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Old 07-18-2009, 11:23 PM   #21 (permalink)
Engineering first
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Location: Huntsville, AL
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Originally Posted by dcb View Post
Bob, not everyone can ditch their car and go buy a prius, but everyone can learn effective techniques for saving fuel, of which p&g is easily the most effective. . . .
You may remember I'm pointing out the problem diesel, gas, and other non-hybrids have with sustaining a steady speed of 30 mph. I'm also explaining how the hybrid achieves a higher vehicle efficiency at City speeds.

I have no problem with a separate discussion of P&G. But if it is brought up, I will simply answer with the facts and data, the obvious limitations of P&G in traffic.

Originally Posted by dcb View Post
. . .
Seriously, you need to experience p&g first hand before putting it down with grossly inaccurate portrays and invalid assumptions. There are plenty of actual bad drivers on the road to complain about, you are targeting skilled drivers who have to pay the most attention while driving.
I am always interested in the facts and data, direct measurements:
  • peak speed (posted speed*)
  • lowest speed
  • time-to-peak speed
  • time-to-bottom speed
If you have a Garmin nuvi or can borrow one, we can analyze the P&G profile. This will give not only the parameters but also the average speed over the track. Then it is a simple matter to look at the relative MPG of P&G versus the equivalent steady-speed.

I've done it with my Prius and reported my results from the field. As the data shows, it is eminently reproducible but to achieve an 11% savings required a rather large dV.

I ran a second set of P&G tests whose average speed was centered about the maximum range speed of 18-20 mph. In this case, P&G came in much worse than holding the steady speed over the course.

Bob Wilson

ps. My tests were conducted on a stretch of road posted at 50 mph on a military base. About six years ago, I was stopped for going 52 mph in a 50 mph zone ... they are that strict. The actual route for my P&G tests:
34 38' 19.98" N 86 37' 44.70" W
34 36' 13.51" N 86 37' 49.49" W
Testing was conducted on a weekend morning when there was almost no other traffic.

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