Continental divide

Earlier I mentioned about the planning involved in making a cross country trip...with a Tesla...pulling a trailer...for the first time.  Since this was our first trip with the trailer much of the planning relied on educated guesses as to whether we could make it to the next destination pulling the trailer.

For most of these segments I was pretty confident we would get there. Except for one segment that stood out from all the others...crossing the Continental Divide. 

With 94 miles between Superchargers the distance wasn't the problem.  On flat terrain the range with the trailer is 170+ miles.  It was the elevation change.  Almost 5000 feet gain in between the start and Vail Pass.  Then another 15 miles downhill to the next Supercharger.

Elevation profile

Grade and elevation changes

Elevation gain of this magnitude consumes energy rapidly and decreases range just as rapidly.  For example on flat ground the Model X consumes the amount of electricity used turning on three 100 watt lamps in your house for an hour...a bright room.

On the steepest climbs the consumption approaches 1500 watt hours for every mile traveled!  A five fold increase.  Turn on fifteen of those lamps in your house at the same time for an hour or run a space heater for an hour...a very bright and/or toasty warm room :-)

My original estimate was that this segment would use about almost three quarters of the battery capacity to travel the 95 miles.  And that assumed good weather (not cold and no headwind).

I did have several backup plans if we ran into weather or trouble:
1.  Stop in Vail for several hours to use a slower charger (1/10 the speed of a Supercharger)

2.  Unhook the trailer in Vail and leave Nancy and the dogs with the trailer while I went ahead with just the car and charged. Then I would return having more "gas in the tank" than when I left. 

3.  Rent a truck to pull the trailer over the pass :-(

I'm happy to report that none of the contingency plans were required :-)  We were able to make it to our destination with 35% battery capacity remaining.

Summary Vail Pass

One more thing.  One of the great things about driving electric is that a large part of energy used going up can be recovered going back down.  Below is a the trip planner for the Eisenhower Tunnel segment going into Denver.

Ignore the grey line and just look at the green line.  Starting at 92% battery capacity we go down to about 75% capacity after the first 10 miles.  A very steep climb to almost 11000 feet.

But then something interesting happens.  Battery capacity goes back up to about 78% by mile 25.  This was a very steep decline.  Imagine if driving a gas car you had more gas in the tank at the bottom of the hill than the top!

You can see the same thing happen just after mile 45.  The capacity goes down to about 67% but a few miles later is back up to 70%.  Another long and steep decline (6% grade).