Efficiency at 70 vs. 75 vs. 80 on highway?

[adoublee]

Is 53 minutes worth $21.39 plus tax, call it $23?

Often yes, sometimes no.

Also - the impact of wind is exaggerated at 80mph. Very different mi/kWh driving an hour in one direction than turning around and going the other.

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[bryan995]

Assuming those are accurate, that's a 10% drop in miles per kWh from 70 to 75, and another 11% drop to 80, and in total a 20% drop going from 70 to 80mph.

Let's put this into MONEY terms.

If you drive 500 miles at 2 miles per kWh, you'll use 250 kWh of electricity in the truck. Assuming ~ 10% loss from DC charger to vehicle, that means you need to purchase 278 kWh. Assuming EA Pass+ rates of 31 cents plus tax in most states, that's $86.18, plus tax, to drive 70.

At 80mph, you'll use 500/1.6 = 312.5/.9 = 347 kWh x 31 cents = 107.57 plus tax.

So you'll pay $21.39, plus tax, to drive 10 miles faster for 500 miles. You'll get there 53 minutes sooner - 6:15 vs. 7:08 total time spent.

Is 53 minutes worth $21.39 plus tax, call it $23?

for anyone buying a $80k it damn well better be !

 

[sotek2345]

Have you ever run the numbers on that? Because they say the opposite. With 50kW charging infrastructure it may well have been true but with 100kW+ chargers the charge time is fast enough to offset the lost time to get the charger and back to the road.

The break points come when you have to add a stop, because you lose so much time getting off the highway, getting to the charger, hooking up, etc.).

If going faster means a 40 minute charge vs. a 30 minute one - faster is better. If going faster means a 40 minute charge followed by another 10 to 15 minute stop (vs. 1 40 minute stop), slower is better.

 

[jb56]

Converted to range, that would be ~260 miles at 70mph (lines up with most testing, maybe a little low), 235 miles at 75mph (the little testing I have seen says this is about right, but maybe a little high), and 210 miles at 80mph. Cut ~30% off in the cold.

In general, given the Lightning's relatively flat and fast charging curve, drive at whatever speed you are comfortable at and gets you to the next charging station with a comfortable buffer.

In our Mach-e, I generally start out with the cruise set to 72, but then start bumping it up part way through the trip when I am sure I have a safe range buffer.

My parents live about 280 miles from me and we take the kids to visit several times a year. I also have to drive to that town for work a few times a year. It's a bit disappointing that I couldn't even make it there on a single charge even at 70 MPH (when the speed limit is 80 MPH and most people act like people driving 70 are terrorists).

 

[swesson]

Have you ever run the numbers on that? Because they say the opposite. With 50kW charging infrastructure it may well have been true but with 100kW+ chargers the charge time is fast enough to offset the lost time to get the charger and back to the road.

I haven't run the numbers for the Lightning., but you can see it in the truck as you drive. Just watch how the faster you drive. It recalculates your range and the time you will need to spend charging at the next charger. Contrarywise, notice if you drive slower, it will suggest skipping upcoming chargers outright. (I had this happe. On a recent trip from Denver to Dallas) And you're correct that charging technology has improved a bit. Here's a link to some data where Tesla supplied the data on the concept. https://teslamotorsclub.com/tmc/threads/ideal-highway-speed.132071/

 

[LightningShow]

I haven't run the numbers for the Lightning., but you can see it in the truck as you drive. Just watch how the faster you drive. It recalculates your range and the time you will need to spend charging at the next charger. Contrarywise, notice if you drive slower, it will suggest skipping upcoming chargers outright. (I had this happe. On a recent trip from Denver to Dallas) And you're correct that charging technology has improved a bit. Here's a link to some data where Tesla supplied the data on the concept. https://teslamotorsclub.com/tmc/threads/ideal-highway-speed.132071/

Just go into ABRP and set a location 1000 miles away and adjust your travel speed to 100% of reference, then run the same trip at 115% of reference speed. I just did this with the trip I did last week, which was 555 miles. The total time was 30 minutes shorter for the faster speed despite requiring an extra charging stop and almost a half an hour more charging. I also increased my charge stop loss time from 5 minutes to 10 minutes. It's still a half an hour faster.

The break points come when you have to add a stop, because you lose so much time getting off the highway, getting to the charger, hooking up, etc.).

If going faster means a 40 minute charge vs. a 30 minute one - faster is better. If going faster means a 40 minute charge followed by another 10 to 15 minute stop (vs. 1 40 minute stop), slower is better.

I've found this not to be the case. 10mph increase in travel speed more than makes up for dead time on extra charging stops. Although, unless you're driving very long distances it's not likely to make a huge difference. Probably best to just drive whatever speed you feel comfortable driving and charge when needed. Making up 30 minutes on a 10 hour drive isn't very meaningful to most people.

 

[swesson]

Just go into ABRP and set a location 1000 miles away and adjust your travel speed to 100% of reference, then run the same trip at 115% of reference speed. I just did this with the trip I did last week, which was 555 miles. The total time was 30 minutes shorter for the faster speed despite requiring an extra charging stop and almost a half an hour more charging. I also increased my charge stop loss time from 5 minutes to 10 minutes. It's still a half an hour faster.




I've found this not to be the case. 10mph increase in travel speed more than makes up for dead time on extra charging stops. Although, unless you're driving very long distances it's not likely to make a huge difference. Probably best to just drive whatever speed you feel comfortable driving and charge when needed. Making up 30 minutes on a 10 hour drive isn't very meaningful to most people.

Thanks! I will try that.

 

[RickLightning]

Just go into ABRP and set a location 1000 miles away and adjust your travel speed to 100% of reference, then run the same trip at 115% of reference speed. I just did this with the trip I did last week, which was 555 miles. The total time was 30 minutes shorter for the faster speed despite requiring an extra charging stop and almost a half an hour more charging. I also increased my charge stop loss time from 5 minutes to 10 minutes. It's still a half an hour faster.




I've found this not to be the case. 10mph increase in travel speed more than makes up for dead time on extra charging stops. Although, unless you're driving very long distances it's not likely to make a huge difference. Probably best to just drive whatever speed you feel comfortable driving and charge when needed. Making up 30 minutes on a 10 hour drive isn't very meaningful to most people.

The problem comes in when you're comparing absolutes in software that doesn't match reality. I put in a 2000 mile trip. At normal settings, ABRP tells me 39:40, with 14 stops of 8:37. At 115% speed, it tells me 39:04, with 18 stops of 10:49. In reality, that 36 minutes of "savings" is going to be eaten up by the following:

- having to switch to a working charger
- having to wait for a charger
- being delayed in getting from the highway to the charger by traffic, and traffic lights.

The less stops, the better. That's why unless I'm traveling to states with per minute EA rates, I charge to 80% even if I only need to charge to 71%.

 

[LightningShow]

The problem comes in when you're comparing absolutes in software that doesn't match reality. I put in a 2000 mile trip. At normal settings, ABRP tells me 39:40, with 14 stops of 8:37. At 115% speed, it tells me 39:04, with 18 stops of 10:49. In reality, that 36 minutes of "savings" is going to be eaten up by the following:

- having to switch to a working charger
- having to wait for a charger
- being delayed in getting from the highway to the charger by traffic, and traffic lights.

The less stops, the better. That's why unless I'm traveling to states with per minute EA rates, I charge to 80% even if I only need to charge to 71%.

Maybe, maybe not. It could go either way based on a number of things out of your control (which is why I said the difference isn't worth changing your normal driving habits). Of course, that's true no matter what speed you travel. If you travel slower you'll likely stop at different charging stations and could end up at a bad one, or a busy one, as a matter of chance. My point is that we know for absolute certain that the cumulative driving and charging time is significantly less when you travel 10mph faster. The extra stop(s) adds potential variability to the arrival time. If that is something that bothers you then you should reduce your speed and stops. If you want to risk a potentially slower extra stop to buy yourself some arrival time then there's nothing wrong with that either. If everything goes well you'll get there a little sooner.

 

[RickLightning]

Another factor to consider is that once you exceed 80, handsfree driving is disabled. I'd much rather drive 75 with handsfree than 81 without.

 

[FirstF150InCasco]

Assuming those are accurate, that's a 10% drop in miles per kWh from 70 to 75, and another 11% drop to 80, and in total a 20% drop going from 70 to 80mph.

Let's put this into MONEY terms.

If you drive 500 miles at 2 miles per kWh, you'll use 250 kWh of electricity in the truck. Assuming ~ 10% loss from DC charger to vehicle, that means you need to purchase 278 kWh. Assuming EA Pass+ rates of 31 cents plus tax in most states, that's $86.18, plus tax, to drive 70.

At 80mph, you'll use 500/1.6 = 312.5/.9 = 347 kWh x 31 cents = 107.57 plus tax.

So you'll pay $21.39, plus tax, to drive 10 miles faster for 500 miles. You'll get there 53 minutes sooner - 6:15 vs. 7:08 total time spent.

Is 53 minutes worth $21.39 plus tax, call it $23?

Edit - it was rightfully pointed out here that I did NOT include stop time in this calculation. BIG OMISSION.

Thanks for turning this into simple to understand numbers. So much better a way to look at things. For me, an extra 55 minutes is worth $23.

 

[Maxx]

Have you guys tried folding your mirror at 80 mph? I couldn’t believe my eyes.

 

[azypather]

I have a leadfoot. My 2022 Lariat SR shows only 221 miles of range when charged to 100% Should I be anxious about a 120 mile trip (in Florida) where I'll probably do 80-85mph? I will recharge at my destination before heading back.

 

[sotek2345]

I have a leadfoot. My 2022 Lariat SR shows only 221 miles of range when charged to 100% Should I be anxious about a 120 mile trip (in Florida) where I'll probably do 80-85mph? I will recharge at my destination before heading back.

Unless you are in poor weather (rain saps range), you should be fine.

 

[azypather]

Unless you are in poor weather (rain saps range), you should be fine.

Thanks, I hadn't even thought about how rain affects range! Does anyone have any data or real world experience?

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