The S197 studs are 1/2" (12.7mm) and the S550 are 14mm. The slight but requisite change in the corresponding hat stud holes really has no impact on clamping force. The torque value stays the same at ~ 100 ft-lbs at each of the 5 studs. If there was a friction reduction between the hat and the hub face, that would be an issue. There isn't. Remember, the hub register (or pilot) is the same diameter between the S197 and at least the GT350 (I don't pay much attention to the Ecoboost Mustangs, etc, but they may be the same as well).
Of note, Filip at Cortex even sells wheel studs in the 1/2" S197 size to be used where the 14mm studs were.
http://cortexracing.com/product/wheel-stud-kit-2015-ford-mustang-front-and-rear-s550/
Of note, Filip at Cortex even sells wheel studs in the 1/2" S197 size to be used where the 14mm studs were.
http://cortexracing.com/product/wheel-stud-kit-2015-ford-mustang-front-and-rear-s550/