Any glider/airline/etc pilots out there, who know of performance charts for the P?

Aerodynamic drag is the major loss for a Prius, so your principal factor will be airspeed. Best mileage for a Prius comes when most of the work is being done directly by the ICE, but aerodynamic losses are still low. You should see the best mileage in the low forties (mph). This would suggest that you slow down into a headwind to keep aerodynamic losses low.

However, with a car, all propulsion is through ground contact, so ground speed is also an issue. The Gen II Prius drive system is also most efficient in the low forties; slowing will push this into the range where a larger portion of the power goes through the electrical path, lowering overall efficiency.

Put together, this suggests that you should slow into a headwind, but not by the total amount of the headwind.

It's not a polar chart, but perhaps this information can get you started.

Tom

 

This is my first chart:

I created it on the drive back from picking up our 2001-03 Prius (sedan style body.)

This is the refined chart, several years later:
Ken@Japan had posted the drag formula so I could add the theoretical graphs modified by measurements of the vehicle, electrical overhead.

When I brought our 2010 Prius, 1.8L, from the dealer, I started and over the next week, completed this chart:

All data points come from a warmed-up Prius at the target speed entering the measured distance. Speed is cruise control maintained. Distance is at least 10 miles (16 km.)

This chart shows user reported speed vs MPG and many include warm-up. It is reasonable to assume shorter trips would have lower average speed and warm-up would play a greater part of the fuel consumption profile:

What this suggests is minimizing warm-up fuel burn is one way to maximize vehicle performance. In my case:

• maximize 50 sec. catalytic converter warm-up speed - by monitoring the ICE rpm, modest acceleration will draw on the traction battery and accelerate up to ~40 mph (+64 km/h.) Then shift into "N" and glide.
• Until the coolant reaches 70C, ICE accelerate at ~2,400-2,600 rpm and shift into "N" - this preserves speed in traffic while letting the engine run at minimum fuel burn during the "N". After the catalytic converter is warmed up, the fuel injection system keeps the engine in an efficient power range.
• At stops and stop signs, shift into "N" while waiting for 70C - in your case, the NHW20, 2004-09 may have logic that allows early shutdown of the ICE at a stop. My NHW11 does not so I simply let it run at 'idle' for minimum fuel burn.

This last chart shows another plot of MPG vs miles per day:

Remember these are miles per day and most trips return to the starting point:

• under 50 miles (80 km) per day - warm-up costs reduce average fuel efficiency
• 50-90 miles (80-145 km) per day - the car is in a high-efficiency zone of speed and warm-up
• over 90 miles (145 km) per day - higher speeds are reducing mileage
• outliers 140 miles (224 km) per day - these may be owners who optimize their highway mileage with moderate speeds or multiple, shorter trips in the day . . . speculation . . . delivery service or taxi?

I've also collected some hill-climb data from 1.5L Prius:


I've also done some hill climb benchmarks with a 1.8L Prius:


BTY, here is my other project and a photo:


Bob Wilson

 

Hi Jen C, from my limited paragliding experience with "speed to fly" and McCready calculations I also want to determine what the best speed is to travel with my 2007 Prius. So I got myself a bluetooth OBD2 adapter, a 7 inch Android tablet PC and the Torque application. I am currently displaying all the gauges that I gathered on PriusChat to be used to indicate the relevant information.

What I have learnt so far is that direction and strength of the wind and the gradient of the road are the main determining factors for finding the best speed to travel in order to get to your destination as quickly as possible while using the least amount of fuel. The worst winds are crosswinds. I think that because the Prius is designed for best aerodynamic performance with wind from straight ahead the crosswind cause the highest aerodynamic drag. Headwinds has the second highest negative effect, followed by no wind and then tail winds. Obviously climbing hills has a greater negative impact than driving on a flat road with downhill being the best for getting to your destination quickly with the least amount of fuel used.

So far I have found that trying to keep the Engine Load to around 82% with the Ignition Timing dropping to around 15 degrees BTDC gives a reasonably good fuel efficiency while going at an acceptable constant speed. I have also tried the Super Highway Mode which gives great fuel efficiency but tends to slow me down somewhat. Since I travel with my privately owned Prius while travelling for work purposes, it is essential for me to get to the sites where I should work as quickly as possible while maintaining reasonable fuel consumption.

So, in short I do the following:

• Accelerate to around 106 km/h (64 MPH) while loading the engine to about 90%
• Switch on the Cruise Control to maintain the speed.
• Depending on the combination of wind strength and direction as well as the gradient of the road, the Engine Load gauge will indicate that the engine is working too hard or not hard enough to give optimal fuel efficiency.
• Adjust the Cruise Control up or down one notch at a time and wait half a minute or so for all to settle.
• Usually when you find the optimal adjustment the Ignition Timing will slowly and all by itself drop down from between 18 to 20 degrees BTDC to round 15 to 16 degrees BTDC.
• At every major change in direction or gradient of the road it may be necessary to make an adjustment in the speed in order to maintain optimal "speed to drive".

Please keep in mind that this is still in experimental stage without any data or measurements to confirm any of this. The only evidence that this is working for me is my fuel consumption figures at PretoPrius (Toyota Prius) All Fuel-ups | Fuelly and PretoPrius (Toyota Prius) | Fuelly with a running average for the last 10 tanks of 4.3 l/100km (54.2MPG US), as well as the time it takes me to get to my destination. Keeping the tire pressures up also helped to increase the fuel efficiency from 6 l/100km (40 MPG US) to around 4 l/100km (60 MPG US).
Also keep in mind that when going uphill or against a crosswind or headwind the Ignition Timing might go up to higher than 20 degrees BTDC, while going downhill or with a tailwind it might go down to 14 degrees BTDC with a corresponding decrease or increase in road speed.
At this stage it is all trial and error for me because there are so many variables but I am confident that there are PriusChatters around that may be able to formulate a McCready ring for the best "speed to drive" for our incredible chariots.