dgpcolorado
Well-known member
I've noticed that there seems to be a common assumption that the only effect of cold weather on range has to do with reduced battery capacity as it gets colder plus increased heater use. However, there are other effects of cold temperatures on the mileage efficiency and range of an EV (or any other car):
•Increased aerodynamic drag due to increased air density
•Increased rolling resistance due to cold tires and gear/bearing lubrication
While I can't begin to calculate the increased rolling resistance due to cold, the air density calculations are straightforward. My tables below show the air density at various temperatures and humidity. As you would expect, increased air density increases drag and reduces mileage efficiency and range.
A factor that explains why those of us who live at high altitude get better gas and EV mileage is the reduced density of air with increased elevation:
[Bear in mind that as one goes up in elevation the temperature tends to decrease, increasing the air density somewhat. A temperature of 20ºC at 11,000 feet would be unusual, for example. So it isn't quite as simple as my table suggests. I use the example of density versus altitude at a fixed temperature and humidity to strip out the complicating factors usually present in density altitude calculations.]
The calculator I used to generate these figures may not agree precisely with other sources. However the purpose of the exercise is to show the relative difference in air density with changes in temperature or elevation and to point out that it is a significant factor in EV range.
•Increased aerodynamic drag due to increased air density
•Increased rolling resistance due to cold tires and gear/bearing lubrication
While I can't begin to calculate the increased rolling resistance due to cold, the air density calculations are straightforward. My tables below show the air density at various temperatures and humidity. As you would expect, increased air density increases drag and reduces mileage efficiency and range.
Code:
Relative Air Density Approx. Drag
Temperature Humidity Altitude kg/m³ Difference
-20ºC (-4ºF) 0% sea level 1.390 -16%
-15ºC (5ºF) 0% sea level 1.363 -14%
-10ºC (14ºF) 0% sea level 1.337 -11%
-5ºC (23ºF) 0% sea level 1.312 -9%
0ºC (32ºF) 0% sea level 1.288 -7%
5ºC (41ºF) 0% sea level 1.265 -5%
10ºC (50ºF) 0% sea level 1.243 -4%
15ºC (59ºF) 0% sea level 1.221 -2%
20ºC (68ºF) 0% sea level 1.200 0%
25ºC (77ºF) 0% sea level 1.180 +2%
30ºC (86ºF) 0% sea level 1.161 +3%
35ºC (95ºF) 0% sea level 1.142 +5%
40ºC (104ºF) 0% sea level 1.124 +6%
45ºC (113ºF) 0% sea level 1.106 +8%
Relative Air Density Approx. Drag
Temperature Humidity Altitude kg/m³ Difference
-20ºC (-4ºF) 50% sea level 1.390 -16%
-15ºC (5ºF) 50% sea level 1.363 -14%
-10ºC (14ºF) 50% sea level 1.337 -12%
-5ºC (23ºF) 50% sea level 1.311 -10%
0ºC (32ºF) 50% sea level 1.287 -8%
5ºC (41ºF) 50% sea level 1.263 -6%
10ºC (50ºF) 50% sea level 1.240 -4%
15ºC (59ºF) 50% sea level 1.217 -2%
20ºC (68ºF) 50% sea level 1.195 0%
25ºC (77ºF) 50% sea level 1.173 +2%
30ºC (86ºF) 50% sea level 1.152 +4%
35ºC (95ºF) 50% sea level 1.130 +5%
40ºC (104ºF) 50% sea level 1.108 +7%
45ºC (113ºF) 50% sea level 1.086 +9%
Relative Air density Approx. Drag
Temperature Humidity Altitude kg/m³ Difference
-20ºC (-4ºF) 100% sea level 1.390 -17%
-15ºC (5ºF) 100% sea level 1.362 -14%
-10ºC (14ºF) 100% sea level 1.336 -12%
-5ºC (23ºF) 100% sea level 1.310 -10%
0ºC (32ºF) 100% sea level 1.285 -8%
5ºC (41ºF) 100% sea level 1.261 -6%
10ºC (50ºF) 100% sea level 1.237 -4%
15ºC (59ºF) 100% sea level 1.213 -2%
20ºC (68ºF) 100% sea level 1.190 0%
25ºC (77ºF) 100% sea level 1.166 +2%
30ºC (86ºF) 100% sea level 1.142 +4%
35ºC (95ºF) 100% sea level 1.118 +6%
40ºC (104ºF) 100% sea level 1.093 +8%
45ºC (113ºF) 100% sea level 1.066 +10%
A factor that explains why those of us who live at high altitude get better gas and EV mileage is the reduced density of air with increased elevation:
Code:
Relative Air density Approx. Drag
Temperature Humidity Altitude kg/m³ Difference
20ºC (68ºF) 50% sea level 1.195 0%
20ºC (68ºF) 50% 500 m (1640 ft) 1.126 +6%
20ºC (68ºF) 50% 1000 m (3280 ft) 1.060 +11%
20ºC (68ºF) 50% 1500 m (4921 ft) 0.997 +17%
20ºC (68ºF) 50% 2000 m (6561 ft) 0.937 +22%
20ºC (68ºF) 50% 2500 m (8202 ft) 0.880 +26%
20ºC (68ºF) 50% 1000 ft 1.153 +4%
20ºC (68ºF) 50% 2000 ft 1.111 +7%
20ºC (68ºF) 50% 3000 ft 1.071 +10%
20ºC (68ºF) 50% 4000 ft 1.032 +14%
20ºC (68ºF) 50% 5000 ft 0.994 +17%
20ºC (68ºF) 50% 6000 ft 0.957 +20%
20ºC (68ºF) 50% 7000 ft 0.922 +23%
20ºC (68ºF) 50% 8000 ft 0.887 +26%
20ºC (68ºF) 50% 9000 ft 0.853 +29%
20ºC (68ºF) 50% 10,000 ft 0.821 +31%
20ºC (68ºF) 50% 11,000 ft 0.789 +34%
The calculator I used to generate these figures may not agree precisely with other sources. However the purpose of the exercise is to show the relative difference in air density with changes in temperature or elevation and to point out that it is a significant factor in EV range.