Daveskater
Premium Member
Registered: 29th Apr 08
Location: Oxford, UK Drives: Jap wagon
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I have heard a few times over the years that people claim to be able to achieve a higher mpg when using a lower gear, e.g. doing 30mph in 3rd instead of 4th etc. One of the theories put forward is that the engine is producing more torque so has to work less.
I'm not entirely sold on the idea, as surely more rpm = more fuel consumed, but have decided to try it out and see what happens. So for this tank of fuel I'll be using one gear lower than I normally would when cruising around. What I think makes it interesting with my car is that the torque curve is very flat, so the difference in torque produced shouldn't have much of an impact.
Once this tank is finished and I refill it, I'll drive in the same style but in the gears I'd normally use, to compare results.
I know that this is very much "cool story, bro", but I thought that by putting it on here, other members might like to try it too, and we can see what happens. So, who fancies an experiment? 
[Edited on 14-02-2012 by Daveskater]
Numberwang!
Originally posted by AlunJ
I like you Dave, you are a man of men
Originally Whatapp'd by Neo
Dave's maybe capable of a drive-by cuddle
Look at my pictures
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Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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revs arent necessarily matched to consumption, eg if you are in 4th on motorway doing 90 and you take your foot off the throttle, your engine will be doing say 5k revs but you will be using zero fuel, and i do literally mean zero
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Jakey
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Registered: 4th Jun 07
Location: Sandbach
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I've occasionally noticed I can get better mpg in 5th rather than 6th depending what speed I'm doing.
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John
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Registered: 30th Jun 03
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The engine will be most efficient in a certain rev rage, that's not necessarily in a higher gear.
From previous experience and not really paying attention I'd say lower gears in a diesel but higher in a petrol.
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Bonney
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Registered: 14th Nov 04
Location: St Helens
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The way i was taught was to get into as high a gear as possable as quickly as possable, Sometimes missing a gear can help, like going from third to 5th.
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Dean_W
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Registered: 13th Dec 05
Location: Downham Market, Norfolk
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True. My Golf will do more MPG on the instant readout in 5th at 60mph than in 6th.
EDIT - It's a derv.
[Edited on 30-01-2012 by Dean_W]
[Edited on 30-01-2012 by Dean_W]
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noshua
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Registered: 19th Nov 08
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I think about stuff like this on the boring daily drive, think the differences would be minimal though,.
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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This is all a bit pow
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stan_the_man
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Registered: 14th Feb 07
Location: Perth, Western Australia
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I got more MPG in 4th than 5th in my Audi according to the MFD.
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stan_the_man
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Registered: 14th Feb 07
Location: Perth, Western Australia
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quote:
Originally posted by stan_the_man
I got more MPG in 4th than 5th in my Audi according to the MFD.
EDIT: @ 30mph
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Daveskater
Premium Member
Registered: 29th Apr 08
Location: Oxford, UK Drives: Jap wagon
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quote:
Originally posted by Bonney
The way i was taught was to get into as high a gear as possable as quickly as possable, Sometimes missing a gear can help, like going from third to 5th.
I quite often so this, like if I'm getting up to 30 I'll usually go in second to nearly 30 and then stick it in 4th.
Neo is also trying this in his 1.6 diesel C2 so will be interesting to see what happens for him also. Although unlike me, he has an mpg readout on the screen 
Numberwang!
Originally posted by AlunJ
I like you Dave, you are a man of men
Originally Whatapp'd by Neo
Dave's maybe capable of a drive-by cuddle
Look at my pictures
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Daveskater
Premium Member
Registered: 29th Apr 08
Location: Oxford, UK Drives: Jap wagon
User status: Offline
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quote:
Originally posted by Steve
revs arent necessarily matched to consumption, eg if you are in 4th on motorway doing 90 and you take your foot off the throttle, your engine will be doing say 5k revs but you will be using zero fuel, and i do literally mean zero
That's different though as the fuel has shut off, whereas if you're maintaining 30 or 40mph then you're just constantly adjusting the amount of fuel to some degree, not regularly taking your foot right off.
Numberwang!
Originally posted by AlunJ
I like you Dave, you are a man of men
Originally Whatapp'd by Neo
Dave's maybe capable of a drive-by cuddle
Look at my pictures
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Matt L
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Registered: 17th Apr 06
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i might give this ago, tbf i got near 50 today on the way home from work even with having a bit of a play with a merc
normally i only get aroun 46 driving normally but then again there is a bit more traffic.
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Mark.W
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Registered: 3rd Jan 07
Location: County Durham
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Just change gear everytime you reach 3k thats what i was advised to do by my first driving instructor but that wasn't really based on fuel consumption but i normally change around 3k or just over.
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AlunJ
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Registered: 3rd Apr 07
Location: Newport
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I'm not sure what to make of this, obviously if you're in too high a gear doing a low speed you're going to be labouring the engine but I was always under the impression that lower revs usually = less fuel consumption. I'll be interested to see the results.
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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I made the Prius drop from 55.0 over 1000 miles to 54.4 in 40 miles today 
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AlunJ
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Registered: 3rd Apr 07
Location: Newport
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I average about 48mpg in the twingo which isn't too bad tbh, it'll do 50mpg at 70ish
[Edited on 30-01-2012 by AlunJ]
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Chris
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Registered: 21st Sep 99
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Sounds like a mythbusters episode.
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Warren G
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Registered: 14th May 06
Location: Kent
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all about throttle loads.
purely it
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Daveskater
Premium Member
Registered: 29th Apr 08
Location: Oxford, UK Drives: Jap wagon
User status: Offline
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quote:
Originally posted by AlunJ
I average about 48mpg in the twingo which isn't too bad tbh, it'll do 50mpg at 70ish
[Edited on 30-01-2012 by AlunJ]
I'm generally pleased as long as my average over a tank is above 30
Numberwang!
Originally posted by AlunJ
I like you Dave, you are a man of men
Originally Whatapp'd by Neo
Dave's maybe capable of a drive-by cuddle
Look at my pictures
|
johnhara1
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Registered: 19th Oct 06
Location: Newcastle upon Tyne
User status: Offline
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I drove to London in a 1.8 16v Focus over Xmas. I sat at 60mph in 5th all the way there and 80-90mph in 5th all the way back.
Appeared to use the exact same amount of fuel over both 300mile trips. 
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corsajay88
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Registered: 22nd Aug 11
Location: Upton, Cheshire
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quote:
Originally posted by johnhara1
I drove to London in a 1.8 16v Focus over Xmas. I sat at 60mph in 5th all the way there and 80-90mph in 5th all the way back.
Appeared to use the exact same amount of fuel over both 300mile trips.
Car was running for less time, other variables but difference was probably 2 hours.
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Paul_J
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Registered: 6th Jun 02
Location: London
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It's pretty simple really... the higher the gear (e.g. 5th / 6th) require more torque / power to turn the gear (as they're steeper) - like when you ride a push bike at low speed in 18th gear, it's hard to turn the pedals, compared to say being in 9th gear.
Now think about the effort required by your engine to do the same 'turning force'. It takes less effort (and thus less fuel) to turn a lower gear like 1st, than 5th / 6th.
However, once you reach a certain speed (and therefore a certain higher RPM) in the lower gears, it's better off changing to the next gear up to keep the revs lower, despite the fact you're now turning a longer gear. As has been said, often there's a sweet spot - say 1.5-2.5k rpm range which you want to keep in and whatever gear matches that at the speed you're going will do. Doing 800 rpm in 5th at 30 mph will net you worse mpg than 3rd at 2.5k rpm, as each time you squeeze the throttle less effort will be required to maintain that speed in that gear.
I ignore all of this and generally sit on dual carriageways in whatever gear leaves me just in the vtec zone, so when the car infront moves over I can go flat out the whole way home. Hence I get about 180 miles to a tank.
[Edited on 30-01-2012 by Paul_J]
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sand-eel
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Registered: 15th Mar 07
Location: carluke/braidwood--IRNBRULAND
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Depends if you have a small weedy engine or not I would say I can drive at idle in 5th at about 30mph and the bmw wavely mpg needle thing stays above 30mpg but if you did that in a small engine it would struggle to fuck and pump more fuel in to stop it stalling (+ICV).
Would normally go at 4th at 30mph as the "wavey mpg needle" stays more constant.
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Ben G
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Registered: 12th Jan 07
Location: Essex
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i've been trying this theory lately and it does work.
if i sit in 5th gear at 30mph, the engine will be labouring more than if i have it in 4th at 30mph.
the onboard mpg calculator shows this as the mpg figure increases.
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