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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.

Weekly Recap: Revisting the BBC report that ended Jeremy Clarkson's Top Gear run

Jeremy Clarkson's long run as a Top Gear host has come to an end, and the reason is clear: His physical assault on one of the show's producers crossed a line, and the government-owned BBC couldn't tolerate it. The incident between Clarkson and Top Gear producer Oisin Tymon was initially described as a "fracas," and Clarkson was suspended. But his popularity and widespread support – even British Prime Minister David Cameron weighed in – suggested that the controversial Clarkson might be given yet another chance. The BBC put this to rest Wednesday when it sacked Clarkson and revealed the findings of its investigation. The report spelled out how Clarkson struck Tymon on the patio of a North Yorkshire (UK) hotel, leaving him with a bloodied, swollen lip. It was severe enough that the producer sought medical treatment. During and after the attack, Clarkson shouted expletives at Tymon and threatened to fire him. The noise carried into the hotel's dining room and even to a bedroom. Local police investigated the incident, but Tymon isn't pressing charges. The huge audience numbers, Clarkson's popularity and the high-octane excitement of Top Gear all melted away in the eyes of BBC director-general Tony Hall, who saw an attacker and a victim. "For me a line has been crossed," he said in a statement. "There cannot be one rule for one and one rule for another dictated by either rank, or public relations and commercial considerations." In that moment, Clarkson was the bad guy, though he was actually the one who reported it to the network and made repeated attempts to apologize to Tymon. He's also urged the media to leave the producer alone. Hall voiced regret in the statement that announced Clarkson's contract would not be renewed, but the BBC decided to move on. Rumors are swirling about possible replacements for Clarkson. The network says it wants to continue Top Gear in 2016 and is looking to air the rest of this season's episodes. Despite the controversy, the show has a global audience of 350 million viewers and is one of the BBC's most valuable properties. It's unclear what Clarkson's co-hosts, James May and Richard Hammond, will do, as their contracts were also reportedly up to be renewed. Other News & Notes 2016 Chevrolet Malibu hybrid charges up with Volt technology Chevrolet is taking some of the learnings and technologies from the 2016 Volt and dropping them into the reborn Malibu hybrid.