Hypermilers are drivers who materially exceed EPA estimated mileage on their vehicles by modifying their driving habits.
- 1 Origin
- 2 General Techniques
- 3 Prius Mileage Tricks
- 4 Hypermilers' Favorite Cars
- 5 Articles
Hypermilers originated from hybrid driving clubs. As people began comparing mileage they noticed that certain driving techniques could greatly improve their mileage. With the aid of real time mileage displays, drivers were able to refine these driving techniques and greatly exceed the EPA rating for their vehicle.
There are many techniques that hypermilers use to optimize their MPG and many vary from car to car. Many hypermilers will put their talents to the test in hypermileage marathons. In these marathons, a route is determined and the drivers must optimize their driving over it until their tank of gas is consumed. Drivers have exceeded 120 MPG in current market vehicles in these marathons, achieving over 1300 miles on a tank of gas.
One of the best ways to optimize mileage (both hybrid and non-hybrid) is to keep up with vehicle maintenance. Key parameters to maintain are tire pressure, tire balance, and proper oil weight and level.
Pulse and Glide
This method is a trick that can be used with hybrids to minimize ICE waste. The idea is to optimize acceleration in order to reach the optimal threshold of the hybrid engine. At this point, some vehicles (when the accelerator is minimally pressed) will glide consuming no power from gas or electric motors.
Driving with Load
Avoid cruise control on hill climbs. Rather than maintaining a precise speed during a hill climb by adding progressively more acceleration, maintain a steady throttle position and allow the vehicle to slow slightly during the climb, then let gravity accelerate the car back up to speed on the descent. Doing so will keep the engine in a more efficient RPM on the climb, and reduce energy wasted braking on the descent at the same average speed. To avoid slowing too much on the climb, it may help to gain extra speed as you approach the climb.
Speed and Acceleration
Maintaining an efficient speed is also very effective in keeping mileage up. Avoiding jackrabbit starts and keeping speed at a minimum are all useful in this regard. When accelerating, the engine should be kept in the peak of the torque curve. A slow acceleration is less efficient.
Auto-stop and Forced Stop
All hybrids have the "auto-stop" feature which engages when the vehicle stops, avoiding waste. Maximizing use of auto-stop is critical because idling causes a severe drop in accumulated mileage (0 miles per gallon). In addition, many hypermilers will actually turn off their cars entirely or put them into neutral when going down hills or in other situations when momentum will carry the car on its own.
Air-conditioning loads (usually a few horsepower) can have a significant impact on mileage. (Relatively more so on hybrids with smaller engines, as it consumes up a greater percentage of the total engine power) When parking in the sun, a reflective visor across the windshield will reduce solar heating, if possible park with the windshield facing the sun. When initially entering a hot vehicle, open the doors for a moment to vent the hot air to escape, or drive with the windows down to clear the hot air before turning the AC on. Run in Recirc mode to keep the cool air in the vehicle longer. Cycling the AC on and off at key points also makes a difference: Turn the AC off during hill climbs and accelerations, run it at a moderate temperature setting on flat stretches, and run it on maximum setting during hill descents -- this will use energy that might otherwise be expended braking to cool the car down.
If ambient temperatures are not unreasonably hot, rolling the windows down is more efficient than AC at speeds below 50 miles per hour<ref>Mythbusters Episode </ref>. At slow speeds, drag from completely open windows is small compared to AC load. At faster speeds, open windows just slightly to allow circulation, without significant resistance from drag. On many vehicles, opening the driver's side window, and the rear window opposite the driver generate a swift air-current passing through the drivers seat.
Prius Mileage Tricks
(Transmission mode in B, speed zero)
Often you will pull up at a stop light that has just changed. In some suburban areas this may entail a wait of several minutes, as the lights cycle through various simultaneous or sequential left turns, cross traffic, pedestrians, etc. If the gasoline engine is running when you approached the stop it will take the better part of a minute before the computer recognizes the situation and shuts off the engine. There is a trick to getting the engine to shut off promptly. If you approached the stop in B (engine assist braking), you may then when stopped with the brake on, command D (drive) - the engine will stop immediately - at least in 2004 US versions.
There is a difference of opinion about this technique in the YahooGroup, Prius Technical Stuff. Two senior NHW20 (04-current) Prius owners believe this at most saves 5 seconds of engine run time on the first engine stop event, normally 8 seconds long. The effect does not occur in the NHW11 (01-03) Prius as long as the blue "cold engine" light is on.
Off throttle shift to electric mode
(Transmission mode in D, cruising speed up to 45 mph (70 km/h), road level.)
When reaching cruising speed it is often possible to briefly go "off throttle", allowing the system to switch to electric only mode. If the road is nearly level a gentle re-application of throttle to just enough to maintain cruising speed in electric mode may enable electric cruising (depending upon road grade, wind conditions, and battery state).
Accelerate from stop to 35 to 45 mph (60 to 70 km/h)
(Transmission mode in D, cruising speed up to 45 mph (70 km/h), road level.)
When running in traffic, a brisk (but not full throttle) acceleration, followed by an off throttle attempt (see previous) will be much more effective than gentle acceleration. This is a general technique applicable to non-hybrid cars. A gasoline ICE engine is more efficient (in terms of power produced/fuel consumption) when operating at higher effort due to smaller throttle losses. This is less important for compression-ignition engines, which do not have throttles but are instead regulated by the amount of fuel provided directly to the cylinder.
Accelerate with no traffic to 25 mph (40 km/h)
Transmission mode in D, cruising speed up to 25 mph (40 km/h), road level.
With substantial patience it is possible to accelerate to cruising speed using only electric power. Owing to the slow acceleration this should not be attempted with following traffic present. Although this will temporarily reduce fuel consumption since you're driving in electric mode, it will not improve the long term fuel consumption, since you have to recharge the battery at some point later (and the generation and use of electricity involve energy conversion losses). As pointed out above, it is better to accelerate at a moderate pace.
Long uphill followed by long downhill
(Transmission mode in D, cruising speed uphill to 65 mph (105 km/h), road uphill, followed by downhill at or below 50 mph (80 km/h) with transmission mode in B.)
The controller is blind to the future; it cannot tell that it would make sense to run the battery down on a long upgrade knowing that it can be quickly recharged on a subsequent downgrade. Nor is it possible for the driver to inform the system that this condition is coming. What happens is that the system will use the engine power when going uphill to charge the battery to normal state. Then, running down hill (with "B" selected) the battery is quickly charged to the maximum before the bottom of the hill. This full charge (battery state shown in green) will then cause the system to use the motor for compressive braking. It would be far more efficient to be able to use the battery capability to assist the motor (rather than taking charge from the motor). A run up the hill at sufficient throttle to demand electric motor assist (within speed limits, both statutory and by road and traffic conditions) may improve overall efficiency in this particular circumstance.
When using "B" on a long (1 to 2 km) downhill (e.g. over 60 mph, 100 km/h) you may find at higher speeds that the motor is used for braking in addition to the power recovery from the generator. Unless the battery is fully charged (showing green on the monitor), this is wasting excess energy which could be stored. By briefly braking to a somewhat slower speed, say 45 to 50 mph (70 to 80 km/h), the motor will not be used to retard the vehicle, all subsequent retarding energy will go to the battery, and so more energy will be recovered than when the motor assists deceleration. This is less useful on a long mountain downgrade where the battery will become fully charged regardless of the technique used.
Gentle rise and descent
A small amount of additional throttle will accelerate the vehicle before the rise is reached and this additional power may be maintained on most of the upgrade. Reducing throttle and paying off the excess speed before the top is reached may enable electric cruise to be entered, with energy recovery on the downgrade. Reapply cruising throttle at the bottom of the hill when reduction to normal cruise speed is obtained.
Slow steady speed
When traveling on relatively flat surfaces at approx 0 to 25 km/h (15 mph), sometimes the engine will run seemingly unnecessarily. By applying the brakes it tells the car to regenerate and is usually enough to shut it down. Sometimes it is necessary to come to a complete stop. At speeds that low, there is no real need for the gas engine. Alternatively, in the US one could re-enable the EV-Mode Button which is standard in EU and JP Prii, this feature allows the driver to request that the engine not start during times when it may not be needed.
Hypermilers' Favorite Cars
The most effective commonly available hybrid vehicles in the hypermileage marathons are the Honda Insight Hybrid, the Toyota Prius Hybrid, and the Honda Civic Hybrid. Other hybrids have also done very well.