In all seriousness, on my gasser (which I suspect might run on a higher RPM range) it seems that if I can keep it at 3k, and about 70-75 MPG, it's good. Which is the safest speed too for here....
70=75 MPG I'm sure the whole forum would like to know how you get economy like that Now an ex-D3 owner after 7 happy years. Miss the car but not the big bills
19th Aug 2011 8:19 am
ZacSmith
Member Since: 26 Aug 2010
Location: Dover
Posts: 709
It isn't just a function of engine speed though. No doubt someone who knows about aerodynamics can explain but resistance goes up exponentially at speed. I did a whole journey down the M1 at 50 in traffic and the mpg was substantially better than at 70.VIN: A175A328***
It isn't just a function of engine speed though. No doubt someone who knows about aerodynamics can explain but resistance goes up exponentially at speed. I did a whole journey down the M1 at 50 in traffic and the mpg was substantially better than at 70.
The vehicle's total resistance has three basic components - rolling resistance, aerodynamic drag and grading resistance. The resistance that is most affected by speed is the aerodynamic resistance as the drag is related to the square of the speed. That is where you get that exponential looking curve.
Worst case is when you're driving a 3 ton D3 with barn door aerodynamics up a steep hill attempting to maintain a high constant speed. Obviously. Visit my car detailing blog at http://maksimumdetail.wordpress.com
The terrain has an impact to the figures. Yesterday on my drive from Poole to Edinburgh I reset the trip computer on the M40 and from there until around Preston I was showing as having averaged 30.9 mpg. Once I started climbing and dropping through the lake district on the M6 and hills of southern Scotland on the M74 the avaerage dropped to 29.2 mpg.
This was achieved while sitting at a cruise controlled 80 mph in a a car heavily loaded with a towbar mounted bike rack with 3 bikes on it. Just before turning off on to the A702 the average speed showed 77.4 mph.
Even when I arrived at my in-laws in Gifford the average was still above 70 mph and I had covered a lot of single carriageway roads.
19th Aug 2011 9:16 am
hughes_jh
Member Since: 09 Jan 2011
Location: Warwickshire
Posts: 294
Don't forget to factor in road conditions....
I agree that just below 70 is ideal on a flat straight road, but for the best mpg don't just set your cruise control to this speed constantly.
You need to allow the car to slow down a little when you hit a hill.... I'd suggest something like trying to lose 10mph consistently so you hit the crest of the hill at just below 60mph. Then of course you build that speed back up on the way downhill, if you're careful you can build this speed back up for "free" and still increase your average mpg. Better still, (on a closed road under controlled conditions....) you will be hitting the next bit of flat road at about 80mph giving you a bit of a chance to allow the speed to slowly average out to the optimum 67/68mph
but all of this is just my opinion
19th Aug 2011 9:29 am
euangibson
Member Since: 24 Dec 2010
Location: Borders
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Seem to remember TG did a London to Edinburgh run on one tank.Think it was Audi A8 4.0tdi if I remember rightly....only way they could do it was by not using the cruise control,the radio or the heating/aircon for the whole journey.....also kept a close eye on average speed ....
There are lots of factors in extracting maximum mpg"Better to remain silent and be thought a fool,than to speak out and remove all doubt" ?.....what rubbish...
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at 66km/hr (you can do the conversion must be around 41mph) turn on the cruise control (cc)
then use the command shift (will not kick down when in cc) you can get it in 6th gear
then sit back and enjoy 50+mpg even on small inclines
this can really bump up your average mpg
Yes it's silly slow but the object was max mpgIt is better to have and not need it then need and not have it.
. . . and coasting back downhill makes a big difference.A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
19th Aug 2011 11:33 am
CMG
Member Since: 12 Jul 2010
Location: USA
Posts: 956
Albourneboy wrote:
CMG wrote:
In all seriousness, on my gasser (which I suspect might run on a higher RPM range) it seems that if I can keep it at 3k, and about 70-75 MPG, it's good. Which is the safest speed too for here....
70=75 MPG I'm sure the whole forum would like to know how you get economy like that
Haha, that was a late night post.... 17 Discovery 5 HSE Si6, Fuji White on brown | 07 LR3 SE 4.4 Java Black on Alpaca
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19th Aug 2011 2:42 pm
albal
Member Since: 31 Jul 2011
Location: Southampton
Posts: 592
Personally I find I can hit 30+ following the trucks down the motorway. However, not following trucks at a constant speed drops to the mid 10's but I've done as low as this (sorry for the fuzzy image it's hard to hold the camera when you are on the run from the police):
19th Aug 2011 4:04 pm
al cope
Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10301
I find mine improves once I take the tintent off the back
On the run home from Bracknell to Brum on tuesday, sat at 67/68 with (lying b'stard) trip comp showing 35. In reality that should be about 30/31, as mine always reads over 3mpg high.
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19th Aug 2011 6:11 pm
JDO330
Member Since: 09 Dec 2009
Location: Hertfordshire
Posts: 95
What mileage do you get out of a full tank?
I've just done a run from Hertfordshire down to the Vendee in France, just over 550 miles on one tank and the fuel meter showing 32.4mpg. The vehicle was 4 up and loaded but no bikes on the roof etc. When we arrived at our destination the range was telling me I had zero fuel left, this journey was done at a constant 70mph (as best I could) in manual mode 6th gear and no cruise. I adopted the speed up down hill and roll up the other side routine rather than flooring it.
On the return journey, I pushed a bit harder and was travelling at anything from 70 to 90 mph, again in 6th gear and no cruise. This cost me about 60 miles on the range, mpg dropped to 30.4 on the computer thingy.
Regards, Jon.
19th Aug 2011 9:32 pm
abernanteagle
Member Since: 10 Aug 2011
Location: South Wales
Posts: 255
Along similar lines, anyone know how low will the range go before spluttering starts? My old Touran would splutter with 20 miles showing - dare not go below that with any car now.Dec 04 TDV6 HSE in Tonga green with Alpaca interior.
23rd Aug 2011 2:23 pm
al cope
Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10301
I've been about 10 miles negative (past 0) and its still been OK. put about 77 litres in, and if I recall its an 80 litre tank.
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I'm sure the whole forum would like to know how you get economy like that 
