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Gravity EPA docs are here.

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Elfin

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Dream actually has less rear power? :confused:
1748528601748.webp
 
There is only so much draw that the batteries can support, so it's unlikely to be a motor limitation. It's still 798 kW total for Dream vs 618 kW for GT.
 
idiot900 said:
There is only so much draw that the batteries can support, so it's unlikely to be a motor limitation. It's still 798 kW total for Dream vs 618 kW for GT.
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Makes no sense to lower rear power though. I assume it's some sort of silly reporting rule or misprint and max power to the rear is the same for both.
 
At max kw at both ends, could potentially be Sapphire territory? Air Sapphire produces 920kw
 
suyoungman said:
At max kw at both ends, could potentially be Sapphire territory? Air Sapphire produces 920kw
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Pretty sure Sapphire has twice the max power in the rear than it has in the front. That's the proper way to design a car for driving forward :)
The sum of the max power of each axle can be more than the total max power. Though I'm not sure how you would specify that in these documents.
 
Elfin said:
Pretty sure Sapphire has twice the max power in the rear than it has in the front. That's the proper way to design a car for driving forward :)
The sum of the max power of each axle can be more than the total max power. Though I'm not sure how you would specify that in these documents.
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Evidently not for the DE, which has 399 @ F and R.
 
Interesting that the TRL50 value (total road load horse power @ 50MPH, from what I can find) is exactly the same for the 21/22 and 22/23 wheels. Did they just not test the 21/22 combo and assign the 22/23 numbers to it?
 
indigo6 said:
Did they just not test the 21/22 combo and assign the 22/23 numbers to it?
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That is most likely the case. Just look at the range numbers they provided, the same for 21/22 as the 22/23 which is impossible. Smaller wheels are more efficient. On the 7 seat configuration the 21/22 have to fall in between the 437 (20/22) and 386 (22/23).
 
AnthonySF said:
That is most likely the case. Just look at the range numbers they provided, the same for 21/22 as the 22/23 which is impossible. Smaller wheels are more efficient. On the 7 seat configuration the 21/22 have to fall in between the 437 (20/22) and 386 (22/23).
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Considering the tires are the same size, wheel weight would probably be the biggest factor.

Nothing in science says smaller wheels have to be more efficient, they are just usually lighter assuming bigger wheels are made the same way/same material.

Some sizes could be forged and lighter, for example.

Or smallest size might be on off road tires which are terrible for efficiency.
 
AnthonySF said:
Smaller wheels are more efficient.
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Wheel size is loosely correlated with wheel efficiency. It is true smaller wheels are frequently more efficient, but that is not always the case,

My Rivian 22" OEM wheels are more efficient than the 20" OEM wheels offered by Rivian - by quite a lot actually.

On the Gravity, the 20/21 wheels with Hankook iON tires are definitely the most efficient wheels. However, it is highly possible the efficiency difference between the next larger sizes is not significant using the EPA test cycle.

The 21/22 wheels have All Season tires. The 22/23 wheels have Summer tires. I suspect the Summer tires have lower rolling resistance than the All Season tires, offsetting the better aerodynamic performance of the 21/22 rims. Rolling resistance makes a big difference, and the EPA cycle does not include a lot of high-speed driving, reducing the benefit of aerodynamics in the results.

I agree with you that at 80 MPH, the 21/22 wheels are highly likely to be more efficient than the 22/23 wheels because they appear to be more aerodynamic. However, wheel aerodynamics are part of a system of air flow around the car, and sometimes a rim that looks more aerodynamic is actually not due to the air flow from the vehicle body.

Visually the 22/23 wheel looks like it would have much higher rotational air resistance (resistance as the wheel spins), but there is no way to know for sure unless you do wind tunnel testing on the vehicle and actually measure it. The EPA test results are exactly that. Your eyes are not better than actual test results.

If you want the most efficient setup, get the 20/21 wheels. If you go bigger, the differences appear to be minor with one caveat: EPA does not test at high speed, so likely one wheel is measurably more efficient than the other at 80 mph, and very likely the 21/22 is more efficient, as you assumed. "Very likely" is still a guess, though.
 
037 said:
Considering the tires are the same size, wheel weight would probably be the biggest factor.

Nothing in science says smaller wheels have to be more efficient, they are just usually lighter assuming bigger wheels are made the same way/same material.

Some sizes could be forged and lighter, for example.

Or smallest size might be on off road tires which are terrible for efficiency.
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Wheel weight does not matter as much at high speeds, aerodynamics does.

Lol correct, nothing in science says smaller wheels have to be more efficient, it just is. It’s quite simple, smaller wheels made of the same material, on a similar tire size and tread are more efficient than larger wheels. It’s aerodynamics and weight. Smaller wheels are lighter and surrounded by thicker sidewall, which the flat surface of a tire is more aerodynamic than the cutout of a wheel design. Regardless of EV or ICE, smaller wheels are more efficient. Why do you think when you select larger wheels in any manufacturer configurator range goes down? Just to mess with us?
 
037 said:
Considering the tires are the same size, wheel weight would probably be the biggest factor.

Nothing in science says smaller wheels have to be more efficient, they are just usually lighter assuming bigger wheels are made the same way/same material.

Some sizes could be forged and lighter, for example.

Or smallest size might be on off road tires which are terrible for efficiency.
Click to expand...

And smaller wheels are typically more aerodynamic, resulting in more efficiency at high speeds. Lower weight helps efficiency when city driving where there is a lot of stop-and-go traffic, and better aerodynamics helps efficiency with high-speed driving. A smaller more aerodynamic wheel with lower rolling resistance tires will be more efficient in all driving.

However, once you start changing all the variables that impact efficiency at different speeds, it becomes a huge guessing game regarding which change matters the most. At high, steady state speeds, weight is irrelevant and only rolling resistance and aerodynamics matter. In slower, stop and go traffic, weight has a measurable impact.

I would trust the EPA data with the understanding that the test cycle is not necessarily the way people normally drive. Personally, I wish they would do a high-speed highway test, since to me that is the only efficiency that really matters. I want to know how far I can go on the highway before I have to stop to charge. The EPA test results don't really help answer that question.
 
Knucklehead said:
Wheel size is loosely correlated with wheel efficiency. It is true smaller wheels are frequently more efficient, but that is not always the case,

My Rivian 22" OEM wheels are more efficient than the 20" OEM wheels offered by Rivian - by quite a lot actually.
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Context matters. Don’t forget to disclose the Rivian 22” wheels are on a 33” summer tire and the 20” are on a 34” all terrain tire. That’s not an apples to apples comparison.

I had the 21” setup with the aerocaps in and averaged 2.31mi/kwh at average speed of 34mph over 5500 miles. Then put on the Rivian 20” AT brights, on 275/60/20 Pirelli AS plus 3 AS tire (not an EV tire) and averaged 2.49mi/kWh at average speed of 36mph over 6k miles. Please let me know how I was wasn’t more efficient on a smaller wheel setup with a non ev tire and a higher average speed.
 
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AnthonySF said:
Context matters. Don’t forget to disclose the Rivian 22” wheels are on a 33” summer tire and the 20” are on a 34” all terrain tire. That’s not an apples to apples comparison.

I had the 21” setup with the aerocaps in and averaged 2.31mi/kwh at average speed of 34mph over 5500 miles. Then put on the Rivian 20” AT brights, on 275/60/20 Pirelli AS plus 3 AS tire (not an EV tire) and averaged 2.49mi/kWh at average speed of 36mph over 6k miles. Please let me know how I was more efficient on a smaller wheel setup.
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This is exactly my point. There are many factors that impact wheel efficiency, and wheel size is an indicator, but it is not true to say smaller wheels are more efficient.

IMO the 22" wheels on my Rivian are more efficient than the 20" because of rolling resistance, mainly. I think aerodynamically the 20" wheel might be better, but that is just a guess. Without controlled test data, there is no way to know.

Your test, while relevant, is not controlled. There are so, so many things that impact efficiency that are outside of your control. Maybe your test result is 100% accurate and your 20" setup is better than the 21" OEM setup. Maybe.

Or maybe not. Did you carefully control the temperature of the test conditions when running the two different wheels to ensure the temperate of the air, road, motors and battery were identical? That is nearly impossible to do, right? If you didn't do that, your test results are not proof. What about road ciditions like rain? How many trips did you take in the rain in one set vs. the other? Do you know? What about speed? Was every drive at the exact same speed?

I agree it is possible to beat the most efficient Rivian OEM configuration with new wheels and tires, but I think it is hard. They picked the 21"combination of tire and rim for a reason, and the reason was maximum efficiency. The tire has low rolling resistance, and the rim is very aerodynamic. Can you beat it with a 20" setup? Possibly. And maybe you did. But I am not convinced you did with the data provided.
 
037 said:
Considering the tires are the same size, wheel weight would probably be the biggest factor.
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Although all three wheels sizes on the Gravity have tires of the same cross section widths, their tread widths on the ground vary considerably. For example, all three rear tires are 285mm in cross section, but their tread widths are: 8.6" for the Hankooks, 8.9" for the Michelins, and 10.0" for the Pirellis. That's over 11% more tread contact with the Pirellis than with the Michelins (and over 16% than with the Hankoooks).

Of course, tread compound and design, sidewall construction, and other factors come into play in rolling resistance . . . but this much more tread width has to matter.


037 said:
Nothing in science says smaller wheels have to be more efficient, they are just usually lighter assuming bigger wheels are made the same way/same material.
Click to expand...

This is something I wish Lucid would tell us more about. On the Air, the 21" Dream Edition wheels were forged while the 21" GT wheels were not, perhaps because the spokes of the Dream Edition wheel were fewer and more spindly and thus needed to be of stronger material than the GT wheels.

The largest wheels on the Gravity also have fewer and more spindly spokes than the mid-size wheels. Although Lucid doesn't make the same claim about any forged wheels on the Gravity, I do wonder about it, especially in a vehicle of that weight.

Of course, there are now some casting techniques, such as flow forming and pressure casting, that allow cast wheels to approach the strength of forged wheels, but forged alloys still produce the highest strength/weight ratio.
 
Knucklehead said:
This is exactly my point. There are many factors that impact wheel efficiency, and wheel size is an indicator, but it is not true to say smaller wheels are more efficient.

IMO the 22" wheels on my Rivian are more efficient than the 20" because of rolling resistance, mainly. I think aerodynamically the 20" wheel might be better, but that is just a guess. Without controlled test data, there is no way to know.

Your test, while relevant, is not controlled. There are so, so many things that impact efficiency that are outside of your control. Maybe your test result is 100% accurate and your 20" setup is better than the 21" OEM setup. Maybe.

Or maybe not. Did you carefully control the temperature of the test conditions when running the two different wheels to ensure the temperate of the air, road, motors and battery were identical? That is nearly impossible to do, right? If you didn't do that, your test results are not proof. What about road ciditions like rain? How many trips did you take in the rain in one set vs. the other? Do you know? What about speed? Was every drive at the exact same speed?

I agree it is possible to beat the most efficient Rivian OEM configuration with new wheels and tires, but I think it is hard. They picked the 21"combination of tire and rim for a reason, and the reason was maximum efficiency. The tire has low rolling resistance, and the rim is very aerodynamic. Can you beat it with a 20" setup? Possibly. And maybe you did. But I am not convinced you did with the data provided.
Click to expand...

Super weird how he was more efficient on smaller wheels in the controlled environment test you wanted to see. It’s almost as if it’s magic.
 
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indigo6 said:
Interesting that the TRL50 value (total road load horse power @ 50MPH, from what I can find) is exactly the same for the 21/22 and 22/23 wheels. Did they just not test the 21/22 combo and assign the 22/23 numbers to it?
Click to expand...
Yeah, the lbf (mostly rolling resistance) and lbf*v^2 (aero drag) terms are both exactly the same with 4 digits of precision. They definitely faked the data (though that may be allowed). Just another example of how inaccurate EPA numbers are (they're also not actually measured by the EPA.)

1748613861480.webp
 
AnthonySF said:
Super weird how he was more efficient on smaller wheels in the controlled environment test you wanted to see. It’s almost as if it’s magic.
Click to expand...
One is running summer tires and the other is all seasons...
Also the Performance wheels are staggered so at least the rear is wider.
 
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