It is natural that people want to conserve their money on
gas because it rapidly tends to add up. The
average person always pays attention to gas prices when choosing a specific gas
station to save the maximum amount of money possible. But do they also know
ways they can save money WHILE driving? The answer to this is most likely no!
There actually is an optimal way to operate your car to maximize your gas
conservation, thus, increasing your money saved on gas.
Now lets assume you’re driving your vehicle a long distance
from point one point to another with no stops and a constant speed. The
question then arises; what is the maximized fuel-efficient speed of which to
drive at? First we have to look at how much power it takes to push your car
down the road from start to finish.
road load power = av
+ bv2 + cv3
“V represents the velocity of the car, and the letters a, b and c
represent three different variables:
The a represents mostly from the rolling resistance
of the tires, and friction in the car's components, like drag from the brake
pads, or friction in the wheel bearings.
The b also represents friction in components, and
from the rolling resistance in the tires. But it also comes from the power used
by the various pumps in the car.
The c represents mostly from things that affect
aerodynamic drag like the frontal area, drag coefficient and density of the
air.”
Of course these constants vary in different places and for
different cars. From the equation, if you were to double your velocity (MPH)
then you greatly increase the amount of power required to move your vehicle.
You would think going at 1 mph would save you the most gas but this is not the
case. Traveling at 0 mph is actually the worst possible case of gas
conservation. The engine consumes gas even when idle to keep
the cylinders moving and the various fans, pumps and generators running. Now,
if you were to increase your velocity to 1 mph, you slightly increase fuel
consumption but you significantly increase the mileage. Now at 3 mph, you
triple your mileage but only increase fuel slightly! If you keep following this
trend, you end up at the most efficient speed for your vehicle.
If you were to assume, a, b, and c, were all equal to 1 then from the table above, you can see a dramatic increase of power needed as you go up only 1 mph. Since the equation is different for each car and the environment, there is a known range of optimal gas conservation. This math of this equation usually falls between 40-60 mph for all cars. Car usually to be bigger and heavier find the right velocity usually in the lower 40’s, while lighter and smaller cars usually fall around high 50’s. The main factors that contribute to this range is the cars coefficient of drag (how aerodynamic a car is), the frontal area (size of the car), and the total weight of the car. Cars able to drive in their recommended range will maximize their gas mileage.
Now that we know cars have an optimal velocity to maximize
their gas mileage, let us apply this to how much money you’re actually saving.
Lets be honest, most people won’t be driving under their maximized gas mileage
speed. If you’re not going to drive at the maximized speed, you will most
likely be driving over your recommended speed. But, is the time you save, worth
the money you pay? We are going to use a Subaru Outback as an example car.
A Subaru Outback is rated at 29 MPG (miles per gallon)
driving straight without stops. The
graph above displays the fuel efficiency varying with speed. We are given the
graph above from data of over 2000 hours of driving with many 2009-2013 Subaru
Outbacks. As you can see, the maximized speed of the Subaru Outback is around
40-50 mph.
Referring back to the question, “Is the time you save, worth
the money you pay?” lets look at a group of drivers who drove at an average of
70 and 55 mph versus a group who drove at an average of 65 mph.
The averages and graph shows that the people going an average of 70 mph (orange) pay an additional $46 a month for only saving 4 minutes per hour. We can see that the people going at an average of 55 mph (blue) save $13 a month and increase there travel time by 10 minutes and hour. The black line indicates the 65 mph average driver. Is the cost of going only 5 mph more to save about 4 minutes worth the additional $550+ dollars per year?
Lastly, everyone wonders about whether windows down or the
air conditioner on is more gas conservative. The real answer is… there is no
real answer. I know it’s disappointing but there definitely common trends. Car
and Driver researched the effect of the AC on fuel efficiency at different
speeds of your car with the windows closed. They found reduced efficiency of
about 15% at 35 mph, about 9% at 55 mph, and then about 6.5% at 75 mph. They
found this to be because the faster your car is going; the harder the AC has to
work to provide you with cool air. Mythbusters also attempted to break the myth
and concluded that the most effective way to conserve gas is to use air
conditioner at about 40+ mph speeds and use windows open when you’re driving in
areas under 40 mph with stops. This is because the air drag force created at
high speeds through your windows causes your car to put more energy into moving
the car the correct speed. Closing your windows at high speeds makes your car
more aerodynamic and helps you to save gas with your air conditioner. Of course
if you were really stubborn with money, you could just never use an air
conditioner and never open your windows!
Bibliography:
http://www.caranddriver.com/features/gas-pains-mileage-myths-and-misconceptions-turn-off-your-air-conditioner-page-2
http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/question4771.htm
http://blog.automatic.com/cost-speeding-save-little-time-spend-lot-money/
http://www.primermagazine.com/2009/field-manual/know-it-all-what%E2%80%99s-better-for-fuel-economy-windows-rolled-down-or-air-conditioning
I thought Cade’s post was very interesting, and informative. I am definitely one of those average people who don’t know ways to save gas while I am driving. I found it interesting to note that forty-five miles per hour seemed to be the most fuel-efficient speed. I would have thought that it was faster, closer to sixty or seventy miles per hour. This post touched a little on how stops affected gas mileage, but it never looked at the effect that the distance between stops has on mileage. I would be interested in this because my neighborhood is loaded with stop signs, and all only have a block or two in between them. I enjoyed this blog post, and I learned a lot of useful stuff.
ReplyDeleteIt is neat to see a blog post that you can relate to a real life situation. I didn't know that the speed that you are traveling could affect the fuel efficiency of your vehicle. I was aware of some factors that could affect your gas efficiency like stopping and going or idling for too long, but I didn't realize that one speed was better than another speed. I liked how one of the graphs showed the money one speed saves compared to another one. Reading this post was eye opening to me and informative and it will allow me to use this and for me to benefit from the knowledge of this.
ReplyDeleteWhen I saw the title of this blog post I had no idea that this would have really anything to do with mathematics, I never really thought about it. The topic itself really relates to real life situations and relates to most people, which I also found very intriguing. All equations in this post seemed very simple but are actually pretty complicated. I also am a driver that does not pay attention to ways to save gas and I found this post extremely interesting and gave me new knowledge of how to improve my ways. I can really benefit from all of this information.
ReplyDeleteI really enjoyed reading this post. I generally do not think about saving money on gas while I am driving, only when I fill up my car. It is very interesting to me that driving at 70mph is so much more expensive than 65 mph. 13 dollars is a large amount for only 5 mph! I also thought it was neat the air conditioning is effective when you’re going faster. It makes pretty good logical sense and I’m more of a windows down girl anyway, so it was nice to know. I thought it was great to see the importance of math in an everyday scenario; I really enjoyed reading about math that was interesting and useful.
ReplyDeleteI believe that this post was very informative and interesting at the same time. Personally, I have not done anything in the past to save gas, but I find it very interesting that there is a way to mathematically save your money behind the wheel. I assumed that because there is city driving gas milage and highway driving gas milage that speed did affect one’s gas milage, but it was a nice to see a more specific explanation for this. Being able to see the graph made what Cade was writing about much easier to understand. All in all it was a great read.
ReplyDeleteWhat surprised me most about this blog post is there’s a massive difference in a very meniscal amount of speed, the $13 difference in just five miles per hour. It is very easy to see however that there is math involved in gas efficiency, since there is math in physics, and speed and velocity are main concepts of physics. I will have to take my speed into account the next time I am driving up to Denver for the day. And even though the air conditioning in my car is broken, I might just have to roll up the windows to save that money in gas each month.
ReplyDeleteWhen it comes to fuel efficiency in my car I would do anything I could to make sure I was getting the best miles per gallon. Having drove on a lot of lengthy road trips I can agree with the data talking about speed and miles per gallon, when I would drive my car at around 70 mph my cars gas mileage was way better than when I drove at 75 or 77 mile per hour. The part talking about the car being clean verse dirty or windows being open or having the air conditioning on effecting the fuel efficiency on Mythbusters was a neat point to be brought up since I’ve seen that episode of Mythbusters.
ReplyDeleteThe gas efficiency post was very informative and applies a lot of equations to a very important question that everyone asks themselves, how can I save more money? The road load power equation shows how power increases as you go faster. I find this information is also valuable and informative to drives because it could help reduce how fast everyone drives, resulting in fewer accidents and deaths a year. If people knew the information Cade provided in his post, people may think twice about driving so fast when they know that they save little time, but their cots go way up. This post has so many real life applicants and was a good read. I know it will change the way I look at driving in respect to my speed and the cleanliness of my car.
ReplyDeleteFirst of all, I really dig the inflection and enthusiasm throughout this post. Secondly, this post was honestly pretty eye-opening for me, as I tend to be a very fast driver (I've only gotten one ticket okay). I've always thought about it as maybe more efficient to go faster because then your car is already in continuous motion for longer which requires you to press down on the gas pedal less. I suppose it makes sense, however, that going faster is less gas efficient because it takes more fuel to propel the vehicle at a more rapid rate. I found this post very helpful and informative, and I am going to try to drive in a more efficient range from now on to both save money, and avoid more speeding tickets!
ReplyDeleteAs a fellow consumer of gas I found this blog post to be very informative. I always catch myself checking gas prices. I'm particularly irritated with them right now since they are so cheap, of course as soon as im not driving anymore they go down. I never knew that there was an equation for figuring out gas efficiency. One part of this in particular was the graph titled The Fastest Drivers Spend a Lot to Save a Little. I don't know about everyone else but I admit to being one of the faster drivers on the highway and it was interesting to see how much more money faster drivers spend on average.
ReplyDelete