700c x 23c? 26" x 1.75"? 80 PSI? Confused yet?

Bike tires come in different diameters, with industry standard measurements (so you are able to find replacements when you run over that broken glass!).

To keep it simple, 700c x 23c is a commonly sized tire. The 700c is the diameter, while the 23c is the width. These are thin, "racing" style tires found on lots of road bikes, including many Vilanos. A thinner tire like this will offer less resistance, as less of the tire's surface area comes in contact with the road. A bit of a thicker tire like a 25c or a 28c would offer a little more resistance, however these would be less susceptible to "pinch" flats. 

Hybrid and comfort style bikes usually have thicker tires, like 700c x 35c or 26" x 1.75". When you learn how to change your own tires, just look at the number molded on the sidewall of your tires, and pick up a set of the same size tubes (it's good to have a spare). Thicker tires will perform better on loose gravel, and knobby (not slick) and thick tires are perfect for trails.

The PSI (pounds per square inch) is the recommended amount of air you need so the tires perform at their best. Sometimes a range is given on the sidewall of your tire, and you want to stay within that range.