Hypermile Club 
Helping to Drive Fuel Efficiency!               
Resources
The Speed Factor: Each car's fuel economy varies with the speed of the car. Below are three graphs - the first from experiments run with a Scangauge II in a 2007 Yaris by a Hypermile Club member. The second is taken from the EPA-run website fueleconomy.gov for a generic vehicle. The third is from the DOE showing multiple cars. The big takeaways are: 1) driving too fast or too slow will dramatically affect your fuel economy and 2) finding the fuel economy curve for your car is the first step towards hypermiling.



(source: G. Morrison)

    Generic Vehicle Fuel Economy

(source: fueleconomy.gov)


(source: Transportation Energy Data Book, ORNL, 28th Ed., Table 4.28)

Vehicle Age Factor:
The age of car will probably affect your fuel economy. The graph below from an EPA-sponsored study shows how fuel economy changes with the age of a vehicle. Note, this study was performed in 1981 -- thus today's cars likely have a flatter curve as vehicle technology has improved.


(source: EPA fuel economy study, 1981)

Other Hypermiling Tips:

  • Drive as if you don't have brakes. Stopping and starting kills gas mileage. Increase the amount of distance between you and other vehicles, don't race to red lights or traffic obstructions. Coast as much as possible. On newer cars (Manual Transmission) if the car is in gear and your foot is off the accelerator, the injectors shut off completely, creating FREE mileage at the cost of some minor engine braking. Engaging the clutch and/or putting the car in neutral causes the car to idle, using up gas as opposed to using none. Coast as often as possible, because if you're smart enough with your coasting, your acceleration won't even cause a hiccup in your cruising mpg.
  • You should keep your foot ready to use the brake so that if you do need to stop suddenly you can react quickly. If using this technique at night, make sure you have clean headlights and that they are working properly. Obviously, you still need to obey all traffic laws and common sense. For example, you wouldn't roll through stop signs; the increased risk of a car accident and/or traffic ticket is not worth a few extra cents saved in fuel costs.
  • Be gentle with the accelerator. When you slam down on the gas pedal, it pushes more fuel into the engine, making it run faster (and lowering the fuel economy and increasing your output of pollutants). Push the pedal down slowly, and lift it up as soon as you know you're going to need to stop (when you see a red light, a stop sign, or brake lights from the car ahead of you) so that you can coast the rest of the way. You should never need to push down the pedal by more than an inch (2.5cm).[2] Some cars are even being designed with pedals that "push back" when you're accelerating too aggressively![3]
  • If you have a choice between various routes, go for the one with the least number of stops; country roads are good because you don't have to stop (and go) as much and you don't have to accelerate/brake to get on/off (like with the highway).
  • Fuel efficient vehicles actually generate better gas mileage when a "brisk" acceleration method is used. Acceleration makes for terrible mileage, so get the acceleration out of the way so that you can cruise (excellent mileage!) Slow acceleration will yield less mileage on efficient cars.
    Avoiding stopping on an incline heading upwards. Starting from a dead stop on a hill is the worst scenario in terms of fuel economy. Stop at the top of the hill, or stop before you climb the hill (if it's safe).
  • When coming down a hill and faced with a red light at the bottom (where it levels out), try to stop well before the light so that you can use the remaining downhill slope to your advantage when you need to move again.
  • Avoid idling. Turning off the engine when you stop for more than one minute can improve fuel efficiency by 19%.[4] In cold weather, letting your car idle to warm up reduces fuel economy and creates additional pollution; all you need to do is drive gently for 5-10 minutes[5] and if you're following the previous two steps, you're going to be driving gently all the way anyway.
  • If you have multiple stops in one trip, plan it so that you go to your furthest destination first and make the rest of your stops on your way back. By taking your longest drive at the beginning, you give the car enough time to warm up for the remainder of the trip; if you took the short trips first, your car would take longer to warm up (because of the brevity of each trip). Since engines do not operate efficiently until they are warm, taking your longest drive first increases fuel efficiency.
  • Stopping and starting kills gas mileage. Increase the amount of distance between you and other vehicles, don't race to red lights or traffic obstructions. Coast as much as possible. On newer cars (Manual Transmission) if the car is in gear and your foot is off the accelerator, the injectors shut off completely, creating FREE mileage at the cost of some minor engine braking. Engaging the clutch and/or putting the car in neutral causes the car to idle, using up gas as opposed to using none. Coast as often as possible, because if you're smart enough with your coasting, your acceleration won't even cause a hiccup in your cruising mpg.

 Other Important Thoughts:

  • Go slower up hills, and faster downhill. Going uphill slower allows you to use your momentum to help keep your car from using extra gas to get up the hill. If you plan for a hill by going faster you'll get further up the hill before you need to use extra gas. While going downhill you can go faster using less gas, as such don't lay off the pedal completely, use it until you're going a little faster than normal. If you combine the two in areas with small hills you'll see much higher mileage.
  • Minimize the engine load. Generally, it's better for your fuel economy if you maintain a steady speed, which is why using cruise control and driving at or below the speed limit is an important part of hypermiling. If you're driving on a hill or any kind of varied terrain, however, you need to consider how much work the engine is doing. Sometimes, a steady speed means unsteady strain on your engine, which lowers fuel economy. Let's say you're approaching a hill. When you go up the hill, you should slow down, or else your engine will have to do extra work to maintain your previous speed. Practice with caution as you may annoy other drivers.
  • Park for easy departure. Instead of searching for the perfect spot close to an entrance (which will involve stop and go driving, especially with pedestrians involved and other drivers pulling in or out of their spots) pull into a spot that's further away from the entrance. Look for the parking spot with the highest elevation and park face-out so that when you start the car and the engine is cold (at the lowest efficiency) you can use gravity in your favor without having to spin your car around.
  • Check tire pressure regularly. If the tires are incorrectly inflated, then there will be excess drag, or not enough surface contact with the road. The car therefore suffers a drop in efficiency. According to the Dept of Transportation, every 8 psi a vehicle's tires are underinflated yields a 5% drop in fuel economy.
  • Reduce the junk in the trunk. The more weight you're carrying, the more the engine and drive-train have to work. Removing all of that unused junk in the trunk increases efficiency.
  • In a hybrid, Pulse and Glide. If you own a hybrid car, you can increase your mileage by learning to pulse and glide. Pulse and glide is a technique that can dramatically increase your mileage, but is best when you are on a road where there are few other people around. "Pulse" or accelerate up to a speed that is the higher end of a range of speeds that are appropriate. Do this using one of the sweet spots for mileage/power ratio on your car. For the prius these spots are ~15mpg and 25mpg, and correspond to times at which the gas engine is powering the car and charging the battery. Glide between acceleration, but use the accelerator to provide electric assist. This requires knowing how hard to push and in which circumstances, but is very easy to see on the consumption screen. Get used to the maximum electric assist you can use and you'll go further between pulses, further increasing your mileage.
How to Get Into the Hypermile Club
1) Go to the EPA website on fuel economy: www.fueleconomy.gov
2) Click on "Find and Compare Cars..." in the upper left
3) Find the year and make of your vehicle
4) Click on "Compare to Official EPA Window Sticker" on the right side of the screen
5) Use the "Old Hwy" Fuel Economy (which should be the highest number on the sticker unless you have a Prius)
6) Calculate your fuel economy on one tank of gas by dividing miles driven by fuel purchased

Does the amount of gas you pump vary from gas station to gas station?

The answer is... probably not. The simple mechanical design of the fuel dispensers ensures that fuel stops flowing when the level of the fuel reaches the nozzle. 


Here's how it works... Almost all newer fuel dispensers work via a venturi pump which is located in the handle of the dispenser. There is a small line at the tip of the nozzle that sucks air back into the handle from the empty fuel tank. Once the level of the gas tank rises to the nozzle, that line stops sucking air and tries to suck liquid fuel. The extra vacuum needed to move the desner fluid means the pressure drops inside the small return line and subsequently flips a mechanical latch that stops fuel from flowing.


Do frequent oil changes contribute to GHG emissions more than they save?

This question was recently posed by Club Vice President Tai Stillwater...  Perhaps a new graduate student wants to answer it?


How much has fuel economy changed in the past 3 decades?

Not much. The Obama Administration will change that starting in 2011 but the graph below shows the lax federal standards. Fuel economy was better in the US in 1988 than in 2007!!!


(Source: Transportation Energy Data Book, ORNL, 28th Ed., Table 4.20)


How much does tire pressure matter?

Most people do not regularly check their tire pressure. However, one study shows that the average American car's tire is 4-8 psi under-inflated. How much does that affect fuel economy? The EPA estimates that there is a 0.3% decrease for every 1 psi under-inflated. Thus, if all four of your tires are 8 psi under-inflated, you're giving up 2.4% of your fuel to your tires! 


The design of a tire can also affect fuel economy (often called rolling resistance). There is no federal law that regulates tire design or that requires rolling resistance labeling on tires. If consumers are aware that Tire A may save them money/gas over Tire B, they may be willing to spend the extra $40.  A widely-cited study on the matter was conducted by the Transportation Research Board in 2006 (http://www.energy.ca.gov/2006publications/TRB-1000-2006-001/TRB-1000-2006-001.PDF).


What's the most accurate way to measure fuel economy? 

A company out of Arizona, Linear Logic LLC, makes devices called Scangauge IIs which provide instantaneous fuel economy readouts. The devices hook into a vehicle's OBD II connector and receive speed and fuel data from the vehicle's digital sensors.


Which cars are exempt from CAFE standards?

Due to a loophole in federal CAFE standards, any vehicle over 8500 lbs is exempt from the standard. When the CAFE standards were originally written, only large work trucks exceeded this weight threshold...  but now, several mass-market vehicles do.

  • Chevy Avalanche 2500 series

  • Dodge Ram 2500 series

  • Ford F-250/350 series

  • GMC Sierra series

  • Ford Excursion

  • GMC Yukon

  • Hummer H-1

Copyright . Geoff Morrison. All rights reserved.
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