error: [undefined procedure: default][default { discard }]

Try this indentation and with just two variables (performance +up):

when HTTP_REQUEST {

    set host [string tolower [HTTP::host]]
    set uri [string tolower [HTTP::uri]]

    switch -glob $host {
        "topgear" {       
            if { $uri contains "car"  } {
                SSL::disable serverside
                pool toyota_pool
            }
            else {
                if { $uri equals "/"  } {
                    HTTP::respond 301 Location "https://cars.com"
                }
            }
        }
        default {
            discard
        }
    }
}