OT: mpg question

Not in a traffic jam.

That's not a fact. In fact rigid speed limits end up with people braking and accelerating all the time to keep to them. Biggest fuel burn for me is roads with humps in them and chicanes that are one way. Every time I slow or stop the car it takes a cupful of diesel to get it moving again

idling in traffic queues also burns a shitload

LOL!

Ther have been some horrendous accidents when people failed to do that. I made it a rule never to travel much faster than 20mph more than the people I was overtaking. Hurtlng past an old codger doing 60 mph and

There are no hard and fast rules - it's a balance between engine efficiency, profile drag and rolling resistance. My current car is actually best at around 50-70mph in top gear. Stopping ruins the fuel economy.

I always get more MPG on the way to the office than on the way back in both the van or the car. 41 mile round trip.

I have decided it's the roundabouts (17 of the bastards), other traffic and a heavy right foot. In a morning most of the roundabouts are usually clear so I do not have to stop. On the way home I have to come to a stop at the most of the roundabouts. It's the acceleration from standstill that causes the loss of MPG.

Have a go on the M1 from junction 34 to 32. 60MPH for air quality - applies to all vehicles including electric ones. And when there was 25 miles of 50MPH road works further south I got brilliant MPG going to Watford.

Not following this unfortunately. Are you saying a gallon of petrol will take you more miles travelling in first and second gear with lots of stop-start than it would driving at a steady speed on a motorway?

No, that staying in fifth gear doesn't work in a traffic jam.

What 55MPH instead of your usual 35MPH? I also got caught in a traffic

Back to your normal 35MPH without the traffic jam, and got 48.8 mpg.

Mike

I think we are at cross purposes here.

I said I got better mpg travelling north despite a traffic jam, and attributed this to the wind. You responded that driving in lower gears for longer in the traffic jam may also have been a contributory factor [to the improved mpg]. I simply queried the suggestion that a traffic jam would improve fuel economy as I cannot see how this can be correct. .

No mate - efficient vehicle:

Which was the point of my question, which others have already answered, thanks.

it will depend on the aerodynamics of the vehicle. I find my Enyaq is best at 62mph.

Airspeed rather than groundspeed I assume :-)

In anything with weight and a large engine that is absolutely the case. I monitor fuel consumption on a per tank basis. Two stops to let people past on a narrow country road will take a 10 mile trip from 35mpg down to 30mpg.

There is no single 'most economical speed' For a Boeing 737 its around

Personally, I find this highly doubtful.

Given the way that wind resistance rises with the square of speed (in general) it seems incredibly improbably that 55 mph should be more economical than 40 mph say.

Far more likely is that the OP had a weak headwind (say just 10mph) one way and a tailwind the other way.

Whilst a 10mph wind might not be noticed it effectively makes a 20mph difference in wind on a return journey.

I suspect the 55 mph figure has been taken out of context. More likely it?s a figure quoted and being significantly more economical than 70 mph but still allows reasonable progress to be made in real world traffic.

Tim

That's because you're discussing with rod speed.