pretty sure R Dodge is referring to the Xray SOLID aluminum chassis. As far as flex goes, the chassis are as follows:

Softest: Carbon
Medium: Flex Aluminum
Hard: Solid Aluminum


I think the point he was making is that the 17 solid chassis has more flex than previous years, while still being the stiffest offering for the car.

And from what he said, Alex has opted to run the solid chassis for most carpet events, as the little flex that the solid chassis does have seems to be enough for him to be competitive.