51 MPH

My best mpg (71 point something) was achieved around 35mpg. That's where hypermileing is most efficient. It's simple physics. Slower speed means less wind resistence, and thus better mpg.

 

<div class='quotetop'>QUOTE(Tripod137 @ Oct 15 2007, 06:10 AM) [snapback]525786[/snapback]</div>

The "70's and 80's" seems a little high even for an NHW20 model. If there were any decrease in altitude, it would make sense.

If you could, please repeat your test in long enough segments to get a stable MPG readings. This can lead to a graph of MPH vs MPG (need temperature and relative wind direction too). If this is a route frequently used, try to get data both directions to handle any altitude changes.

This is the technique I used to plot points that became this graph:




The chart and data are good enough that I can predict my MPG for any given speed and be within 10%.

Bob Wilson
efficient driver

 

Hi Tripod137,

Looks like you found SH (Super Highway) mode. Various people have been talking about it on CleanMPG.

There is also a thread in the fuel economy list on PC here about various highway modes.

 

Be sure to put one of these slow moving vehicle placards on the rear hatch window of the prius and stay in the far right lane. :lol:

It should protect you from any road rage incidents....

Normal Hwy speeds here are 65-70 and the transplants will still try to run you over. the interstates are again 65-70. Real life? 80-100mph, police present, 69-77mph.

 

They really should offer a Hypermiler drivers kit as an option and include one of these for the lower rear window & right lane driving instructions......



Think about it, it would work! and the rabid SUVs could zoom by in the left lanes.
As a general rule slower traffic is supposed to use the right lane, but they still poke along in the left lane..

 

At 62 mph I easily get 55mpg with cruise control, no mods and 44psi at 70F going from Baltimore to DC and back!

I use Mobil1 and Shell gas and drive alone without climate control.

Somehow your graph predicts 47-48mpg

<div class='quotetop'>QUOTE(bwilson4web @ Oct 15 2007, 12:45 PM) [snapback]525878[/snapback]</div>

 

<div class='quotetop'>QUOTE(ystasino @ Oct 16 2007, 02:55 PM) [snapback]526488[/snapback]</div>

The drag curve for a 31% efficient engine shows 47-48 MPG but you'll notice the green dots that correspond to the 50-55 MPG range. I've been looking at the ICE specific fuel consumption and up to about 68 mph, this corresponds to a high efficiency range. Toyota claims the ICE can achieve 37% efficiency. What I haven't figure out, yet, is a way to combine the ICE efficiency data with the drag curve:



I use the green dots for my cross country performance and since I captured those points, I've brought the tire pressure up and brought the oil level between E and F. I also use Mobil 1 and Shell.

There is an additional rule I need to add to the model. Above 68 mph, the NHW11, 2001-03 Prius has to run the ICE at higher rpm than just idle. This causes a distinct fall off in vehicle efficiency. The same inflection point occurs in the NHW20 between 85-90 mph.

Bob Wilson

 

With better instrumentation (scan gauge) it is easy to get into this state and hold at any highway speed. Low 50s has a wider window with the pedal position to get into it.. at least that is what I've experienced.. so you're getting into it easier there.

 

Hi Ystasino,

You are also not driving a Generation 1 Prius. The curves were measured on Bob's 2003 Prius.

 

<div class='quotetop'>QUOTE(donee @ Oct 17 2007, 06:28 PM) [snapback]527122[/snapback]</div>

Indeed the 2004-current, NHW20 model has a lower coefficient of drag, 0.27 versus the 0.29 for the 2001-03, NHW11. We need to check the profile of the NHW11 and NHW20 because the aerodynamic drag is the area of each vehicle times to the coefficient and the velocity squared. I haven't measured the area of both vehicles but understand the NHW20 is a little larger. However, the NHW20 has a number of control law and internal changes that improve performance in some areas with a superior warm-up cycle:

• 45-52 - original NHW11 city/highway mileage
• 52-60 - original NHW20 mileage

My recommendation is to treat the drag-efficiency curve as the upper limit for NHW11 Prius and the lower limit for NHW20. If your performance at any given speed is significantly lower, it makes sense to see what is going on:

1. maintenance - oil, tires, alignment, other
2. route planning - improve the warm-up and cool down segments

Bob Wilson

 

<div class='quotetop'>QUOTE(bwilson4web @ Oct 18 2007, 08:33 AM) [snapback]527272[/snapback]</div>

Bob,

What do you mean by cool down segments? I do have a few options for the last 2 miles of my 16 mile each way journey to work. I have experimented with warm-up but have never considered cool down.

 

<div class='quotetop'>QUOTE(gazz @ Oct 22 2007, 07:03 AM) [snapback]528743[/snapback]</div>

For the last 1-2 miles, select a route that supports maximum EV mode. With my NHW11, I keep the speed at or below 30 mph. This typically adds 3-5 MPG to the end mileage. With a fully warmed Prius, the final EV is very efficient, much more so than a couple of hours later when the ICE and transaxle have had a chance to cool off.

Bob Wilson

 

<div class='quotetop'>QUOTE(bwilson4web @ Oct 22 2007, 07:18 AM) [snapback]528745[/snapback]</div>

Thanks for that, I do use EV mode fro the last 1/2 mile will see if I can extend that. Had not thought about the EV efficiency.

Another quick question regarding cruising speed. I am in two minds on slower roads whether to cruise at 41 mph or 50 mph. I am aware that speed equals drag. But the roads I drive on are windy hilly roads so I get short opportunities to glide. If I am at 41 mph I can get an engine off glide which I assume is the most efficient, if it is 50 mph then the engine is being turned. The point is, is that if the glides are short the ICE keeps firing up at the slower speed when at 50 mph it is already turning. Have you any thoughts.