Speed verses driving range

[jeffand]

How does speed affect the driving range of electric vehicle?
There are three things to take into consideration where the energy is going to propel the vehicle down the road.

The first is tire rolling resistance. This is a relatively constant value, and is affected significantly by load and tire pressure.

The second is drive train losses. In an electric vehicle these would be CV joints, bearings, transmission losses, and electric motor and inverter losses.

The third is aerodynamic drag. The faster you go the more energy it takes to move the vehicle.

Here are some of the calculations for energy use at various speeds to over come aerodynamic drag.
:arrow: 0.295 Drag Coefficient

Speed - Watts used - Watt hours /Mile
10 MPH, 43 Watts, 4.3 Wh/Mile
20 MPH, 342 Watts, 17.1 Wh/Mile
30 MPH, 1155 Watts, 38.5 Wh/Mile
40 MPH, 2738 Watts, 68.4 Wh/Mile
50 MPH, 5347 Watts, 106.9 Wh/Mile
60 MPH, 9239 Watts, 154.0 Wh/Mile
70 MPH, 14672 Watts, 209.6 Wh/Mile
80 MPH, 21901 Watts, 273.8 Wh/Mile

You can see from the numbers that speed does have a significant effect on energy usage. The energy used to overcome the tire rolling resistance of the tires will be about the same for a given distance. If you travel further you will use more energy for tire rolling resistance.

For every minute the vehicle is on it is using power from the battery. So the longer trip, the more energy is used to run the electronic in the car. So at a certain speed you will achieve maximum driving distance. I think this is between 25 and 35 MPH.

 

[michael]

Tesla published a graph showing this for their cars

http://www.teslamotors.com/forum/forums/range-vs-speed-graph

You can see the Model S has maximum range around 20 MPH, and the old roadster just a bit slower.

Values for the FFE will be somewhat different no doubt, but I'm sure it's quite slow just as jeffand says. If you run the heater, drive a little faster!!!

 

[WattsUp]

60 MPH, 9300 Watts, 155 Wh/Mile

When I cruise at 60 mph in my FFE, it uses much more than 155 Wh/mi. More like 255 Wh/mi.

Where did your numbers come from?

 

[v_traveller]

Says that the #s in the table are the Wh/mi required to overcome aerodynamic drag of a vehicle with .295 Cd. Does not include other losses, I presume.

I get about 100Wh/mi more than those numbers too, for speeds above 40mph.

jeffand - I'm curious as to where the #s are from too, how it relates to Cd... I would think that the frontal area would have to factor in somewhere, and is the .295 Cd from a FFE? ... geek that I am, this is interesting stuff.

 

[jeffand]

Yes frontal area was used in the calculations.
I couldn't find the manufactures specifications for frontal area. So I used the height and width to calculate the frontal area.
I did find a formula that used, Speed MPH, Area (square feet) and drag coefficient to give me the horse power.
Watts = HP * 750
Watt hours = Watts * hours
WH/mile = Watt hours / miles

An interesting thing I found out is that the 4 door has a lower drag coefficient of 0.274. One of the reasons Ford choose the 5 door is because the frame is stiffer than the 4 door, and could handle the added weight better.

I did find a calculator for estimating the HP at a given speed at the Web Site listed below. But this is not how I came up with my calculations.
http://www.apexgarage.com/tech/horsepower_calc.shtml

 

[v_traveller]

Thanks! That's a pretty cool website.

 

[alexistexas]

Nice calculation.

 

[JimB_FFE]

Cruising at 70 mph, I see about 320 Wh/mile.
Speed kills range.

 

[pjam3]

I rarely ever drive on freeways. I try to stick to 25-40MPH roads where I know there aren't going to be a ton of people banging on their horn as I try to glide down hills. The few times I do take freeways, it kills my range.