New member with mpg story

Welcome to the fold and nice on the mileage for being so fresh to the Prius.

 

You are doing terrible.. you need to get down and dirty into the 30's!

 

Tell us where you live (you can put it in your profile).

 

congrats, all the best!

 

Your photo shows:

• Time 0:40 (we'll assume minutes)
• Distance 38.0 mi
  • 38 miles / (40/60) = 57 mph
• Consumption 65.0 MPG

So let's see:

This is well within the variation of the expected 62 MPG range on a flat road, standard day using cruise control. Given warmer weather, a modest tail wind, and a decrease in altitude, easily achieved.

Bob Wilson

 

The Blue line is his MPG by the Screen, the green line is the hand calculated MPG (most Prius screens are optimistic)

He has some data from 4k and ken and tried to measure Pulse and Glide(which is much less repeatable)

 

25

Jim got it right. It was on the original tires straight from the dealer including original tire pressure. Later, I found the original tires were 'undersized' which explains most of the observed differences between the indicated (solid line) and thin, calibration adjusted. The two lines give a range of values likely to be observed.

To replicate the solid line, find a flat road or loop at least 10 miles long. Drive the car for 15-20 minutes to throughly warm up the transmission. If using a flat road, do two passes in opposite directions on a loop, use the same start and stop point. Set the car on cruise control and passing the first 'start/stop' point, reset a trip meter. At the second point, memorize or photo the MPG and if possible the speed. Record the values and repeat the test at the same speed in the opposite direction to take out elevation and wind effects. Average the the results.

I added the other points to make sure other Prius were getting similar results. There will be some variation due to tire pressure and temperature. So using the chart:

• The thin line is what someone who drives the car a long distance, say a couple of hours; tops off the tank and calculated the mileage would get. This is the protocol I used for my first 'mph vs MPG' in our used 2003 Prius. Call that the 'pump measured' MPG.
• The thick line is from the 10 mile, two-pass, method using the indicated MPG. It is what most folks report, especially when they take a photo.

So when someone claims 'special driving' achieved some given MPG, I look for speed and route information. Then I check the NOAA site for weather conditions and Google Earth for elevation changes. So far, I'm finding these folks come pretty close to the two lines.

The usual reason for Prius MPG running under the lines is the 'warm-up' cost, ~30 MPG for the first 1-2 miles of each trip. People have different average trip distances and those who take longer trips, come closer to the lines.

As folks drive more per mile, we can safely assume they are driving longer trips than others. Assuming at least two trips per day, you looking at a peak around 30 miles per trip. But as the distances increase per day, the velocity increases, and mileage decreases. Then we have the unexplained folks who drive high miles per day yet get good MPG. This would be a great area for further investigation.

Now this is another interesting chart of ad hoc 'mph vs MPG':

Notice how the higher MPG outliers approach or meet my controlled, benchmark chart lines. We know there is a 'warm-up' cost, about 30 MPG for the first 1-2 miles. But there also appears to be some who either by accident of route or design, have mastered how to minimize the warm-up cost. These were first year, new Prius.

With today's used Prius, poor MPG performance can be due to previously undiagnosed problems: a failed repair; poor maintenance; bad oil change, or; other externals. Depending upon routes (aka., 'drive 0.6 miles') it can be 'warm-up' overhead. But there is one hypothesis that bothers me . . . driving style.

I'm an advocate of using:

• cruise control - is reproducible and comes with each Prius to eliminate human error
• slowest speed traffic allows - there are always a few vehicles slower than the rest of traffic, use them as pace vehicles
• optional "N" and "B" on downgrades or "D" - a tweak, not necessary for good mileage
• minimum speed, 25 mph, for the first 1-2 miles, or sitting on the driveway during the first 1-2 minutes of warm-up - this minimizes the 'warm-up penalty'

There are other driving styles and I've tested "pulse and glide."

My testing suggests it works if one is willing to change the car velocity by a factor of nearly two (i.e., 25-40 mph) for a 10-15% improvement over the cruise control, equivalent speed, 34 mph. There is an SAE paper that claims much higher performance(*). But changing between 25 and 40 mph is impractical impractical in traffic. The SAE paper makes this statement:

Source: SAE 2009-01-1322, "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy", Lee, Nelson, and Lohse-Busch (my emphasis)

Bob Wilson

* - Some of the data in the 2004 Prius part of the SAE paper raises some technical questions:

• Simulation shows 71.8 MPG @25 mph and 75.9MPG @35 mph
• Testing shows 89.1 MPG @25 mph and 81.0 MPG @35
• Pn

I would be happier to see credible replication of the SAE paper results. I trust my own with the NHW11, 2003 Prius. But now we have a 2010 Prius and I might try to replicate the SAE results.

 

So you live in Radford as well? Awesome! Nice to see a local, fellow PriusChat member!

HTC Evo 3D