Ford Focus Forum, Ford Focus ST Forum - View Single Post - Optimizing Accel and Decel
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Old 09-06-2012, 08:17 AM   #30
suss6052
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Quote:
Originally Posted by kam327 View Post
It can be explained very easily. The main assumption here is that you have to travel further at speed before coasting in gear in order to reach the stop sign at the same speed you would reach it coasting in neutral, since you'll decelerate more quickly in gear than in neutral.

The Focus burns say roughly 0.3 gal/hr at idle, and roughly 1.3 gal/hr at 45 mph (I'd have to confirm these numbers but rough order of magnitude they're pretty good).

In the coast in neutral scenario, you're burning 0.3 gal/hr for the full 60 seconds to the stop for a total burn of 0.005 gal. In the coast in gear scenario, you're burning 1.3 gal/hr for say the first 20 seconds and then 0 gal/hr for the next 40 seconds for a total burn of 0.0072 gal, a 44% increase over the coast in neutral scenario.





Yes of course there is a difference by coasting in gear versus speeding up to a stop and then slamming on the brakes. The point is that theoretically you can do slightly better by coasting in neutral.
The question is what if you're going to have to stop anyway, why would you hold the higher speed longer before coasting in gear vs coasting in neutral to try and maintain a higher speed at the end of the coast?
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