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: 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 %" So keeping the same tire pressure (add air when colder) and speed (62 mph is a good number), use that particular consumption in Wh/mi and multiply it by the "power %". For example: 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 This was a 'back of the envelope' analysis. Another, non-dimension number, Reynold Number, can modify the power so I've posted the cube. This was mostly to give a math model, the background, to estimate the range loss as a function of temperature at a given speed with tire pressure kept at a constant value. 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) Now I wait for a noon to 2 PM window with a temperature close to 50 F (10 C). Repeat the calculation and see how close we come to "223 Wh/mi". Bob Wilson
