While tire technology may appear to be converging on a single ideal as far as sizing is concerned, different manufacturers obviously have disparate ideas about how to construct a tire for best performance. What goes on inside your tire (and we're not talking about the air) gives it that all-important grip and feel?
A basic tire consists of two wire bead threads wound to fit around the wheel rim, with some form of carcass material (the sidewall plies) wrapped around them to give the tire its shape. Plies of tread material are laid to give the tire a profile, and finally the rubber tops everything off. Virtually all sportbike tires are of a radial construction, which means some tread plies lie at (or close to) 90 degrees to the direction of rotation. These plies give a tire its grip characteristics, as cornering force tries to lengthen the cords. But a true radial requires some form of additional plies laid more in the direction of travel to prevent the tire from growing at speed. These plies are added at an angle to the radial plies to prevent tire growth, aid in stability, and to give a tire acceleration and braking grip.
In general, the number of tread plies and the way they lie has a big effect on a tire's characteristics. Generally, more plies add to a tire's weight, stiffness and heat buildup (as the individual cords rub when the tire flexes), but those plies can be laid at different angles to create both stability and grip. Different materials can be used to vary the strength and weight of any individual ply, and the cords can be wound in a number of different ways to subtly vary its effect.
The front tire's profile can affect the handling of your bike. A "pointy" front tire will have quick turn-in characteristics, as the bike wants to fall into the turns, off the point of the tire. In addition, this profile can have a larger contact patch at a certain lean angle, as the tread angles away from the point and is relatively flat. But once that tire is leaned over onto its side, a lot of effort is required to lift it back up, resulting in higher effort steering. A rounded profile tire will provide more moderate steering effort with a better ability to make midcorner corrections, as there is no flat spot at any particular lean angle. Conversely, there isn't one portion of the tire that gives a larger contact patch for better grip.
And the final ingredient, considered by many to be the "black magic" of tire construction, is the rubber compound. Obviously a softer tread will wear quicker but provide more grip, but it's the subtle interactions on a molecular level-more art than science-that gives a good combination of both.
This story was originally published as part of the tire test in the February 2000 issue of Sport Rider.