Maximum speed driving cross country

[Hazard One]

Distinguished owners and followers of the Best Truck on the Market,

Greetings,


I'm a Tesla newbie by most standards, bought a 2024 MY for my wife 18 months ago and a 2025 CT for me a few months ago. Love these vehicles! Spent 25 years in the USAF as a pilot, now make my living working for a think tank part time. Translated, means I'm a warrior nerd if ever was such a thing. Anyhow, I did some analysis on the question of what is the optimum speed to drive a CT if minimizing total transit time is the goal on a cross country. In other words, how fast to drive if the intent is to get "there" as soon as possible. With gas powered cars the answer is: as fast as the vehicle goes! since the "fill up" time is so short. But with EV's the equation is more complex because of the non-linear recharge time. Punchline for the CT: using 250 kW Superchargers, 75 mph is the best cruise speed assuming 5 minutes from highway exit to "on charge." If using less cable chargers, say 125 kW, the optimum speed to drive on the highway lowers to 68 mph.

Jeff

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[HaulingAss]

Distinguished owners and followers of the Best Truck on the Market,

Greetings,


I'm a Tesla newbie by most standards, bought a 2024 MY for my wife 18 months ago and a 2025 CT for me a few months ago. Love these vehicles! Spent 25 years in the USAF as a pilot, now make my living working for a think tank part time. Translated, means I'm a warrior nerd if ever was such a thing. Anyhow, I did some analysis on the question of what is the optimum speed to drive a CT if minimizing total transit time is the goal on a cross country. In other words, how fast to drive if the intent is to get "there" as soon as possible. With gas powered cars the answer is: as fast as the vehicle goes! since the "fill up" time is so short. But with EV's the equation is more complex because of the non-linear recharge time. Punchline for the CT: using 250 kW Superchargers, 75 mph is the best cruise speed assuming 5 minutes from highway exit to "on charge." If using less cable chargers, say 125 kW, the optimum speed to drive on the highway lowers to 68 mph.

Jeff

I'm not going to do the math for you, but I assure you the answer depends upon the density and power level of the Superchargers enroute. On most routes that are well covered by 250 kW or higher Superchargers, the fastest arrival time, assuming no speeding tickets or accidents is 112-113 mph, the top speed (software limited) of the Dual Motor.

It's a rare freeway Supercharger stop that takes me 5 minutes from exiting the freeway to plugging in. Where I travel in the American West it's usually only a minute or two. Sometimes less than a minute.

 

[Hazard One]

I'm not going to do the math for you, but I assure you the answer depends upon the density and power level of the Superchargers enroute. On most routes that are well covered by 250 kW or higher Superchargers, the fastest arrival time, assuming no speeding tickets or accidents is 112-113 mph, the top speed (software limited) of the Dual Motor.

It's a rare freeway Supercharger stop that takes me 5 minutes from exiting the freeway to plugging in. Where I travel in the American West it's usually only a minute or two. Sometimes less than a minute.

Do you know what the Wh/mi average is at 113 mph in an AWD? Would be an easy calculation from there….I’m using 800 Wh/mi at 85 mph for instance

 

[TS_Buffalo]

I’m using 800 Wh/mi at 85 mph for instance

Wow, 800 seems really high. I commute daily with the majority of the distance on the freeway at 80-85 mph and my average is much lower than that. I'm getting about 520-550 wh/mi this time of year (will get worse in the winter, of course). Do you have add-ons that are affecting your aerodynamics?

 

[Hazard One]

Wow, 800 seems really high. I commute daily with the majority of the distance on the freeway at 80-85 mph and my average is much lower than that. I'm getting about 520-550 wh/mi this time of year (will get worse in the winter, of course). Do you have add-ons that are affecting your aerodynamics?

the 800 Wh/mi figure came from searches on the net and this forum...but, would love to tweak in the model with good data! Lemme re-run using your figure of 535 wh/mi at 82.5 mph....

 

[mongo]

Distinguished owners and followers of the Best Truck on the Market,

Greetings,


I'm a Tesla newbie by most standards, bought a 2024 MY for my wife 18 months ago and a 2025 CT for me a few months ago. Love these vehicles! Spent 25 years in the USAF as a pilot, now make my living working for a think tank part time. Translated, means I'm a warrior nerd if ever was such a thing. Anyhow, I did some analysis on the question of what is the optimum speed to drive a CT if minimizing total transit time is the goal on a cross country. In other words, how fast to drive if the intent is to get "there" as soon as possible. With gas powered cars the answer is: as fast as the vehicle goes! since the "fill up" time is so short. But with EV's the equation is more complex because of the non-linear recharge time. Punchline for the CT: using 250 kW Superchargers, 75 mph is the best cruise speed assuming 5 minutes from highway exit to "on charge." If using less cable chargers, say 125 kW, the optimum speed to drive on the highway lowers to 68 mph.

Jeff

What about the leg distance?
Ideally, you arrive at the same low SOC each stop for high charge rate. Departure SOC depends on how long the leg is and your Wh/mile. At some point, the extra charge time needed is greater than the time saved, but it varies by leg length since that sets minimum departure SOC and thus charge rate.

 

[Hazard One]

What about the leg distance?
Ideally, you arrive at the same low SOC each stop for high charge rate. Departure SOC depends on how long the leg is and your Wh/mile. At some point, the extra charge time needed is greater than the time saved, but it varies by leg length since that sets minimum departure SOC and thus charge rate.

Totally agree! For now I'm modeling a trip where you drive down to 20% battery and then recharge to 80%. Will add more variability as the model matures...which starts with getting good baseline numbers on watt-hours / mi at various speeds. Eventually will get to changes in temperature, air density, and elevation changes...maybe even turn it into an app.

 

[Hazard One]

the 800 Wh/mi figure came from searches on the net and this forum...but, would love to tweak in the model with good data! Lemme re-run using your figure of 535 wh/mi at 82.5 mph....

Ok, updated the model using 535 wH/mi @ 82.5 mph. Moves the "optimum" cruise speed up to 93 mph assuming 5 min from exit to on charge, 20% to 80% charging (average 150 kW delivery rate on SC3) for 29.5 minutes. Does anyone have any high speed wH/mi data?

 

[mongo]

Totally agree! For now I'm modeling a trip where you drive down to 20% battery and then recharge to 80%. Will add more variability as the model matures...which starts with getting good baseline numbers on watt-hours / mi at various speeds. Eventually will get to changes in temperature, air density, and elevation changes...maybe even turn it into an app.

Ohhhh....
So you are maximizing average speed for 60% SOC usage.
That explains our difference in results. It really depends on good charge curve and Wh/mile coefficients but my rough spreadsheet indicates faster is faster (ignoring changes in the number of stops)

 

[HaulingAss]

Totally agree! For now I'm modeling a trip where you drive down to 20% battery and then recharge to 80%. Will add more variability as the model matures...which starts with getting good baseline numbers on watt-hours / mi at various speeds. Eventually will get to changes in temperature, air density, and elevation changes...maybe even turn it into an app.

Who charges to 80% on a road trip? I unplug at around 60-65% SOC unless I'm still busy taking my rest break! The only time I charge to 80% or beyond is when I'm using level 2 destination charging and I'm asleep!

 

[HaulingAss]

Ohhhh....
So you are maximizing average speed for 60% SOC usage.
That explains our difference in results. It really depends on good charge curve and Wh/mile coefficients but my rough spreadsheet indicates faster is faster (ignoring changes in the number of stops)

True, but the real question is why is the OP's question a real question. Just drive with the flow of traffic and don't worry if it's going to take you a few more minutes to arrive. I'm a big fan of leaving earlier and enjoying the ride.

If I'm going to drive in the triple digits it will be because I want to, not because I'll arrive a little sooner. If I want to arrive sooner, I leave sooner.

 

[HaulingAss]

Ok, updated the model using 535 wH/mi @ 82.5 mph. Moves the "optimum" cruise speed up to 93 mph assuming 5 min from exit to on charge, 20% to 80% charging (average 150 kW delivery rate on SC3) for 29.5 minutes. Does anyone have any high speed wH/mi data?

The optimum cruise speed to arrive as early as possible is as fast as it will go. That's why EV Cannonball Run winners drive in the triple digit speeds whenever they feel it's safe to do so.

But regular folks shouldn't be in that much of a hurry.

 

[L3it3R]

On the highway I typically stay around 70-75MPH - but will get up to about 80 if necessary. Just put it in FSD and stay in the right lane.

372 Wh/mi over the last 29k miles - I do a lot of 'avoid highways' because they're simultaneously boring and insane around here

 

[mongo]

The optimum cruise speed to arrive as early as possible is as fast as it will go. That's why EV Cannonball Run winners drive in the triple digit speeds whenever they feel it's safe to do so.

But regular folks shouldn't be in that much of a hurry.

It's not though (at least with Cybertruck), at the higher speeds your additional energy usage takes longer to recharge than the time you save.

True, but the real question is why is the OP's question a real question. Just drive with the flow of traffic and don't worry if it's going to take you a few more minutes to arrive. I'm a big fan of leaving earlier and enjoying the ride.

It's an interesting problem, though more applicable if towing a trailer. I started messing with open source mapping data to create a Supercharger to Supercharger routing map (like the old travel maps had for distance). Given a known leg length, what is the optimum departure SOC and speed.

 

[REM]

If you also haven't found it already, A Better Route Planner can help you calculate quite a few variables to give you good estimates.

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