springs that are wider and capable of greater load handling. The design features 3-inch-wide leaves, with front and rear spring sections of different lengths to reduce the twisting that can result in axle hop and loss of traction. The 2500HD uses a two-stage design with a rating of , and 3500HD models have a three-stage design with and ratings on single and dual-wheel models, respectively. Engines Production location switch For the 2011 model year of the Silverado/Sierra, the production of 1500 crew cab models partially moved from Silao, Mexico to Flint, Michigan. Safety The Silverado comes standard with four-wheel ABS. StabiliTrak and side curtain airbags are optional on certain trim levels. 2007 NHTSA crash test: Frontal Driver: Frontal Passenger: Side Driver: Side Rear Passenger: Rollover: The IIHS gave the Silverado a "Good" score in their frontal crash test. The 2007-09 models equipped with or without optional side curtain airbags received a "Poor" rating in the side impact test. For 2010, the side structure was strengthened, side torso air bags were added, and side airbags became standard leading to the IIHS side impact overall rating improving to "Acceptable" and the overall side structure rating improved from "Poor" to "Acceptable". The crew cab variant of the 2011-13 Silverado is also rated "Marginal" in the IIHS roof strength test. Electric version In 2011 developer of the Chevrolet Volt and former vice chairman Bob Lutz joined VIA Motors in developing electric versions of the Chevrolet Silverado/GMC Sierra called VIA VTrux. Third-generation Silverado / fourth-generation Sierra (K2XX; 2014) On December 13, 2012, the redesigned 2014 Chevrolet Silverado and GMC Sierra were both introduced in Detroit, Michigan, later making their public debut at the North American International Auto Show. GM dropped the 900 platform and changed to K2XX. The third generation Silverado 1500 has three gas engine options; a 4.3 L EcoTec3 V6, a 5.3 L EcoTec3 V8, and a 6.2 L EcoTec3 V8. Chevrolet's MyLink touch-screen multimedia interface system became available on most models. It included A2DP stereo streaming technologies, Bluetooth hands-free telephone, USB hookups, and an input for an Apple iPod or iPhone. When connected via the USB port, an iPhone 4/4S, iPhone 5/iPhone 5S, iPhone 6, or iPhone 6 Plus is able to stream music from Pandora Radio. A Bose premium audio system, as well as a Bose surround sound audio system is available on most models. OnStar became standard on all models.