Hypothetical Question: Optimum Driving Speeds

See http://hybridcars.about.com/od/news/a/100mpgrecord.htm and http://www.post-gazette.com/pg/05220/550484.stm.

 

<div class='quotetop'>QUOTE(efusco @ Mar 3 2007, 06:36 AM) [snapback]399479[/snapback]</div>

According to Wayne Brown's Hybrid Synergy Simulator it's between 20 and 21 mph. I don't know how close that is to real world, but the temperature makes a bigger difference that speed alone. Of course, wind and wind direction make dramatic differences. Going from 9 C to 39 C gives about a 12% mpg boost.
It's no wonder we need to block our grills in the winter.

Dave M.

 

<div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 02:35 PM) [snapback]399617[/snapback]</div>

See Advanced Techniques under http://www.hybridcars.com/gas-saving-tips/...yota-prius.html. Unfortunately, my commute isn't very conducive to this. I can only do this for a very short portion of it and only in the day for safety reasons.

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Mar 3 2007, 08:57 AM) [snapback]399470[/snapback]</div>

I'll agree with the above speed range of 40 mph to 57 mph. When I drive 57 mph to work I maximize my tank's overall fuel economy. During the month of January '07 with temperatures less than 35F, my brand new Prius tank fuel economy averaged 48 mpg. The instantaneous fuel economy indicator falls if the speed increases above the 55-57 mph range. In stop-and-go traffic, I can still maintain this economy if I travel as low as 40 mph. But, it's important to wisely use the regenerative break. To maximize fuel economy requires careful and thoughtful driving, like watching traffic patterns ahead of you.

 

<div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 04:36 PM) [snapback]399681[/snapback]</div>

I noticed the mention of neutral too. I think that the whole part "engine on but not turning over and transmission in neutral" is ambiguous/wrong. I don't think it's a good idea to run in neutral and you really DON'T want the ICE running while gliding as it's consuming gas.

BTW, I stumbled across/rediscovered http://www.toyota.com/html/hybridsynergyvi.../fall/mpgs.html. One of the marathoners talks about his technique at the bottom. There are more quotes at http://www.toyota.com/html/hybridsynergyvi...l/marathon.html.

 

my optimum speed is 35 mph. i previously thought, the lower the better, but that does not seem to be the case.

 

<div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 07:36 PM) [snapback]399681[/snapback]</div>

You'll probably enjoy CleanMPG. I encourage you to check it out.

This thread from CleanMPG in particular might interest you. It describes pulse & glide as well as a higher-speed technique that some call "Warp Stealth" (a bit of a misnomer, but that's beside the point). While you're in that thread, explore the link in post #25 from Hobbit. Hobbit (a member here too) has done some fascinating research in optimal driving speeds and techniques, especially at higher speeds where P&G isn't practical. It's a bit technical, but it's a great read if you really want to understand the how and why of higher-speed FE.

 

My best mpg is at 35 also.

I expect this is near optimum since going faster prevents electric ice off mode, at least over 42. Also adds drag. Going slower makes for inefficient ice runs even with load to charge the battery.

I can't drive 35 enough around here to know what my mpg would be but I expect it would be around 80 mpg if I was where I could do it. I have sustained over 75 mpg for some extended periods going around 39 mph.

I think this optimum may depend on having rolling hills. If everything was flat then a different speed might be optimum where engine was kept running. So then maybe 43 mph would be good. But with small hills clearly keeping engine going is bad on the down grades.

With pulse and glide added then pulsing between 5 mph and 35 mph might make sense. Or with hills you need to adjust this so engine is on for uphill and off for downhill.

So my numbers may be off a bit but clearly there are at least 3 optimums depending on terrain and driving steady vs pulsing.

 

<div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 02:35 PM) [snapback]399617[/snapback]</div>

What were your results at 20-21 mph, and what had you expected?

Dave M.

 

I try to iron out the peaks and troughs on a journey and aim to drive at the average speed for that journey. My weekend commute takes me around 2 hours 20 minutes over 86 miles of A roads. My average is 37mph and my zen is get my top speed as close to my average as possible. The hills throw in an added dimension, the steep short hills are good for going up and the long gradual hills are good for going down.

My typical fuel use is 65mpg (UK) with a best in the summer of 72mpg. I used the minor roads for that journey and averaged just 29mph. My target is to do the whole 86 miles from a cold start on one gallon, a hard target but fun. It's acceleration that uses the fuel and keeping a steady speed into a headwind or up a hill is the equivalent of accelerating.

 

I get the absolute best MPG between 1 and 4 mph, using pulse and glide, with the engine off and my hands pressing on the hatchback instead of my foot pressing on the gas pedal. When I get tired of pushing, I let the car coast to 1 mph and then begin pushing before the car comes to a full stop to avoid start up inertia and cohesion of the wheel bearing grease molecules. Occasionally, when near large intersections, someone will jump out of their car to help me get across several lanes quickly. Thats a nice bonus. I find that I can avoid oil changes entirely this way. I'm thinking of having the gas engine and battery removed next week to lighten the car up. Of course I will need to figure in the cost of having the speakers moved outside of the car so that I can hear them. It's complicated.

Dan, 3rd gen from the sun