The new tires showed excellent grip, stability and steering characteristics on the track, although the edge compound on the rear tire is a bit soft for all-out track use. The softer sides are of more benefit on the street, where they provide fantastic grip with little chance of overheating.
Following What Can Only be described as a rocket ascent from nonentity to the pinnacle of MotoGP achievement, Bridgestone has released a street tire using technology culled from that experience. The BT-016, successor to the BT-014, is labeled as a performance tire for street use and the occasional track day and features multiple compounds for both the front and rear tires. The front BT-016 uses a three-layer compound (3LC), one compound for the center of the tread and a second for both edges. The rear tire goes one step further, however, with 5LC (five-layer compound): The center of the tread is a hard compound for wear, and two successively softer compounds are found between the center and edge of the tread on each side. The transition compound of the rear tire is identical to the front tire's center compound, while the edge compound is the same on both. Furthermore, the center compounds offer high tensile strength in the circumferential direction, while the edge compounds have high tensile strength in the radial direction.
MSB (Mono Spiral Belt) is a continuously wound thread around the circumference of the tire that adds stability and minimizes growth at speed, and the front and rear BT-016 both use steel for this belt. While the front BT-014 was a cross-belt construction, the front BT-016 has a single strand of two filaments wound around its circumference. The rear BT-016, similar to the rear BT-014, has a single strand with five filaments. The company reports that steel adds stability and absorbs sudden shocks better than the aramid fiber used in the BT-002 race tires. The front tire's tread pattern has grooves across the center for wet braking while the rear tire does not, improving driveability in dry conditions. The S-shape of the front grooves and the L-shape of the rear grooves are designed to influence carcass deflection and thus tune characteristics such as stability and shock absorption across the tread's profile. Interestingly, the tread pattern also affects noise, which is evidently becoming increasingly important in tire design.
New tread patterns are significantly sparser than those of the BT-014; the front tire has S-shaped grooves for stability, bump absorption and handling, while the rear tire's L-shaped grooves are for bump absorption and, according to the press material, rear-wheel steering.
Bridgestone introduced the new tire in Jerez de la Frontera, Spain, with a day on the MotoGP circuit and a day's street ride in the surrounding hills. As I discovered at the Suzuki GSX-R600 introduction (the '08 GSX-R is equipped with an OEM variant of the new Bridgestone), a fresh front BT-016 can make steering awkward until it is fully scrubbed in, but after a couple of laps steering is quick, neutral and stable. I rode a GSX-R600, CBR600RR and ZX-6R in the morning sessions, and on the middleweights, grip from the front tire was outstanding, especially when trail-braking into turns. Rear grip is very good, although the edge compound can overheat and become a bit slippery. This was especially evident in one particular section of the Jerez circuit where two long, fast left-handers are strung together. In the first turn edge grip was fine, but the rear tire was definitely overheating in the second left with noticeably less grip. In the afternoon sessions I rode a GSX-R1000 and ZX-10R, and the too-soft characteristic was even more evident. Additionally, the bigger bikes (generating more speed and more braking forces) worked the front tire hard enough that it also was overheating on the edge. Still, this degradation was consistent over each session and nothing to cause alarm, as feedback is excellent and I knew at all times what the tires were doing. For a street tire, overall performance on the track is excellent.
The front BT-016 tire has two compounds, while the rear has three. The edge compounds (yellow) are identical for both tires, while the center compound on the front tire (orange) is the same as the transition compound on the rear. The center of the rear tire has a third compound (red) that is another step harder for better wear properties.
Aboard a Kawasaki Z1000 the following day for an 80-mile trip through the surrounding countryside, the tires again showed light, neutral steering characteristics (a far cry from that bike's OEM tires, which display a tendency to fall into corners) and impressive grip on the roads' finely grained pavement. In this environment the soft edge compound is a welcome feature, as it increases grip just when you desire it down a twisty road and there is almost no chance of it getting too hot.
Variants of the new tire are used as OEM equipment in the U.S. on the '08 Suzuki GSX-R600 and 750 and the '08 Kawasaki ZX-10R. A significant difference between these OEM variants and the production BT-016 is the use of a single-compound front and only two compounds in the rear as opposed to three. The BT-016 will be available in the U.S. in midyear, with four front and seven rear sizes; the rear range includes both 190/50 and 190/55 sizes. For more information visit www.motorcycle-karttires.com.-A.T.