As everyone knows, convertibles are less structurally sound than coupes. The lack of the fixed roof element manifests itself into chassis flex and cowl shake. Additonal support material welded into the convertibles helps reduce these undesirable effects somewhat (and makes the convertibles weight more than the coupes). To further improve the ride quality in the convertibles, softer sping rates are frequently used on the convertibles (versus stiffer spring rates on the coupes). Even your 2001 SVT Cobra convertible came from the factory with softer spring rates than my 2001 SVT Cobra coupe.

SVT engineers had been quoted in past interviews as saying that 18" wheels and tires were the optimum size for the S197 Mustang chassis. This was specifically given as the reason the production GT500KR came with 18" wheels versus the 20" wheels on the KR prototype. However, once the 2009 Challenger and 2010 Camaro came out with 20" rims, Ford felt pressured to at least offer 19" wheels on the Mustang. The 2010 GT500 coupes get the 19" wheels, but the smaller sidewall of the 19s would magnify the chassis flex and cowl shake on the 2010 GT500 convertibles. So the 2010 GT500 convertibles keep the 18" wheel size of previous year GT500s in order to improve ride quality.

“To compensate for the reduced structure of an open car, engineers often will make the suspension softer, making the convertible a boulevard cruiser,” said Oppenheiser. “Instead, we took the more difficult, but better path of bolstering structure rather than softening the suspension. We didn’t change a strut, bushing or spring rate from the Camaro coupe.”