I was surfing Polish web pages to see what they have to say about saving fuel and it's mostly "
n steps to increasing your FE". In one 12step plan, step #10 advises to reduce your speed. OK, we all know that, but here comes the fun part:
Quote:
You will increase your FE by 15% if instead of driving 100 km/h you go 85 km/h."

I know enough about aerodynamics (but please correct me if I screw something up) to tell that a 15% reduction in speed reduces the drag by more than 15%. Drag is proportional to the
square of velocity, so if 100 km/h is 17.65% faster than 85 km/h (100=1.1765x85), then the drag @ 100km/h is over 38.4% greater than at 85 km/h. In other words, the drag @ 85 km/h is about 72.24% of what it is @ 100 km/h. So drag
decreases by 27.75%. Add to that losses from other sources like rolling resistance and you're saving a lot.
If you are telling someone to slow down to save fuel, 30% is a better argument than 15%. Not everyone liked math at school