Thread: Fuel usage more on highway than city driving???

Pushing a vehicle with aerodynamics only slightly better than a garden shed takes a lot of power and uses a lot of fuel. The D1 is not designed to be efficient at 115km/h.

The faster you go, the more power is needed and it increases at an alarming rate. The following explanation shows just how dramatic the increase is.


Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula.
http://en.wikipedia.org/wiki/Drag_(physics)

Driving at 115 km/h, there is about 52% more drag to overcome than there would be at 100 km/h.

There are a lot of other factors involved, so it isn't quite as simple as saying that you will use 50% more fuel at 115, but you will certainly use a significant amount more.

One of the factors that makes driving in the city uneconomical is the constant stopping and starting, slowing and accelerating. Highway driving is normally at a fairly constant speed, so there is no need to regularly use extra fuel to accelerate.

If you drive fast enough, especially in a vehicle shaped like the D1, you can easily use more fuel than sedate driving in the city.

Your consumption is pretty much what I would expect.

If you want to improve your highway economy, then slow down.

Our Defender is the first vehicle that we've owned that achieves better mileage around the city than on a trip....something about what a previous poster has said, "pushing a garden shed", obviously has something to do with it!
Pickles.

Work out the difference in time between 115km/h and the more legal 100km/h.

Then do it in real time on a real road... You don't save much , as the reality is.... you are slowed by traffic and road conditions, road works, known speed traps etc

Thank you all for the info!!! I mainly wanted to verify that it is not something to do with my engine that would make it increase the consumption at constant approx. 2700 RPM.

Aerodynamics certanly make sense.

Actually mentioned difference between 100 and 115 is quite noticable as well inside the car as far as noise and wind.

Thanks once more!!!