Originally Posted by Camber

2008 Mercedes ML320CDI. Rated at 7200 lbs towing. Diesel with air suspension, towing kit which includes modified ECU to respond to trailer problems. Tow a GT3 on a Trailex open trailer with tire rack. My experience

1. Towing trailer with tires at 65 - 70 MPH: 15 - 16 MPG
2. Towing trailer without tires at 65-70 MPH: 16 - 17 MPG
3. Highway driving at 65 MPH without trailer: 27 MPG (really)
4. Highway driving at 55 MPH without trailer: 29 MPG