I assume this is for a rental based in the US? If so, a Trailblazer is considered Group W: Standard SUV, seating 5. The other types of SUV's in the US are: Standard SUV, seating 7, Intermediate SUV, Full Size SUV and Premium SUV. In the mind of Avis, a Premium SUV (Suburban, Navigator, Expedition, Sequoia & Enclave) is a several-class upgrade from W.
There is a list of known cars & classes
HERE. Note, this list isn't an official Avis list, but a list from what FTers have rented and reported.