Someone posted up a few weeks ago that being behind an arctic lorry was increasing their mpg figures, so the other night I tried it out and guess what, it does, I wasn't tailgating the HGV more like about 4-5 lengths behind him and the dash comp was dropping until I pulled out and went by, no doubt if I'd got close enough to inspect his cargo I would've entered the windless zone and things may have been different, so here's my tip don't follow a HGV cos it will cost you over a longish trip.