Is it true the most economical speed to drive is about 56mph?

Question

I have a diesel and was told if I drove at around 56mph on the motorway, I would use a lot less diesel than driving at 70mph. Is this true? And is 56mph the best speed for this?

Answer 1

As long as you are in top gear and the engine is turning a low rpm. There will be less wind resistance and less drag, so you will get better mileage. The maximum mileage will be obtained when you are in top gear and going as slow as you can and still remaining in top gear. A lot of the time it isn't practical to do that, so 55 or 50 is about the best speed for mileage.

Answer 2

With gasoline prices exceeding $3.00 per gallon the Clean Air Partnership of Williamson County wants you to know that each 5 mph you drive over 55 mph is like paying an additional $0.15 per gallon for gas. Over 50 percent of the energy required to move a vehicle down the road is spent overcoming aerodynamic drag. When driving faster, the aerodynamic draft and rolling resistance increase. Therefore, the fuel economy decreases rapidly. According to EPA (Environmental Protection Agency) in normal traffic conditions, most cars operate most efficiently between 35 and 45 miles per hour; lower or higher speeds are less efficient. Therefore, if you drive 55 miles per hour on the highway, you can increase your gas mileage by as much as 15 percent.

Answer 3

Watch your rev counter and save the motor vehicle on the cruising speed for distance travelling - must be around 50 mph. i've got in basic terms pushed the 5 sequence so i'm not familiar with what's appropiate for the three. whenever you depress the accelerator slightly extra, your intake will boost. do not enhance up hard - take her up and down gently and use your equipment container. Brake gently. undergo in strategies that each and each passenger and each little bit of extra weight will boost your gasoline intake. do not use air con if pointless - that's extra much less costly to open a window

Answer 4

In short it is in top gear at a little over stall revs so that the engine isn't chugging, so that the wheels turn the most to each turn of the engine, in larger 6 and 8 cylinders this is especially effective because they put out more potential power but it still helps your economy in smaller cars too

Answer 5

It depends on the car.
The factors that influence it are:
The gearing
The aerodynamic drag
The engine speed for greatest efficiency
The rolling resistance of tyres
The friction in other bearings

It will also be affected slightly by the wind speed and direction.

However, it is around 50mph in top gear for most cars.
aerodynamic drag is proportional to the square of the speed, so if you double the speed, the drag is four times as much.
This means that above 50mph, drag starts to seriously affect the car's efficiency.

Answer 6

I have read somewhere that if you are running out of fuel, you will get more mileage driving at 56mph in 5th gear. Don't know if it was petrol or diesel though.

D.
X

Answer 7

It depends on the vehicle.
It also isn't necessarily the speed you travel at but the Revolutionary speed of the engine that is important. If you are doing 56 in third gear, I can assure you, its not the most economical.

Answer 8

Probably about right, if you're in top. If you have a rev counter, try to drive at about peak torque revs (it'll be in your handbook or the dealers will tell you) or a little above, NOT at peak power revs.

With my car, peak torque is at 2200 rpm, peak power at 3400rpm (turbo diesel) and I find around 2500 rpm to be the best compromise between performance & fuel consumption.

Answer 9

Colin M is correct, it's peak torque in the highest gear.

For my car it's 3000 rpm in 5th gear = 55mph.

Answer 10

Yes it is about right. you will be travelling about the same speed as the lorries so stick in the slow lane and not annoy the rest of us who want to get there faster.