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Originally Posted by ninetres
That’s crazy. Learn something new everyday. I’m just one guy....so not exactly a large sample size. But I would have figured in the 20-odd years I’ve been a gear head drag racing, half mile racing, and time attacking I would have stumbled into a conversation like this if it’s somewhat common in the scene.
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I doubt that very many drag racers or half-milers pay much attention to chassis stiffness, and if there are any that do they're keeping it quiet as a competitive advantage. As a serious time-attack competitor might do as well.
Yes, it is something that takes at least an engineering outlook for it to be very useful. And it makes more sense when (as an engineer) you're aware that every piece of structure and every mechanical component is some kind of spring when it comes down to following loads and load paths. For a car's chassis, in overview it's just the one big spring connecting the front and rear suspensions as springs. Among other things its stiffness determines in large part how effective any given suspension tweak is at shifting the distribution of lateral load transfer (i.e. how effectively you can shift the handling balance with things like specific bar adjustments and spring changes).
It's also something that's subject to diminishing returns, so there's probably some practical limit (perhaps some multiple of suspension roll stiffnesses or a multiple of the difference between front and rear roll stiffnesses?). And I think that sometimes the 'diminishing returns' aspect goes unrecognized in the chase for still bigger numbers for the sake of having big numbers.
I have a few comparisons that might be of specific interest here. Except as noted, values are in units of Nm/deg (Newton*meters/deg). Divide them by 1.355 for ft*lb/deg numbers. It should be apparent why I'd like to see the relationship between frequency and stiffness.
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Chevrolet
Chevrolet Camaro Convertible (2011 – 2015) 18 Hz (torsional, dynamic), 21 Hz (bending, dynamic) Link
Chevrolet Cobalt 19,300
Chevrolet Corvette C5 9,100
Chevrolet Corvette C7 (2014 – ) 14,500
Chevrolet Cruze 17,660
Chevrolet Malibu (8th-gen, 2013 – 2016) 23,000 (w/o moonroof)
Chevrolet Malibu (9th-gen, 2016 -) 23,600 (w moonroof)
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Ford
Ford Fiesta 3-door (3rd gen, 1989 – 1997) 6,500
Ford Focus 3-door 19,600
Ford Focus 5-door 17,900
Ford Fusion (2010 – 2012) 17,453 (1,000 kNm/rad) Link
Ford Fusion (2013 – ) 19,286 (1,105 kNm/rad) LinkFull document part 1part 2
Ford GT 27,100
Ford GT40 MkI 17,000
Ford Maverick 4,400
Ford Mustang 2003 16,000
Ford Mustang 2005 21,000 . . . . (15,500 ft*lb/deg approximately)
Ford Mustang Convertible (2003) 4,800
Ford Mustang Convertible (2005) 9,500
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Norm