I've driven on nothing buy the OEM 19" rims and tires for nearly 80k miles until my referral program 21" Arachnids were installed last Thursday. On Friday I drove over 180 miles to Kansas City, MO, so had a chance to see what sort of impact the new rims/tires would have. While this general issue has been discussed many times before in comparing 19" to 21" OEM rims, I hadn't seen it specific to the arachnids. While I can't give an exact percentage comparison, I can tell you that I didn't really see a measurable difference in energy efficiency/range. On the Trip up there is a slight (400') elevation decrease and winds were calm. Driving the speed limit I averaged ~282Wh/mi over the ~183 miles to the supercharger arriving with ~65 miles to spare after a 252 mile range charge. Coming home was a bit more sketchy as with the elevation gain I also had a stiff headwind or quartering headwind the entire drive and my energy efficiency was closer to 333Wh/mi. That leg is always less efficient than the Northbound trip. Also, I had started with only 240mi rated range and arrived home with about 25 miles of rated, again right at 183 miles total. Hoping this alleviates some of the anxiety I had before starting the trip for others making the switch.