I have an 88,000 mile 2007 Mercedes-Benz C-Class diesel automatic estate, a lovely car. I normally follow the fuel filler flap advice and keep to 32F/33R tyre pressures for my lightly loaded lifestyle, which mainly involves a 12 mile trip to Croydon over country roads at an average of 35-40mph. This gives me 32mpg, which is worse than the 38mpg ‘Combined’ figure. We also tow a boat and last week took it to the Isle of Wight before which I followed the advice on the flap and pumped up to 36F/45R. After arrival and decoupling of the trailer, I noticed an immediate improvement on rural roads to between 38 - 45 mpg, which was better than the returns I get here on similar roads. We are always encouraged to keep pressures right for fuel economy. Is it wise to keep to these substantially higher pressures if not towing?