This week I drove from Westminster to Laguna Beach. The freeway portion was on a new tank so correcting for the guage it looked like 42.5 trip MPG with the AC on.
Getting to the beach it dropped down to about 40 MPG due to some traffic lights. When I reached the summit of Alta Laguna Park (The Top of the World) it had dropped down to about 28 MPG in one just mile of hill climbing.
What went wrong? Why does the Fit do so poorly on hills. I had to know.
There was another Silver GE Fit at the summit, BTW.
When I got back I did some physics calculations and best case trip MPG would have been about 31 MPG to the summit not counting the stop signs. As it turns out the park is about 1036 feet above sea level. I estimate the car with two people and hiking gear to be 2900 lbs. It takes a huge amount of energy (3.9 megaJoules) to haul even a subcompact up a mere 1000 feet in one mile. The math suggests less than 7 MPG. Bottom line: any car will douse MPG with a large hill unless you can coast the backside at a safe speed without the brakes on (or have a hybrid to convert the hill into charge).
Other physics fascinations is how much gas it takes to accelerate to 65 MPH highway speeds - I estimate 0.020 gallons a shot. Doesn't seem like much but on a short trip it is costly, so coast as much as possible. There should be an optimum acceleration rate as well. Too slow wastes gas almost as much as jackrabbit. The engine has an optimum power and RPM range where it is most efficient at converting the thermal enegry of gasoline to kinetic energy (motion).
If there is interest I would like to share some physics insight into what we should expect for real MPG and how to make the best of it. It would be nice if some of you can do some experiments and we can estimate HP to cruise at various speeds with and without AC, tire specs, AT vs MT, 1.2 vs 1.3 vs 1.5, D vs S, 87 octane vs gasohol, warm-up waste, etc. It's nice to know the best you can achieve and not get frustrated. Then we can concentrate on our driving skills.
For openers, I estimate that the 2009 Sport AT (L15 i-VTEC) requires 15 HP to cruise at 65 MPH with AC on, 43 MPG steady state. This suggests the L15 is 20.3% efficient on 87 octane (it is probably better than this). Useful data from our Scanguage brethren would be gallons per minute and coastdown times such as 65 to 60 (useful for calculating real rolling HP).
A gallon of gas should contain 124,000 BTUs = 130.8 MJ = 175,400 HP-sec of energy.
Coastdown from 65 to 60 MPH is 109 HP-sec for 2900 lb. Example: 15 HP cruising would take 7.3 seconds to coast down.
Silver 2009 Sport At