Mpg Vs. Mph

for most cars the most efficient speed is (in top gear) 42-62 mph, the peak efficiency is between 53-57mph, its really stupid tho since if you drive that slow on the motorways ull prolly get in an accident and if you went that fast on normal roads ud get a ticket

What is the difference between 'most efficient speed' and 'peak efficiency'?

"Peak efficiency" is what you would be achieving at the "most efficient speed." The Most Efficient Speed would be the one where you make the best compromise between fuel utilization and getting where you're going in a reasonable amount of time. Finding a particular automobile's Most Efficient Speed would most likely take some experimentation, but I know that my 2003 Corolla LE automatic, when cruising at a steady 62 MPG with the cruise control set, will achieve in excess of 44 MPG on the highway. It is actually possible to cruise at this speed on the open road, but you'll be permanently locked into the right lane, except when encountering the occasional 18-wheeler trundling upgrade or other slower-moving vehicles. However, in the heavily-trafficked high-speed corridors through major cities, such as I-95 through Philadelphia -- which I must condend with -- going 62 could get you killed.

Lower speeds, like a consistently-held 55 MPH, could squeeze another MPG or so out of the tank, but at that speed, you get a perceptable increase in the amount of time your trip is taking -- which is why the "Double Nickle" National Speed Limit was so unpopular. If they made it 62 MPH (100 kph) there would have been much less antagonism, and probably much greater compliance.

For a 95 corolla, what would these peak efficiency and most efficient speed be?

thx

Perhaps the question could be re-phrased to read:

Where time is not important, at what speed can we get from point A to point Z while consuming the least amount of gasoline?

At higher speeds, it is wind and tire resistance that cause inefficiencies. At lower speeds, it is the mechanical resistance in the engine and drive train that causes inefficiencies.

If we plotted a curve of mpg versus mph, we would see that it rises with speed, plateaus out, and then drops off.

The best speed on the curve is just before the plot begins to drop off after the plateau.

There are a number of cars on the road with fuel flow sensors that measure fuel flow in gallons per hour and their computers display miles per gallon in real time. These drivers surely know at what speed their mpg is at its peak.

Since the computer on the Corolla knows the time duration of the fuel injection, in theory, it should be able to estimate fuel flow in gallons per hour without actually having a fuel flow sensor. Fuel flow sensors are not that accurate for low fuel flows such as those found on these relatively small engines like our 1800cc motors.

My guess is the optimum speed is closer to 55 mph than 65 mph.

That is why speed limits were reduced to 55 in the seventies.

In theory, (ignoring terrain, weather, road conditions, traffic laws, safe driving practices, and common courtesy - which is actually very uncommon) at what speed would the current generation Corolla be most fuel efficient?

0 mph

 

 

I read this recently somewhere on the net, and the numbers are vey close, but my memory may have faded a bit.

The slower you drive in top gear, without lugging the engine will get you the best mpg, say...30-40 mph.

Rolling and wind resistance are the main forces you are trying to overcome. Wind resistance becomes the greater force over rolling resistance once you get up to around around 40-50 mph.

The faster you drive the greater the wind resistance becomes. After about 50 mph, the resistence increases more and more for each additional mph (exponentially).

This example is pretty close to true....you need 5 hp to drive a steady 30 mph, and 30 hp to drive a steday 60 mph (on level ground, no head wind..it's just physics/laws of nature). hp is a function of burning fuel/combustion.

There are efficiencies at play, but generally....the more power you have to make...the more fuel you have to burn....just a law of nature...

>>>

Here was some of the stuff..can't find it all

Wind and Rolling Resistance

Wind Resistance. Wind resistance is a not-so-funny thing. What makes it so devilish is that it actually gets greater the faster you travel. It is almost like the wind is penalizing those who are the fastest the most. Not only does it increase with speed, but it increases exponentially! So if you double your speed, your wind resistance will increase four times (two squared). If you triple your speed, your resistance will go up by nine-fold (three squared). To overcome the wind resistance the cyclist must generate power equal to the wind resistance times the velocity. Therefore, the power needed is the cube of the change in velocity. So if you double your speed, you will need to increase your power by eight times (two cubed).

At around 20 mph, wind resistance makes up 90% of the total resistance. At 25 mph, it makes up almost 100%. As a result, streamlining is extremely important.

Rolling Resistance. On the other hand, the resistance incurred from the tire rolling on the ground is constant at all speeds. Thank god! Otherwise, we would never get above 20 mph! At around 20 mph it makes up only 10% of the total resistance and drops off to almost 0% by 25 mph.

Rolling resistance is made up of several factors, however. These include tire pressure, tread, wheel diameter, and weight. Higher body or bike weight, smaller wheel diameter, less air pressure, and a larger tread all increase rolling resistance and make it harder for you to move.

ray...only if the car is not running...

otherwise 0 mph is the LEAST efficient....

In theory, (ignoring terrain, weather, road conditions, traffic laws, safe driving practices, and common courtesy - which is actually very uncommon) at what speed would the current generation Corolla be most fuel efficient?

0 mph

 

This coming week I'll be doing just as you suggest as I am starting a new job about 2 miles from home. If weather allows I'll be back on a bicycle after 7 years of driving to work. Maybe I can loose a few of the pounds I put on since then.

 

 

The mileage ratings from the EPA are based on tests created in the days of the 55 speed limit. Unfortunately, cars are designed to get optimal mileage under those tests---not under real world conditions.

All vehicles reach peak effeciency around the same speed. About 45-60mph. THis ends up being the best compromise between speed of travel and consumption of fuel. Under 45, your're often going too slow to use the top gear AND have a high enough RPM to get good effecency out of the engine. In most engines, under 2000 RPM, the engine's production of torque drops off, this directly corelates to how much pwoer is produced for each unit of fuel consumed.

IN Europe, they measure effeciency in a more logical manner. You come ot the same conclusion... but it's nice because yo uare always trying to achieve the lowest number not the highest. They use Liters consumed per 100km. This is the more typical format to use in science.

I drove a Peugot 307 with a 2.0L Turbo Diesel and 5 speed manual. It achieved an average of 6.5L/100km. And had the lowest consumption at around 70-100 kph. Or as mentioned above, Under 70kph... the engine fell under 2000RPM in 5th gear. 2000RPM is where the turbocharger begins to deliver more power than it consumes and therefore the engine makes more torque and is subsequently more effecient.

SO bottom line, lugging the engine is not always the best practice on a smaller displacement engine, especially if it has a turbochrger.

Oh and if you think a Diesel engien is a good solution. Think again. The air quality o nthe freeway in Europe is very bad. They are terribly underwpoered for use in the US... and only make good useable torque for quick acceleration in a VERY narrow RPM range. This particular engine was good only between 2000-3500RPM. It ran like a bat out of hell in that range. Under that it falls flat on it's face, and above it's it runs out of steam and the power falls off fast. You need very short gearing and a close ratio gearbox to make good use of the motor.