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The winter driving advantages of all-wheel drive high-performance cars, crossover vehicles and SUVs have enhanced their popularity in recent years. Since many of these high performance vehicles have drivelines designed to monitor and distribute power to the tires with the most traction, they have become known for their ability to accelerate with ease compared to vehicles that feature only front-wheel or rear-wheel drive.
To complement these high performance, all-wheel drive crossover and sport utility vehicles, Bridgestone developed the Blizzak LM-25 4X4 tire as an addition to their existing Blizzak LM-25 Performance Winter / Snow tire for cars. Featuring the same basic tread design and internal construction, the Blizzak LM-25 4X4 now offers winter performance in appropriate sizes for these larger vehicles.
In order to get a better understanding of how much traction is provided by the tires on all-wheel and rear-wheel drive systems when conditions are at their slipperiest, members of Tire Rack team conducted an Ice Rink Performance Drive on the glare ice of a skating rink to compare Bridgestone's Blizzak LM-25 4X4 and Blizzak LM-25 tires. We've found that an Ice Rink Performance Drive provides the best conditions for experiencing acceleration traction in a controlled environment where the ice is just as frozen and slick as the polished intersections we'll encounter later this winter.
We used 255/55R18-sized Blizzak LM-25 4X4 tires mounted on 18"x8.0" wheels on our 2006 model year Porsche Cayenne. The Cayenne lists a curb weight of 4,784 pounds and its power is distributed through a Tiptronic automatic transmission and permanent four-wheel drive featuring Porsche Traction Management.
We used 205/55R16-sized Blizzak LM-25 tires mounted on 16"x7.5" wheels on our 2006 model year BMW 325i E90 sedan. The BMW 325i lists a curb weight of 3,351 pounds and its power is distributed through a STEPTRONIC automatic transmission and rear-wheel-drive featuring BMW All Season Traction.
*Traction Index identifies the relative performance vs. the best available (higher is better).
The Driveline Technology
Porsche Traction Management (PTM) distributes power using a standard torque split of 38% to the front axle and 62% to the rear; however, up to 100% of the torque can be delivered to either axle depending on driving conditions. PTM sensors continuously monitor steering wheel and throttle positions, as well as vehicle speed and lateral acceleration before determining the amount of power distributed to each axle. If one of the tires begins to lose traction, PTM uses the Cayenne's Automatic Brake Differential system to apply braking on that wheel, transferring torque that would otherwise be delivered to the slipping tire to the opposite tire instead. If both tires on one axle begin slipping, the Cayenne's electronic engine management system reduces power to reduce wheelspin.
BMW All Season Traction (AST) provides better stability and control in slippery road conditions all year long. The system continually processes input from the anti-lock brake sensors. Any time AST senses a rear tire is beginning to lose traction, the system modifies the engine's electronic throttle and ignition timing to reduce torque. It also can apply the rear brakes individually or simultaneously to reduce wheelspin. BMW Dynamic Traction Control also aids driving in deep snow.
However, it's important to remember that regardless of the vehicle's driveline technology, it will ultimately be the tires that provide the traction and determine how fast the vehicle will accelerate on slippery roads.
What We Learned on the Road
Our 5.6-mile Real World Road Ride loop of public expressway, state highway and county roads near our South Bend headquarters provides a great variety of everyday road conditions with a mix of city and highway speeds, smooth and coarse concrete, as well as new and patched asphalt road surfaces. This course allows our team to experience the everyday handling, ride quality and noise comfort of the products we drive on, just as you would during your drive to work.
Both the Blizzak LM-25 4X4 and Blizzak LM-25 winter / snow tires were praised for providing acceptable ride quality and noise comfort along with predictable dry road handling. Both tires were felt to be roughly equivalent to good all-season tires during everyday driving.
What We Learned on the Ice
In place of our normal test track drive, our team went to a skating rink to experience these tires' ice traction. In order to quantify the traction provided by each tire, we recorded the time it took for each vehicle to cover 60 feet (to the center of the rink) while accelerating as fast as the tires will allow.
Accelerating the Porsche Cayenne equipped with Blizzak LM-25 4X4 tires on ice proved to be an easy task. Porsche Traction Management (PTM) worked exactly as promised and driver after driver covered our 60-foot measured distance in an average of just 4.041 seconds.
Accelerating the BMW 325i equipped with Blizzak LM-25 tires on ice also proved to be easy. In spite of BMW's Dynamic Traction Control working as promised, it took our drivers an average of 5.954 seconds to cover our 60-foot measured distance. Even considering the BMW 325i weighed about 1,400 pound less than the Cayenne, its rear-wheel-only drive still took 1.9 seconds longer to cover the distance.
Unfortunately we didn't have a 325xi with BMW's xDrive, intelligent all-wheel drive system at our disposal. Even though the 325xi sedan's curb weight is about 300 pounds more than our rear-wheel drive sedan, its intelligent all-wheel drive would have made an interesting comparison.
There's no doubt that all-wheel drive provides more acceleration on slippery surfaces by driving more wheels. And there isn't any doubt that electronic driver's aids like Porsche Traction Management and BMW All Season Traction provides better stability and control in slippery road conditions. But in the end, the task of providing winter traction comes down to the tires. In this case, both the Blizzak LM-25 4X4 and Blizzak LM-25 winter / snow tires showed they could combine dry road handling with ice traction.
The Blizzak LM-25 and Blizzak LM-25 4X4 are Bridgestone's Performance Winter / Snow tires developed for the drivers of high performance sports cars, sport coupes and sport sedans, as well as crossover and sport utility vehicles that require winter driving traction on dry, wet and snow-covered roads. They are designed to combine good snow and ice traction with "European" high-speed winter driving performance.