to 40 to 65 psi” molded on and a tag that says “On – 65 psi, Off – 40 psi.” What does “On” and “Off” mean? Why the discrepancies in recommended pressures? What does Bike Friday recommend?
This is a multi-part question, so let’s review all the information printed on the sidewall of your tire.
The first thing to note, is that it lists the tire size, 37-406(20×1.35) for example. The first number, 37, is the width in mm. The second number, 406, is the bead diameter in mm. The second set of numbers, 20×1.35, are the same measurements, but in British. Presenting all of this information to your local bike shop will get you the correct size tube replacement, or tire replacement.
(Side note: you will notice when converting 406mm to 20 inches, there is a big gap. the 406 measures the bead diameter, at the inside of the tire, and the 20 measures for the furthest outside point diameter.)
Next up are the psi ratings. These are listed in a variety of ways, including minimum and maximum inflation, different ways of measuring inflation (PSI and Bars), and recommended inflation.
The minimum and maximum inflations, are important to observe, as they will reduce the chance of damaging the wheels, and blowing off the tire.
The most common measurement types for inflation are psi and bars. Use whichever one you like (or is listed on your gauge). 70psi = 5 bars.
The recommended inflation will come in a variety of forms, such as “On” and “Off.” These are recommended inflations (generally in psi) for either on, or off-road cycling. Tire pressure is completely up to individual taste and riding style, Bike Friday recommends that you stay within the range of the minimum and maximum pressures listed on the tire.
Some of you may have noticed that when you order a 20×1.25-1.35 tube, you get an 18×1 3/8 tube. This is not an error, it is merely a discrepancy in international labeling. These two tubes are one and the same.