Good question, found this on the web after a look >
First the basics; there are two types of tire construction: bias-ply and radial. A safe generalization is that most cruisers use bias ply tires, and sportbikes use radials. (Spoke wheels require a tube to maintain tire pressure, while cast wheels allow for a tubeless tire). A bias-ply tire has a round profile, and tall sidewalls. A radial tire has a flatter profile, and shorter sidewalls.
In a bias-ply tire, the carcass (the material beneath the tires tread) is made up of overlapping layers of nylon or rayon cords. Each of the several layers stretch across the tire at opposite angles forming an X pattern, hence the term "bias." Some tires add another layer on top of the plies, called belts, and those run in the direction of the tire rotation. As a tire rotates, the small portion of the tire that meets the pavement, the "contact patch," flattens out for a split second. So as the tire rotates, it is constantly flattening out, and rebounding into shape. That constant flexing action generates heat, which is good for grip. But too much heat is the enemy, as it decreases performance and accelerates tire wear.
A radial tire has its plies running "radially" at a 90ø angle to the direction of the rotation. This design reduces heat generation, so the tires run cooler. The downside is that the sidewalls flex easier, so they are given a shorter profile. The lower profile means that they can't handle heavier loads that a large heavy cruiser, with a passenger and baggage, requires. A cruiser's suspension design and cornering needs are better suited to bias ply tires, so always check to make sure a tire is approved for your particular bike before buying.
The introduction of radial tires required changes to certain characteristics of the motorcycle. The development of the radial tire led to frame modifications, new steering geometries and suspensions. That's why it is recommended that a motorcycle be used with the type of tire construction that it came with originally.
More reading here: http://www.motorcycle-usa.com/379/74...uct-Guide.aspx
Hope this answers your question, it did mine.