Quote:
Originally Posted by hackish
I think P&G is the biggest farce out there. Physics does not support it. People who claim it gives them better fuel economy are seeing gains because of a lower average speed. They pulse up to 70mph and coast down to 50mph then compare it with a constant drive at 60mph while in actual fact their average speed is more like 56mph.
If it were valid then why would the scientists who work on eco - competitions not do it? Why wouldn't hybrids do it too? I mean they could P&G with electric and fuel.
An accelerating engine consumes more fuel per unit of energy produced. Since transporting your vehicle from point A to point B requires that x amount of fuel be turned into energy the most efficient way is to output the energy required in such a way that it consumes the least fuel, not deliver the energy in inefficient spurts.
Finally, P&G pollutes significantly more. Most vehicle emissions are tied to the cat temps. When you shut the engine off, the cat cools below it's effective range, restart it and for the next 20-30 seconds you will be sending somewhere around 5-10x the pollutants out the tailpipe.
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Every one of these assertions is incorrect or unsubstantiated, for all the reasons other have cited and more. But you should also take a look at the
test I recently did on P&G technique. Note the average speeds.