Tahoe Snow Report

[sowbug]

Successful trip from San Francisco Bay Area to Tahoe City last night in an early-vintage (VIN 002009) Model X 90D. These were under harder than normal conditions:

• 5 people (2 adults, 3 mid-size kids), new 20" snow tires (the ones Tesla sells).
• Normal amount of cargo for 5 people.
• Yakima Swingdaddy hitch rack + Yakima HitchSki attached to the trailer hitch (no cargo on it, just transporting the rack itself).
• Temperatures ranging from mid-50s Fahrenheit to a low of 32 degrees at the summit (elevation 7,200 feet).
• No weather to speak of, though it did start snowing a few hours after our arrival.

Following are the interesting data points.

• Start San Mateo, CA.
• End Tahoe City, CA.
• Typical I-80 route.
• I normally drive speed limit + 7, and use Autopilot whenever it's available.
• At trip start, all-time mileage was 8,799, 359 Wh/mi. At trip end, 9,037 miles, 362 Wh/mi.
• Total trip: 238.2 miles, 486 Wh/mi.
• Started trip with charge at halfway through trip range (95% or so).
• Ended with about 32 indicated remaining miles (probably about 12%).
• One stop at Rocklin Supercharger, charged 11 mins more than the point where we got the "enough to continue your trip" notification. I recall it was about 220 remaining miles.
• Unfortunately I didn't note the Wh/mi at Rocklin or the top of the mountain, but I know that that leg hovered in the 600-680 Wh/mi range.
• I dialed down to speed limit + 0 (65mph) because the estimated range remaining was 25% at Rocklin but steadily dipped as we started up the hill. It stabilized around 16% when I reduced speed, but as it got colder it began dipping again, finally getting to 11% at the summit.
• I also switched to range mode when I slowed down.
• Interior temperature was set to 70 degrees.
• We turned on the defroster around 5,000 feet elevation and left it on for the rest of the trip.
• We didn't use the seat heaters.
• We didn't feel stressed-out enough to stop at the Truckee Supercharger. My wife did ask about it, but she agreed that we still had enough options left at that point that it wasn't worth the trouble.
• There was absolutely no traffic from Rocklin to Tahoe City.

As I say, I consider this a successful trip. However, I did have to take precautions (range mode, 65mph, and a solid charge at the bottom of the hill) that I could see a newbie not knowing enough to undertake. And had there been stop-and-go traffic up the hill (as there often is on ski weekends), or snow/rain that likely would have substantially reduced our aerodynamics, we would have had less margin for error.

I can't decide whether it would be a good idea to have one more Supercharger in between Rocklin and Truckee. On this trip, I probably would have stopped there for 15 minutes that I didn't actually need, which means that every other owner would probably do the same, which would mean that we'd be rate-limited to (60 / 15) x 8 = 32 Teslas per hour going to Tahoe North Shore. However, for days with traffic, having that SC option might make the difference between people arriving and people getting stuck. So it would have to be an "only if you really need it" Supercharger, which is a pipe dream.

 

[ecarfan]

had there been stop-and-go traffic up the hill (as there often is on ski weekends), or snow/rain that likely would have substantially reduced our aerodynamics

Thanks for your report. I wonder though, doesn't energy consumption per mile traveled go down in stop-and-go traffic compared to normal freeway speeds? Drag (aerodynamics) is much less at slow speeds even if they are stop-and-go and drag is the principal factor determining energy consumption. Snow/rain does increase energy consumption but I believe most of the increase is due to increased rolling resistance (tires plowing through water/snow on the road) and only some of it is due to increased drag.

Anyway, glad you had an uneventful journey to Tahoe, and enjoy the snow!

 

[thefortunes]

Thanks for your report. I wonder though, doesn't energy consumption per mile traveled go down in stop-and-go traffic compared to normal freeway speeds? Drag (aerodynamics) is much less at slow speeds even if they are stop-and-go and drag is the principal factor determining energy consumption. Snow/rain does increase energy consumption but I believe most of the increase is due to increased rolling resistance (tires plowing through water/snow on the road) and only some of it is due to increased drag.

Anyway, glad you had an uneventful journey to Tahoe, and enjoy the snow!

Yes, from years of driving EVs I can attest that you will get phenomenal energy consumption in stop-and-go traffic vs freeway speeds.

Just experienced this the other day - 5 mile backup on the freeway which took 30 minutes to clear and my wh/mi were in the 200 range for that segment vs the 260-270 I am currently experiencing at speed (this was in my Roadster, so you cannot apply the actual numbers to an S or X, but the physics still apply).

 

[aesculus]

A mini support of your efficiency findings: We came up over Donner Pass in the AM yesterday. Left about the same place further down the Sierra's and came out just above Auburn. Rolling travel up and down but the elevation difference was about the same. Speed was about 45 mph prior to getting on I80.

This image is at the Truckee supercharger with 482 Wh/mi for the climb and decent to Truckee. Only two of us plus junk so we probably had a total of 500 lbs in load. Drove aggressively with the temp set to 76 F.

There was only one Model S charging at Truckee and you can see the rate. Not bad. It was this way all across NV where we never saw another Tesla and every supercharger was ours exclusively.

I learned I don't like how the Trip Planner works. For us it seemed to error on getting you to the next stop in a muli-leg trip versus getting you to your destination quickest. For example it wanted us to charge longer at two supercharger stops and have us skip the alternate ones. That would have increased our travel by almost an hour (11 hour trip) versus charging less and stopping two more times.

 

[sowbug]

I wonder though, doesn't energy consumption per mile traveled go down in stop-and-go traffic compared to normal freeway speeds?

I've generally seen that to be true in my workday commute on 101. However, this particular kind of trip might have unusual factors that tip the balance. First, because it's mostly uphill, I don't think we can recapture much in regen, especially when it's I-80 winter-style stop and go (at best 5-10 mph where you don't have a lot of momentum). Second, there's a high fixed cost per unit time just to keep the car running in cold weather -- conditioning the batteries and the cabin. But I don't have either hard numbers or intuition to quantify those two concerns vs. the overall cost of moving 6,000 pounds up a mountain. They could be significant or minuscule.

 

[sowbug]

only some of it is due to increased drag

Yes, thanks, that's what I meant. Pushing water or snow aside isn't free.

 

[sowbug]

For us it seemed to error on getting you to the next stop in a muli-leg trip versus getting you to your destination quickest.

I griped about this elsewhere on this forum. It would be nice to tell the planner that you are comfortable running close to 0% and thus are willing to skip Superchargers if possible. Or, to put it closer to the way you've described it, that you want to minimize Supercharger time by scheduling charging when the battery can handle the highest charging rate.

 

[aesculus]

Successful trip from San Francisco Bay Area to Tahoe City last night

BTW. This is what you missed by driving last night.