Optimal speed for best mpg??

most definitely. with all things being equal and wind resistance increasing as speed goes up, then the slower you go, the better

 

What does this have to do with "Appearance Modifications"?

:?:

 

what does a question about "appearance modifications"
have to do with a post in the "fuel economy" forum?

 

<div class='quotetop'>QUOTE(smtrader\";p=\"81001)</div>

If I'm reading you correctly, you're saying you get better mileage doing 70-75 than you do going 65-70. If you think that, then you're mistaken. There is no way you're going to get better fuel economy by going faster (at least not at the speeds you're talking about). The best fuel economy is achieved from about 35-55 mph.

 

i have found 2 speeds that are maximal for fuel economy...after doing the calculas and plugging in all the parameters...the following numbers are...in the city the maximal fuel economy occurs at 38mph and on the highway it occurrs at 62mph...these numbers will ,of course, vary, given wind direction and speed, however, given constant values...these numbers are pretty close...

 

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"81024)</div>

Obviously, a moderator or an administrator of PriusChat has moved this thread from the "Appearance Modifications" forum to the "Fuel Economy" forum since I posted this question. This thread originated in the "Appearance Modifications" forum.

 

ahhh sooo!!

your question fell on alert ears then

 

My best mileage occurs between 40 and 60 mph but more specifically at around 50 mph.
The best mileage possible however is achieved at around 38. I saw the screen on another group where the guy drove almost a thousand miles at a 35 mph average and got 967 miles at 87.6 MPG. That number might be off by a fraction. I can't do that in my driving but I have tested various speeds and found that above 50 mph, mileage drops off about one MPG for every one mph in increased speed. If 70 mph is getting you your best mileage, I can only guess that the rest of your driving involves lots of stopping and starting. Also cruise control will not achive as good of a mileage figure as a conscious driver; because, it is far to aggressive with the throttle and the regen.

 

The best fuel economy I have seen to date occurred over the last weekend when I went for a 3 hour drive. Due to concern over possible flooding from the heavy winter snow that is melting, the road crews were clearing out all the culverts.

This required closures to one lane on sections of the Trans Canada with 70 km/h (Around 42 MPH) speed limits. My MFD claimed an average of 3.6 L/100km at that speed, which lasted around 20km.

78 MPG Imperial Gallon or around 65 MPG US gallon.

I will agree that going *too* slow will kill the fuel economy as the ICE will cycle on and off. But there must be a "sweet spot" for highway speed that maximizes fuel economy.

My daily commute has around 5km at 70 km/h, 3 lights, and the MFD will claim an average of 3.8-4.2 L/100km. It really helps having the temps back up to +15 to +20C. That -40 was killing me.

OTOH at 110 km/h and no wind, the MFD will claim 4.8 L/100km or 58 MPG Imperial gallon. I would think that given how air drag can express almost a logarithmic change with increase in velocity, there is no way a car will get better fuel economy at 75 MPH instead of 45 MPH, unless there is something odd with the gearing.

 

I am glad that someone else made the observation that I have noticed concerning cruise control. I thought I was going crazy because everyone recommends using cruise control for the highway but I have always been able to achive better results operating manually ( maybe not a consistant ).

Now on to the direct topic. My daily commute is 67 miles one way. 59 miles is highway traffic. I normally get the best results when I stay within the 68-72 mph range. any faster and I take a severe MPG hit. Any slower and I take a big safety and ego hit driving that slow on a major interstate

 

cruise control is good for a lot of reasons. but it does over-react to small hills. when i use it, i am constantly adjusting it so its not to maintain a constant speed. i have learned where and how cruise control will work and learned to adjust it accordingly. this will take time and soon you will instinctively know how to adjust it even for areas you are unfamiliar with.

as to driving slower than 68, that has more to do with the age of the driver than it has to do with driving conditions.

 

I find I get the best mpg during the main stretch of my morning commute where I'm usually around 80 to 85 km/h for about 10 km. The MFD always shows gas consumption between 2.3 to 2.8 L/100 km. It's my favorite part of the morning.

 

MAGIC SPEEDS
The following are for level ground, nominal battery charge:
31 mph- above this the ICE MUST be used to accelerate
41 mph- above this the ICE will always be on
54 mph-most PRODUCTIVE speed where mph=mpg

So to max out mileage:
Learn to accelerate to speed, lift off the gas for 1 second, then cruise. This will allow MG cruising when possible.
Go 40 mph max around town.
Go 55-65 mph on the freeway. When going up small hills-overpasses slow about 3-5mph then accelerate on the downside back to cruising speed.
When slowing from highway speeds, Coast down to 40 mph-then cruise if needed before slowing more.
Use brakes as little as possible, if needed- brake at 2 mph/second deceleration-this produces maximum energy regeneration.
Don't drive when it's cold, mileage is worse in the winter then the summer.

 

Is 2MPH/sec a fairly light touch on the brake? I always wondered exactly where regen braking works best, and figured long and slow would help to keep heat produced down. Plus batteries in general like to take a charage more gradually so I am figured Prius works the same. Too bad there's no "regen efficiency" screen that displays instead of 99.9MPG.

 

My 2mph/sec is light to moderate braking. You can gauge this by taking 30 seconds to stop from 60 mph, etc..
This number is from another post on PriusChat where someone(?) hooked into the ECU bus and measured the current being recovered at different decelerations.

 

I generally find a "sweet spot" at 41 to 51 mph with cruise control and get 55 to 67 mpg at that speed (moderate air temperatures, only a few traffic lights, old freeway that is now a parallel expressway, offers 12 miles of continuous, low traffic travel). Roadway is gently rolling, but mostly level.

I get optimum fuel economy and 7+ green bars on the battery.

 

i notice that mileage seems best at 25-35 mph, then seems to take a dip at just above 40 mph, but seems to get better at 45-55 mph... seems strange and probably not an accurate observation since im only going by estimates based on real time readings of the MFD

 

all right! i always wanted an excuse to not go to work in the winter...
'sorry boss, i won't be in today due to excessively low mpg.'
:wink: