Hypermilers know this already, but What Car?, the British automotive media outlet, released the results of a study today that shows just how much money can be saved by some sensible - in this case slower - driving. The savings can be pretty dramatic: up to £1.20 ($2.34USD) every eight minutes. How? By driving the car at its most economical. What Car? asked fuel economy expert Peter de Nayer to test five cars - a Toyota Aygo, Nissan Qashqai, Volkswagen Passat, Citroen C4 Picasso and Land Rover Freelander - to find out at what speed they are the most efficient. De Nayer's test found that, on average, going 100mph uses five times as much fuel as going 50mph. Not sure why that matters, as not many people are cruising around at 100mph, but the advice to slow down is a good one. What Car? recommends a 70mph top speed on the highway, driving in the highest gear possible and not racing a way from stoplights or slamming on the brakes. What Car? also found that 62 percent of motorists in the UK don't know what the right speed is to save the most fuel while you're on the go. Their "Slow down, save fuel" project goes live today, and you can read more after the break.