I just bought a new Honda Fit. What driving speed will generate the best gas mileage on this vehicle?
Typically that is the slowest speed you can drive in with the highest gear, without lugging the engine. Probably about 40mph, maybe 30mph.
Best economy is by alternate accelerating gently from say, 20mph to say, 50mph, shutting engine off and coasting back to 20. Repeat. But this is unsafe, and is not practical.
Best, as Steve says, drive gently, as slow as you can without disrupting traffic.
See: http://community.cartalk.com/posts/list/837610.page
for another post with lots of comments about fuel economy.
You’ll probably get the “best” mileage around 55 mph…But as long as you keep it under 75 mph on the freeway you will do fine. Do some experimentation, it will be fun.
Even if you had a proven speed, which is likely to be in the 35-50 mph range, you would have no place to drive for miles and miles at that speed. Instead you will generate your best fuel economy by always using gentle driving – modest acceleration, steady cruising, and long coasting to predicted stops.
Interesting info about about Honda’s engines for the Fit http://asia.vtec.net/Series/FitJazz/lseries/
Any engine that uses a mechanical camshaft for controlling the valve lift, duration and timing is going to have one speed at which it gets its best fuel economy, but it is not a peak but a gently rising curve. That is if the most efficient RPM is say 2200 rpm, the engine will be almost as efficient from 1400 to 3000 rpm. The difference would probably be less than 1 mpg. Considerations of safety and efficient traffic flow are far more important here.
I guess you saw the TV movie “The Painted House” where the old man told the young kid that he always drove his truck at 37 mph because that was its most efficient speed. In the time era depicted in the movie, where engines had carburetors and mechanically controlled distributors, the single most efficient speed was more noticeable. Modern engines with fuel injection and computer controlled ignition have flattened the curve quite a bit. Engines that have variable valve timing flatten it even more.
There are engines in development that will use computer controlled valve event timing and duration the will flatten the curve completely. These will be needed to provide Americans with the big vehicles we seem to love but still get fuel economy to meet the new mandated CAFE requirements.
Thanks Americar . . . interesting article. Rocketman
I have a new Fit, also; the sport with manual transmission. It is so much fun to drive I can’t imagine driving for mileage. I get in the low to mid 30’s, mostly in a large city. Why not enjoy?
he’s not asking for most efficient engine operation, but best mileage, which has to include rolling friction and wind resistance.
Most engines achieve their lowest specific fuel consumption at close to full throttle at the engine’s maximum torque rpm. That’s why a lot of fuel economy records were established with intermittent engine runs. The car is accelerated at the engine’s most efficient power output and then the coasts with the engine off for a long ways and the process is repeated. Hypermilers call this “pulse and glide”.
At steady speeds, the engine gets less efficient as it is throttled down to lower speeds but the lower horsepower needed to achieve the lower speed offsets the lower engine efficiency. Thus the most efficient steady speed is a tradeoff between good engine efficiency and lower power needed to maintain a lower cruising speed.
Again, it’s not the engine lowest fuel consumption we are seeking, The engine is in a car moving down the highway against rolling resistance and wind resistance.
pulse and glide is done at low speeds to minimize wind resistance.
In a given car, the best engine efficiency may be when the car is moving at 75mph, but the best mpg is at a much lower speed. My own experience is I can get 26mpg at 70 and 30mpg at 50mph. I just have those two points, but I am pretty sure I can increase mileage by driving even slower.
Yea. Exactly what I was trying to say. If engines had a flat efficiency curve, that car that got 26 mpg at 70 would get close to 50 mpg at 50 mph.