The Unmitigated Truth About Motorcycle Tires – Bias Ply Versus Radial Tires

Getting Your Motorcycle Tire Knowledge Up to Speed

When it comes to your motorcycle and how much you enjoy your riding, you might think your seat or your handlebars or your grips are the most important elements of the machine.

I won’t dispute that, but I would like to suggest that there are two things more important than any of the above; your front and back tires.

Nothing short of your engine has more impact on your motorcycle’s overall performance than the tires. What does it really matter how much horsepower you’ve got in your mill, how much money you’ve dumped into tuning your suspension, or how excellent your new Brembo brakes are if your tires can’t translate all that glory to the ground?

Not much, amigo.

Here’s how your tires work to take care of that important business. As wheels rotate, a small elliptical area of the tires generally referred to as the “contact patch” meets the road. A whole list of factors determine the size of that patch; the tire dimension, the construction method and the amount of weight riding on it all influence the ultimate size of the patch, but on an average bike with an average-sized rider, something like ten square inches of of each tire are actually providing traction and stopping power. In effect, you have two spots the size of playing cards meeting the road as you crank it on heading toward 80 mph.

Tires have traction because of friction, and the amount of friction is determined by the condition of the road. It’s the tread pattern and compound of which your tire is constructed that makes all the difference in how your machine deals with laying that friction down. The softer the compound, the more traction you have.

Tire geeks and manufacturers talk about something called “hysteresis,” and it’s a way to refer to how easily a tire deforms – and then returns – to its original shape. High hysteresis tires deform readily and rebound slowly. The higher the hysteresis, the easier (and longer) your tire engages the road and stays that way. Along with the the type of surface you’re riding on, the profile and carcass construction of your tire, and the stiffness of the tire’s sidewalls, hysteresis creates all the traction you’re going to get.

Tires are made starting with a bead bundle,which is the ring of rubber compound that holds the tire to your wheel rim, and it has to be strong yet flexible. The bead bundle is nearly always made, at least in modern tires, with steel or composite wires.

Next comes a slab of fabric or steel belting called a body ply or cord which is impregnated with rubber and adhesive. The ply is layered over each bead, and that forms the structure for supporting the tire’s tread, and we’ll get to that later.

When this basic frame is complete, manufacturers create an inner liner to seal out moisture and make the tire air tight. They slap on another series of belts to reinforce the tread and once the sidewalls are bonded to the whole shebang, you my friend, have a completed tire.

To understand the difference between radials versus bias belts tires, try to imagine  a tire as it rotates against the road. As the tread makes contact with the pavement, the sidewall of a tire flexes outward and causes the tire to flatten and form a contact patch. While the tire revolves, the patch lifts from the road, the sidewall bounces back into shape, and the next section of the tire’s tread replaces the previous section to maintain the patch. Bias-belted tires have cords angled from 27 to 45 degrees across the center line of the tire, and they make for a very thick and inflexible sidewall. Tires of bias-ply construction are tough as a three-dollar breakfast steak, but not nearly as flexible as is ideal.

Radial tires, on the other hand, use cords place at a 90 degree angle to the center line and provide lots more flexibility. Flexibility is the radial tire advantage. Lots of energy goes to making a bias ply tire’s sidewall stiff, and that generates heat, and heat is a tire’s worst nightmare. You need some heat to make a tire work properly, but too much will cause the tire to fail. Tubeless tires run cooler, but that’s yet another story.

The sidewall of a radial tire flexes with ease, and as a result, there’s little or no friction between the belts and that means less heat. It’s the heat advantage that also makes radial tires considerably more durable. The additional flexibility of a radial tire also makes for a larger contact patch and gives you much, much more traction, and that’s a good thing.

Motorcycle Tire Manufacturers

Photo courtesy Michelin Motorcycle Tires

Now we’ve hepped you to the inside truth about motorcycle tires, so we’d like to suggest you consider how you’re going to take care of them – and the rest of your motorcycle. Check this out…

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