FORT STOCKTON, Texas-With the introduction of the Bridgestone R227 steer-axle radial, Bridgestone/Firestone Inc. believes it has taken a dramatic step toward achieving the goal of a million-mile truck tire casing. More than five years in development, the new tire incorporates the latest Bridgestone technology, including two new patented design features: ``side grooves'' and ``equalizer ribs.''
BFS debuted the R227 to a group that included tire and trucking industry journalists, as well as representatives of long-haul fleets, March 6 at its Fort Stockton proving grounds.
In designing the new Bridgestone radial, particular emphasis was put on tire mileage and wet traction, the two areas deemed to be of greatest importance to fleet users, said Dave Laubie, BFS director of sales engineering.
To improve treadlife, Bridgestone engineers focused on reducing irregular wear, the principal cause of tires' removal from service, Mr. Laubie said. Shoulder wear received particular attention.
One outcome was the development of the side groove, which replaces the defense/decoupling groove common in current-generation truck tires.
Moving the groove away from the road surface prevents it from wearing or picking up stones and puts more tread rubber in contact with the road. The side groove also adds flexibility to the shoulder, promotes normal contact pressure across the tread pattern, and reduces heat build-up in the shoulder area, Mr. Laubie said.
Another new design feature of the five-rib R227 are equalizer ribs-small ribs in the two outer, or shoulder grooves that are recessed 2/32 inch from the tread surface.
Slip forces that initiate ``wavy'' or ``river'' wear are diverted into the equalizer ribs, causing them-and not the main ribs-to wear away. These small ribs also are angled to prevent stone retention, Mr. Laubie said.
BFS also changed the design of the new tire's all-steel casing, altering the contour to optimize stresses in the tread, sidewall and bead areas, which in turn lowers heat buildup and improves rolling resistance.
This change was implemented only after much testing, Mr. Laubie said: ``We don't do it (alter the casing design) lightly!''
The R227 achieves improved wet traction as a result of its unidirectional tread pattern, which combines straight grooves and sipes for water evacuation, and a new tread compound that incorporates both synthetic (styrene-butadiene) and natural rubber.
The new tire should regularly deliver more than 200,000 miles of even wear on its original tread, according to company literature, and is designed to be highly retreadable.
The side groove, located right at the buff line, will disappear when the tire is retreaded, Mr. Laubie said. This is not a critical loss, he explained, as most retreads are returned to service in drive or trail positions.
In actual highway testing, which involved some 3,000 tires on 200 fleets and more than one-half billion test miles, BFS said the R227 significantly outlasted its leading competitors, based on actual removal mileage: by about 50 percent in long-haul applications; 40 percent in regional hauling.
The R227 is available in sizes 295/75R22.5, 285/75R24.5 and 11R24.5, with 11R22.5 to be added by year-end.