I was wondering if there is a theoratical weight to calculate the mpg at a given weight at the same speed if one mpg number and one weight number is given.
Say I know I get 50 mpg at 65 mph with a car that weighs 2200. I look at my car and wonder what the mpg would be at the same speed if I manage to take off 100 lbs of the weight. Is there a formula for this at all?
Well, chances are the graph would not be linear. It would probably be doable adding 100 lbs extra and then 200 lbs, then get the mpg's for a controlled trip and then extrapolate (is that English) the graph in the other direction to see where this would get you. Just thought of this.
The reason I started thinking of this is the gastank that I usually fill up to be able to calculate my mpg, but which I usually only drive till half a tank, so I carry 4 to 5 gallons in extra weight with me. Add to that a spare tire that could be thrown out (hey I am an AAA member anyway) and some other things.It made me wonder if it would be worth it...
Mass only affects acceleration not constant speed driving.
Force=Mass X Acceleration
It takes more energy to accelerate a heavier car at the same acceleration as a lighter car.
Or using the same energy, (fuel) the rate of acceleration of a heavier car is slower then that of a lighter weight car.
The amount of force (or fuel) it takes to drive a car at a constant speed depends on air resistance, rolling resistance and mechanical losses (friction in transmission, bearing, engine etc..) The weight of the vehicle only slightly affects rolling resistance when traveling at a constant speed. But this factor is insignificantly small.
So the equation you are looking for does not and cannot exist in a way that can be applied to different cars.
And the P&G working better with a heavier car does make sense.
Edit: Well, no reason there would be a lessening of FE in P&G with weight.
Though you may be using slightly more gas to accelerate during the pulse, you can coast at least enough longer to cancel out that loss. Extra weight equals extra momentum.
For example, if you apply 10 seconds of acceleration to a light car, you'll get going faster but also slow down sooner once those ten seconds are up.
You apply the same force for that same 10 seconds to a heavy car, you won't go as fast, but you'll take a lot longer to slow down.
Theoretically, in an ideal environment, you do those tests next to each other, the cars will go the exact same distance, but the light car will get there sooner.
Of course, this is all if I remember my physics correctly.
skewbe: Yeah... EOC is excellent. I was a bit scared of it at first, but now I actually PREFER the feel of no power steering and non-assist braking! If only we could figure out a way to ACCELERATE with EOC (on an upgrade)! haha..
Bonus of EOC is that you can be moving a ton or 1000lbs... doesn't matter. Each one gets infinite miles to the gallon. Definitely one of the most important techniques for hypermiling!