Speed vs Efficiency with respect to total travel time

Lets imagine a 1000 mile road trip on an interstate that had no speed limit. In a gasoline powered car, you will always arrive at your destination sooner the faster you drive. You'll have to stop for fuel more frequently if you drive faster, but considering how quick it is to refuel, there is no practical limit to your speed with respect to arriving at the destination sooner.

Now consider the same trip in the Bolt. It takes longer to recharge, and the closer to full the battery becomes, the slower the recharge. Driving 100 MPH on this trip likely wouldn't get you to the destination quicker than driving 65 MPH considering the extra stops needed to recharge.

Has anyone done the math to determine the optimal speed vs efficiency to arrive at a long distance destination the quickest? What does that formula look like, especially given the non-linear charging characteristics?

This graph is what got me thinking about the topic:



Some very rough estimates based on this graph show that traveling at 70 MPH will require 5 full charges (1000 mi distance / 200 miles per charge). At 100 MPH, you would need 10 full charges (1000 mi distance / 100 miles per charge). At 70 MPH, it would take about 14hrs 17min of driving to cover 1000 miles. At 100 MPH, it would take 10hrs, for a difference of 4hrs 17min.

It would certainly take more than 4hrs 17min to get 5 more full charges, so clearly traveling at 100 MPH on a long road trip wouldn't get you to the destination quicker than traveling at 70 MPH.

What is the optimal speed given this scenario?

To complicate the question, should the vehicle be charged to full each time, or is it more time efficient to only charge to a certain percentage, and make more frequent charging stops?

Interesting question, but the current state of DCFC introduces too many variables and driving the Bolt at 100 is impossible because it's speed limited to about 92 mph.

For me, averaging 90 mph is the magic number (yes, I know that's above the speed limit). This spring, I drove our VW from Vegas to Edmonton (about 1500 miles) in two days, with only one night in a hotel. That worked out to about 8 hours of driving per day + breaks. Perhaps that trip could be made in two days at 90 mph with a 100 kWh Tesla, but it would be impossible (even hypothetically) with a Bolt in two days given the relative lack of DCFC charging stations, and the time it takes to charge on DCFC.

At 90 miles per hour with a Bolt, the graph suggests you'd be stopping every 140 miles, I assume for at least 1.5 hours (three 30 minute EVGO sessions) to charge on DCFC. For that reason, you'd instead drive at 50 mph on the Interstate so you could theoretically achieve 375 miles of range. With that said, 375 miles on a 60 kWh battery assumes efficiency of 6.25 miles/kWh at 50 mph so I'm taking the data in the graph with a grain of salt. The 140 miles @ 90 mph seems overly pessimistic while the 375 miles at 50 mph seems overly optimistic.

My math shows:

At 45 mph 1000 miles will take 22.2 hours and you will need (3) x 90 minute 50 kw charger cycles.

At 65 mph 1000 miles will take 15.4 hours and you will need (4.5) x 90 minute 50 kw charger cycles.

At 75 mph 1000 miles will take 13.3 hours and you will need (6) x 90 minute 50 kw charger cycles.


Hypothetical under ideal conditions which you will NEVER find.

A) the DCFC stations are never exactly where you need them. You will spend both time, and use up miles of range looking for them.

B) not all DCFC stations put out the full 50 kw

gpsman said:

My math shows:

<span>At 45 mph 1000 miles will take 22.2 hours and you will need (3) x 90 minute 50 kw charger cycles. </span>

<span>At 65 mph 1000 miles will take 15.4 hours and you will need (4.5) x 90 minute 50 kw charger cycles. </span>

<span>At 75 mph 1000 miles will take 13.3 hours and you will need (6) x 90 minute 50 kw charger cycles. </span>

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So, total trip times (traveling and charging) for these three are:

1. 26 hours, 43 minutes
2. 22 hours, 8 minutes
3. 22 hours, 20 minutes

At 60 MPH, you'd spend 16 hours, 40 minutes driving and need 4 charge stops at 90 minutes each. Total trip time would be 22 hours, 40 minutes. Unless my math is different from gpsman's, 65 MPH seems to be the sweet spot for shortest time, given that quick chargers are evenly spaced, open, functioning, and operating at full power. However, having just driven across the country and back in a hybrid, 13 hours of driving in one day is a killer. I'd run whatever speed suits the road and gets me to a charging station near the bottom of my charge, QC to full, then drive to a hotel for the night (about 8-9 hours of driving with an overnight L2 charge to start you fresh in the morning).

PV1 said:

So, total trip times (traveling and charging):

2. 22 hours, 8 minutes

At 60 MPH, you'd spend 16 hours, 40 minutes driving and need 4 charge stops at 90 minutes each. Total trip time would be 22 hours, 40 minutes. Unless my math is different from gpsman's, 65 MPH seems to be the sweet spot for shortest time, given that quick chargers are evenly spaced, open, functioning, and operating at full power.

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Bold = A lot of ifs.

Or, 85 mph in a gasoline vehicle. 11 hours, 46 minutes driving plus 2 stops. 1 - 30 minute break for lunch and one additional 15 minute break to stretch your legs. Total trip time - 12 hours, 31 minutes. You arrive in one day, about 9.5 hours earlier, and don't have to pay for, and lay up in a hotel room.

Isn't this whole 1,000 mile thing hypothetical?

Anyway, modern EVs have still only been on the market for 6 years (excluding the limited production Tesla Roadster). The fact that they are so competitive with technology that's had a solid 100+ years of work and innovation is astounding.

On our cross-country trip, the first day was 890 miles and was a stretch, even in a gasser hybrid. The rest of the trip was around 500-600 miles per day with a rushed but still legal pace, which given functioning infrastructure, could easily be done in the Bolt. It could've been done today with Tesla's Superchargers.

85 MPH, given that you don't get pulled over, ticketed, or arrested .

PV1 said:

Isn't this whole 1,000 mile thing hypothetical?

85 MPH, given that you don't get pulled over, ticketed, or arrested .

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In the hypothetical world, you can drive any speed you want without risk of getting pulled over, ticketed, or arrested.

That is true :ugeek: .

I believe the physics of the current state of lithium-ion batteries is such that the efficiency drops off above 52 MPH, so driving at 85 MPH in a Bolt EV will eat up your storage capacity like a hot knife through butter.

I have seen this phenomenon first hand in my trips from Los Angeles to Santa Cruz. When I recharge in Paso Robles, I have plenty of capacity to make it to Santa Cruz, so I sometimes get a little competitive when a sports car or Tesla passes me by!

I watch my Mileage Gauge just start to drop mile by mile much quicker than the mileage remaining on my Nav!!

EVs can have performance, they can have range, they just can't have both at the same time in today's state of the art!

oilerlord said:

Or, 85 mph in a gasoline vehicle.

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You and I are obviously very different. For me, trying to drive 85mph (almost 140 km/h!) over a stretch of 12 hours would be an accident just waiting to happen. And it would be a bad one.

PV1 said:

The rest of the trip was around 500-600 miles per day with a rushed but still legal pace, which given functioning infrastructure, could easily be done in the Bolt. It could've been done today with Tesla's Superchargers.

Click to expand...

Nice hypothetical about Tesla opening up their network of Superchargers to the rest of us. It would be awesome, but not going to happen given up to 500K Model 3's will be hitting the road soon. GM didn't exactly pay to play either. They seem more interested in selling trucks...but I digress.

Car & Driver reported a trip they did with the Bolt at 75 mph with climate control at 72 degrees. Yielded 190 miles of range. To the OP's point, and what's been discussed here, it looks like a 600 mile trip @ 75 mph would involve around 5 hours on the charger. While it can be done, it's a crazy amount of time to waste. Perhaps hypothetical Bolt v2.0 will charge at 150kW, and there will be a hypothetical build out of one DCFC station for every 100 miles on every Interstate in the US. That would cut down charge time down from 5 hours to a little over 1 1/2.

SeanNelson said:

oilerlord said:

Or, 85 mph in a gasoline vehicle.

Click to expand...

You and I are obviously very different. For me, trying to drive 85mph (almost 140 km/h!) over a stretch of 12 hours would be an accident just waiting to happen. And it would be a bad one.

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Well, it all depends. When I lived in Europe, I routinely drove just a tad over 130 km/h in France (the speed limit), and over 160 km/h in Germany on the autobahn. When not surrounded by idiot drivers, it isn't a problem. I would imagine a drive across Montana (to, say, Dickinson ND) would be similar simply due to scarcity of vehicles.

SparkE said:

Well, it all depends. When I lived in Europe, I routinely drove just a tad over 130 km/h in France (the speed limit), and over 160 km/h in Germany on the autobahn. When not surrounded by idiot drivers, it isn't a problem. I would imagine a drive across Montana (to, say, Dickinson ND) would be similar simply due to scarcity of vehicles.

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It does all depend. Considering 80 mph is becoming the new normal in some states, 85 mph isn't much of a stretch:



Now, I don't advocate being stupid, like ripping through construction zones or residential areas, but there are stretches of highway outside city limits in Utah, Idaho, and Montana that are all but deserted. Going 5-10 over, on a flat, wide-open, double lane, nearly deserted divided highway, with a German engineered vehicle that was designed to be capable of driving on the Autobahn, isn't necessarily dangerous.

MichaelLAX said:

I believe the physics of the current state of lithium-ion batteries is such that the efficiency drops off above 52 MPH, so driving at 85 MPH in a Bolt EV will eat up your storage capacity like a hot knife through butter.

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Has nothing to do with the physics or current state of the art Lithium-Ion batteries.

It has evertything to do with the aerodynamics of the car. Which in the Bolt's case is not great.

oilerlord said:

PV1 said:

The rest of the trip was around 500-600 miles per day with a rushed but still legal pace, which given functioning infrastructure, could easily be done in the Bolt. It could've been done today with Tesla's Superchargers.

Click to expand...

Nice hypothetical about Tesla opening up their network of Superchargers to the rest of us. It would be awesome, but not going to happen given up to 500K Model 3's will be hitting the road soon. GM didn't exactly pay to play either. They seem more interested in selling trucks...but I digress.

Click to expand...

That would be nice, but opening up the Superchargers isn't what I was hinting at. Using the network with a Tesla vehicle is what I meant. Going across Nevada, Tesla is about the only infrastructure out there except for campgrounds. Cross country is still possible in a Bolt using non-Tesla equipment though (I spent a few hours on PlugShare seeing if it was possible to buy a Bolt while in CA and drive it back home to Pennsylvania).

Between the Bolt and Model 3, the only reason I had to get a Model 3 over the Bolt was their charging infrastructure. Everything about the Bolt outweighed that benefit, so Bolt is what I chose. Based on my range figures, my driving will yield about a 260-270 mile range if not more (used half a charge driving less efficiently than I normally do. So far, I've driven 148 miles with 138 miles remaining). I normally drive main roads at speeds between 35-50 MPH with no HVAC unless above 90 F. With the Bolt, I've driven a mix of highway and main roads, punched the throttle a few times, and use A/C to keep in the new car smell. Of course, I won't know for sure until I charge it. I plan to meter the consumption at the EVSE, so I'm waiting until my meter comes in before I charge.

Of course this is hypothetical, which is why I'm emphasizing the math.

I put together a spreadsheet and plugged in some numbers. At 50 MPH, the total trip time would be 23hrs with 3 charging stops. At 90 MPH, total trip time would be 21.1hrs and 10 charging stops.

The sweet spot turned out to be 71 MPH for a total trip time of 20hrs and 6 charging stops.

This assumes the car starts the journey at 100% charge and is driven down to 10%. It also assumes chargers are so plentiful that you can pull off anywhere to charge, and that the charge rate is 40kWh delivered in 1hr of charging.

One thing not considered in the spreadsheet is that if you only had 15 miles left in your journey, you wouldn't stop to get a full DCFC. In fact, the spreadsheet assumes you will spend 1hr on the last DCFC regardless of how many miles remain in the trip.

oilerlord said:

It does all depend. Considering 80 mph is becoming the new normal in some states, 85 mph isn't much of a stretch:

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The map shows Oregon as 70MPH, but I've only ever seen 65... just Googled, and it looks like a small section of I84 near the Idaho border recently was bumped to 70. I wouldn't consider Oregon a 70 MPH state though.

SparkE said:

SeanNelson said:

oilerlord said:

Or, 85 mph in a gasoline vehicle.

Click to expand...

You and I are obviously very different. For me, trying to drive 85mph (almost 140 km/h!) over a stretch of 12 hours would be an accident just waiting to happen. And it would be a bad one.

Click to expand...

Well, it all depends. When I lived in Europe, I routinely drove just a tad over 130 km/h in France (the speed limit), and over 160 km/h in Germany on the autobahn. When not surrounded by idiot drivers, it isn't a problem. I would imagine a drive across Montana (to, say, Dickinson ND) would be similar simply due to scarcity of vehicles.

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It's not the speed. It's 12 hours at that speed. Any highway you can drive at 140 km/h is going to be a well protected, boring highway that would lull you (well, lull me anyway) into a stupor after driving for that long.

I've done long drives before, and I've had a few too many moments where my mind has started to shut down on me. I'm a lot more conscious of my state of alertness and I make a point of pulling over for a catnap when things on the other side of the windshield are starting to swim.

In all fairness, Oilerlord did say that his 12 hours included rest stops and food breaks. But I've come to a nice mellow point in my life where driving for that length of time just doesn't appeal to me. I prefer to take my time and enjoy the journey.

gpsman said:

It has evertything to do with the aerodynamics of the car. Which in the Bolt's case is not great.

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People keep saying this, but the Bolt keeps getting great range. Consumer Reports just tested the Bolt with it's 60KWh battery against a Tesla Model S with a 75KWh battery - guess which one went farther?

I did not say bad.
I said "not great".

My Gen 1 Honda Insight was great.

gpsman said:

MichaelLAX said:

I believe the physics of the current state of lithium-ion batteries is such that the efficiency drops off above 52 MPH, so driving at 85 MPH in a Bolt EV will eat up your storage capacity like a hot knife through butter.

Click to expand...

Has nothing to do with the physics or current state of the art Lithium-Ion batteries.

It has evertything to do with the aerodynamics of the car. Which in the Bolt's case is not great.

Click to expand...

So you are claiming that range is linear?

Lithium ion batteries will support 50% of range at 100 MPM than they will at 50 MPH so long as the aerodynamics of the car is properly designed?

I don't think so!