2011 Ford Mustang GT 5.0: A Live One
February 09, 2011
It probably happened around the time when our longterm 2011 Ford Mustang GT was heading down the assembly line in Flat Rock. A new or revised Mustang is introduced to the media, and the subsequent reports from a half-dozen hacks inevitably gush "you can't even tell it has a live axle!"
Those journalists need to have their asses recalibrated.
The subject of the Mustang's live axle ignites heated arguments among enthusiasts nearly as effectively as do pushrods. Ford's justification for the live axle in modern times has been that their customers that drag race demand it, and, well, it's cheap. Fair enough. Mustang enthusiasts point to the car's impressive handling numbers. Also a fair point. But don't be fooled into concluding that a live axle out-points an independent layout on every pole of the spider graph.
Live axles have loads of unsprung mass, far more than that of an independent suspension. This is the technical description you've heard before, and the way unsprung mass manifests itself in the real world is a busy up-and-down action originating from the rear of the car. It's not really ride harshness per se, it's more of an exaggerated bobbling motion, and it's obvious. You notice it even when cruising down a freeway if that freeway is not completely smooth, a description that includes nearly every metropolitan-area freeway.
On smooth surfaces like racetracks, unsprung mass is far less of a liability (unless the best lines on the track are those that entail driving over berms...). A live-axle'd tire has no camber change due to body roll (i.e. it runs perpendicular to the track surface), an aspect that is no bad thing for grip and traction and is part of the reason drag racers like 'em. Of course, unlike live axles, independent layouts can have the luxury of toe and camber adjustments, allowing the user to take advantage of camber thrust for additional grip.
Roads in the real world are bumpy. When driving on said bumpy roads that also decide to turn, unsprung mass re-enters the equation and the Mustang bucks uncouth-ly. It's like some large, invisible hand is yanking the back of the car to and fro. Ford engineers have gone to some lengths in tuning the rear damper forces in attempt to manage this inherent behavior, and in doing so have extended the effective life of the stick axle layout.
But then you drive a car like the current Camaro over the same section of road and realize just how much less ass-end-derived drama and nonsense there can be (note: I'm not referring to oversteer, which is the kind of ass-end nonsense I can get behind). The difference in chassis control and composure is real.
This is one of the few areas in which I prefer the Camaro over the Mustang.
Jason Kavanagh, Engineering Editor