Has anyone ever done any research as to the speed at which a vehicle gets its optimum gas mileage?
I seem to recall many, many years ago that someone said that it was about 35 mph–but that person didn’t have any sources.
It sounds like something some government agency with too much time on their hands would love to figure out.
Not that this is an answer, but I’d certainly have to say that whatever answer it is, it HAS to be different for each type of engine. Somehow I doubt that a Ferrari engine gets the best MPH at the same speed as the Geo Metro.
Whoops, make that MPG. I need to learn how to type…
It will vary depending on the engine’s torque and efficiency curves, the aerodynamic resistance of the vehicle, the rolling resistance, the gear ratios and gear friction loss involved. But, if you want the wild-ass guess of an ME who has had a couple IC Engine Grad classes, I would say for the average passenger car 30-40 mph is a good estimate. I do know that for one car I used to own (a FIAT X 1/9), a company in England did detailed research on what was the optimum speed for maximum gas mileage between about 30 and 100 mph. Their answer was 38-40. How’s that for a sample size of one?
I would agree with circa 40 mph. I was told in YD that the best speed was 64kmph, which is 40mph.
As for tires, I remember it being around 80kmph, or 50mph.
Anthracite, as an ICME, answer me this. Don’t IC engines have a BEP? Isn’t it somewhere around 2k RPM? It seems to me the optimum speed would be where you’re in high gear at BEP. Most cars I’ve driven , automatic and standard, seem to feel best at about 45 MPH, but maybe that’s just me.
I’m not an automotive engineer, nor do I play one on the internet, but it ‘seems’ logical that the best mpg for a specific car would be the slowest speed, (to minimize drag), at which it will stay in its highest gear, (without ‘lugging’ the engine.) This speed would vary greatly from one type of car to another, but should be in the 35-50 mph range, I’d think.
What do you want for Christmas, Crow? I want to decide who lives and who dies!
Air resistance increases as the square of the speed after about 35 MPH (it’s more linear till then), which lends weight to the 40 MPG guesses. KarmaComa: was the 50 MPH optimal tire speed due to centrifugal tire distortion (or whatever the proper term is) reducing the rolling resistance?
I remember reading years ago about a “race” in which all the contestants had equal fuel and the winner was whoever traveled furthest with it. Unfortunately, the vehicles all looked like shrouded recumbant bikes, so the information (if I ever find it again) may not directly relate.
Sure, I’m all for moderation – as long as it’s not excessive.
Whoa - I’m no expert on IC engines - I did have a couple classes in grad school, like I mentioned (I am an expert at coal power plants, however…). Anyways, looking in my “Haywood” and “Fayette Taylor” books on IC engines, I can’t find an exact definition of the abbreviation “BEP”. Assuming you are referring to a “Best Efficiency Point” or something similar, I agree with your observations. I do know my old X 1/9’s best efficiency was about 3300 rpm for the 1.3 L engine, 2800 for the 1.5 L (a lot to do with the very large bore/stroke ratio). My current car (98 Mustang GT 4.6L) is supposed to be most efficient at about 1750 rpm.
I recall also that BMW was working on a series of engines in the 1980’s (I think they were called the “Eta” series) that were supposed to develop their maximum efficiency at very low RPM’s - like about 1000-1500, to try and get really low brake specific fuel consumptions. Last I heard they abandoned it in the late 1980’s as their focus shifted towards performance.
Another thing about your observation - I also believe that my cars simply “feel” better at their maximum efficiency point.
Not really related, but I had a Porsche 911SC that “felt” the best around 4,500 RPM. It was near there that it seemed to accellerate best. I don’t remember what speed that was (I usually drove RPM unless there was a CHP around), but it might have been about 90 mph. Average fuel economy in it was about 22-23 mph in L.A. traffic, freeways, roads, etc.
The Cherokee (Jeep, not Piper ;)) will get about 22 mpg the way I drive it, but then I get into traffic and it can drop to 18 or less. Driving in-town seriously reduces the mileage due to the accelleration/decelleration cycles. I wish I’d opted for the standard transmission. I’ve never liked automatic.
The Yamaha, with its 600cc engine likes about 4,500 rpm.
Seems to me I read somewhere (Motorcyclist or Sport Rider) that engines have the best torque vs. HP at a little over 5,000 RPM. There was an equation to explain it, but I no longer have the magazine.
To get best MPG for your specific car (in real time), install a manifold vacuum gauge. You’re looking for the highest vacuum at a constant speed in your highest gear.
This thread kinda answers your question…