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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:    

Is the skill of rev matching being lost to computers?

If the ability to drive a vehicle equipped with a manual gearbox is becoming a lost art, then the skill of being able to match revs on downshifts is the stuff they would teach at the automotive equivalent of the Shaolin Temple. The usefulness of rev matching in street driving is limited most of the time – aside from sounding cool and impressing your friends. But out on a race track or the occasional fast, windy road, its benefits are abundantly clear. While in motion, the engine speed and wheel speed of a vehicle with a manual transmission are kept in sync when the clutch is engaged (i.e. when the clutch pedal is not being pressed down). However, when changing gear, that mechanical link is severed briefly, and the synchronization between the motor and wheels is broken. When upshifting during acceleration, this isn't much of an issue, as there's typically not a huge disparity between engine speed and wheel speed as a car accelerates. Rev-matching downshifts is the stuff they would teach at the automotive equivalent of the Shaolin Temple. But when slowing down and downshifting – as you might do when approaching a corner at a high rate of speed – that gap of time caused by the disengagement of the clutch from the engine causes the revs to drop. Without bringing up the revs somehow to help the engine speed match the wheel speed in the gear you're about to use, you'll typically get a sudden jolt when re-engaging the clutch as physics brings everything back into sync. That jolt can be a big problem when you're moving along swiftly, causing instability or even a loss of traction, particularly in rear-wheel-drive cars. So the point of rev matching is to blip the throttle simultaneously as you downshift gears in order to bring the engine speed to a closer match with the wheel speed before you re-engage the clutch in that lower gear, in turn providing a much smoother downshift. When braking is thrown in, you get heel-toe downshifting, which involves some dexterity to use all three pedals at the same time with just two feet – clutch in, slow the car while revving, clutch out. However, even if you're aware of heel-toe technique and the basic elements of how to perform a rev match, perfecting it to the point of making it useful can be difficult.

Ram 1500 bests new F-150 in MT pickup shootout

Ford's 2015 Ford F-150 is a technological tour-de-force, what with its aluminum-intensive construction and its powerful and efficient new 2.7-liter EcoBoost engine option. But now that it's hit the market, it's time to get down to brass tacks and find out how just the latest F-150 actually stands up to its rivals in the hyper-competitive fullsize segment. Motor Trend is among the first to round up the Ford (in Lariat 2.7-liter 4X4 guise here) and put it up against the Ram 1500 Outdoorsman EcoDiesel 4x4 and 5.3-liter-equipped Silverado 1500 LTZ Z71 to find out how Dearborn's new-think truck measures up. The test put the trio through over 1,000 miles of tough driving in California and Arizona in a variety of conditions from just cruising around unladen to hauling a trailer. MT found all three trucks to be competent, but the most praise got heaped on the Ram and the Ford, with the Chevrolet falling a step behind its competitors in many tests. Among the Ford's most-liked features was its 2.7-liter, twin-turbo V6 that helped make the F-150 easily the quickest of the group, with some editors saying the engine felt about the same whether driving around with cargo in the bed or not. There was some minor turbo lag during acceleration while trailering, but that issue affected the Ram, too. The Ram's powertrain was lauded, as well. The EcoDiesel was torquey around town, and the 1500's combination of an eight-speed automatic and air suspension was judged to be the best of the lot. It was the most difficult to get into the bed, though. The Ram also won the fuel economy award by netting 20-miles-per-gallon city and 28-mpg highway in the test to beat its Environmental Protection Agency ratings of 19/27. The Ford's EcoBoost managed 17/22, one mpg off each from the EPA numbers, and using a lot of throttle really depleted its efficiency. As MT notes, however, it would take time for the diesel's mileage savings to pay off at the pump for these two trucks. In the end, the Ram just barely eked out the win, with the title partially earned because of "the Ford's unknown maintenance and aluminum repair costs," according to MT. Go check out the full comparison to read all of the details, then let us know what you think in Comments.