Correct Me If I'm Wrong...Increasing MPG Easily

[parimento1]

Wouldn't an easy way to get more MPG out of cars be to just raise the speed limit? I mean if you are traveling at 90mph instead of 50mph, aren't you naturally getting more MILES out of a gallon of gas by travelling faster, and getting to your destination faster?

 

[Quattro Pete]

LOL! Of course not. Look at it in terms of miles traveled. Say, you have to travel 100 miles. A) while doing 90 mph Say you get 25 mpg at that speed. So it takes you 4 gallons to travel 100 miles (100/25). B) while doing 50 mph Say you get 33 mpg at that speed. So it takes you 3 gallons to travel 100 miles (100/33). Fuel consumption in MPG takes time out of the equation. All you need is to know miles and gallons. And unfortunately the faster you go, the fewer miles you can travel on that same gallon of gas.

 

[parimento1]

yes, that is true, but you are getting to your destination alot quicker, and thereby shutting off your car quicker. Your engine is running for less time by driving faster. So instead of it taking you an hour to get home, it takes you a half hour and allows you to shut off your engine a half hour ahead of time and save gas.

 

[jigen]

A lot also has to do with the amount of gears you have and gear ratio of the car. Some cars peak MPG maybe be at 40mph, others 65mph.

 

[Quattro Pete]

 Originally Posted By: parimento1

yes, that is true, but you are getting to your destination alot qukcker, and thereby shutting off your car quicker. Your engine is running for less time by driving faster. So instead of it taking you an hour to get home, it takes you a half hour, and lets your engine be off for 1/2 hour.

It doesn't matter. Time is not a factor. Distance is a factor, and distance is the same in both cases (100 miles). In case (A) you burned 4 gallons. In case (B) you burned 3 gallons of gas. So, which one resulted in less gas consumed?

 

[javacontour]

No because drag, windresistance, whatever you want to call it increases as a square relative to speed. So when you double your speed from 30 to 60, wind resistance quadruples. So at some point, fuel economy has to drop as you go faster.

 

[Kestas]

paramiento, you logic is entertaining to us. One benefit to driving faster is that your time on the road is shortened. If everybody drove faster without traveling more miles there'd be fewer cars on the roads at any given time.

 

[parimento1]

It would be interesting to adjust it for time as well, I guess thats what gallons/hr is for. Like if I went on a 1000 mile road trip driving 30 mph instead of 90 mph, I wonder which would use more gas overall.

 

[Quattro Pete]

 Originally Posted By: parimento1

yes, that is true, but you are getting to your destination alot quicker, and thereby shutting off your car quicker. Your engine is running for less time by driving faster. So instead of it taking you an hour to get home, it takes you a half hour and allows you to shut off your engine a half hour ahead of time and save gas.

If you want to look at it from a time perspective, then you would need to measure your fuel consumption in gallons per hour. At 50 mph, the car may consume 2 gallons per hour. At 90 mph, the same car may consume 5 gallons per hour. So, even though you got to your destination in half the time, during that half you burned more than twice the amount of fuel. So you are worse off in the end.

 

[javacontour]

 Originally Posted By: parimento1

yes, that is true, but you are getting to your destination alot quicker, and thereby shutting off your car quicker. Your engine is running for less time by driving faster. So instead of it taking you an hour to get home, it takes you a half hour and allows you to shut off your engine a half hour ahead of time and save gas.

OK, so let's go with some easy numbers. If at 50MPH your get 25MPG. To travel 100 miles, you will burn 4 gallons of fuel, or 2 gallons/hour. Just to break even with respect to gallons/hour, you would have to get 50MPG at 100MPH in order to maintain the 2 gallon/hour fuel consumption rate. I don't know of any vehicles that get 25MPG at 50MPH and 50MPG at 100MPH. If I did, I might buy one. Chances are more likely that you would get 25MPG at 50MPH and something in the range of 15-20MPG at 100MPH. Let's go with the 20MPG. You would burn 5 gallons of fuel to go 100 miles at 100MPH, while you would burn 4 gallons of fuel to go 100 miles at 50MPH. I can't see many cases where going much over 60MPH is going to net better fuel economy.

 

[parimento1]

Yea Quattro Pete, thats excatly what I was getting at, is it worth it? OR do you burn so much by just going faster that it negates any savings by letting the engine be off.

 

[javacontour]

 Originally Posted By: Kestas

paramiento, you logic is entertaining to us. One benefit to driving faster is that your time on the road is shortened. If everybody drove faster without traveling more miles there'd be fewer cars on the roads at any given time.

I have laughing used the Mr Miagi approach to driving. The way to avoid an accident is "No be there." So when traveling at a higher rate of speed, I spend less time at any given "there" thereby reducing my exposure to an accident should it happen at any one of the infinite numbers of theres along my route. Therefore, the faster I drive, the less exposure I have to an accident.

 

[2sld3kf2bt]

At higher speed your car has to fight more wind resistance and your engine has to run at a higher rpm, which means you have to burn more gas. Most cars peak MPG is in the 55-60 mph range. My engine runs at 2000 rpm at 70, and 2500 rpm at 80, roughly. the difference is 25% more rpm's, so 25% more fuel consumption, yet you are only driving 14% faster. Speed limits are just set low to increase revenues through tickets, but I guess that is for another thread.

 

[Mr Nice]

Aero Drag will kill you gas mileage. Java, You are 10000% correct that driving slightly faster and NOT allowing yourself to get stuck in a 'moving traffic jam' will reduce your chances of an accident.

 

[bepperb]

"No because drag, windresistance, whatever you want to call it increases as a square relative to speed" That's the rub. And because of it, eventually all vehicles get worse mileage as they go faster (once the overcome the overhead of keeping AC, Alternator, PS pump.. etc running. This eventually comes pretty early on. That's why there's always talk of the national 55mph speed limit. Or, to put it more simply, the reason you're travelling faster is because you pushed the gas pedal down further, right? You're not taking that into your "I got there faster = used less gas" equation.

 

[Trajan]

 Originally Posted By: parimento1

Wouldn't an easy way to get more MPG out of cars be to just raise the speed limit? I mean if you are traveling at 90mph instead of 50mph, aren't you naturally getting more MILES out of a gallon of gas by travelling faster, and getting to your destination faster?

No, it wouldn't. Gearing, aerodynamics, lots of things. A Bugatti Veyron, for example, gets less than 10mpg, in US units, in combined driving. Now, if you decide to run it flat out in your scenario, 254mph, sure, you get there fast. However, you'll empty the 26 gallon tank in 12 minutes. Just as well, as the tires would melt in about 15 or so. The best milage I've ever gotten, at a steady 55, with the top up,and just the vents on, was, the car told me, was 44mpg. Do it on paper, it was more like 38 or so. No way would it get better doing 100. Besides, the huge speeding ticket you'd get for doing 90 will more than wipe out any savings you think you'll get.

 

[parimento1]

ah java countor, very nice and simple explanation!

 

[PeteTheFarmer]

"I'm not speeding officer, I'm only trying to save gas!"

 

[Quattro Pete]

 Originally Posted By: parimento1

It would be interesting to adjust it for time as well, I guess thats what gallons/hr is for. Like if I went on a 1000 mile road trip driving 30 mph instead of 90 mph, I wonder which would use more gas overall.

You don't have to wonder. I can guarantee you that you'll burn less gass when driving 30 mph vs 90 mph, as long as you stay in the tallest gear. You can always convert from MPG to gallons/hr. Still, the end result (in terms of gas consumed) will be the same. Back to my previous example: -------------- (A) 90 mph - and you get 25 MPG at that speed. 25 MPG = 3.6 gallons/hr (90/25) at 90 mph, it'll take you 11.1 hours to cover 1000 miles, so you'll burn a total of 40 gallons (3.6x11.1) -------------- (B) 50 mph - and you get 33 MPG at that speed. 33 MPG = 1.5 gallons/hr (50/33) at 50 mph, it'll take you 20 hours to cover 1000 miles, so you'll burn a total of 30 gallons (1.5x20)

 

[Pablo]

Earth to brake fluid in the crankcase. Come in. This is Earth.