Efficiency / range at 80 mph?

Arky

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Consider some physics behind this. Looking at the blue curve (Rivian has a low Coefficient of Drag) of an aerodynamic car in this exaple chart, air drag force is under 100 Newtons from 0 to 40. Just to go from 70 to 80, it’s an additional 100 Newtons. You need 25% more energy from 70 to 80 on an aerodynamic vehicle. At 60, you need half the energy, as compared to going 80. Higher Speed has a huge impact on range.
That's not quite true. Yes, going slower is more efficient, but you're looking at an instantaneous force chart, the car going 80mph will experience approximately double the drag force, but since your travel time has been reduced by 25% at 80 vs 60 you don't double the energy usage. It's actually only about 50% more energy spent fighting drag (2x drag * .75 time = 1.5x)

 

Zoidz

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That's not quite true. Yes, going slower is more efficient, but you're looking at an instantaneous force chart, the car going 80mph will experience approximately double the drag force, but since your travel time has been reduced by 25% at 80 vs 60 you don't double the energy usage. It's actually only about 50% more energy spent fighting drag (2x drag * .75 time = 1.5x)
What part of what I said is not true? Where did I or the chart mention total energy consumption over any given time or distance? My point was to clearly illustrate that the amount of energy required at any given speed it is not a linear Increase.
 

Otisbrick

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87D39C7E-7BFF-452A-B5CF-1976B4E49C6D_1_102_o.jpeg

Road trip from Chicago to Nashville 10/2/22. I got 2mi/kWh on average. Driver assist and cruise at 85mph. Config in sig.

Edit: In conserve mode (leaf below 85 in photo). Lowest ride height. Ambient temp ~68F. Didnt run AC much. Since it was a nice day.
 
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loudog3114

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87D39C7E-7BFF-452A-B5CF-1976B4E49C6D_1_102_o.jpeg

Road trip from Chicago to Nashville 10/2/22. I got 2mi/kWh on average. Driver assist and cruise at 85mph. Config in sig.
Conserve mode?
 

Otisbrick

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Conserve mode?
Yes. Should have posted that. The little leaf below the 8 in the lower right corner of photo. Temp was about 68F. So not running AC much.
 


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loudog3114

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Yes. Should have posted that. The little leaf below the 8 in the lower right corner of photo. Temp was about 68F. So not running AC much.
Awesome, sounds like conserve mode makes a massive difference. I wonder if it backs off battery heating and HVAC like the Tesla range mode does. That would be a reason to use it sparingly but until I hear otherwise I plan on kicking it on for every road trip.
 

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The fasted travel time is achieved by driving fast and charging only to where charge speed is significantly reduced. However this approach really only works today on the interstate with many charging location. So usually only Tesla.

So fast and charging in the range from 5-10% to 50-60%.

I have done many 1000 mile plus days in a gas car. In reality, with an EV, I would not attempt that even with max pack. There's no way to quickly add 300+ miles of range with an EV
I used Electrify America 350kW chargers and they start out charging at 400+ mph they stay high up to about 80% then slow down.
 

zipzag

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I used Electrify America 350kW chargers and they start out charging at 400+ mph they stay high up to about 80% then slow down.
cool. So typically to minimize travel time you would want to stay at that charger until that rate slowed down. When you can charge faster at the next charger it is time to leave. (Assuming, of course no other factors of when and where you want to stop next)
 

Denver_Dan

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Along the same lines here but added layer to the question - I live in CO and am constantly driving to a higher elevation through the mountains and then back down.
Does it make sense to drive to higher elevation in all purpose mode to get the power of all 4 motors and potentially put less stress on the two motors if it were in conserve mode? Same thing going down in elevation.. does it make more sense to use conserve going down?

* assuming this is primarily highway driving of 65+ speed limits
 
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loudog3114

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Along the same lines here but added layer to the question - I live in CO and am constantly driving to a higher elevation through the mountains and then back down.
Does it make sense to drive to higher elevation in all purpose mode to get the power of all 4 motors and potentially put less stress on the two motors if it were in conserve mode? Same thing going down in elevation.. does it make more sense to use conserve going down?

* assuming this is primarily highway driving of 65+ speed limits
My two cents with very little actual knowledge is that electric motors are most efficient when they’re putting out as much torque as possible. Hence why conserve mode saves so much juice over the motor split all purpose mode does (you can watch the torque split in the rivian modes video). So I’d say don’t overthink it, if you want to conserve, use conserve.

My only worry is conserve mode might lower battery heating/cooling as well like the Tesla does, which is not good for the long term health. But until I hear that it does so I’ll be using conserve most of the time.
 

 
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