So, as charge gets very low, how accurate is the range estimate?

On the energy graph, placed on average and not instant, the available miles left (projected) is very accurate for any charge level (high or very low) given you keep the average energy consumption rate. Sounds complicated but its not.

Rated range on the speedo assumes that you are traveling at a specific energy usage per mile. If you drive very fast, have a strong headwind, cold weather, etc, then the remaining range will be wildly optimistic. As Kalud says, take a look at the energy graph's projected range. That's based on your recent driving history (5/15/30 miles depending on what you've selected) so can't project the type of conditions you'll experience in the future. If they are substantially similar to what you just drove then it will be quite accurate. If you have a big mountain at the end, not so much.

As others around the forum have mentioned, make use of EVTripPlanner. It will give you good guidance. Lastly, I keep an eye on how quickly my rated range and remaining distance to destination converge. For example, if I'm using 12 miles of rated range for every 10 miles I drive, then it's simple for me to determine if I'm going to make it without changing my driving style (that is, slowing down).

See if this video helps you out...

efusco said:

See if this video helps you out...

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Evan, that is a very nice video explaining how to use average. Thank you!

In the west, going up or down long grades, you can still get in trouble using the 30 mile average. We have climbs and descents that are very long, so the ups and downs don't get averaged out, even over 30 miles. Here is an example 30-mile average coming down from the Eisenhower Tunnel towards Golden, CO that cannot be maintained. At 0 Wh/mile you can go even further than 999 miles... :biggrin:

It shouldn't matter how accurate the low mileage readings are.

DON'T DO IT...

Allowing the Model S batteries to get very low on charge puts the batteries under greater stress and could impact battery life.

When driving, I try to plan for a 30 mile cushion - and if it looks like I may go below that while driving, I'll adjust my speed to get that cushion back.

For planning purposes, assuming relatively flat driving in reasonable weather conditions, I usually take the distance, add 30%, plus an additional 30 miles - and that's the range I want to have before leaving for the next charger or destination. And I then periodically compare estimated range with remaining distance (something the navigation software should do) and if it looks like I'm eating into my 30 mile cushion, then I'll slow down - and the earlier that's done, the better.

Argelius said:

I am in the middle of my first road trip and based on the projected range, I should be able to make it back to my house with 15 to 20 miles left.
Is that pushing it too close? I certainly realize it's not necessarily advisable to try to push it too closely -- just trying to get a handle on how the car responds when approaching "empty".

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I found the range estimage towards the end to be pretty accurate. Of course keep in mind that ranted range is based on a fixed consumption, while the energy graph shows you usage from your actual driving. The only dangerous situation is when you look at the usage of the last 5 miles from a flat road and then hit an uphill section.

Hills are the most challenging part about planning trips. Your average consumption goes up and down as you drive and you can't use your average to project range when the up or downhill sections are longer.

Tesla is collecting massive amount of actual driving data from all kinds of road and temperature conditions and different driving styles. I'm pretty sure it won't be too long when they add a projected range based on your navigation system. Based on your speed and temperature and current energy consumption they can compare your data with the data collected over the years and give a much more accurate range prediction.

As for driving down the battery all the way to zero. It's not good for the battery, but it makes a huge difference how you drive. If you go easy on the speed and accelerator, it's fine. If you go 80 uphill when the car has 10 miles left, that's not good for the battery and the car might even shut down before you read 0 miles. I have been able to go passed zero several times while going very careful and slow. You should always have a buffer when arriving, but if you have to use the buffer for some reason, just go easy and don't worry.

David99 said:

As for driving down the battery all the way to zero. It's not good for the battery, but it makes a huge difference how you drive. If you go easy on the speed and accelerator, it's fine. If you go 80 uphill when the car has 10 miles left, that's not good for the battery and the car might even shut down before you read 0 miles. I have been able to go passed zero several times while going very careful and slow. You should always have a buffer when arriving, but if you have to use the buffer for some reason, just go easy and don't worry.

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^^^ This. One thing that will mess up your estimate is wind, which is hard to plan for other than by leaving a large enough buffer. I had one trip where the last leg was against an unexpected head wind so I ended up with 17 rated miles left (29 projected miles) instead of 60+ rated miles. I did have a couple of places where I could have charged if it came to it.

@efusco
Very helpful video. Thanks!

The range meter very accurately describes how much energy is left in the battery. Using "Rated Range" it's 300wh per mile. So if it says you have "5 miles of range left" you can be very confident that you can get to another (5 * 0.300) = 1.5kWh of energy in that battery.

But what catches people out is that over short periods of driving (especially if you happen to be climbing a very steep hill, or going fast, or pushing rain/snow out of the way) you can easily hit a high burst of required power, and in that case you might only be able to go 2 miles.

Then again, if you're heading down the mountain from the continental divide into silverthorne, you'll be fine. ;-)

+1 on the ev trip planner and headwind.

I recently made a trip from Phoenix to Flagstaff, which has 10k feet of elevation gain. I had done the trip before and used the trip planner so I knew what to expect, but I found myself with a high headwind cruising uphill at 80mph. Over the second half of the trip I used 130 rated miles over 70 actual miles.

Thanks to the trip planner and watching the energy graphs I was able to keep an eye on things and arrive with plenty of battery left (30 miles).

jerry33 said:

^^^ This. One thing that will mess up your estimate is wind, which is hard to plan for other than by leaving a large enough buffer. I had one trip where the last leg was against an unexpected head wind so I ended up with 17 rated miles left (29 projected miles) instead of 60+ rated miles. I did have a couple of places where I could have charged if it came to it.

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bob_p said:

It shouldn't matter how accurate the low mileage readings are.

DON'T DO IT...

Allowing the Model S batteries to get very low on charge puts the batteries under greater stress and could impact battery life.

When driving, I try to plan for a 30 mile cushion - and if it looks like I may go below that while driving, I'll adjust my speed to get that cushion back.

Click to expand...

+1

a) We keep our cars forever
b) I never run my ICE cars to "E", the same goes for the P85
c) I want to treat the most expensive component(s) of the S with utmost care

In my view, running the battery down close to empty once in a while when needed is nothing to be concerned about. Tesla has a buffer beyond empty to ensure it is never fully discharged and provided you charge it right when you get to your destination, just like not letting it sit with a range charge, you should be able to enjoy the full range without sweating it, on those occassions it's needed.