The Story Behind the Development of a New Tire

In case you wonder why Bridgestone felt the need to abandon the Battlax BT-021 tire and present a successor, the answer is really simple. It wasn't a bad tire, but the competition has improved a lot over the past two years. Dunlop launched the Dunlop Roadsmart, Michelin the Pilot Road 2 and Metzeler cam up with a brand-new Roadtec. And, in most comparison tests, the Bridgestone Battlax BT-021 usually didn't come first.

Bad tests mean bad sales. It must have hurt, too, especially since the sports-touring tire segment is the most important tire these days. Apart from dirtbikes and scooters, sports-touring tires are an option for practically all motorcycles. Light, budget motorcycles perform so well, they can benefit from sports-touring tires. And the other way around, sports-touring tires offer so much grip and handle so well, many super- and hypersports riders prefer them to the real hypersports tires.

For those who mostly ride their motorcycles on the street, grip is sufficient and durability is so much better that is is the only sensible option. And, of course, the ever-growing group of touring riders need them too, as touring motorcycles have evolved into fast, agile transporters. And they really do distances, so they buy a lot of tires: in Europe, about 30 percent of all tires sold are sports-touring tires. So can you blame Bridgestone for trying to stay the number-one tire company in the market section where most of the money is.

Still, it must have been a tough job to improve the Battlax BT-021 tire, as it is already contained most of Bridgestone's top technologies. It had, for instance, the so-called 'Mono-Spiral Belt' (MS belt). Usually, the radial belt was made from a mat, cut to size and wrapped around the carcass with a small overlap. At that overlap, there would be a stiff spot, disturbing the balance and the continuity of the tire properties. The Bridgestone MS belt is not a mat but a very long card, wound around the circumference of the tire.
Changing the pitch – the distance between the windings of the cord – changed the properties of the tire. In the middle, the cords are close to each other, giving more stiffness and straight-line stability. Near the sides of the tread, the pitch would be bigger, so the tire would be more flexible at higher lean angles, thus offering more mechanical grip in corners.

Bridgestone, which has been using the MS belt for years, improved the technology in 2003 when it introduced the 'High-Tensile Super-Penetrated Card' (HTSPC). This consists of five high steel wires separated by a rubber coating. This way, the cord tension is equalized and constant, and Bridgestone claims that they can tune stiffness, flexibility and shock absorption even more precisely.
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