[Longsnowsm]

To the original poster, the question about a calculator for figuring out the break even is you and your vehicle. Your vehicle will give the the feedback on where it gets the best fuel economy, as you increase speeds you will see that figure drop reflecting the additional fuel burned. At some point as you continue to push your speeds higher you will see your vehicle fuel economy start to suffer in greater percentage/proportion for the speed travelled. At that point back off and see where your fuel economy starts to make the biggest moves upwards. That is generally what I refer to as the sweet spot where your making the best return on the fuel burned as long as your willing to accept that your burning fuel at a faster rate than if you slowed down to the place you see the best fuel economy your vehicle can return.

Then from there decide what you have more of at that point. Time or fuel. Some vehicles when idle or coasting burn little fuel and have a fuel over run where the engine is basically acting as a pump, but not really consuming much fuel. So don't let the run times of the car be the indicator. If you have a Scangauge you can set the liters per hour or gallons per hour as the case may be and note the burn rates when coasting, idling, running steady speed, accelerating etc. It isn't a constant so actual time your running your vehicle really cannot be used as the yardstick for determining if your wasting fuel by taking longer.

Over time if your driving the same routes you start to figure out where you can coast, where to watch for traffic lights, where to accelerate, and where to shut it down to coast or idle down to reduce your fuel rate over the same distance and likely you will improve the time it takes to do it in the process as well. Practice makes perfect. On unfamiliar ground you really have to be scanning ahead, watch your gauges, and know your vehicle and you will figure out where the break even point is in maximizing your time and fuel.