This weight is unsprung and rotating weight, so removing it has a larger positive effect than simply removing that much weight from the chassis. The iron friction ring of the rotor and the hat are bolted together.
These spacers bolt solidly to the friction ring face but allow about 0.012″ of free play between the friction ring and the hat. Special steel lips prevent the movement of the spacer from digging into the softer aluminum.
In a race car, free float is not an issue, but for a street application the rotor can bang around and make noise when the brakes are not in use. For this rotor, you can see that there is a spring clip right under the nut that applies tension on the hat to prevent the rotor from moving enough to make noise.
Free floating the rotor helps because your typical one-piece rotor distorts like a cone as it gets hot. This reduces pad swept area in extreme cases and can make for a long and mushy pedal and uneven pad wear in less extreme cases of brake overheating.
Floating the rotor can also reduce a rotor’s tendency to warp under repeated heating cycles of hard use.
On a C7, upgrading the rear brakes is important due the car’s 50/50 weight bias. The C7 carries more weight in the rear than most cars. The rear rotor is a whopping 365mm in diameter and 25mm thick.
The caliper piston size and all other dimensions that we could measure are the same between the big brake kit and the stock Z51 caliper.