after reading the post about max airplane speed, I started thinking…“if the airline companies know how fast a plane should fly to achieve maximum time/fuel efficiency, do the automobile companies have the same data?”
so… do they? Can I get in contact with ford to find out how fast I should drive my Mustang on the freeway to achieve maximum fuel efficiency, or do they leave that up to the consumer to find out? That would be a really handy statistic to have for my 14 hour road trips.
Keep in mind there are a lot of factors at stake here.
IMO Keeping your tires properly inflated is probably the best thing the average car owner can do in this department.
#3. The value of time. Sure, I can achieve a higher MPG ratio if I drive like a tool@55 on major highway, but in the real world you get there a lot quicker by wasting a litle fuel efficiency at the expense of time efficiency.
Things like keeping the windows rolled up, having a clean air filter and clean injectors, and other stuff i can’t remember but saw on tv a few months ago improve fuel efficiency also.
Internal combustion engines are at their most effecient when they are either running at max throttle, or shut off. World record fuel effeciency contests use a technique called burn and coast.
First, inflate your tires to about 50 psi. Then, start your mustang. Put it in gear and floor it up to about 35 mph. Take it out of gear and shut off the engine. Let the car coast down to a little less than 10 mph. Turn on the ignition, but don’t turn over the engine. Put it in first and let out the clutch. When the engine starts up again, floor it back up to 35 mph.
They had a stock geo metro get over 500mpg with this technique. Their custom built cars were getting almost 3000 mpg, I believe.
For constant speeds, the optimum effeciency used to be about 45mph at sea level. With today’s aerodynamics and modern engines, that should be a little above 50mph. Above that the effeciency goes down exponentially. Above 75mph is where the real damage starts to happen. I averaged about 105mph for half a tank through the desert and I was about 5mpg below EPA, but at 80mph, I was a little above EPA. Don’t think I’ve ever driven 55 for more than a block, so can’t really compare.
I doubt the car companies have that info handy. Like the other posts have said, it varies but usually ranges from about 45-55 mph.
The next 14 hour road trip you take you can find out your most efficient highway speed by making mpg calculations every half tank of gas or so. I have done this with my car, by taking the mpg at 65, 70, 75 mph, etc. Using your mpg findings you can figure out which speed you want to drive by seeing how much gas you’re willing to sacrifice by driving fast. Does that make sense? It’s late and I’m pretty tired…
Here’s some interesting info about EPA calculations. It’s from an internal (but not confidential) document so I can’t link to it:
emphasis mine
The same paper also says that real-world tests indicate that most vehicles get worse mileage than the EPA estimate would indicate, and get substantially better mileage than EPA estimates estimate.
I have to believe that we have actual fuel consumption data available for everything. We’re completely Six-Sigma so we measure everything. I have to assume that the results just aren’t available on our intranet. We also have a crappy search engine that doesn’t understand simple boolean queries, so I just may not be searching right, either.
When the industry added the required sealed fuel tanks and vapor recovery canisters, real-life calculations became impossibly vague. Carmakers had to add internal baffles to the tanks to insure enough airspace for heat expansion. You can fill your tank 'til the nozzle shuts off, then, by patience and rocking the car, dribble in another 3-5 gallons of fuel. You never really know how full your tank is. Thus, your tank-by-tank calculations may be off by a few mpg for no apparent reason.
The internal baffles don’t ensure air space for internal expansion; they prevent the fuel from sloshing around too much when the level is low. That could cause the pump to run dry, which can stall the car and shorten the lifespan of the pump. I had a Bonneville that was notorious for stalling when taking a cloverleaf a little too fast on a near-empty tank. I had to replace the fuel pump eventually, too (not saying they’re related, but I don’t doubt it). The Taurus/Sable has a baffle like this – it’s a zig-zag bracket with holes in it that runs along the length of the tank. It’s only welded to the top half of the tank.
The Taurus is also a good example of a car that you don’t want to overfill or top off too much beyond the gas station’s auto pump shutoff. Doing so can flood the carbon cannister with liquid gas (it’s for vapor recovery). Once flooded, though, you can have a really hard time putting in more than a half a tank!
Most tanks don’t have baffles, though. They have a cup that surrounds the fuel pump that acts as a resevoir so that taking a curve as mentioned above doesn’t starve the fuel pump. The Mustang is exactly this way.
Additionally, some tanks don’t have baffles or resevoirs, or they have resevoirs in the diesel-version but not gasoline (or the other way around). The super-duty Ford trucks come to mind as being this way. I guess you’re not going to race those too much.
Finally there aren’t currently a whole lot of requirements for “sealed” tanks. All plastic tanks (the majority of tanks in newer vehicles) seep some vapor components of their fuel. This means they pollute when turned off and parked! The don’t leak liquid, though, which is the current industry standard. The new, evolving standard for some new models though is PZEV, or Partially Zero Emission Vehicles. The fuel system is completely sealed. Tanks are good old fashioned steel, and guaranteed to pass abolutely no vapor components. These are truly sealed tanks. Look for 'em on the Focus and Escape.