I suppose it's obvious when you think about it, I noticed a difference between towing the van with the xc70 and the discovery, but that's more to do with volvo power compared to landrover torque than aerodynamics.
Certainly 60 mpg into a headwind and even the volvo tells you its working by the amount of fuel it uses, still less than the landrover at 40 mind.
In effect you are towing a wall, any ramp must improve matters as airflow is smoothed but modern cars are designed in wind tunnels to optomise airflow, chuck a wall behind them and all the calculations are void.
Paul.
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