Fast Or Slow Acceleration For Best Mpg?

[Julian30 3]

Hi,

Quick question (and I have searched the web and this forum but seem to find many different answers) that I'm hoping other Prius owners can answer for me based on experience or real knowledge.

Economy wise, is it better to accelerate slowly or to accelerate faster? (I'm not talking foot to the floor 'faster', just more 'normal').

I'm in a 2008 2nd Gen Prius which I've had for 6 weeks now and my only 'niggle' is that I feel I 'should' accelerate slowly rather than 'normally' to try to preserve the mpg.

I've read articles / posts that say the faster up to speed and then coast/glide the better, others say the opposite and some say no difference.....

Anyone got any real world experience or solid information / opinion?

Many thanks.

[Sooty 34]

Just accelerate normally and all will be fine.

[Julian30 3]

I'm a Prius driver, I want better than fine!

(Seriously, thanks for your reply)

[korat102 69]

hah - the problem is you never lose the mpg obsession...I have a Verso now and I still look at the flamin' mpg display all the time.

Anyway, when I had my Prius I never really noticed any real difference between 'slow' and 'normal' acceleration. Extra time spent on the throttle used up any fuel I saved by gaining speed slowly. The only time it actually made any appreciable difference was when I managed to prevent the ICE starting. That's not really practical in the real world (unless you want to be overtaken by an irate milkman on his float) and the Battery quickly needs recharging anyway which will fire up the ICE so there's not much of a saving there either.

Do a search for 'hypermiling hybrid' if you really want to read more than you'll ever want to know about extracting every last bit of distance from your fuel...

[Uncle Buck 92]

Hi Julian - I don't own a Prius but I would recommend driving in your normal fashion out of safety's sake. Why do I say this ? Very simply I drive for a living & have noticed a huge increase in the number of people accelerating away extremely slowly from junctions. The misconception is that they're being eco-minded & saving the planet, when they're actually putting themselves in unnecessary danger & causing others to brake hard to avoid them. I'm not for one minute suggesting you or all Prius drivers do this, but I have noticed many hybrid drivers doing this. So my tuppenceworth would be to accelerate 'normally' & get up to the other traffic's pace to avoid having someone having to avoid your boot ..... After all, they can't simply overtake you on a junction or when there's oncoming traffic. Hope I haven't offended anyone, it's just an observation from everyday life :)

[Sooty 34]

I'm a Prius driver, I want better than fine!

(Seriously, thanks for your reply)

Julian,

What I meant was just drive normally as if you were in a conventional car.

I have owned my prius for a couple of years and tried all sorts to get the "magical MPG".

Believe me it is "magical". I have since learnt that driving normally tends to get the best MPG anyway.

HTH.

[Cyker 388]

There have been other threads on this, but it seems accelerating slowly is actually worse than accelerating a bit more briskly. In my D4D, I find getting into the higher gears earlier saves more fuel than slowly accelerating.

The HSD's seem to have similar behaviour from what I've read here; The consensus seems to be that accelerating as fast as you can to your target speed, but keeping within the ECO band, seems to yield the best mpg's.

[Julian30 3]

Thanks to everyone for their replies, the general viewpoint seems to be for mpg (and safety) to drive up to required speed as one would normally, in other words not boy-racer but not milk-float like either ).

Uncle Buck - Not offended personally, I have moved off glacially slow (only on battery) when traffic has been non-existent but wouldn't do it if traffic was about (and it's really really tedious doing so!).

Korat102 - Have read plenty of 'hypermiling' articles / posts which is where my confusion arose, some swear by and others swear against slow acceleration!

Sooty - Thanks for your Prius experience based words of wisdom.

Cyker - Thanks for your point, sadly the 2nd Gen doesn't have the ECO band you're talking about, I think that's a 3rd Gen display, I just have to watch my flashing arrows and mpg count!

Cheers all

[Ten Ninety 277]

The consensus seems to be that accelerating as fast as you can to your target speed, but keeping within the ECO band, seems to yield the best mpg's.

This.

Although, of course, it is just one factor in achieving high mpg; on its own it is unlikely to make a huge difference. It's also difficult to provide quantifiable evidence either way. I have experimented with "snail's pace" acceleration a couple of times and seen lower journey averages than those achieved with brisk acceleration. However, there are so many factors which affect a single journey that it's hardly a scientific comparison.

Hi Julian - I don't own a Prius but I would recommend driving in your normal fashion out of safety's sake. Why do I say this ? Very simply I drive for a living & have noticed a huge increase in the number of people accelerating away extremely slowly from junctions. The misconception is that they're being eco-minded & saving the planet, when they're actually putting themselves in unnecessary danger & causing others to brake hard to avoid them. I'm not for one minute suggesting you or all Prius drivers do this, but I have noticed many hybrid drivers doing this. So my tuppenceworth would be to accelerate 'normally' & get up to the other traffic's pace to avoid having someone having to avoid your boot ..... After all, they can't simply overtake you on a junction or when there's oncoming traffic. Hope I haven't offended anyone, it's just an observation from everyday life :)

I suspect that these are often the same people who pull out in front of you despite there being a clear road behind you and - quite often - who then force you to slow down again within a short distance when they decide they need to turn off / turn right / stop for no apparent reason... in which case I don't think it's got anything to do with being a hybrid driver, it's to do with being a ****.

I remember my dad complaining about similar folk when I was a boy in the back seat of his Morris Marina, so I'm not convinced it's a new phenomenon. However, you're right that it does seem to happen a lot these days. Or perhaps I just notice it more - ironically - because I'm the one who's hypermiling and the ****s who do it force me to brake, which costs me mpg!

I'm a Prius driver, I want better than fine!

(Seriously, thanks for your reply)

Julian,

What I meant was just drive normally as if you were in a conventional car.

I have owned my prius for a couple of years and tried all sorts to get the "magical MPG".

Believe me it is "magical". I have since learnt that driving normally tends to get the best MPG anyway.

HTH.

There's nothing wrong with driving normally - you'll get respectable mpg without the effort and inconvenience of hypermiling. However, it is simply not true to suggest that driving normally will get the best mpg, nor is it true to suggest that getting anything better is 'magical'.

[Opifex 13]

An article I bookmarked some time ago (http://techno-fandom.org/~hobbit/cars/sweet/refl.html) comes to the conclusion that

"One of the core efficiency techniques is to use the gasoline engine as
productively as possible, or not at all. That's the essence of the
"pulse and glide" routine, and plays on the simple fact that the typical
internal-combustion engine is *not* very efficient when driving light
loads. If you want the best output for your fuel dollar, you have to
make it *work* against a load but not against itself, which means high
output shaft torque but at fairly low RPM. As non-intuitive as it sounds,
trying to baby an engine generally does not return its best fuel economy --
for the moment discounting special cases like lean-burn designs"

The author then goes on to explain how he arrived at this conclusion with a few thousand words and numbers. If you have the stamina it makes interesting reading. Unfortunately the source isn't identified so it's difficult to judge if the info is reliable.

[Julian30 3]

Thanks 1090 and Opifex.

I think that I'm just going to get up to speed 'normally' and then use hypermiling techniques where applicable. So far the Prius is returning about double the mileage my last car did (£ for £ from the pumps) so I'm very happy anyway!

Any views on best speed on motorways (for economy) and whether cruise control is positive or negative as got a couple of 300 mile journeys upcoming.

[PeteB 901]

55-60 on m'ways will give a small advantage, 70 not too bad, starts to get worse above 70 (all on the clock, so about 7-8% below true speed)

Cruise will generally do better the a human most of the time (unless you're very light footed and 100% attentive), except on hills; uphill it throws economy out of the window and does its best to maintain speed (sometimes with a slight delay, as it increases engine power progressively); down hill it will allow speed to increase on anything more than a slight gradient as it uses the same regenerative braking as simply lifting off the accelerator. It's often necessary to use the brake pedal when descending to control speed, which of course disconnects the CC.

[Joseph D 121]

Thanks 1090 and Opifex.

I think that I'm just going to get up to speed 'normally' and then use hypermiling techniques where applicable. So far the Prius is returning about double the mileage my last car did (£ for £ from the pumps) so I'm very happy anyway!

Any views on best speed on motorways (for economy) and whether cruise control is positive or negative as got a couple of 300 mile journeys upcoming.

Along the lines of what Optiflex quoted from techno-fandom article, I find a brisk acceleration is more efficient in the long run. Specifically for the Gen II, I do this. From a standing start, initially accelerate at 16 mpg (18 l/100 km) until about 15-20 mph and then feather (it will actually naturally feather quite quickly) to 24-31 mpg (12-9 l/100 km) until you've reached your target speed. The quicker acceleration will balanced by cruising at optimal gas usage for longer-- depending on conditions, I normally fluctuate between 60-113 mpg (4.7 -2.5 l/100 km) while cruising at 57-60 mph.

I like quantifiable info, so I hope this helps you. I'd be keen for your feedback of what you think about this, if you decide to give it a try.

As for cruise control, I find it works quite well by and large. In some circumstances I find helping it (undulating terrain e. g.) is good, but otherwise I let it do it own thing. On long trips, it is useful as trying to hypermile on long trips can be quite tiring.

Cheers,

Joseph.

[PeteB 901]

... sadly the 2nd Gen doesn't have the ECO band you're talking about, I think that's a 3rd Gen display, I just have to watch my flashing arrows and mpg count!

Thinking back to my Gen 1 & 2 days, I used the instant MPG bar graph (or instant mpg in main display on the Gen 2) and limiting my acceleration so that it never went lower than 25 mpg whilst accelerating - I found that seemed to help.

[Guest]

Just completed a 330 mile round trip, mostly motorway with about 10 miles of that on single carriageway. I did nothing out of the ordinary, kept it to 70mph ish, used the CC wherever possible and the figures showed 330miles, 66mpg and average speed of 53mph. That will do for me any day of the week. I guess if I wanted to eke it, i could reach 70mpg, but for 4mpg and a very relaxed ride (as there were no real problems on the whole journey), I'll take that every time.

[Grumpy Cabbie 421]

Just take it steady on the motorways and you'll be fine. Keep darting in and out of the fast lane and it'll drop.

I know one shouldn't but I keep up behind a HGV in it's slip steam. Now there's close and dangerous. I keep close with a safe gap, but even doing this you can tell when you 'fall' outside its influence. Makes a big difference to enconomy.

I move off if a HGV starts to follow me as I have seen too many accidents in my life and don't wish to become the filling in a HGV sandwich!

[Julian30 3]

Thanks 1090 and Opifex.

I think that I'm just going to get up to speed 'normally' and then use hypermiling techniques where applicable. So far the Prius is returning about double the mileage my last car did (£ for £ from the pumps) so I'm very happy anyway!

Any views on best speed on motorways (for economy) and whether cruise control is positive or negative as got a couple of 300 mile journeys upcoming.

Along the lines of what Optiflex quoted from techno-fandom article, I find a brisk acceleration is more efficient in the long run. Specifically for the Gen II, I do this. From a standing start, initially accelerate at 16 mpg (18 l/100 km) until about 15-20 mph and then feather (it will actually naturally feather quite quickly) to 24-31 mpg (12-9 l/100 km) until you've reached your target speed. The quicker acceleration will balanced by cruising at optimal gas usage for longer-- depending on conditions, I normally fluctuate between 60-113 mpg (4.7 -2.5 l/100 km) while cruising at 57-60 mph.

I like quantifiable info, so I hope this helps you. I'd be keen for your feedback of what you think about this, if you decide to give it a try.

As for cruise control, I find it works quite well by and large. In some circumstances I find helping it (undulating terrain e. g.) is good, but otherwise I let it do it own thing. On long trips, it is useful as trying to hypermile on long trips can be quite tiring.

Cheers,

Joseph.

Thanks Joseph, I like figures as well and yours will be useful. Quick question, are you basing your figures on the Prius speedometer as I've just realised mine (and apparently other Prius) reads about 4-5mph faster than true (according to GPS).

[Julian30 3]

... sadly the 2nd Gen doesn't have the ECO band you're talking about, I think that's a 3rd Gen display, I just have to watch my flashing arrows and mpg count!

Thinking back to my Gen 1 & 2 days, I used the instant MPG bar graph (or instant mpg in main display on the Gen 2) and limiting my acceleration so that it never went lower than 25 mpg whilst accelerating - I found that seemed to help.

Thanks Pete, sounds like a good general rule.

[Joseph D 121]

Thanks 1090 and Opifex.

I think that I'm just going to get up to speed 'normally' and then use hypermiling techniques where applicable. So far the Prius is returning about double the mileage my last car did (£ for £ from the pumps) so I'm very happy anyway!

Any views on best speed on motorways (for economy) and whether cruise control is positive or negative as got a couple of 300 mile journeys upcoming.

Along the lines of what Optiflex quoted from techno-fandom article, I find a brisk acceleration is more efficient in the long run. Specifically for the Gen II, I do this. From a standing start, initially accelerate at 16 mpg (18 l/100 km) until about 15-20 mph and then feather (it will actually naturally feather quite quickly) to 24-31 mpg (12-9 l/100 km) until you've reached your target speed. The quicker acceleration will balanced by cruising at optimal gas usage for longer-- depending on conditions, I normally fluctuate between 60-113 mpg (4.7 -2.5 l/100 km) while cruising at 57-60 mph.

I like quantifiable info, so I hope this helps you. I'd be keen for your feedback of what you think about this, if you decide to give it a try.

As for cruise control, I find it works quite well by and large. In some circumstances I find helping it (undulating terrain e. g.) is good, but otherwise I let it do it own thing. On long trips, it is useful as trying to hypermile on long trips can be quite tiring.

Cheers,

Joseph.

Thanks Joseph, I like figures as well and yours will be useful. Quick question, are you basing your figures on the Prius speedometer as I've just realised mine (and apparently other Prius) reads about 4-5mph faster than true (according to GPS).

The speeds I quoted above were based on my current Prius that over reads by only 2 km/h (so 50 km/h indicted is actually 48 km/h) so the difference once converted to mph is negligible. However, my UK Prius' error was about 10%, so 77 mph indicated was actually 70 mph. In my posts where speed is critical to what I'm saying I usually will use the term "mph indicated" or "true mph" to be clear about my meaning. I've noticed other posters here doing this as well.

As for what I posted above, it is not the speed that is critical, rather instant consumption figure. Once you get a feel for the "take-off at 16 mpg feather off to 24-31 mpg", it will quickly become second nature and you will not be looking at the MDF so much -- not that you would be glued to it in any case! (I hope!). Also, I hope you will notice that the rate of acceleration remains constant, even though the gas pedal is feathering, and at no time should the ICE sound like it is racing.

What I'm trying to convey is that the Prius can accelerate quite healthily without sacrificing overall economy. It is also a general principle and may need modifying depending on circumstance. For example, if you have (relatively short) stretches of road interspersed with roundabouts (Milton Keynes springs to mind), you may find a slightly gentler acceleration or a slower cruise speed works more efficiently. Consistent speed for long periods is still best in the grand scheme.

HTH

[Julian30 3]

Thanks Joseph

[cmclean 4]

Have a look at the official Lexus internet site and it has a section on getting the best mileage out of hybrids. I'm sure it recommends something like accelerating quickly to get to your optimal speed, didn't sound right, but who knows only testing will tell.

[puckdrop 2]

A few things to remember - the hybrid is a "system" - a combination of power sources. If you floor it and the engine is in the "too much power" zone - it will recharge the Battery using the excess. Sure this has losses involved, but you're not chucking petrol in for nothing.

Equally, the sooner you get up to speed, and into the correct wamup stage ( if starting from "cold" ), the sooner you'll get the economy that comes from the low HP required to maintain speed ( rather than accelerate up to that speed which uses more ).

I also find it quite fun ( in a sad way ) to try and keep the power flow away from the Battery ( in or out ) - showing that the engine itself is possibly in the efficient zone - remember any energy to/from the Battery incurs losses during the process.

Wind direction is another factor too - a tail wind, even a slight one, can give you 5-10mpg easily.