Speed kills the economy

[riddick]

I have just come across an article saying that driving at 100km/h can kill the economy by as much as 50% and driving at 110 km/h can decrease the economy by 70%.

I am not talking about the Leaf and the article is in Royal Auto. 

They are talking about a diesel Audi with an average consumption of 3.4l/100km, but this increases to 5.0l/100km at 100km/h and 5.8l/100km at 110 km/h.  This has been measured in a car shadowing the solar cars in the Darwin to Adelaide race.

Now, we Leaf owners all know this stuff, but looks like it is now filtering to the diesel heads as well as these cars are becoming more efficient.  The petrol heads are still thinking that driving on a freeway is more efficient then slowly in the city, because their cars are just so terribly inefficient...

The only petrol heads that are really aware of the speed vs economy issue are the Germans as they can drive very fast on the autobahn.  When I drove at 210-220km/h on the autobahn, I could not believe how fast my petrol gauge was dropping, at some point I had to actually slow down :-) as I wasn't going to make it to the next petrol station.

[stewartm]

Double the speed, four times the energy. KE = 0.5 x mass • velocity squared
The Bugatti Veyron, fastest production car, at full speed of 400+km/h, it empties its 100l fuel tank in 12 minutes.
Hence the LEAF uses more energy at 100, also the efficiency of the electric motor drops at much higher speed.
When you are in a nice comfortable car, does it matter spending a few more minutes in there, and save some energy?

[markrmarkr]

May 8, 2014 19:15:20 GMT 11 stewartm said:

Double the speed, four times the energy. KE = 0.5 x mass • velocity squared

...

When you are in a nice comfortable car, does it matter spending a few more minutes in there, and save some energy?

The Kinetic Energy calculation is not really appropriate as it relates to speed change. When your sitting on 110km on a highway your speed is constant so there is no KE change. even though your using ~20KW. The bad energy-economy comes mainly from overcoming wind resistance, and to a lesser extent, greater inefficiency in the motor/battery at that speed. Power required to overcome drag due to wind resistance is proportional to velocity³.

...


I have to admit, there are times I drive slower, and spend more time in the car than I have to, as an escape from the daily grind. I never did that in my old car.

[Deleted]

I almost didn't make it to Mandurah in imiev even though I was nanna driving
ie. 19kmh below speed limit
on mitchell fwy.

had a headwind
Monkeyboy travels at 70kmh on the side roads.
forums.aeva.asn.au/imiev-measured-data_topic3870_post50280.html?KW=mandurah+monkeyboy#50280

Kurt recommends 80kmh in his imiev.

went to york travelling at 70kmh.
just made it without going into turtle mode.
was a truck route; one truck was doing 60kmh.

forums.aeva.asn.au/imiev-measured-data_topic3870_post50552.html?KW=york#50552

[Brian]

I knew about the aerodynamics, but not that the efficiency of the electric motor drops at higher speeds. So, in layman terms, that means you have to ' pump in exponentially more ( electrical )juice ' than at lower speeds ?

[unnefer]

I don't know if it decreases economy by 50%, but it definitely has a noticeable effect on range when driving at 100km/have.

Approx half my commute to work is on the motorway/freeway at 100km/h - approx 30km each way - but I still manage 140km of range from a full charge.

On the weekend, keeping at 80km/h or less, my range increases to approx 155km. That's only a difference of approx 15km when not traveling at 100km/h for 60km.

Not a scientific measure at all, just a real world observation

I've ordered an elm327 bluetooth obd scanner off ebay, so I can check the actual reported power usage at 100km/h and do some proper math to see if it really would effect economy by 50% if you would like?


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[Brian]

That would be great, thanks.