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Honda Fit Real World MPG

2438 messages,  Last post on Dec 01, 2009 at 1:51 PM

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#2381 of 2438 Re: Driving Technique For Maximum Mileage [huisj] by greenee09 May 29, 2009 (3:21 pm)
Replying to: huisj (Mar 25, 2009 8:37 am) Back in Dec of 2006, I had gotten 39 mpg driving a used manual 1998 Ford Contour during a trip from home in north NJ to Wash. DC. Terrain had mostly gentle slopes, both up and down. I believe the good mpg was achieved because I was cruising most of the time at or below 60 mph. You can read my original post as greenee07 back in 1/2007 for more details.   As for fuel economy involving going up hill versus downhill, here's my view:   A trip is made by the same car from point A to point B and then back to point A, all at the same speed.   If point A is at a significantly higher elevation than point B, then mpg should be higher for trip from A to B than the return trip from B to A because the potential energy at the higher elevation can be converted to kinetic energy (motion) when traveling from A to B. Extra chemical potential energy in the form of gasoline has to be used to return the car and passenger from point B to point A.    I agree with the response from wistlo.
#2382 of 2438 41 to 47 highway mileage by gatortom1 Jun 03, 2009 (6:50 am)
Fit Highway Mileage: I just completed my first road trip in my 2009 Base Fit with AT that had 2800 miles on the odometer at start. I traveled I-26 and I-95 from Asheville to South Florida and return with 165 pound driver plus about 40 pounds of baggage. I held speed as close to 65 as possible without having cruise control. The overall result was 1471 miles on 34.6 gallons of gas or 42.5 mpg. The worst highway mileage was 40.8 on the last leg of the trip climbing back into the Western NC mountains. The best was 47.5 (5.84 gallons to go 278 miles) on I-95 in Florida and south Georgia where I think I was picking up drafting benefits from the large number of 18-wheelers.   My usual around town mileage in Asheville continues at 35 mpg in warm weather and 32 mpg in mid winter. (I got my Fit in September, 2008.)
#2383 of 2438 Re: Driving Technique For Maximum Mileage [bobw3] by robotaz2 Jun 15, 2009 (8:56 am)
Replying to: bobw3 (Mar 24, 2009 7:42 am) Um, actually if a biker tells you that it takes much less energy to pedal on flat ground over the same distance than going up and down hills that cover the same total distance then they do not know what they are talking about and obviously neither do you. Sorry, but true. Pick up a high school physics book and see for yourself. Replies to this message: kipk (Jun 16, 2009 3:16 am) gatortom1 (Jun 16, 2009 10:07 am)
#2384 of 2438 Paul Meyers by pmeyers Jun 15, 2009 (12:42 pm)
robotaz2 is in error, as he is neglecting the effects of aerodynamic friction. Wind resistance goes up as the square of the velocity (given the same frontal area). As any bicyclist knows, much of your gains going downhill on a bike are eaten up by increased wind resistance, which, is HUGELY greater at 30-70 mph going downhill than at 10-20 mph going uphill. YOU NEVER GET THAT ENERGY BACK! It goes into heating the air. So, your bicyclist friend is right, in that pedaling on flat ground over the same distance uses much less energy than going up and down hill, as any aerodynamic textbook will tell you. Besides, it's impolite to tell someone that they don't know what they're talking about. I would never say that about you. Grin.
#2385 of 2438 Re: Driving Technique For Maximum Mileage [robotaz2] by kipk Jun 16, 2009 (3:16 am)
Replying to: robotaz2 (Jun 15, 2009 8:56 am) >"Um, actually if a biker tells you that it takes much less energy to pedal on flat ground over the same distance than going up and down hills that cover the same total distance then they do not know what they are talking about and obviously neither do you"   Those of us, that have been out of high school for a while, understand that driving in the mountains results in poorer mileage than driving on flat ground. If the grades are steep enough to require brakes on the declines, the mileage suffers even more. Fuel mileage is greatly affected by several factors. Gravity is one of them.   Many think that because they might get 20 mpg going up one side of a mountain and 40 going down the same distance on the other side that the "average" for the two is 30 mpg. Not true!   I've read several times that due to the size and weight of it's body and the size and speed of the wings, physics can prove that a Bumble Bee can not fly. Really?   Kip
#2386 of 2438 Second Law by wistlo Jun 16, 2009 (6:31 am)
Those of us who have been out of high school and also engineering school for a while would disagree.   Both the the First and Second Laws of Thermodynamics apply. The First Law states that energy cannot be created or destroyed, only transformed.   When driving on hills, the First Law tells us exactly the same energy expended climbing a hill is recovered during descent. Think of a roller coaster that gets pulled up by force and then travels its course without any mechanical input. The coaster speeds up as it moves down, converting potential energy from its height into velocity. As it climbs, the momentum is transferred back to potential energy.   The reason mileage drops on hills comes from the Second Law, the fact that processes are inherently inefficient to some degree. Internal combustion engines are most efficient at steady state. Also, hilly driving usually means curves and speed variation. To conserve all the energy gained going uphill, a car would have to be allowed to accelerate freely downhill, which on long grades results in unsafe downhill speed.   On longer grades, the use of brakes or engine braking dissipates energy and reduces efficiency (Hybrids recover some of it).   Bikes are a terrible analogy because we perceive the great effort required to muscle up hill. But in terms of actual energy expenditure, difficulty does not correlate to energy expended or recovered. A car or bike that can traverse hills without using braking will be less efficient only because of incremental differences in engine performance and rolling resistances at varying speeds. Replies to this message: kipk (Jun 22, 2009 4:04 am) wistlo (Jun 22, 2009 6:54 am)
#2387 of 2438 Re: Driving Technique For Maximum Mileage [robotaz2] by gatortom1 Jun 16, 2009 (10:07 am)
Replying to: robotaz2 (Jun 15, 2009 8:56 am) Sorry robotaz2 but you have your nose TOO deep in a physics book. In a vacuum, without factors such as wind drag, you would be correct but not in the real world. Bike a few 50 to 70 mile days over differing terrain for yourself as I do. At 10 to 12 mph, wind drag is nearly insignificant while at 30 mph a biker is exerting nearly 80% of his/her energy just to overcome wind resistence. (The increase with speed is logorithmic and not direct.) When you climb a steep hill you expend and store significant potential energy to overcome gravity. On the way back down you gain the advantage of that stored energy MINUS the extra you loose to significantly increased wind resistence. At least I suspect that is the physics behind the clear fact that multiple hills suck more energy than flat terraine. (My gently rolling training route of 36 miles consistantly takes several minutes less time than my 32-mile round trip climbing route that includes 3200 feet of altitude change.)
#2388 of 2438 Trip MPG by dadof6 Jun 21, 2009 (12:55 pm)
Geez Louise you guys take this stuff way to seriously. '07 Sport AT 40,000 miles. 3488 miles and 99 gals used comes to 35mpg. (am I allowed to round numbers) Trip was from western SD to NY city,1% was in stop & go traffic and 80% was driven at speeds higher than 65mph. Indiana,Iowa,Minnesota & SD have limits of at least 70mph. We used cruise about 95% of the time,stopped every 2hrs for breaks. 3 adults & 1 12 yr old child + baggage for a 9 day trip. Yes we bottomed out the suspension in the rear a handfull of times. BTW I replace the air filter 1/2 way thru the trip & it had no affect on mpg.
#2389 of 2438 Re: Second Law [wistlo] by kipk Jun 22, 2009 (4:04 am)
Replying to: wistlo (Jun 16, 2009 6:31 am) >"When driving on hills, the First Law tells us exactly the same energy expended climbing a hill is recovered during descent. Think of a roller coaster that gets pulled up by force and then travels its course without any mechanical input."   Good analogy.   A roller coaster, with only one mechanical assist, is pulled to it's highest point at the beginning. From that point it is released and gravity takes over. The combination of the up hill grades is less distance and/or angle than the combination of the downhill grades. So it reaches it's destination at the bottom. Some of the larger, longer, roller coasters require more than one mechanical assist.   Engineers use physics and other stuff to figure in the factors to make the "Coaster" function as it should. I expect those same engineers can dig up some formulas that explain exactly why a car in mountainous terrain gets less mileage than on flat ground.   A marble allowed to roll down a given hard surfaced grade will not continue and roll up an identical grade for the same distance. It will always fall a little short. When it stops forward momentum and begins to roll backward, it will fall short going back up the first grade and so forth until it eventually stops. That marble likely has nowhere near the resistance to movement as a moving car. When a skate boarder in a half pipe stops exerting extra energy, he will quickly come to a stop at the bottom, because there is simply not enough energy built and stored by the gravity effect to make it all the way to the top of the other side of the half pipe, in the real world.   So far we haven't found a way to overcome the "slow down" factors in real world, without exerting "Extra" energy.   Until we do, we are forced to live in a world that requires more fuel to be used in mountainous driving than flat ground driving.   Kip Replies to this message: wistlo (Jun 22, 2009 6:54 am)
#2390 of 2438 Re: Second Law [kipk] by wistlo Jun 22, 2009 (6:54 am)
Replying to: kipk (Jun 22, 2009 4:04 am) The "slow down factors" do not vary significantly with the angle of incline. In all the examples cited (marble, skateboard, etc), similar frictional losses exist in both flat and variable inclines.   The major source of loss in hilly driving is braking, regardless of source of friction (brakes or engine pumping against a closed throttle). Hybrids recover some of those losses by converting deceleration forces into stored energy.   Engine performance does vary under load, but it's a moderate to minor effect. The evidence is out on the highway: On hilly I-81, I get within 1-2 MPG of the mileage as I do on flat I-10 in both a FIt and a Civic, both with manual transmissions.

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