Camaro Z/28 engineers get a grip on wheel slip

While running fast laps at several of the country’s most challenging tracks, Camaro Z/28 engineers noticed the tires were providing so much traction and the brakes so much stopping force that the wheels rotated inside the tire – an unexpected challenge that required fast thinking. “We were told to build a fast car – period,” said Mark Stielow, Camaro Z/28 program manager and pro-touring expert. “We knew on Day One we’d need to bring some of the best suppliers onboard to make it happen.” The suppliers included Pirelli and its P Zero™ Trofeo R tires and Brembo for carbon-ceramic brake rotors. The Trofeo R tires have a track-oriented tread design and compound that, together with the carbon-ceramic rotors, help the Z/28 achieve up to 1.5 g in deceleration force. It was a perfect combination, but engineers quickly found that when the Z/28’s capability was tested, the wheels were rotating – slipping – inside the tires. They sought the root of the problem by marking one of the Pirelli P Zero™ Trofeo R tires at the beginning of a lap with a chalk line relative to the valve stem on the wheel. At the end of the lap, they recorded where the chalk line ended up and noticed the tire had rotated at least a full 360 degrees from where they started. Racers use an abrasive paint around the bead of the wheel, where the tire meets the rim, to combat the problem on race cars. The Z/28’s engineers tried it, but it wasn’t strong enough to prevent the slippage, so other approaches were tried. Finally, they tried media blasting, which involves shooting a gritty material through an air gun at the wheel's surface, adding texture to the paint for the tire to grip. “Media-blasting the wheel created an extremely aggressive grit on the rim, which finally got the tire to hold,” said Stielow. Along with the tires and brakes, some of the tire slip can also be attributed to the 7.0L LS7 engine helping spin the wheels with an SAE-certified 505 horsepower (376 kW) and 481 lb-ft of torque (652 Nm). While going around corners, the helical-gear limited-slip rear differential also sends power to the wheels so well that differences in tire slip can be observed from side to side on the rear axle. The 2014 Camaro Z/28 arrives in dealerships this spring. Source: GM