Optimum gear to use for maximum MPG
Discussion
Short answer: yes, very occasionally, and even some turbo engines.
If you look at fuel consumption numbers from when they used to be quoted at 56mph and 75mph, a very few highly strung cars recorded better consumption at 75 than 56. IIRC, these included the Corvette ZR1 and the Lotus Esprit SE (so two Lotus engines, then
)
If you look at fuel consumption numbers from when they used to be quoted at 56mph and 75mph, a very few highly strung cars recorded better consumption at 75 than 56. IIRC, these included the Corvette ZR1 and the Lotus Esprit SE (so two Lotus engines, then
)Buff Mchugelarge said:
I always keep it between 1&3k rpm if I'm doing the economy thing.
Laboring an engine is one the worst things you can do.
That's in my highly strung Seicento btw
I tried the governments 'change up at a lowest rpm' advice didn't work, but my mates advice from his Driving instructor of changing up at 2500 seems to be the best way. Laboring an engine is one the worst things you can do.
That's in my highly strung Seicento btw
Too many variables for one magic rule. Different engines have different characteristics and need driving differently. One of the best things that you can always do is drive smoothly, look a long way down the road to allow you to anticipate and avoid braking so yo just keep rolling along.
littleredrooster said:
Hooli said:
I put mine in 'D'.
Further to this, if I put mine in D and drive gently, it keeps the revs between about 1700 and 2300. Ergo, if the manufacturers millions were wisely spent, one would imagine that this is where it operates most efficiently. Perhaps.
littleredrooster said:
Further to this, if I put mine in D and drive gently, it keeps the revs between about 1700 and 2300. Ergo, if the manufacturers millions were wisely spent, one would imagine that this is where it operates most efficiently.
Perhaps.
You're only reminded once a couple of weeks or so if your car is inefficient (if over-revving for performance). You're reminded every time you press the throttle that it's slow (if under-revving for economy). Though I suspect 1700 is about right under most conditions.Perhaps.
This is one of the few sources I've found that cites actual data, if only for two cars: a 318i (unknown model but I believe 2007 at latest) being most efficient somewhere round 60km/h, and a Prius somewhere below 40km/h. Quite a useful source if you're interested in learning about energy usage (so long as you bear in mind it's a very broad overview, so any calculated figures are necessarily based on simplistic assumptions that are hopefully not too wrong: it's more worth it as a look at how you would go about quickly estimating something. Still worth a look IMO)
littleredrooster said:
Hooli said:
I put mine in 'D'.
Further to this, if I put mine in D and drive gently, it keeps the revs between about 1700 and 2300. Ergo, if the manufacturers millions were wisely spent, one would imagine that this is where it operates most efficiently. Perhaps.
Vyse said:
Ever since Ive been driving Ive been told that to try and shift into the highest gear possible to get the best MPG. Can being in too high a gear at too low a speed in fact decrease MPG. For example being in 6th gear at 30mph in a highly strung NA car?
Yes, it can decrease MPG, think about trying to cycle along in the wrong gear ...It can also 'labour' the engine, which can cause damage and wear in the long term.
Some time back, I went for a 'spirited' drive - having reset the average MPG. Long story short, that drive gave me one of the highest averages I had seen on the car - despite using 'firm' acceleration and holding the gears - why, because I used the engine efficiently, not labouring it.
The advice to change up asap is the biggest load of b*****ks every ...
Willy Nilly said:
We don't get quoted efficiency figures for cars, only economy. They are not the same thing. Efficiency is work out for effort in. It's fine pouring loads of fuel into an engine if you are getting loads of work out. The 26,000 litre Wartsila boat engines are very efficient, 196 grammes per kw/hr iirc. I doubt many cars can get near that.
I suspect dumping a 2,300 tonne engine in my car would be that efficient.What you need is a BSFC chart for your engine, this determines the most efficient point point in the engines rpm range for efficiency.
Like this nicked from the ecomodder forum
Volkswagen Jetta TDI 1.9L ALH 1999.5-2003
ALH BSFC map with power hyperbolae.png
Each curve represents a constant horsepower developed by the engine. If you are driving on a given road with a constant grade, speed, and ambient conditions, regardless of which gear you are in, it requires roughly the same amount of power to overcome aerodynamic drag, rolling resistance and driveline losses. Therefore, regardless of what gear you're in, you're riding anywhere along the same blue curve; exactly where you sit on that blue curve being only dependent on the gear you're in and therefore the RPM at which the engine is turning over.
In the case of the TDI BSFC chart, if I take the example of operating on a certain speed such that the power is 20 HP, the lowest BSFC occurs when running at the gear that corresponds to about 1250 RPM. If I run at either a higher- or lower RPM from this point, my BSFC will increase. This is about the only point in the entire engine map where it would be disadvantageous to operate at an even higher gear if one were available (lower RPM) because of the worsening BSFC. Almost everywhere else, the lowest BSFC is achieved at the lowest possible RPM at a given power.
While we are at it here is a gear/speed/fuel efficiency graph one for one of my cars a Lupo 3L (Possibly the most fuel efficient ICE production car to date)
Like this nicked from the ecomodder forum
Volkswagen Jetta TDI 1.9L ALH 1999.5-2003
ALH BSFC map with power hyperbolae.png
Each curve represents a constant horsepower developed by the engine. If you are driving on a given road with a constant grade, speed, and ambient conditions, regardless of which gear you are in, it requires roughly the same amount of power to overcome aerodynamic drag, rolling resistance and driveline losses. Therefore, regardless of what gear you're in, you're riding anywhere along the same blue curve; exactly where you sit on that blue curve being only dependent on the gear you're in and therefore the RPM at which the engine is turning over.
In the case of the TDI BSFC chart, if I take the example of operating on a certain speed such that the power is 20 HP, the lowest BSFC occurs when running at the gear that corresponds to about 1250 RPM. If I run at either a higher- or lower RPM from this point, my BSFC will increase. This is about the only point in the entire engine map where it would be disadvantageous to operate at an even higher gear if one were available (lower RPM) because of the worsening BSFC. Almost everywhere else, the lowest BSFC is achieved at the lowest possible RPM at a given power.
While we are at it here is a gear/speed/fuel efficiency graph one for one of my cars a Lupo 3L (Possibly the most fuel efficient ICE production car to date)
Edited by cptsideways on Thursday 13th February 00:07
SystemParanoia said:
i cruise the mway @ 3.5k rpm
My 9-5 is topping 100 if I do this in top (5th) gear I find that not labouring the engine helps, if you're in too high a gear I'd imagine the extra throttle you have to use to keep the speed up cancels out the fact that there are fewer revs?
When accelerating I tend to change up at about 2500-3000rpm...
CB2152 said:
My 9-5 is topping 100 if I do this in top (5th) gear
I find that not labouring the engine helps, if you're in too high a gear I'd imagine the extra throttle you have to use to keep the speed up cancels out the fact that there are fewer revs?
When accelerating I tend to change up at about 2500-3000rpm...
I find that not labouring the engine helps, if you're in too high a gear I'd imagine the extra throttle you have to use to keep the speed up cancels out the fact that there are fewer revs?
When accelerating I tend to change up at about 2500-3000rpm...
Type R was terrible because of the high rev range, even in 6th gear
3500rpm = 70mph
4500rpm = 90mph
When doing MPG trips i try and keep it below 2000rpm in every gear except 6th where i try not to go over 4000 - makes treble the difference to overall MPG vs normal driving.
got over 50mpg from my VXR traveling to centreparcs last year using this style of driving ( 4 adults, clothes for a week and shopping) !
3500rpm = 70mph
4500rpm = 90mph
When doing MPG trips i try and keep it below 2000rpm in every gear except 6th where i try not to go over 4000 - makes treble the difference to overall MPG vs normal driving.
got over 50mpg from my VXR traveling to centreparcs last year using this style of driving ( 4 adults, clothes for a week and shopping) !
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