I'm wondering if I've calculated the fuel efficiency of cars accurately. The car I drive is a Honda Civic, and it seems to use more fuel than the previous car I drove,which was a Daihatsu hatchback. I'm guessing my Honda does roughly 39 mpg, and it can hold 11 gallons of fuel, so a full tank should let me travel roughly 429 miles. However, I would have thought that the Daihatsu which was smaller would hold less fuel and give me less than 429 miles on one full tank, but I'm wondering if the Honda uses more because it's automatic. I heard of a Mercedes S-Class which does 39.3 mpg, and this has been officially tested, according to What Car. Although it doesn't sound like much for a diesel car, The fuel tank holds 19.8 gallons, which means a full tank could let you travel roughly 739 miles, which is more fuel efficient than the previous 2 cars. This surprised me, considering the Mercedes is a luxury car. Apart from transmission, driving at fast speeds and harsh braking, is there anything else which could result in the Honda being less fuel efficient than a small Daihatsu hatchback?
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City driving, more commonly called "stop and go" driving can be harder on gas mileage in some cars than others.
The Honda is probably heavier because of new regulations put in place since the Daihatsu was made. But it's also probably more aerodynamic so at higher speeds the Honda should still get better mileage, and in the city the Diahatsu should be better.
The Diahatsu probably can't even go fast enough for aerodynamics to become an issue. Is that thing even street legal?
The other thing is the Honda has more power, so it's capable of burning more fuel. You could baby it, or tune it down to get better mileage, but 39 is already more than most people get out of it.
Diesel engines are 1.6 times as efficient as gas ones.
If your Daihatsu was a stick, that's better than an automatic in most cars, and the Civic is also a larger car (if the Daihatsu is the one I'm thinking - in the US it was called a Charade). So you'd expect less mileage.
You're also confusing efficiency with range. Efficiency is measured in miles/gallon. Range is miles/gallon x gallons in the fuel tank. The Mercedes is about as efficient as the Honda.
DK
To calculate "fuel efficiency" we fill the tank, and make a note of the odometer reading. Some time later we fill the tank again and note the odometer reading difference (distance traveled) and the amount of fuel required from the last fill. Dividing the miles traveled by the gallons used gives us a miles per gallon rating. IE a vehicle that traveled 16 miles and used .5 gallon of fuel would have a "fuel efficiency" of 16/.5 or 32 miles to a gallon.
Size of the fuel tank relates to range not fuel efficiency.
Things that affect fuel efficiency are aerodynamics, rolling resistance (type of tire and air pressure,) over coming inertia (weight of vehicle,) drive train resistance, efficiency of the engine, and operator choices (hypermiling & type of driving.) In our times of changing fuel blends some consideration may have to be given to the fuel used as well. A higher ethanol content will decrease fuel mileage. Diesel fuel (for a diesel engine) should increase fuel mileage (compared to gasoline in a petrol engine.)
Vehicles are ranked by their combined rating (weighted by 55% city and 45% highway). Ties are listed alphabetically. In classes where the most fuel-efficient is a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV), a conventional or regular hybrid is also listed. These lists were created using information available as of December 5, 2012.
Tested is condition better for the car manufacturer. For our conditions increased weight of the car will reduce efficiency. Then we move, stop, slowdown, keep the car idling which adds up. Would be surprised if I really kid off my car just cause it was not so efficient today. Ideal way is to keep proper tire pressure, periodic oil change, and stuff like that which increase efficiency.