In getting to Yellowstone on I90 this (late) spring, there is a SupC gap between Rapid City, SD, and Billings, MT, of 318 miles. I am guessing I will need to find an RV park in Sheridan or Gilette. But I was also wondering about the potential of driving 50 mph for 6 hours (go the 318 mi but go slow method). A wonderful algebra problem is in here. If this or something like it would work, then: If a couple drive their MS from Rapid City, SD, to Billings, MT, which is faster: Driving at 50 mph to make it from one SupC to the next OR Driving to Sheridan, 255 mi, getting enough charge at a 220 outlet RV park (for how long?) and getting to Billings, MT, SupC while driving 70 mph the whole way? Please show your work... And thanks for the help...

I don't have a Tesla, but if I let EVtripplanner do the work: 2 hours from Rapid City to Gillette + 5 hours charging (assuming full power at outlet) + 3:20 to Billings = 10.5 hrs. 6.5 hours @50mph straight through. I probably wouldn't be brave enough do do it straight through, and since it is uphill then downhill, I'd be freaked out at the halfway point. Don't go by me, I'm always wrong about everything.

You might consider altering your route and exiting I90 near Whitewood and taking a state highway to Belle Fourche and then driving US212 to Broadus to charge at an RV Park there for several hours before rejoining I90 south of Billings. I think some around here have used that route instead of driving the interstate the entire way. You could more easily rate your speed on a two-lane road than on an interstate. I haven't checked the mileage, so do not know if it is shorter or not.

Your math is probably correct, but assumptions I question! When 220 outlet can get you 27 miles per hour of charge, why charge for 5 hours? How about 2.5, which should be sufficient with buffer? That makes it more like 7:50 @ 65 with stop vs. 6:30 @ 50 without. HOWEVER, I really do not think you are likely to make it 318 miles at 50 mph. Pretty iffy, and at mercy of traffic, weather, etc. I think you'd be doing 40 or 45 to get that far. It is miserable torture to drive that slow. So, to me, it's a no brainer: Drive 65 and take 2.5 hours at a 50 amp service on the way. Maybe you only need 2 hours.

Going 45 you should be able to make it. I would preheat the car for 20-30 minutes before you left. Just make sure you take range mode off before then put it back on once you start driving. You might be able to make it going 50 depending on elevation, temperature, and wind.

Yes, I have done the shortcut route multiple times, each time stopping in Belle Fourche at the RV Park just outside town (I put it on PlugShare). This route is FAR shorter, and a very pleasant drive. The speed limit is 70mph, though if you are hypermiling, obviously you should go slower. There is very little traffic on this route, so setting your own pace is not a problem, even for a 2-lane blacktop. Actually, I really wish Tesla would just put a supercharger in Belle Fourche and give us this as a full speed option. Back when I drove ICE cars, I always went this way anyway!

From this chart: It looks like you can make it going 55 mph (YMMV). I think it's preferable to just drive slow and take the most direct route. You wanted math: 318 mi / 55 mph = 5.7 hours Everything else (detours and charging) will take longer. More info on the blog: Driving Range for the Model S Family | Tesla Motors

For 315 miles you want a total of about 360 miles of range--more if the weather is bad--because stuff happens (and it happens to everyone). Somewhere around the 200 mile mark, I'd find an RV park with 50 amp receptacles or a kind Tesla owner (PlugShare) with an HPWC and charge until you have 190 miles of range. There's really no reason to doing anything else. This is how you eliminate range anxiety.

For 315 miles you only need 315 miles of range. If bad stuff happens, drive slower. There is an amazing gain in range as you slow down.

Does OP have cyclones? Bump the tire pressure of course. Look into those flat hubcaps. Then you could probably go 55 easy.

That's the 318 mile direct route the OP was asking about. You're right, of course, charging along this route is the way to go. I made the mistake of answering the question asked. I thought it was a test.

Note that there's a supercharger planned for Sheridan WY. It's "coming soon" on Tesla's map. If you're really lucky it will be done before your trip

Unless your driving into a headwind then the efficiency of going slower can be overcome by the extra time you have to travel against the headwind. The exact opposite is true if you have even a small tailwind.

Not my experience. The range listed on Tesla's website is from 100% to the point where the car shuts off. It is not where it shows 0 miles. I would not go by Tesla's graph that was posted here. It unrealistic. And driving it below the zero % line is bad for the battery and pretty much a gamble. If there is anything uphill in the last few miles you are definitely going to get stuck. 230 miles is really pushing it in an 85 in normal traffic. more than 300 is painful as you have to drive 45-50.

I laughed at this graph when I saw it initially, and I'm still laughing at it today. It shows a 200 mile range in a P85D at 85 MPH! I'm not sure 200 miles is even possible at 75 MPH. When it gets warmer and I have more time I plan to test my hypermiling skills some more, though, and we'll see. Just the other day starting at 100% charge I did 229 miles in my P85D with an average speed of 70 MPH (mostly between 65 and 78 MPH) in pretty much ideal conditions (~60F, virtually no wind) arriving with 0% (1 rated mile) charge at the supercharger. This is the closest I've come to this graph, which says ~260 for this speed. With the superchargers it almost doesn't make sense to slow down a lot of the time. For example, I was able to get 50% charge in ~23 minutes. That's 128 rated miles for me. Add 5 minutes for on/off highway for this stop (~.5 miles), travel ~95 miles to the next supercharger at ~75 MPH average and I've now gone 324 miles in 4 hours 49 minutes for an average speed of 67.3 MPH. This graph says I can go ~275 miles at that speed (doubtful) and 325 miles is somewhere around ~57 MPH (also doubtful), which would take 5 hours 42 minutes. Save nearly an hour driving faster using superchargers. Sorry for OT, just had this in mind when I saw that graph. lol.

No cyclones. Thanks for all the responses. We look forward to the adventure. Any further comments would be examined carefully as well. At this point, I am tempted for the shorter route, RV park, and others have done that ahead of me. We are novices at interstate travel, with a Model S, and off the SupC network in particular. And I have seen the Sheridan proposed SupC, which would make a difference; I watch supercharger.info regularly to see what might pop up in this Billings to Rapid City gap. I was, previously, watching the I80 gap through Nevada, and it is filled in (and that was quick).

The chart says 19" Primacy, your signature says 21". There goes ~10% HW range. Add some tire pressure difference, wheel (mis)alignment, non-constant driving (real world is never constant and average is not the same as constant) and voila. Do not be like those ppl who look at EPA range numbers and scream liars! because they don't get exactly the same numbers. 50 mph for one hour results in same average speed as 33 mph for half an hour (16,5 miles) and 66mph for half an hour (33 miles). At 33mph MS consumes about 150Wh/mile, at 50 about 210Wh/mile and at 66 about 290Wh/mile. 50 miles at constant 50 mph will thus consume 10,5kwh. Same 50 miles at 33mph and 66mph for half an hour each will consume 2,5 + 9,5 = ~12kWh There you have 1,5kWh or 15% difference in energy consumption at same distance and same average speed just because some par of the driving was at a bit higher speed. General rule for high range is maintain constant speed at all times.

According to EVTripPlanner (which I've found to be pretty accurate) you'd need to drive at less than half the speed limit (or an average of about 30mph) to make the trip without charging and it would take over 10 hours. Slowing down can get you a some extra range, but 318 miles is even above ideal range.

Does anyone have eyes on the SC coming to Sheridan? Where is going to be, close to the Hwy? Has it been started? Is there going to be on in Gillette? Questions questions inquiring minds want to know!

I just checked EVTripPlanner and it tells me that you can make it (using 261 rated miles) by going 0.8 of the Google Map traffic based speed (this is not the speed limit... it is generally higher than the speed limit). 318 miles / 6:25 hours is an average of about 50 MPH. The trip planning software (current version, not the new 6.2 version due to be released real soon now) is actually very good. I find that it estimates battery usage over terrain accurately. When you do this route, set your destination and watch the graph. You will find that as you adjust your speed, it will give you a fairly accurate end point battery state. If you find that it is going into negative numbers, slow down and watch the graph adjust. It's also important to remember to keep you speed steady (use the TACC). Due to the non-linearity of drag (it's exponential), you can't average half the trip at 60 with half the trip at 40. The time will come out to an average speed of 50 but the energy consumption won't.