Ideal highway speed?

[Leewx]

I haven't gone on any long road tips with my MS yet but I'm wondering if there is an ideal speed to travel at. Obviously the faster you travel the more juice you use to overcome wind/road resistance and then end up spending more time superchargeing so you may not make it to your final destination any faster. In planning a trip using the Tesla/google map does the app assume you will be traveling the posted speed limit or more realistically 5-10 mph above the speed limit?
Is there a resource that has strategies for driving a tesla on long trips (and daily commuting for that matter)?

Thanks

 

[Rockster]

Typically, the app in the car assumes you'll be driving the speed limit. Online tools like evtripplanner.com and abetterrouteplanner.com have settings for your expected speed, as a function of how many mph over posted you'll be going.

There's no cheating physics, so yes, you'll definitely use more energy going, say, 80 versus 65; however, this usage is easy to monitor as you're traveling. If there's any doubt whatsoever as to your ability to reach your destination with the charge you have, the best approach is to drive conservatively in the first half of your journey and, if the energy graph* shows enough surplus you can speed up during the last half of your journey. This is far less stressful than driving quickly at the start and being forced to slow way down to make it to your destination.

The in-car nav system will warn you if it thinks you must slow down to reach your destination, too. For example, you may see a message along the lines of "Reduce speed to 65 mph to reach your destination."

*After you set your destination on the nav system there's a graph that shows your expected usage for the journey, with the expected remaining charge upon your arrival. This graph updates dynamically as you drive and is a great resource for selecting your ideal speed as you go.

 

[Leewx]

Great! Thanks for the reply. Can't wait to go on my first long trip with my awesome new ride!

 

[Barry]

Someone did the math 3-4 years ago. I don't recall if it's on this forum or the tesla.com forum. if it's there, you'll never find it, as there's no search.

Bottom line, the most time-efficient speed is 75-80 mph. if you go faster, you'll use energy faster than the Supercharger can replace it, so you're net trip time will increase. If you were going to stop for a meal or the night, then the speed of that leg really doesn't matter.

 

[milleron]

Why not just drive the speed limit, conserve energy, save a little money, lengthen range, lessen the CO2 burden on the atmosphere, increase your survival chances in an accident, increase your accident-avoidance ability, and ease your mind about radar cops? You have to be driving quite a long way before the difference between 65 mph and 75 mph makes a really meaningful difference in arrival time, and how often does arrival time matter, anyway? It's probably a factor only if you're driving between business appointments. When did Americans start believing that it's their solemn duty to always drive 10 mph over the speed limit?
"Life moves pretty fast. You don't stop and look around once in a while, you could miss it." [Ferris Bueller, certified American hero]

 

[Mediocrates]

Why not just drive the speed limit, conserve energy, save a little money, lengthen range, lessen the CO2 burden on the atmosphere, increase your survival chances in an accident, increase your accident-avoidance ability, and ease your mind about radar cops? You have to be driving quite a long way before the difference between 65 mph and 75 mph makes a really meaningful difference in arrival time, and how often does arrival time matter, anyway? It's probably a factor only if you're driving between business appointments. When did Americans start believing that it's their solemn duty to always drive 10 mph over the speed limit?
"Life moves pretty fast. You don't stop and look around once in a while, you could miss it." [Ferris Bueller, certified American hero]

How often do you drive 10mph under the speed limit?

 

[FlatSix911]

Here is a graph of speed vs range... you can be the judge on the ideal highway speed

 

[FlatSix911]

Maximum range and lowest Wh/mile is achieved at a speed between 15-20 mph... not very useful for highway cruising

 

[Buster1]

Where did those graphs come from? @blincoln produced some graphs from ABRP data on thousands(?) of cars and for Model S the most efficient (distance vs Watts) speed was about 40mph.

Just curious.

 

[kavyboy]

@Barry is correct, as far as I can remember of that thread. About 75-80 MPH was the shortest trip time when taking into consideration supercharging time as well as travel time. That seems to fit with my own experience. Anything above 75 MPH seems to increase consumption a lot, and at an exponentially increasing rate with higher speeds.
Also agree with @milleron. I go 5 MPH over limit so as to not obstruct traffic. It's a good pace with no range anxiety. I often have other Tesla drivers leapfrog me on the highway going a lot faster than me, but I see them at every supercharger stop. Their extra speed isn't helping them.

 

[BJD3388]

Here is the Range/Speed info written by the main engineer who built Tesla and is its CTO today (link below and graph)

Model S Efficiency and Range

Source of Energy consumption by speed:
Can EVs handle the distances we drive? • A Study

 

[scottm]

I think the answer to "ideal" highway speed is where you keep aerodynamic losses below your drivetrain losses.

That crossover happens at about 50 mph for model S.

So drive at 50 mph. Unless you're going downhill, then speed up to whatever allows green regen to disappear (keep the needle flat).

My car is rated for about 425 km actual range (not ideal range). Which I see from the other graph above, was set using a constant driving speed assumption of 65 mph.

If I trace the ideal 50 mph constant driving speed assumption up the graph... that should give my S a range of about 540km. I bet flicking my range units over to "energy" and "ideal" on a full battery would report about that.

 

[Leewx]

Thanks for all the info. Bottom line sounds like I won't need to alter my current driving habit of driving 5-10 mph above the speed limit. Most of the time this is just going with the flow of traffic or a little bit faster. I feel that driving with the flow of traffic is probably safer than driving at the posted speed limit and causing others to lane change around me needlessly. Good to know that driving faster than 75-80mph will actually lengthen total trip time. Thanks again. Really liking this forum!

 

[Dodo]

While the Wh/mile graphs seem correct, the exact answer is more complicated as you have to take into account the charging time and that depends on the travel distance and the locations of the SuperChargers. Driving a bit faster could mean having to charge 10% more. If this extra charging is done from 40% to 50%, that is no problem and we are talking about mere minutes in total time differences over a broad range of speeds. But charging from 90% to 100% takes more time, so you will be better of slowing down a bit.

When traveling, I try to plan my stops so that I avoid having to charge beyond 80%-90% because of that extra charging time. Other factors are how nice the location of the SuperCharger is, and when it is lunchtime. If the navigation system says, that I will reach my next SuperCharger with 10%* left, I am off (unless I haven’t finished my lunch yet). Driving at a comfortable speed, you will quickly see the estimated remaining battery percentage increase or decrease. If it decreases, you just slow down a bit till the estimate is back on 10%. If it keeps decreasing, you slow down a bit more. Range increases enormously when slowing down till the optimum of 20 mph, so at highway speeds you should always have plenty of reserve.

*The reason for the 10% minimum is that the 12V battery doesn’t get charged when the main battery is too low. A taxi driver in Norway got stuck because of an empty 12V battery with still a few % left in the main battery.

 

[Leewx]

Again thanks for the info! Changing the subject a bit, why is there a separate 12 volt battery and where is it. Can I use it to give an ICE a jump start if no other options are available. Does it need to be changed every 4-6 years as if used in an ICE?

 

[The Duke]

Throw out all the math and graphs!
Go fast enough that you can relax and eat at your charge point. If I went 60 MPH to Gustine I would charge in 30 minutes and have to walk out during breakfast to move the car. I do 85 and have 45 minutes to charge, just right for breakfast. And I can sleep in a few extra minutes.

The onboard planner will minimize your time, it's up to you to maximize your fun.

 

[FlatSix911]

Where did those graphs come from? @blincoln produced some graphs from ABRP data on thousands(?) of cars and for Model S the most efficient (distance vs Watts) speed was about 40mph.

Just curious.

The data is from Tesla... 20 mph is clearly the most efficient speed to maximize range

 

[Shock-On-T]

I haven't gone on any long road tips with my MS yet but I'm wondering if there is an ideal speed to travel at. Obviously the faster you travel the more juice you use to overcome wind/road resistance and then end up spending more time superchargeing so you may not make it to your final destination any faster. In planning a trip using the Tesla/google map does the app assume you will be traveling the posted speed limit or more realistically 5-10 mph above the speed limit?
Is there a resource that has strategies for driving a tesla on long trips (and daily commuting for that matter)?

Thanks

I believe the most efficient speed is very low, around 25 mph. That’s about how fast they drive when trying to break distance records.

Basically the slower you go the further you go, if you’re faster than about 25mph. But who can stand that!

 

[Barry]

The data is from Tesla... 20 mph is clearly the most efficient speed to maximize range

There were a couple of guys who hypermiled a Model 3 at about 20 mph and drove about 600 miles on a charge.

 

[milleron]

How often do you drive 10mph under the speed limit?

Almost never. Why do you ask?