Some basic physics can help. If we keep the rolling drag constant by keeping the tires at a constant pressure, then aerodynamics defines the performance. Aerodynamic drag is driven by the air density so I copied this chart from Wiki and added details:
The modifications:
In reality we need to air up the tires on a cold day and then run a series of round-trip, benchmarks recording the Wh/mi and temperature. Then wait for the temperature to increase, deflate the tires to the target pressure, and rerun the benchmark. With enough data points, we can derive the Wh/mi as a function of temperature.
Once the function is derived for one Tesla or EV model, other EV models can do a benchmark and scale the function. Sloppy but close enough for the GOM.
BENCHMARKS
The blue line shows the Wh/mi from earlier benchmarks. Reading up the 60-65 mph speed, we're seeing ~230-235 Wh/mi:
NOTE: This chart was made using Tesla inflated tires, ~45 psi in part to match what an OEM Model 3 would achieve. Fully inflated, the blue curve is lower and range longer.
A math model needs to be validated. So I drove both directions on a 20 mi route with the tires at 50 psi before dawn at 34 F (1 C):
Bob Wilson
The modifications:
- added a grid
- added the (fahrenheit) to celsius values
- used 20 C / 68 F as a Standard Day temperature (what I use for performance benchmarks instead of 15 C (59 F))
- added the "drag %" and "power %"
- 229 Wh/mi = 250 Wh/mi * 91.5% -- the warm weather, 86 F advantage
- 250 Wh/mi = 250 Wh/mi * 100% -- Standard day, 68 F
- 282 Wh/mi -- 50 F day
- 311 Wh/mi -- 32 F day
- 348 Wh/mi -- 14 F day
- 389 Wh/mi -- -4 F day
In reality we need to air up the tires on a cold day and then run a series of round-trip, benchmarks recording the Wh/mi and temperature. Then wait for the temperature to increase, deflate the tires to the target pressure, and rerun the benchmark. With enough data points, we can derive the Wh/mi as a function of temperature.
Once the function is derived for one Tesla or EV model, other EV models can do a benchmark and scale the function. Sloppy but close enough for the GOM.
BENCHMARKS
The blue line shows the Wh/mi from earlier benchmarks. Reading up the 60-65 mph speed, we're seeing ~230-235 Wh/mi:
NOTE: This chart was made using Tesla inflated tires, ~45 psi in part to match what an OEM Model 3 would achieve. Fully inflated, the blue curve is lower and range longer.
A math model needs to be validated. So I drove both directions on a 20 mi route with the tires at 50 psi before dawn at 34 F (1 C):
- 276.6 Wh/mi measured / 124.2% ~= 223 Wh/mi @68 F (20 C)
Bob Wilson