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Another Mpg Question.....


branwell

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Having purchased a 2wd 2.0L Yeti with cruise control I was wondering what speed will give the optimum MPG with cruise control on, assuming a flat level road and benign conditions? I have been setting it at 59 mph (95km/hr) and this seems to give good results but is there a better speed? Thanks in advance. 

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If you know what revs coincide with the beginning of the torque plateau you could try that point in the rev range in top gear of course.......as a starting point at least.

Edited by Ryeman
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Slower is almost always more efficient, given that aerodynamic drag increases with the square of speed (and the power needed increases with the cube). However, you need to balance efficiency with the need to get somewhere and not be a nuisance.

As suggested, use the instant mpg display to see how it goes, but take the results with a decent pinch of salt, as this is a highly unscientific method which will yield little more than suggestive results.

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Have been through the 20 miles of 50mph contraflow on the M1 Jun 28-32 a few times recently. The mpg just keeps climbing, 60mpg at one point, but have to stop myself falling asleep, its sooooo sloooow.

 

Andy

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Due to published economy figures most manufacturiers again for maximum economy at 56mph.

 

Optimum, maybe, but not maximum.  Maximum economy is achieved coasting with the engine off (I know, I know - not safe but the point is valid).  Besides, the drive cycle used to determine fuel economy and CO2 emissions does not have a "56 mph" region and it has been decades since fuel economy at 56 mph was a required figure.

 

In reality the "NEDC" (New European Drive Cycle) is so detached from real-life driving that it bears little resemblance to what one might achieve (as we all know).  Furthermore, manufacturers use as many ways as they are allowed to improved the results from the NEDC.  For example, They charge the battery fully before the test.  They remove all non-standard items from the car (hence why spare wheels are increasingly optional).  Have a poke around in here for some detailed analysis of how the tests are manipulated.

 

In general terms, the best economy is achieved at the slowest speed you can comfortably maintain in the highest gear.  The biggest influence on fuel economy is the nut that connects the steering wheel to the seat.  After that, you can improve things by losing weight (car and you!), keeping on top of maintenance, keeping tyres inflated, keeping the tracking aligned, even (yes, really) using decent fuel and oil.

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Do you want to be a hazard to others on a motorway?

I am sorry i don't understand? Why is driving under the speed LIMIT a hazard to others?

My question does not ask how fast I can go but rather what speed give the optimimum fuel economy using cruise control.

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I am sorry i don't understand? Why is driving under the speed LIMIT a hazard to others?

My question does not ask how fast I can go but rather what speed give the optimimum fuel economy using cruise control.

Didn't mean to offend ....more an obtuse way of getting more info.

If you want MAX economy don't use cc unless you're an habitual throttle pumper.

Cc's problem is it's inability to predict unless the road is laser flat.

I use fixed throttle angle and let the speed vary but that only works these days with little traffic because most seem to nail a speed with cc and they get confused with variable speed of the vehicle in front.

Best speed for economy in absolute terms might be down near 40.

Sent from my iPad using Tapatalk

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56mph is about the sweet spot with my monster (2wd 2.0 tdi 110ps). The Maxidot shows around 60mpg on a good run down the M4, so I would work that out as 53-55mpg in real life figures. I hasten to add this isn't my regular cruising speed, it's nearer 65-70mph but I have done a few runs where I have tried to see what the optimum mpg mph is. I find that if you keep it below 65mph, fuel economy doesn't take as major a hit as going above these speeds does.

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I am sorry i don't understand? Why is driving under the speed LIMIT a hazard to others?

My question does not ask how fast I can go but rather what speed give the optimimum fuel economy using cruise control.

Assuming traffic and weather conditions allow, the expectations are that traffic will be maintaining a minimum speed - basically that of a speed limited HGV. It may not be ideal, but motorists aren't expecting to see cars doing abnormally low speeds, and won't necessarily react as well as they could.

If you are doing 56mph or thereabouts then you can sit in the left lane without causing and problems. The small speed differential means that anyone approaching from behind has plenty of time to see you and overtake safely.

If you're crawling along at say 40 or less then the closing speeds will be much faster, giving less time to react, and more chance of people having to brake or swerve to avoid you. If you've got two HGVs coming up behind you, the rear driver may not be aware of you at all. If the front one only moves to overtake when very close then all of a sudden the rear HGV is just behind you, going quite a bit quicker than a car he's only just seen. He can ether brake harshly or swerve, both of which are dangerous and caused, in part, by the slow car.

The big reason motorways are relatively safe given the volumes of traffic is that all the vehicles are going in the same direction at the same speeds - that's why small motorbikes aren't allowed on there. If you don't want to do HGV speeds when it's safe to do so, you probably shouldn't use them.

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I think a lot of that is nonsense. HGV's for a start have a better view of what is ahead, and if one indicates to move into the next lane I would think the one behind would notice and realise why. What happens if you have to drive to get off the motorway with an emergency tyre on ( speed limited to 50mph)?

I'm not advocating driving at slow speeds, but if you keep your distance, read the road ahead and concentrate on driving, you'll be fine.

 

Lastly, if all vehicles are going the same way at the same speed, nobody would have to overtake.

Edited by Anzio
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?.....

but if you keep your distance, read the road ahead and concentrate on driving, you'll be fine.

Unfortunately 'down here' too many truckies tailgate thus denying themselves the 'big picture'.
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I would imagine dust could also be a problem in some areas in your neck of the woods. We have lots of drivers who have laser vision, so don't have to slow down in fog or other inclement weather. :D

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There's zero tailgating between trucks on unmade roads, that's 'roadtrain' territory......they are frightening and you simply get out of the way.

Our rogue truckie problem is on motorways transiting the greater city area which are almost permanently heavily trafficked.

Too many of them end up in jail for the deaths they've caused.

On motorways I have a v good sense of possible outcomes heightened by age.

Being retired I'm rarely forced to use them.

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Just my view, I don't see the point of using Cruise control on our roads. Too much traffic.

 

I use it all the time.

Depends what roads you use and what speed you wish to travel.

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