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Why an independent rear suspension for GM's new, full-sized SUVs wasn't easy

A Motor Trend report last month laid out how Cadillac's 4.2-lier twin-turbo Blackwing V8 could be an orphan due to cost concerns in the GM empire. Last-minute chassis changes to Cadillac's new sedans and XT6 crossover led to engine bays that couldn't fit the Blackwing. On the SUV side, according to the report, the new independent rear suspension for big people haulers cost so much to implement that GM ruled out reworking the Escalade to accept the Blackwing. At least one commenter rightly asked how could a suspension swallow that much money. A new piece in Motor Trend has the answer. The excellent Alissa Priddle spoke to Tim Herrick, GM's executive chief engineer for full-size trucks, about why the clean-sheet IRS cost "multimillions of dollars."  First, GM would need to build a new body shop at the Arlington, Texas plant that assembles the automaker's big SUVs to stamp the numerous wholly new parts and panels accommodating an IRS. Then GM would need to design and pay for a new assembly process. On top of those up-front costs, there was the incremental cost of the four-link IRS components being more expensive than those in the trucks' former leaf-sprung solid axles. Herrick endured so many rejections for so long that he remembers the date and time when he got approval for the new unit. He said it came down to a meeting where he told a higher-up, "I'll make you a deal: If we get to the reveal, or if we launch this and you think this was a dumb idea, I'll hand you my badge and let you walk me out." Head to Motor Trend to read the full story. Based on Herrick being on stage to help present the new SUVs to the press, and on our First Ride in the new Chevrolet Tahoe and Suburban at GM's Milford Proving Grounds, it appears this will have a happy ending for all involved. Furthermore, since Herrick worked on the T1 platform that supports the big SUVs as well as the light- and heavy-duty pickups, he understood the demands on the commercial side, too. That could be why when Roadshow asked Tim Asoklis, chief engineer of the Tahoe and Suburban, if the new IRS could endure life in the Chevrolet Silverado and GMC Sierra, Asoklis answered, "Oh, absolutely." Related Video:    

2021 Chevy Silverado, GMC Sierra fuel economy to go down due to global chip shortage

Production of the 2021 Chevy Silverado and 2021 GMC Sierra is continuing, but the global semiconductor chip shortage is resulting in a mid-year change. Or rather, an omission.  Basically, the availability of cylinder deactivation for the 5.3-liter V8 will be significantly reduced, resulting in a reduction of 1 mpg combined for affected models. This applies whether that engine has the six- or eight-speed automatic, as well as to both the regular Active Fuel Management and the more advanced Dynamic Fuel Management cylinder deactivation systems. DFM does remain with the pairing of 5.3-liter V8 and 10-speed automatic that comes standard on the LT Trail Boss and High Country. "Due to the micro controller shortage, the components that control AFM/DFM in the engine control module (ECM) have been removed," GM spokesperson Michelle Malcho told Autoblog. She also indicated that the engines will still have the AFM/DFM hardware in place, but that GM will not allow activation of the systems in the future with an ECM change.  Malcho also confirmed to Autoblog that the Silverado and Sierra's other engines will continue to have AFM and DFM, including the 2.7-liter turbo inline-four, 4.3-liter V6 and 6.2-liter V8. In an earlier statement to Reuters, she declined to say the volume of vehicles affected. "By taking this measure, we are better able to meet the strong customer and dealer demand for our full-size trucks as the industry continues to rebound and strengthen," Malcho wrote Reuters in an email. The change runs through the 2021 model year, she said. Malcho told Reuters it would not have a major impact on the Detroit automaker's U.S. corporate average fuel economy (CAFE) numbers. "We routinely monitor our fleet for compliance in the U.S. and Canada, and we balance our portfolio in a way that enables us to manage unforeseeable circumstances like this without compromising our overall (greenhouse gas) and fuel economy compliance," she said. GM's fleetwide fuel economy in the 2018 model year was 22.5 miles per gallon and was projected to rise to 22.8 mpg for 2019, according to a report by the Environmental Protection Agency. To meet federal CAFE requirements, automakers like GM often use credits from either earlier years where they faced less stringent rules and performed better than the requirements or buy credits from other automakers. GM said last month the chip shortage could shave up to $2 billion from this year's earnings.

Watch this week's Top Gear America used-car challenge

Top Gear America is back for the penultimate episode of the first season. Used car challenges were some of the highlights of the original UK edition. In our exclusive clip, Tom Ford, Antron Brown and William Fichtner run their $7,000 sports cars in a drag race. As expected, the trio chose very different cars for the challenge. Watch the video to see if a Subaru WRX's all-wheel drive can overcome a power deficit to beat a Ford Mustang and a Chevy Corvette. Brown and Fichtner also spend some time relaxing with an old Jeep Wagoneer. Like them, we're really hoping Jeep will bring back the Wagoneer nameplate. Brown also drives a Maserati Levante, proving that not all family cars need be boring. This week's guest star is actor, rapper and former host of Pimp My Ride, Xzibit. Top Gear America airs Sundays at 8 p.m. Eastern on BBC America. Related Video: Celebrities TV/Movies Chevrolet Ford Subaru Top Gear exclusive top gear america