About once a month I've been heading up to Milwaukee to visit my grandmother. So, I've gotten to be very comfortable with the drive and knowing how much range I need given various weather conditions (sun, rain). So as I prepared for my latest trip I assumed it would be relatively stress free. I got my car in January, so I know (or at least I thought I knew) what to expect heading up north now that the temperatures were dropping. Oh, but what a difference 40 degress F makes. So I usually leave the house with around 254 miles of charge, then hit Normal which is 203 miles away, then Rockford (another 124 miles) then head up to the hotel in Milwaukee (86 miles from Rockford). I've been driving 70 to 75 mph all the way up this summer. I usually arrive in normal with 30 miles to spare and Rockford and Milwaukee aren't even an issue. Now, in addition to the dropping temperatures (it was 37 degrees F when I left home), I also have new tires (Hankook 19s, used to have the Goodyears) and the dreaded 5.8 with no lowering is installed. But I figured I was ok. I'd do a range charge, run speed limit and keep the thermostat at a reasonable temperature. No problem. Right. So, my first surprise was my range charge. The car only charged up to 251 and then after I heated it up I ended up leaving with only 249 miles of range. Ok no problem. I figured the slower speed would make up for leaving the heater on so I headed out at a steady 65 mph with the heater set at 72. About 30 miles east of St. Louis I realize I am running thru my buffer like crazy. I had already consumed 17 mile of buffer and had barely covered a 1/4 of the distance. It was 37 degrees out. We were consuming 359 Wh/m. Way too much. So my son turned off the heat and I slowed down to 60. That was with about 160 miles to go. So huddled under a blanket and only getting a little heat in the car when I needed to defrost the windshields we made it to Normal with 14 miles remaining. The rest of the trip was relatively smooth. With the short distance to Rockford and Milwaukee we just charged a little longer and had enough buffer to run speed limit (65 mph) and keep the heat on 72 degrees. By the time we hit Milwaukee we were using 394 Wh/m. Crazy. But doable. Can't wait till we get the Supercharger between Normal and St. Louis will make these runs much smoother. Not looking forward to the ride home. It's supposed to be even colder, so looks like that stretch from Normal to home will be slow and a bit nippy. Glad I had the forsight to bring a blanket. Hope this helps others not make this same mistake. It's easy to get complacent about the range when it's warm out.