Why is 4 mi/kwh the max in the Efficiency screen?

[mikehmb]

FWIW my Tundra would never show over 30mpg on the efficiency computer, for the same reason.

Coming back from Tahoe I would see it pegged at 30 for 50+ miles. lol

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[azbill]

They should just dump the graph and provide a single value of mi/kwh for the current drive, like most other EVs do.

 

[Wing]

I didn't even know the graph went green, I've only ever been below the line...

 

[Greg Chick]

Sure, but living in/near the mountains it's not uncommon to pin that graph for more than 15 minutes at a time. Kinda fun trying too.

I am at 5,000 ft. at home, when I drive 50 miles from home to the valley floor I drop over 4,000 ft. in elevation. Most of that elevation is in 15 miles. I peg @ 4 MPK, always wanted to see if I could get much more, but it will be "Stupid" pay back upon returning home. At the end of the day, it seems to be a moot point. Or even a penalty on the climb back up that is more than the gain on the way down.
Also if I start out with a high charge, say 85%, the first "gain" is lowered by the software saying "regen reduced due to high charge" or something like that. That may be the reason for the loss on the return vs regen.
Maybe we should just put a fireworks graphic on the console display when regeneration and "congratulations" in strobe. "Free energy" or such?

 

[Greg Chick]

?

 

[HaveBlue]

The efficiency doesn't jump to "infinity" as the car still consumes power going downhill but I've seen 8mi/kwh over extended distances when you do the math. Here's a good one where I drove 88 miles and averaged 3.47mi/kwh.

 

[ksurfier]

I've landed on an answer to MPK vs Wh per mile (WhPM) that works for me...

In Rivian's case values between 1.5 to 3 MPK are in the normal-ish range, if they used WhPM these would translate to 333 - 667 WhPM...we'd essentially be evaluating 435 WhPM vs 455 WhPM as the difference between 2.2 and 2.3 MPK. For the higher efficiencies we'd be looking at 400 vs 417 WhPM for difference between 2.4 and 2.5 MPK. I get lost trying to differentiate between 440 and 415 WhPM, but for some reason 2.27 vs 2.41 MPK seems more understandable/relatable to me.

Also, calculating range is easier with MPK (2.2 x 128 kwh = 282 miles). Whereas 455 WhPM is a division of pack size over KwhPM (128 kwh / 0.455 = 281 miles).

Ultimately MPK is easier and possibly more logical to use, some of us here have been brain washed by Tesla's use of WhPM (myself included)...

The question ultimately goes to why aren't gas vehicles using gallons per mile (GPM)?
If they were, 10 MPG would be 0.1 GPM, 50 MPG would be 0.02 GPM, and 100 MPG would be 0.01 GPM.
Comparing efficiency, it makes sense that a higher value is MORE efficient than a lower value...

Handing the win to Rivian on using MPK versus Tesla using WhPM...

 

[clockwork crane]

Seems like there is a hard limit @ 4 mi/kwh on the efficiency screen no matter how slow or how much you descend. That screen and the max efficiency was the same for our R1T with 20” AT as it is for the dual motor R1S with 21” AS tires.

Anyone know why?

Setting aside whether it was a good decision on Rivian's part, the logic is simple:

a) Rivian chose 2 mi/kwh as the center of the y axis.
b) 0 mi/kwh is a natural minimum for the y axis since you can't get less than that.
c) To preserve linear scaling (not distort the shape of the curve), the maximum of the y axis has to be the same distance from the center as the minimum is from the center. 2 + 2 = 4 mi/kwh.

Theoretically the graph continues to infinity, but the part sampled on your screen cuts off at 4.

In a more efficient vehicle, the center value will be higher, and the max will just be double the center value. For example in the R2 reveal, the efficiency graph in the R2 uses 3 mi/kwh as the center value, so the max is 6: https://www.rivianforums.com/forum/...12-mi-kwh-3-99-average-at-reveal-event.24930/

 

[sfvR1S]

Slightly OT, but my Bolt EUV gets 4 kwh. My R1S is ~2.5 kwh.

Bolt EUV weighs 3,700 lbs and R1S QM is 7,000 lbs.

Seems like Bolt should do better. Or R1S isn't so inefficient?

 

[clockwork crane]

Slightly OT, but my Bolt EUV gets 4 kwh. My R1S is ~2.5 kwh.

Bolt EUV weighs 3,700 lbs and R1S QM is 7,000 lbs.

Seems like Bolt should do better. Or R1S isn't so inefficient?

Rolling resistance is based on weight, and increases linearly with speed. Aerodynamic drag is based on drag coefficient and frontal area, and increases as the square of the speed. At highway speeds you're spending a huge chunk of your energy just shoving air out of the way, so the weight matters proportionally less. So the R1S does better than you might expect from just the weight, because Rivian put so much work into optimizing the aerodynamics.

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