It may overload the rear axle in the eyes of the law but let take this example:
- I have a car transporter trailer attached to the rear of my Transit.
- Car Transport trailer is twin axle.
- I drive Ford Fiesta 1.8D onto trailer (nose first) so that the front axle of the Fiesta is in front of the first axle on the trailer.
- The Fiesta doesn't have a long enough wheelbase for the back axle to be behind the second axle on the trailer.
Therefore the above combination is almost equal to the forces that would be experienced on the rear of the SWB if you used a spec lift. You've got the weight of the trailer and probably 65-70% of the weight of the car on the towbar.
I know my Transit would have no bother towing the trailer with the above combination (nevermind heavier cars) and it's only an 80.
I think a SWB 150 would be ideal - or a SWB twin wheel but we can only dream
