R2 Highway Range at 70MPH = ~250 Miles (Modeled)

[mkg3]

What you wrote is true of ICE vehicles, but EVs do not behave the same way. While it may take more power to accelerate, EVs are able to recapture much of that when decelerating. It's the steady state power needed to overcome air resistance that is unrecoverable, and hence the main driver of EV energy use.

EVs typically get HIGHER MPGe ratings on the city cycle than the highway cycle. E.g., the Gen 1 R1T has an EPA rated MPGe of 74 city, but 66 highway.

True to a point, and it also depends on the regen setting. Many EVs have variable regen setting more than Rivian's High-Std-Low. Also it depends on how hard one accelerates when driving.

There are many technical papers that proves coasting is more efficient than constant transient between power-on and regen on open highway driving.

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[DCFC]

K, I'm a bit more with it this morning. Assumed 250 miles at 70mph as the reference point to calculate a constant to bundle in battery capacity, drag, frontal area, etc. Plotted out. Of course, this is a much more simplified calculation which leaves out the details of linear scaling of rolling friction, etc. Just wanted to see the shape of the curve which my initial intuition was incorrect about.

 

[tivoboy]

I didn't dig into the calculations the AI did, but I think something is amiss. I plotted out the numbers and the curve has the wrong inflection. As speed increases, the range should drop exponentially. As noted, the power requirement goes up to the 3rd power with velocity. I drew in a representative curve shape, ignore the position. Be careful about trusting AI.

Edit: I was wrong about the inflection of the curve

This is one of the things that has always confused and confounded me.

IT SEEMS logically, as speed increases, energy to maintain or increase speed should increase measurably (if not truly EXPONENTIALLY), but that has never been my actual experience.

I go back to the days living in Germany working for a large german OEM.. having the pick of the litter from the executive garage stable. Doing long duration and distance road trips, I could measure over time, distance and speed the change in MPG at various LARGE deltas of speed.

65mgh, 100mph and 150+mph..

At say 90mph, I could get my battle axe CLK AMG55 to do ~ 18mpg on an unrestricted autobahn for long stretches (mostly at night or early AM heading south to Switzerland)..

But taking it up to 150mph, and traveling at around those speeds, sometimes higher sometimes lower, but avg 150mph I would only see MPG drop to ~ 15-16 mpg.. Now one would expect to see a near doubling in speed essentially HALVE the overall MPG, but that was not the case, it was more like a 15-20% reduction in efficiency. So even straight line maths didn't math, and EXPONENTIAL increases in energy consumption didn't either.

I could never really get an engineer at the OEM to explain this to me, the how and why. Other than to say, at SOME point there IS a sleight re-gain of efficiency (or signifiant slower or stopping of the IN-EFFICIENCY curve), so directionally it doesn't just keep going up but they couldn't math it for me.

Had the same experience though with other cars, even large top product sedans, heavy with big V12 (slightly worse though, those things were pigs to begin with)

And with an America Roadster I had but the top sustained speeds were even higher.

So we know there are optimal speeds for any vehicle, ambient temp, environmental conditions, terrain, etc, and then there are SUB-OPTIMAL as speed increases, but even though it gets worse as speed increases, it wouldn't appear to be a straight straight line, or a J curve

I would imagine in the OP post, the blue dots would stop falling, and just flatten out at some value X for range/measure of energy.

 

[Dreadknight25]

gonna piss off a lot of highway drivers locking Autonomy+ at the posted speed limit

 

[mkhuffman]

This is one of the things that has always confused and confounded me.

IT SEEMS logically, as speed increases, energy to maintain or increase speed should increase measurably (if not truly EXPONENTIALLY), but that has never been my actual experience.

I go back to the days living in Germany working for a large german OEM.. having the pick of the litter from the executive garage stable. Doing long duration and distance road trips, I could measure over time, distance and speed the change in MPG at various LARGE deltas of speed.

65mgh, 100mph and 150+mph..

At say 90mph, I could get my battle axe CLK AMG55 to do ~ 18mpg on an unrestricted autobahn for long stretches (mostly at night or early AM heading south to Switzerland)..

But taking it up to 150mph, and traveling at around those speeds, sometimes higher sometimes lower, but avg 150mph I would only see MPG drop to ~ 15-16 mpg.. Now one would expect to see a near doubling in speed essentially HALVE the overall MPG, but that was not the case, it was more like a 15-20% reduction in efficiency. So even straight line maths didn't math, and EXPONENTIAL increases in energy consumption didn't either.

I could never really get an engineer at the OEM to explain this to me, the how and why. Other than to say, at SOME point there IS a sleight re-gain of efficiency (or signifiant slower or stopping of the IN-EFFICIENCY curve), so directionally it doesn't just keep going up but they couldn't math it for me.

Had the same experience though with other cars, even large top product sedans, heavy with big V12 (slightly worse though, those things were pigs to begin with)

And with an America Roadster I had but the top sustained speeds were even higher.

So we know there are optimal speeds for any vehicle, ambient temp, environmental conditions, terrain, etc, and then there are SUB-OPTIMAL as speed increases, but even though it gets worse as speed increases, it wouldn't appear to be a straight straight line, or a J curve

I would imagine in the OP post, the blue dots would stop falling, and just flatten out at some value X for range/measure of energy.

I have read that tires that are high speed rated actually get more efficient as speed increases (rolling resistance decreases as you drive faster). I suspect this is one of the reasons you didn't see a bigger drop in efficiency.

 

[mkg3]

This is one of the things that has always confused and confounded me.

IT SEEMS logically, as speed increases, energy to maintain or increase speed should increase measurably (if not truly EXPONENTIALLY), but that has never been my actual experience.

I go back to the days living in Germany working for a large german OEM.. having the pick of the litter from the executive garage stable. Doing long duration and distance road trips, I could measure over time, distance and speed the change in MPG at various LARGE deltas of speed.

65mgh, 100mph and 150+mph..

At say 90mph, I could get my battle axe CLK AMG55 to do ~ 18mpg on an unrestricted autobahn for long stretches (mostly at night or early AM heading south to Switzerland)..

But taking it up to 150mph, and traveling at around those speeds, sometimes higher sometimes lower, but avg 150mph I would only see MPG drop to ~ 15-16 mpg.. Now one would expect to see a near doubling in speed essentially HALVE the overall MPG, but that was not the case, it was more like a 15-20% reduction in efficiency. So even straight line maths didn't math, and EXPONENTIAL increases in energy consumption didn't either.

I could never really get an engineer at the OEM to explain this to me, the how and why. Other than to say, at SOME point there IS a sleight re-gain of efficiency (or signifiant slower or stopping of the IN-EFFICIENCY curve), so directionally it doesn't just keep going up but they couldn't math it for me.

Had the same experience though with other cars, even large top product sedans, heavy with big V12 (slightly worse though, those things were pigs to begin with)

And with an America Roadster I had but the top sustained speeds were even higher.

So we know there are optimal speeds for any vehicle, ambient temp, environmental conditions, terrain, etc, and then there are SUB-OPTIMAL as speed increases, but even though it gets worse as speed increases, it wouldn't appear to be a straight straight line, or a J curve

I would imagine in the OP post, the blue dots would stop falling, and just flatten out at some value X for range/measure of energy.

Probably because higher powered engines required not much increase in the engine RPMs. If you had done the same with a small lower HP vehicle, the engine would be wide open at max RPM around 5000 vs AMG running between 2500~3000 PRMs.

In other words, the fuel consumptions increase was smaller in a high HP vehicle than a low HP vehicle. In pure MPG perspective, smaller vehicle with less HP may still be more economical but the relative fuel consumption percentage difference between the speeds impacts lower HP vehicle more.

 

[NoMoreGas71]

So is this not correct??


Driving slower and charging less often is more efficient. Here’s why:
Aerodynamic drag is the key factor. Air resistance increases with the square of your speed, meaning the power needed to overcome it grows cubically. Going from 60 to 80 mph doesn’t just add a third more drag — it nearly doubles the energy required to push through the air.
Battery efficiency also drops at high speeds. EV motors and inverters operate less efficiently at high power outputs, and regenerative braking can’t recover energy lost to air resistance (only to deceleration).
Charging has its own losses. Every charge cycle loses some energy as heat — typically 10–20% depending on the charger and battery state. More frequent charging means more of these losses stack up over a trip.
The numbers in practice: At highway speeds, going from 70 mph to 80 mph can cut your range by 15–25%. Slowing to 60 mph can extend it by a similar margin.
The one nuance: this assumes steady cruising. Stop-and-go city driving at low speeds is surprisingly costly due to frequent acceleration, though EVs partially recover that through regenerative braking. The optimal speed for most EVs is roughly 25–40 mph — well below typical highway speeds.
Bottom line: Speed is the enemy of EV efficiency. The slower you drive (within reason), the fewer kWh per mile you use, and the less you need to stop and charge.

 

[TexasBob]

So is this not correct??
...
Bottom line: Speed is the enemy of EV efficiency. The slower you drive (within reason), the fewer kWh per mile you use, and the less you need to stop and charge.

That is all correct but that does not get you there faster. Using a simple example:

550 mile trip avg fast charging speed 150kw:

60 mph -3 mi / kwh

• Start 75 kwh usable charge -> 225 miles/60mph = 3.75 hours
• Charge stop 1 -> recharge 60 kwh = 0.4 hours
• Leg 2 another (60kwh x 3) 180 miles = 3 hours
• Charge stop 2 -> recharge 48 kwh = 0.32 hrs
• Leg 3 (48 kwh x 3) 144 miles = 2.4 hrs
• Arrive total miles 225 + 180 + 144 = 549
• Arrive total time 3.75+0.4+3.0+0.32+2.4= 9.87 hours
• Total kwh: 75+60+48 = 183kwh

80 mph ~2 mi / kwh (extreme example)

• Start 75 kwh usable charge -> 150 miles/80mph = 1.87 hours
• Charge stop 1 -> recharge 60 kwh = 0.4 hours
• Leg 2 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 2 -> recharge 60 kwh = 0.4 hours
• Leg 3 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 3-> recharge 60 kwh = 0.4 hours
• Leg 4 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 4 -> recharge 20 kwh = 0.13 hrs
• Leg 5 another (20 kwh x 2) 40 miles = 0.5 hrs
• Arrive total miles 150+120+120+120+40 = 550
• Arrive total time 1.87+0.4+1.5+0.4+1.5+0.4+1.5+0.13+0.5= 8.2 hours
• Total kwh: 75+60+60+60+20 = 275kwh

 

[Jeremy3292]

It's funny this thread exists bc I have always assumed on every Tesla I have owned (3/Y LR) that 250 miles is a fair estimate for highway speed range, even at avg 80 mph speeds. If it's cold out you may get less, if it's warm out you may get more but 250 miles is the number I settled on when determining my trips. It also has proven to be an accurate estimate over the years too.

 

[Jeremy3292]

We are splitting hairs here, but the EPA range is 335 miles on the R2, not 330.

It's 330 miles.

Source: https://rivian.com/r2

 

[racekarl]

But taking it up to 150mph, and traveling at around those speeds, sometimes higher sometimes lower, but avg 150mph I would only see MPG drop to ~ 15-16 mpg.. Now one would expect to see a near doubling in speed essentially HALVE the overall MPG, but that was not the case, it was more like a 15-20% reduction in efficiency. So even straight line maths didn't math, and EXPONENTIAL increases in energy consumption didn't either.

Many of the things that stand out about EV vs. ICE behavior can be explained by the huge gulf in efficiency between the two.

An EV powertrain is something like 80-90% efficient, whereas as an ICE powertrain is more like 20-30% efficient.

When 80% of the fuel you burn in an ICE just goes to heating the air around it, you don't notice the changes in efficiency from weather, speed, etc. as easily. In your example, the doubling of speed would only affect the 20-30% of consumption actually used to move the vehicle.

 

[NoMoreGas71]

That is all correct but that does not get you there faster. Using a simple example:

550 mile trip avg fast charging speed 150kw:

60 mph -3 mi / kwh

• Start 75 kwh usable charge -> 225 miles/60mph = 3.75 hours
• Charge stop 1 -> recharge 60 kwh = 0.4 hours
• Leg 2 another (60kwh x 3) 180 miles = 3 hours
• Charge stop 2 -> recharge 48 kwh = 0.32 hrs
• Leg 3 (48 kwh x 3) 144 miles = 2.4 hrs
• Arrive total miles 225 + 180 + 144 = 549
• Arrive total time 3.75+0.4+3.0+0.32+2.4= 9.87 hours
• Total kwh: 75+60+48 = 183kwh

80 mph ~2 mi / kwh (extreme example)

• Start 75 kwh usable charge -> 150 miles/80mph = 1.87 hours
• Charge stop 1 -> recharge 60 kwh = 0.4 hours
• Leg 2 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 2 -> recharge 60 kwh = 0.4 hours
• Leg 3 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 3-> recharge 60 kwh = 0.4 hours
• Leg 4 another (60kwh x 2) 120 miles = 1.5 hours
• Charge stop 4 -> recharge 20 kwh = 0.13 hrs
• Leg 5 another (20 kwh x 2) 40 miles = 0.5 hrs
• Arrive total miles 150+120+120+120+40 = 550
• Arrive total time 1.87+0.4+1.5+0.4+1.5+0.4+1.5+0.13+0.5= 8.2 hours
• Total kwh: 75+60+60+60+20 = 275kwh

Excellent! Thank you!

 

[NoMoreGas71]

It's 330 miles.

Source: https://rivian.com/r2

They haven’t updated the website for some reason. EPA rated range came back at 335 miles for Performance version on 21” wheels.

 

[DCFC]

This is one of the things that has always confused and confounded me.

IT SEEMS logically, as speed increases, energy to maintain or increase speed should increase measurably (if not truly EXPONENTIALLY), but that has never been my actual experience.

I go back to the days living in Germany working for a large german OEM.. having the pick of the litter from the executive garage stable. Doing long duration and distance road trips, I could measure over time, distance and speed the change in MPG at various LARGE deltas of speed.

65mgh, 100mph and 150+mph..

At say 90mph, I could get my battle axe CLK AMG55 to do ~ 18mpg on an unrestricted autobahn for long stretches (mostly at night or early AM heading south to Switzerland)..

But taking it up to 150mph, and traveling at around those speeds, sometimes higher sometimes lower, but avg 150mph I would only see MPG drop to ~ 15-16 mpg.. Now one would expect to see a near doubling in speed essentially HALVE the overall MPG, but that was not the case, it was more like a 15-20% reduction in efficiency. So even straight line maths didn't math, and EXPONENTIAL increases in energy consumption didn't either.

I could never really get an engineer at the OEM to explain this to me, the how and why. Other than to say, at SOME point there IS a sleight re-gain of efficiency (or signifiant slower or stopping of the IN-EFFICIENCY curve), so directionally it doesn't just keep going up but they couldn't math it for me.

Had the same experience though with other cars, even large top product sedans, heavy with big V12 (slightly worse though, those things were pigs to begin with)

And with an America Roadster I had but the top sustained speeds were even higher.

So we know there are optimal speeds for any vehicle, ambient temp, environmental conditions, terrain, etc, and then there are SUB-OPTIMAL as speed increases, but even though it gets worse as speed increases, it wouldn't appear to be a straight straight line, or a J curve

I would imagine in the OP post, the blue dots would stop falling, and just flatten out at some value X for range/measure of energy.

This is actually easy to explain. Internal combustion engines are notoriously inefficient at low loads. At higher loads, their efficiency goes up (less throttling losses as the throttle body is open more, more heat energy goes into pushing the piston down instead of into the coolant/oil/exhaust, etc). Every internal combustion engine will have what's called the Brake Specific Fuel Consumption map. The units in this particular plot are grams of fuel burned to get a kWh of energy out of it. So, the lower the number the better. This study had a bunch of different drive cycles plotted on the map. I drew in the red line to illustration going from a lower cruising speed/lower load to a higher cruising speed/higher load. At the higher load, you can see the BSFC values get lower which means better efficiency. Peak internal combustion engine efficiency is always at high load and low-mid engine rpm. Engine friction increase exponentially with engine speed.

 

[R2dreamer]

It's 330 miles.

Source: https://rivian.com/r2

330 is the Rivian estimate. EPA range came in at 335

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