johnlocke wrote: ↑
Sat Aug 01, 2020 4:11 pm
GRA wrote: ↑
Sat Jul 25, 2020 7:46 pm
alozzy wrote: ↑
Fri Jul 24, 2020 11:33 pm
I'd.be very surprised if the Model 3 has a larger surface area on it's front end than the LEAF, so I still contend that the larger spread between "real world" and EPA for the Model 3 comes must be due to more aggressive driving vs the results for the LEAF.
LEAF: 71"W x 61-62"H = 4331- 4,402in.^2
Model 3: 73"W x 56-57"H = 4,088-4,161 in. ^2.
I suspect it has more to do with different temps and winds.
The numbers above don't reflect ground clearance or body shape. the Leaf is rather square in cross-section while the Tesla is more ovoid. Cross-section data for most cars is surprisingly hard to find. I suspect that it has to do more with the different temperature ranges during the drive tests. Colder weather while driving the Tesla would tip the scales. Different cars on different days and different weather. Not surprising that the results differ from the EPA numbers. The Tesla hit 74% of it's EPA range while the Leaf got about 85% it's EPA range. At 75 MPH that is surprisingly good and the Tesla still went 50 miles further than the Leaf.
AIUI, Cd is the factor that modifies frontal area, with 1.0 essentially being a rectangle normal to the airflow (the reference below shows a cube @ 1.05), although skin friction also has an effect (individual Model 3 panel gaps might hurt it as well):
The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the projected frontal area of the vehicle. This may not necessarily be the cross-sectional area of the vehicle, depending on where the cross-section is taken.
The practical way to know is to drive both cars in the same conditions and accurately measure power consumption, after first trying to take account of differences in rolling resistance (tires etc.). And unless testing takes place in the same wind tunnel, Cd will vary considerably for the same car.
To the extent possible, C&D does their range tests under the same conditions, but those obviously can vary.
They also tested their long-term Model 3 at the test track at Chrysler's proving grounds, which eliminates any altitude effects and reduces the effects of winds. I'm guessing the Model 3 was hurt by the lack of a heat pump, as C&D found heater use (they test all cars with the climate control set to 72 deg.) could knock over 60 miles off the Model 3's range @ 70 mph, with seats and heater both on:
https://www-caranddriver-com.cdn.amppro ... v-range%2F
How Much Does Climate Control Affect EV Range?
We cranked up the heat in our Tesla Model 3 to find out just how much of an impact it has.