What miles per hour speed driving the Prius C using the ICE gets the highest mileage?

Just look at the blue line (mpg) in relation to speed. This pretty much applies to most cars but the c is close enough to the GenIII for this to be within spitting distance. In general the slower you can go the better. On highways 50-55mph seems to produce 60-65mpg+-.

Image produce by Bob Wilson

 

The graph F8L shows (Bob Wilson's work) is steady state speed on flat land. So e.g., you would probably go slower up a hill to keep the ICE from revving above 3000 rpm.

Fuel economy in a Prius on the highways is mostly a matter of the following factors. Sometimes they conflict with each other:

• Air friction. Slower is better
• Gliding below 46 mph. Rare on highways
• Low torque (restricted air throttle). May be seen in very low power demand cases
• RPM: lower is better, all else equal

One cannot really say: drive like THIS all the time for best fuel economy; the road conditions change. A mixture of lower speeds for the most part and DWL (driving with somewhat constant load) work the best for me. The driver has little control over torque, but the car has a e-CVT transmission -- so keep a steady foot on the fuel pedal, and let the car find the 'gear' that operates the car ICE efficiently. In hilly terrain this results in the car varying it's speed, so not possible all the time.

 

If we are talking only about freeway speeds, that is about about 50 MPH then air drag dominates. And air drag is proportional to velocity squared. That "squared" thing is a big deal because it means you loose mileage very quickly for only a small increase in speed. The graph begins to show this effect at about 55.

I've found that for best economy on flat freeways speeds of about 50 to 60 is beast. But here in LA that means driving at way off peak hours. Mostly freeways don't move at even close to the speed limits and i get pretty good mileage. The Prius C lets 35 to 45 MPH on the freeway even if the driver does not.

Slower is not better. I drove for under 10 MPH once for about 50 minute and has getting under 30 MPG. The traction battery quickly drained and then the ICE had to run full time

Maybe another question is "What is the least cost speed". I can drive at 60 mph and get almost 60 mpg. So the cost is $4 per hour. But now lets' say you value your time at $12 or $25 or $50 per hour. Driving faster burns more gas but uses less of your time.

 

With all due respect, I'm calling B.S. on your claim of driving 50 minutes @ 10 MPH. At 10 MPH, when the traction battery drains and the ICE comes on, the ICE also shuts off after the battery is recharged to computer's satisfaction. The ICE does NOT 'run full time.' You would have discovered this if you drove 50 minutes @ 10 MPH.

In fact, I sacrificed part of the time I usually reserve for a 'Sunday drive' to see what really might happen at 10 MPH. First, driving at 10 MPH is incredibly boring, even for a low-brow knuckle-dragger such as myself. I could only endure about half an hour. In that half hour I laid out a roughly 1 mile loop and drove around it 5 times so elevation and wind would be no factor. I will admit this is not a long enough test to determine exactly what's going on at 10 MPH, but it IS long enough to disprove a claim of only 30 MPG at that speed.

I began my test with the battery depleted to 2 bars, so that the ICE woulld need to come on relatively soon. I found after a couple of on/off ICE cycles that MPG's bounced between 70 and 90. Starting with a full charge would, of course, have improved the MPG numbers.

 

That was in cold temperatures no less. At 95F mpg would have likely been in the mid-high 70s.

 

I think the difference is that I really was not driving 1o mph. I was doing zero and then 15 mph and then 5 and back to zero. Also in close traffic you tend to use the brakes quickly and don't recover much energy. I got poor mileage on the way to my destination. But then on the way home I was able to drive the speed limit and got my normal 50+ mpg.

 

You began your statement with the sweeping. 'slower is not better,' and then proceeded to offer an anecdotal (with a false assertion, that is, that the ICE runs full time) instance to corroborate. Now you are fine-tuning your one-time anecdote. I used practically no braking and consequently negligible regeneration in my test. Accelerating to 15 MPH in close traffic also does not scream of excessive use of fuel. I'm still not buying it... with all due respect.

 

I have found that the C acts strangely in these situations. Happened again yesterday in a traffic jam on the highway. ICE turns off initially, but the slow EV crawl (0-10 mph)with no regen and a slight uphill grade quickly ran the traction battery down to 2 bars. The ICE kept cycling on and off ( I had HVAC off to conserve power) running in a high RPM mode, charging back to 3 bars or so and then cutting off. Over and over. Quickly knocked my indicated MPG way down. The engine cut on and off with brake pedal use.

Once the traffic cleared 45 minutes later, I had to build the TB charge back up again, further reducing MPG.

 

Actually, CAlbertson was just politely correcting your faulty reading of his first post, where he said "I drove for under 10MPH..." Your so-called "test' therefore is not only irrelevant, it is in no way indicative of real-world driving outcomes.

The posts by CAlbertson and crebble are what forums like this are about; to inform readers what to expect in real conditions. Unfortunately I can't say the same about your replies.

 

The C, or any hybrid, gets best mileage at a STEADY, slow to moderate speed. ...say 25 mph. As speed picks up, wind and rolling resistance become more of a factor.

 

I disagree. This forum is about learning what the Prius can do in all situations and conditions then learning how to apply such knowledge to improve your experience. Since no one has beat ufourya in terms of fuel economy I can only assume he knows what he is talking about. Rather than blast him, just read what he has to say and see if you can learn from it. If you disagree with him then you are free to post your observations in detail.

 

Sounds to me like CAlbertson ended up with a low MPG because of the braking. A longer following distance might help.

 

Instead of just shooting from the hip, I actually went out and attempted to duplicate CAlbertson's clained 30 MPG. I have not responded to crebbie. You will find, if you look elsewhere, that CAlbertson makes assertions in other posts that are simply not true and usually does not bother to return to the thread to find he has erred: Less wear and tear with hybrids? | PriusChat (See if you can spot any errors here.) I have not the time to correct them all, so I chose only one. In fact, speaking of misreading things, CAlbertson misreads the chart and makes an incorrect assertion regarding it in this very thread. I did not bother to point it out.

What spurred my response to CAlbertson was that he took one instance of driving experience to make a broad statemant that 'slower is not better' AND that the ICE 'had to run full time.'. This is simply false.

You may read into my replies anything you wish. With all due respest, I suspect you are transferring your own passive aggressive tendencies onto others. My experiences driving a Prius c and reporting what I find to be interesting, valuable, erroneous or amusing will continue and I suspect they'll be more valid than yours. Although you may prove me wrong at any time and these interchanges are what make forums such as these valuable.

Now if you'd like to go out and drive under the same conditions as you imagine CAlbertson has done, and then report back with photographic evidence, I'd be delighted to admit I am mistaken and apologize profusely to all concerned.

I don't doubt CAlbertson means well, I just dispute some of his claims.

 

Once again, you don't/can't accept you made an error in interpreting the original post, and respond to that. Your so-called test is of no use to anyone, because driving around in circles for up to an hour at a constant speed is not something that readily springs to mind as being a useful thing to do in real life.
As long as you continue to attack the person rather than their message, your meaningless psycho-babble will just turn readers off, and ultimately you will be ignored. You keep on saying "With all due respect", but you show no respect at all.

 

It seems to me you want to be argumentative for no other reason than that you enjoy it. With all due respect I suggest a topic that you may know something about and perhaps we can have a real life argument

You're overlooking the importance of the word 'due,' with all due respect. I've made over 1,000 posts here, you've made 11. With all due respect, you've already managed to annoy me.

With all due respect, you seem to be having a little trouble with discerning the difference between disputing a claim someone makes with attacking the person who makes it. Show me where I have impugned CAlbertson as a person.

By the way, I do do (can you still say that?) many things that have absolutely no value in what you think might be 'real life'.

 

Without going into technical details, I would like to clarify that rolling resistance is essentially independent of the car speed.

This was not a deliberate attempt to redirect the focus of our discussions, but I will be happy if it has this effect.

 

Normally I do not respond to the same comment more than once. In this case I will make an exception.

First off let me state that I CAN drive my car so that it would show an MPG figure UNDER 30 and a speed UNDER 10 mph. Doing so would relate to circumstances having kess to do with speed and more with things that tax the traction battery unduly and do not fit CA's second, amended description of his driving experience.

His one time experience was offered to bolster a claim that 'slower is not better' as it pertains to MPG. Not having a particularly effective crystal ball, I attempted to replicate his experience as I understood it. In your opinion this was a monumental waste of time. CA returned to explain in more detail the experience he first cited. I stated that I still did not believe his car, which he has not indicated has any problems, would run only on the ICE or attain UNDER 30 MPG.

Having been stung by your rebuke and scarcely able to sleep last night thinking perhaps I had unfairly criticized a fellow Prius chatter, I took it upon myself to meet as many of the exact parameters set out by CA (may I be allowed to abreviate?) as possible.

So, this morning, first thing, your injurious comments ringing in my ears, I set out to replicate as closely as possible the drive of CA as further explicated. I drove as I imagined he would in close traffic. I accelerated to 15 mph, braked, slowed to 5, braked to a dead stop, accelerated again, crept at 6 mph or so, accelerated, braked, accelerated to 15, coasted there for a while, and repeated these events arbitrarily until 50 minutes had passed. I certainly did not look forward to you pointing out that anything over or under 50 minutes would completely invalidate my efforts. I also took great pains to make sure that I averaged under10 mph lest this raise your ire as well. I estimate that I came to a complete stop over 100 times.

This is what happened:


I hope this meets with your approval (although I'm not holdong my breath.) I think most rational and fair-minded observers will see that rather than running full time after the traction battery is first depleted, ICE was actually napping 69% of the time. They mnight also observe that 56.4 MPG is somewhat above a figure under 30 MPG.

So, with all due respect, have a nice day, mate.

 

I've had the car do unexpected things that I cannot explain as well, but they are infrequent and have nver lasted long enough to concern me. In the little 50 minute test above, I never noticed the rpm's above 1800.

 

I find that test interesting (more the results rather than the test itself). I believe that most vehicles suffer when constantly accelerating, stopping, and accelerating again as far as MPG is concerned. Its good to know that the Prius c doesn't suffer the same setbacks. Though in that test, were you particularly lead footed to get up to that 15 mph and so forth? Its possible that the results may be different if you did. Thank you for doing your research on the subject (nice to see educated replies, and grammar ).