I have two Model S, one 2014 S85 and one 2017 S75 (both are RWD). I designated the S85 as my road trip car since it had a slightly larger battery and free supercharging. However, with the recent free supercharging changes, my S75 now also has free supercharging, so the choice of which car to take is not as obvious as it used to be. My understanding is the following, 2014 S85 - Usable battery capacity 77.5kWh when new, but I have about 5% degradation at 90,000 miles, so that leaves 73.6kWh usable battery 2017 S75 - Usable battery capacity 72.6kWh hours new, almost no degradation, but let's round down to 72kWh. So, it seems that there is almost no difference in available battery capacity, generously the 2014 S85 has 2kWh more battery available, which certainly may be the difference between reaching the next supercharger and getting stuck.. .... but here is when it gets confusing. When I plan road trips with the two cars, I get wildly different results. For example, one segment on my road trip this summer is Lone Pine, CA to Beatty, NV via Badwater in Death Valley. I calculate the segment using the same parameters, 800 lbs load, 1.1 speed multiplier, 78F cabin temp, 120F outside temp and 10mph wind. The segment is 180.5 miles. S75 19" tires - energy used 52.6kWh (292 Wh/mile) S85 19" tires - energy used 63.8kWh (353 Wh/mile) There is a huge difference between the two cars here, and if they are correct, it makes the S75 the obvious choice. It doesn't seem reasonable to me at all, the cars are almost identical. On EVTripping, I get the following result, S85 - energy used 52.5kWh (292 Wh/mile) S75 - energy used 46.8kWh (260 Wh/mile) Are these numbers to be expected? I tried Harris Ranch to Tejon supercharger as well, and I get similar results, EVTripping S75 - 42.4kWh (364 Wh/mile) EVTripping S85 - 46.7kWh (403 Wh/mile) EVTripPlanner S75 - 45.6kWh (393 Wh/mile) EVTripPlanner S85 - 52.4kWh (451 Wh/mile) Is the S75 really that much more efficient than the S85?