Most economical speed
- Thread starter whuy
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I've tried to find the answer to that myself. But the mpg or l/100km on the DIS is very sensitive to throttle position and can quickly change, for example from 80mpg to 140mpg. Also, I've not found a road long and flat enough to get an accurate answer anyway. But more generally though fuel economy is proportional to drag, which itself is proportional to the speed squared. So there is a lot of mpg to be gained by just driving slowly. It will be interesting to hear what other people have to say on this.
2004 1.4 TDi (90) SE, Cobalt Blue, Climate control, Cruise control, DIS, Sport seats, Winter pack, Symphony II.
2004 1.4 TDi (90) SE, Cobalt Blue, Climate control, Cruise control, DIS, Sport seats, Winter pack, Symphony II.
56mph used to always be quoted as the most economical speed. So I'd use this as a good starting point and the magic figure will probably be +/- this by a small margin. Much past these speed and as Will says, aerodynamics take over.
Thinking about it though, the A2 is a very slippery shape (1.2TDi has a 0.26cd drag - one of the lowest ever)so maybe a few mph more and you'll still get good results.
Also, with the DIS, don't use the instantaneous mpg (except for being silly), use the average feature over say 5 or 10 miles. This will give you more of a true indication.
Don't drink drive! Not only is it socially unaceptable, it also harms A2's.
Was a Merlot Red 1.4SE petrol originally.
Now an Ebony Black 1.4SE petrol with Red Leather, CC, Symphony + all the previous options we had.
Thinking about it though, the A2 is a very slippery shape (1.2TDi has a 0.26cd drag - one of the lowest ever)so maybe a few mph more and you'll still get good results.
Also, with the DIS, don't use the instantaneous mpg (except for being silly), use the average feature over say 5 or 10 miles. This will give you more of a true indication.
Don't drink drive! Not only is it socially unaceptable, it also harms A2's.
Was a Merlot Red 1.4SE petrol originally.
Now an Ebony Black 1.4SE petrol with Red Leather, CC, Symphony + all the previous options we had.
swiv
Member
I don't have DIS, but I've been wondering about something that seems relevant in this discussion:
Is it possible that it would be more economical to drive in 4th gear instead of 5th?
So that's where the speed comes in: I can drive about 90km/h@2000rpm in 5th, but is that more economical than, say, 70km/h@2000rpm in 4th gear?
Can I tell how economical something is by looking at how far I need to depress the accelerator?
For example: if I'm doing 80km/h in 4th (about 2200rpm) and shift up to 5th, without altering how far I'm stepping on the gas, I notice that I'll fall back in fifth and actually have to give it more in order to stay at 80km/h. So is it less economical then?
Edo
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
Is it possible that it would be more economical to drive in 4th gear instead of 5th?
So that's where the speed comes in: I can drive about 90km/h@2000rpm in 5th, but is that more economical than, say, 70km/h@2000rpm in 4th gear?
Can I tell how economical something is by looking at how far I need to depress the accelerator?
For example: if I'm doing 80km/h in 4th (about 2200rpm) and shift up to 5th, without altering how far I'm stepping on the gas, I notice that I'll fall back in fifth and actually have to give it more in order to stay at 80km/h. So is it less economical then?
Edo
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
humps
A2OC Donor
swiv,
generally, the higher the gear the better fuel econ you get because you travel faster under lower rev which means using less fuel. That's also why some cars have over drive (popular in US) to help reduce rev while on the motorway.
However, it does as you say depends on how much fuel it is consuming at the time of travelling. Because wind resistance is not directly porportional to speed, the resisance increases a lot more as you speed up. The more resistance you have, the more fuel you need regardless of your gear (conservation of energy). Lower gear means more push per drop of oil, but then it also means higher rev for faster burning of each drop of oil! You get the idea. So there is a sweet spot where resistance is just ok and you're travelling fast enough at a low rev. This sort of answered your first 3 questions.
Your example is unlikely given the speed you're mentioning, unless there is a very strong head wind or you're climbing up hill, I don't see how you need more fuel to travel at 80km/h in 5th than 4th.
humps
1.4SE Cobalt Blue, Bose and leather
generally, the higher the gear the better fuel econ you get because you travel faster under lower rev which means using less fuel. That's also why some cars have over drive (popular in US) to help reduce rev while on the motorway.
However, it does as you say depends on how much fuel it is consuming at the time of travelling. Because wind resistance is not directly porportional to speed, the resisance increases a lot more as you speed up. The more resistance you have, the more fuel you need regardless of your gear (conservation of energy). Lower gear means more push per drop of oil, but then it also means higher rev for faster burning of each drop of oil! You get the idea. So there is a sweet spot where resistance is just ok and you're travelling fast enough at a low rev. This sort of answered your first 3 questions.
Your example is unlikely given the speed you're mentioning, unless there is a very strong head wind or you're climbing up hill, I don't see how you need more fuel to travel at 80km/h in 5th than 4th.
humps
1.4SE Cobalt Blue, Bose and leather
I find 5th gear, foot on clutch, not going anywhere gives oohhhh, days and days of running on a tank.
Sorry, couldn't resist.
On topic again, just, but my Corolla trip computer reports my fuel consumption up into the high 70mpg. Way-hay! I'm off the patent office to get this little baby under my name and sold around the world making me a fortune.
Or trip computers could be a bunch on liars!
Steve - 2002 1.4SE petrol, Silver, black/black interior, Then an identical replacement 2003 A2. Now a Toyota Corolla 1.6 T-Spirit
Sorry, couldn't resist.
On topic again, just, but my Corolla trip computer reports my fuel consumption up into the high 70mpg. Way-hay! I'm off the patent office to get this little baby under my name and sold around the world making me a fortune.
Or trip computers could be a bunch on liars!
Steve - 2002 1.4SE petrol, Silver, black/black interior, Then an identical replacement 2003 A2. Now a Toyota Corolla 1.6 T-Spirit
swiv
Member
Thanks for the explanation, Humps. It confirms my own ideas - which are correct in theory at least.
Small sidenote on the 'lower revs equals better economy' though.
How about driving up a steep hill? No doubt, you can imagine that at some point when running in a high gear, you can only keep your pace by depressing the accelerator further and further. I imagine that as large quantities of fuel being burned in order to get the most power out of each stroke at those low revs. And there certainly is a point where these 'slow large sequences of detonations' are less efficient that 'smaller faster sequences of detonations'.
(Yes, I'm ignoring the fact that the engine has a power band too, below which it runs lousy anyway)
Well, enough of this. I'll just run in whatever gear suits me best. Doing about 50mph in 5th is not a situation in which you can react to traffic, IMO. So if I want that, I run in 4th. But when I'm 'not going anywhere', as Steve puts it, I'll happily stick to 5th. Heck, my boss is paying my fuel anyway
I can go up that 12% hill in 5th with less than 1500rpm and full throttle! Never mind the smoke behind my car
Happy cruising!
Edo
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
Small sidenote on the 'lower revs equals better economy' though.
How about driving up a steep hill? No doubt, you can imagine that at some point when running in a high gear, you can only keep your pace by depressing the accelerator further and further. I imagine that as large quantities of fuel being burned in order to get the most power out of each stroke at those low revs. And there certainly is a point where these 'slow large sequences of detonations' are less efficient that 'smaller faster sequences of detonations'.
(Yes, I'm ignoring the fact that the engine has a power band too, below which it runs lousy anyway)
Well, enough of this. I'll just run in whatever gear suits me best. Doing about 50mph in 5th is not a situation in which you can react to traffic, IMO. So if I want that, I run in 4th. But when I'm 'not going anywhere', as Steve puts it, I'll happily stick to 5th. Heck, my boss is paying my fuel anyway
I can go up that 12% hill in 5th with less than 1500rpm and full throttle! Never mind the smoke behind my carHappy cruising!
Edo
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
Interesting conversation. I am from the old school of having a car back in the 70’s with an optional overdrive.
I am one of those drivers who still is happy to use my 5th gear at every opportunity and that includes driving around town at 30mph at 1000rpm, and knowing that the car can cope [1.4tdi- chipped to produce 115bhp/258Nm]. Torque does talk in these situations.
Taking that all on board then I find my most economical speed is 60mph. A tank to tank reading, gives me on a very long motorway run, over 500m per refuel [35L + 7L in reserve].
The DIS is very misleading as is more useful as a guide to how to monitor your right foot. Used smartly, it can help reduce costs. If I work on the DIS reading only, then when on an appropriate flat road, a constant 110mph in 5th reads around 25mpg, yet a constant 55mph will read around 50mpg. Of course this is all dependent on the overall road conditions and things like the use of the cruise control.
Last year I took the car out on a long run and ran it at 70mph with 20L of fuel in it [pump to pump measurement] and managed 245 miles. At the same time the DIS showed an average of 46mpg. If I worked on the calculation that it worked out then I would have only have covered 202 miles.
The accuracy of the speedometer also plays a part as my Sat Nav mileage manager is always different from my car's speedo reading, but to answer your main question then I would say around 2200rpm appears to mine. 3000rpm is fun time and it is often hard to resist feeling the pull when there is a large amount of readily available torque at your disposal and this only leads to worse overall fuel readings.
I am one of those drivers who still is happy to use my 5th gear at every opportunity and that includes driving around town at 30mph at 1000rpm, and knowing that the car can cope [1.4tdi- chipped to produce 115bhp/258Nm]. Torque does talk in these situations.
Taking that all on board then I find my most economical speed is 60mph. A tank to tank reading, gives me on a very long motorway run, over 500m per refuel [35L + 7L in reserve].
The DIS is very misleading as is more useful as a guide to how to monitor your right foot. Used smartly, it can help reduce costs. If I work on the DIS reading only, then when on an appropriate flat road, a constant 110mph in 5th reads around 25mpg, yet a constant 55mph will read around 50mpg. Of course this is all dependent on the overall road conditions and things like the use of the cruise control.
Last year I took the car out on a long run and ran it at 70mph with 20L of fuel in it [pump to pump measurement] and managed 245 miles. At the same time the DIS showed an average of 46mpg. If I worked on the calculation that it worked out then I would have only have covered 202 miles.
The accuracy of the speedometer also plays a part as my Sat Nav mileage manager is always different from my car's speedo reading, but to answer your main question then I would say around 2200rpm appears to mine. 3000rpm is fun time and it is often hard to resist feeling the pull when there is a large amount of readily available torque at your disposal and this only leads to worse overall fuel readings.
ianjohnsonws14
Member
Oddly enough our old passat was more economical if you used the power to get up to speed quickly and then held a steady speed rather than gently accelerating!
Don't drive the A2 often enough to notice.
Ian
2002 1.4 Petrol SE, silver with climate control for SWMBO (1.4 Petrol SE, Ebony Black, grey leather, heated seats, climate, opensky, five spoke alloys on order) Honda Accord Tourer 2.2 iCDTi for me.
Don't drive the A2 often enough to notice.
Ian
2002 1.4 Petrol SE, silver with climate control for SWMBO (1.4 Petrol SE, Ebony Black, grey leather, heated seats, climate, opensky, five spoke alloys on order) Honda Accord Tourer 2.2 iCDTi for me.
humps
A2OC Donor
hey EF Max, I remember the overdrive nob on the gear stick used to be called 'sports mode' on the 80's auto 'boxes. I guess that sounded a lot cooler even for a teenager sitting in a volvo (how I 1st came across overdrive).
How interesting with your fuel consumption, I take it your reading is with all that heavy duty stuff you carry at the back of your car as well? Makes me thinking those extra hourses you have is making a good different not just on acceleration.
humps
1.4SE Cobalt Blue, Bose and leather
How interesting with your fuel consumption, I take it your reading is with all that heavy duty stuff you carry at the back of your car as well? Makes me thinking those extra hourses you have is making a good different not just on acceleration.
humps
1.4SE Cobalt Blue, Bose and leather
swiv
Member
Erskine, I get your point and I'm with you too. Luckily I don't have DIS to distract me, just the difference between the speedo and the satnav
Ian: I was taught the same strategy by my driving instructor and still practice it today. Especially the dash to 80km/h and skipping 4th is almost a habit. Or to 50km/h in 4th, skipping 3rd.
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
Ian: I was taught the same strategy by my driving instructor and still practice it today. Especially the dash to 80km/h and skipping 4th is almost a habit. Or to 50km/h in 4th, skipping 3rd.
--
(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)
Sometimes I take the stuff out for one reason or another, and for a short while I am refreshed to what a difference 110kg less feels like.. it reminds me of my drive home from the chipping company in Kent,, was like a excited boy with a new girlfriend who was on a promise..
As for overdrives, I had an old Triumph Vitesse with the switch on the steering coloumn,, didn't like it there so I got one for a gear stick from a Triumph 2000,, looked miles cooler and was easier to place your hand on,, also found a way to make it work on 2nd gear so effectively I had a seven speed gear box.. fun days, brings back nice memories, except for the unreliability of car in the 70's with twin carbs set up badly.
chivers
Member
Werner
I found the most economical speed for my TDi 75cv in 5th gear is exactly 52mph [=83kmh.] The most economical conditions are:
Empty out all the rubbish, family, most of the fuel etc. from the car to make it lighter.
Find a piece of road which is straight, completely flat, dry, has a smooth surface [not concrete] and has little traffic.
Choose a day with no wind, no rain, and as hot as possible [so the air is less dense.]
Turn off the air-conditioning [if fitted] and everything that uses electricity. Do not try this at night.
Close the windows and Open-Sky [if fitted.]
Make sure the engine is warmed up properly.
Make sure the tyres have enough air in them, preferably the pressures for a heavy load.
Drive the car using cruise control if you have it.
Under these circumstances my car DIS moves up and down between 95mpg and 110mpg. That is 2.94 l/100km to 2.53 l/100km, and my car is not one of the most economical A2's. I think the DIS reading changes because the alternator starts and stops.
NB The DIS on my car is never more than 1% different from the consumption I get from calculating fuel and distance.
Chivers ''
'02 A2 1.4TDi SE
I found the most economical speed for my TDi 75cv in 5th gear is exactly 52mph [=83kmh.] The most economical conditions are:
Empty out all the rubbish, family, most of the fuel etc. from the car to make it lighter.
Find a piece of road which is straight, completely flat, dry, has a smooth surface [not concrete] and has little traffic.
Choose a day with no wind, no rain, and as hot as possible [so the air is less dense.]
Turn off the air-conditioning [if fitted] and everything that uses electricity. Do not try this at night.
Close the windows and Open-Sky [if fitted.]
Make sure the engine is warmed up properly.
Make sure the tyres have enough air in them, preferably the pressures for a heavy load.
Drive the car using cruise control if you have it.
Under these circumstances my car DIS moves up and down between 95mpg and 110mpg. That is 2.94 l/100km to 2.53 l/100km, and my car is not one of the most economical A2's. I think the DIS reading changes because the alternator starts and stops.
NB The DIS on my car is never more than 1% different from the consumption I get from calculating fuel and distance.
Chivers '
''02 A2 1.4TDi SE
Thanks, Craig! Surprisingly, that's way better than even Audi's own 80+ mpg 'best'. But it
shows why people who use secondary roads (in the UK, where you have about 1/10th of the number of traffic lights as compared to Belgium..) generally have better mpg than
the ones using motorways - where 52 mph is too slow.
Werner
2001 1.4 TDI 75
shows why people who use secondary roads (in the UK, where you have about 1/10th of the number of traffic lights as compared to Belgium..) generally have better mpg than
the ones using motorways - where 52 mph is too slow.
Werner
2001 1.4 TDI 75
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