You are here: Forums Hatchbacks Honda Fit Honda Fit Real World MPG

Honda Fit Real World MPG

2432 messages,  Last post on Oct 29, 2009 at 4:50 AM

You are in the Honda Fit Forum. Your Host is pf_flyer

What is this discussion about? Honda Fit, Fuel Efficiency (MPG), Hatchback

Messages Page 240 of 244 1 ... 237 238 239 240 241 242 243 244 Prev Next Last

Go To Msg # Search This Discussion

#2384 of 2432 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 2432 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 2432 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 2432 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 2432 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 2432 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 2432 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.
#2391 of 2432 Don't take EPA/Edmunds MPG ratings as fact by gr00v3 Jun 22, 2009 (9:35 am)
In my 2007 Fit Sport, I managed 38.5 MPG on a drive from RI to NH, doing 75mph average, with the car loaded up with camping gear, and with the A/C on.   No, I'm not having you on.   All I did was to ensure that the tachometer never--or rarely--went above 3000rpm. Replies to this message: tiff_c (Jun 22, 2009 5:55 pm) pf_flyer (Jun 23, 2009 3:25 am) roxy11 (Jul 03, 2009 5:05 pm)
#2392 of 2432 Re: Don't take EPA/Edmunds MPG ratings as fact [gr00v3] by tiff_c Jun 22, 2009 (5:55 pm)
Replying to: gr00v3 (Jun 22, 2009 9:35 am) Well we live in the middle of NH and our last tank was our best at 37mpg and we have a lot of hills here, not to mention the 10% ethanol required in all gas sold here. Replies to this message: pf_flyer (Jun 23, 2009 3:25 am) roxy11 (Jul 03, 2009 5:05 pm)
#2393 of 2432 Re: Don't take EPA/Edmunds MPG ratings as fact [tiff_c] by pf_flyer HOST Jun 23, 2009 (3:25 am)
Replying to: tiff_c (Jun 22, 2009 5:55 pm) Regardless of the driving conditions where you happen to live, ethanol is a huge cause of decreased mileage performance. The The Inconvenient Truth About Ethanol discussion is a good place to chime in on your ethanol experiences

Messages Page 240 of 244 1 ... 237 238 239 240 241 242 243 244 Prev Next Last

Go To Msg # Search This Discussion

You are here: Forums Hatchbacks Honda Fit Honda Fit Real World MPG