- Joined
- Nov 19, 2021
- Messages
- 10,227
- Reaction score
- 12,111
- Location
- Cupertino, CA
- Cars
- Air DE-P, ZR, 21"
- DE Number
- 241
- Referral Code
- Q1BTN5Y3
They were wrong. You cannot remove the third row seats. I promise.
The rest is all correct.
-
Lucid Gravity Reservation Tracker: Add Your Gravity Reservation
Gravity 75 mph Range
- Thread starter Knucklehead
- Start date
The rest is all correct.
- Joined
- Mar 7, 2020
- Messages
- 6,275
- Reaction score
- 8,697
- Location
- Naples, FL
- Cars
- Model S Plaid, Odyssey
- DE Number
- 154
- Referral Code
- 033M4EXG
Yep, understood that. That's what I meant by the seats all folding to the same level. I didn't mean you couldn't put something like a flat piece of plywood in it. However, if you tried to use an air or foam mattress for camping, you would have to cover that gap unless you don't mind that sinking feeling.
Was that a misquote, or did they really skip a zero there? 1.306 is 30.6% higher.
Some other observations - dictionaries have also embraced the definition that exponentially can cover "quicker and quicker" which basically means anything that is beyond linear. One reference even showed a graph that was mostly linear, but increased in slope, as an example. The slope increase was pretty dramatic, but still. Mathematicitions are rolling in their graves. They usually do also include the mathematical definition as an alternate, but the "quicker and quicker" is listed first.
Also, one of the animations showing the Gravity seats folding shows a barrier magically appear in the last few frames covering the 2/3 row gap. (Crap, I'm in Mexico today and the Lucid web site won't let me in to the Gravity part of the site so I can't go and find it - even though I have the locale set to US - and I'm not going to look into a VPN just for this...)
- Joined
- Mar 7, 2020
- Messages
- 6,275
- Reaction score
- 8,697
- Location
- Naples, FL
- Cars
- Model S Plaid, Odyssey
- DE Number
- 154
- Referral Code
- 033M4EXG
I just copied and pasted the phrase. The only thing I did was to underline the 36%. I think they must have omitted the "0." between the 3 and the 6.
Knucklehead
Active Member
Not yet mentioned is drivetrain efficiency. Rolling resistance is linear. Drag increases by speed squared (basically). Power to overcome drag increases to the cube of speed. So a car doing 80 pulls nearly 50% more power from the battery than a car doing 70*.
With a perfect driveline power wouldn’t matter and we could simply focus on the drag. But the driveline, and in particular the batteries, aren’t perfect- batteries and other electrical parts have internal resistance. Take power out slowly and the impact of this resistance is minimal, but it grows the quicker it’s discharged. How much that matters again depends a lot on battery chemistry, but this effect will add to the range loss calculated from graphs like the above as speed increases.
*(ignoring rolling friction, which is a smaller player)
With a perfect driveline power wouldn’t matter and we could simply focus on the drag. But the driveline, and in particular the batteries, aren’t perfect- batteries and other electrical parts have internal resistance. Take power out slowly and the impact of this resistance is minimal, but it grows the quicker it’s discharged. How much that matters again depends a lot on battery chemistry, but this effect will add to the range loss calculated from graphs like the above as speed increases.
*(ignoring rolling friction, which is a smaller player)
tjhappel
Member
350 is probably real range in ideal conditions doing 80 on the freeway (depending on wheel size of course)One thing I've been curious about is why cars drops so much efficiency at 80mph. Here is the Out of Spec data from their 10% challenge (80mph) and 70mph range test
2025 Air GT 4.3mi/kwh@70mph 2.9mi/kwh@80mph 48% increase in energy
2025 Taycan 3.7mi/kwh@70mph 2.7mi/kwh@80mph 37% increase in energy
2024 Model 3 LR RWD 4.9mi/kwh@70mph 3.3mi/kwh@70mph 42% increase in energy
This seems higher than one would expect even if all losses are aerodynamic drag! (80/70)^2 = 31% increase.
While typing this I think I may have figure it out... The 80mph number is power delivered from charger so it includes charging losses while the 70mph is efficiency from the battery. The difference still seems large.
My prediction for 70mph range
511mi for Lucid Air GT at 70mph
20% more frontal area
20% higher Cd
4% bigger battery
15% increase in energy 75 vs 70
511/1.2/1.2*(123/118)*(70/75)^2 = 322 miles
Hope it's better than that so I'm going to change my guess to 350mi
Ok, I decided to take a crack at this and put some guesses on paper for posterity…
First, based on EPA numbers the gravity appears to be a very efficient vehicle, more than one would expect. According to fuel economy.gov the Air GT gets 512 miles of range on a 118 kWh battery, or more like 505 miles based on the highway figures only. The Gravity has a 4% bigger battery (123 kWh) but it’s ~8% heavier (so that increase in rolling resistance) and it has a ~48% higher drag (CD x area).overall this should equate to ~30% more power used at 55 mph, so you’d assume 505 miles x 1.04 (bigger battery) / 1.303 (increased power) = 404 miles range on the highway portion of the EPA test. The fact that it achieved a combined 450 miles, so ~440 miles on the highway portion alone, is very impressive and either indicates big gains in efficiency or a bad test for the Air for whatever reason (I’m a bit suspicious).
If we believed the EPA tests are apples to apples we could take Out of spec’s Air GT test at 511 miles to dead at 70 mph, account for the fact that Gravity should lose a little more due to drag and convince ourselves that ~445 miles at 70 mph should be possible in the gravity. Unfortunately that would likely be defying the laws of physics.
Let’s try this another way… Taking reported drag and assuming a rolling resistance the Air GT at 70 miles an hour should take roughly 14.96 kW at the wheels to push it down the road, ballpark 159 N of force due to rolling resistance and the rest aero drag. If Out of Spec did 511 miles at 70 mph that’s 7.3 hours. Times 14.96 kW = 109.2 kWh. If the battery really is 118 kW that means 92.5% efficiency battery to wheels including everything else- AC, parasitics, driveline losses, etc. Frankly that’s impossibly high, suggesting factors like battery capacity, speed or my estimates for rolling resistance are inaccurate, but ok. If we make similar assumptions for the gravity but account for the higher vehicle weight, frontal area, etc I get it using 20.25 kW at the wheels to hold 70 mph. Going from a reported 123 kWh pack at the same 92.5% efficiency to the wheels gets us 113.8 kWh of usable energy which we would use up in 5.62 hours at 70 mph. That would mean 394 miles at 70 mph. At 80 we’d lose some driveline efficiency bringing range down to 318 miles.
The thing is the above assumes the same driveline and other efficiencies as the most recent Air GT, but the EPA test and other factors indicate the gravity is actually better. And there are reasons it might be, not just newer electrical and other tech but larger OD wheels, for example, which should lead to lower rolling resistance. Repeating with more aggressive assumptions for rolling resistance, etc, and then assuming a 1% higher battery to wheels efficiency for the Gravity I get:
418 miles at 70 mph and
334 miles at 80 mph
EPA test results vs previous Airs would indicate efficiency is even higher, perhaps adding another 5%, but that would really be stretching and put the Gravity on an efficiency level far above anything anyone’s been able to achieve so far in regards to rolling resistance, driveline losses, etc. So while I can’t rule it out I’m going with the above.
First, based on EPA numbers the gravity appears to be a very efficient vehicle, more than one would expect. According to fuel economy.gov the Air GT gets 512 miles of range on a 118 kWh battery, or more like 505 miles based on the highway figures only. The Gravity has a 4% bigger battery (123 kWh) but it’s ~8% heavier (so that increase in rolling resistance) and it has a ~48% higher drag (CD x area).overall this should equate to ~30% more power used at 55 mph, so you’d assume 505 miles x 1.04 (bigger battery) / 1.303 (increased power) = 404 miles range on the highway portion of the EPA test. The fact that it achieved a combined 450 miles, so ~440 miles on the highway portion alone, is very impressive and either indicates big gains in efficiency or a bad test for the Air for whatever reason (I’m a bit suspicious).
If we believed the EPA tests are apples to apples we could take Out of spec’s Air GT test at 511 miles to dead at 70 mph, account for the fact that Gravity should lose a little more due to drag and convince ourselves that ~445 miles at 70 mph should be possible in the gravity. Unfortunately that would likely be defying the laws of physics.
Let’s try this another way… Taking reported drag and assuming a rolling resistance the Air GT at 70 miles an hour should take roughly 14.96 kW at the wheels to push it down the road, ballpark 159 N of force due to rolling resistance and the rest aero drag. If Out of Spec did 511 miles at 70 mph that’s 7.3 hours. Times 14.96 kW = 109.2 kWh. If the battery really is 118 kW that means 92.5% efficiency battery to wheels including everything else- AC, parasitics, driveline losses, etc. Frankly that’s impossibly high, suggesting factors like battery capacity, speed or my estimates for rolling resistance are inaccurate, but ok. If we make similar assumptions for the gravity but account for the higher vehicle weight, frontal area, etc I get it using 20.25 kW at the wheels to hold 70 mph. Going from a reported 123 kWh pack at the same 92.5% efficiency to the wheels gets us 113.8 kWh of usable energy which we would use up in 5.62 hours at 70 mph. That would mean 394 miles at 70 mph. At 80 we’d lose some driveline efficiency bringing range down to 318 miles.
The thing is the above assumes the same driveline and other efficiencies as the most recent Air GT, but the EPA test and other factors indicate the gravity is actually better. And there are reasons it might be, not just newer electrical and other tech but larger OD wheels, for example, which should lead to lower rolling resistance. Repeating with more aggressive assumptions for rolling resistance, etc, and then assuming a 1% higher battery to wheels efficiency for the Gravity I get:
418 miles at 70 mph and
334 miles at 80 mph
EPA test results vs previous Airs would indicate efficiency is even higher, perhaps adding another 5%, but that would really be stretching and put the Gravity on an efficiency level far above anything anyone’s been able to achieve so far in regards to rolling resistance, driveline losses, etc. So while I can’t rule it out I’m going with the above.
tjhappel
Member
I think you nailed it, I’d imagine 300 to 320 at 80 at the most. Good work
Ah… Face palm. The Lucid Gravity is listed as 65.2” tall, used to estimate frontal area. But I highly doubt that’s in the lowest position. If it drops an inch and a half from there on the freeway that’s 4% less drag, explaining much of the Gravity’s on paper efficiency gap vs the Air right off the bat. If in fact the 65.2” is the highest setting that would make 61 the lowest… ~6.5% less drag. In that case I’d up my estimates to 435 miles at 70 and 347 at 80… Not defying any laws of physics after all.
Is frontal area calculated from the convex hull of the front projection? Or is it calculated continuously? The various height settings shouldn't change the frontal area by much as it would only be a few inches of the tires that would disappear inside the rest of the area. The space under the car would get smaller, but that isn't part of the frontal area, is it?
Knucklehead
Active Member
My gut says 350 at 80. Seems your math matches my gut.
So this gets a bit tricky. First, coefficient of drag is a derived number. You stick a car in the wind tunnel, measure total drag (which is what counts), divide by the frontal area and then report a coefficient. Two points here: First, if you want to report the lowest CD (which is what people recognize) it’s in your interest to divide by the biggest area you can, ie include the area under the car. Second, total drag essentially universally goes down substantially as you reduce the ride height, so if you keep frontal area nearly constant by ignoring the space under the car then you actually get the coefficient of drag dropping substantially as ride height goes down.
The second reason, more than the first, is likely why the entire outside profile or silhouette of the vehicle is counted as the frontal area and the gap under the car is ignored by common practice. It’s calculated as though there’s a piece of sheet metal down to the ground under the car. This might result in some strange things, like the lowest CD is reported at a medium ride height but the lowest drag is recorded at the lowest height.
Any way you slice it this is likely to account for much of the efficiency advantage the Gravity has over the air that I had trouble explaining previously.
My heart tells me that it shall be so. But I am in disbelief at the efficiency that these vehicles get even though I drive one every day.
TahoeMichael
Member
- Joined
- Jul 13, 2023
- Messages
- 31
- Reaction score
- 40
- Cars
- Toyota Highlander
There really isn't any standard for how frontal area or cD is calculated for vehicles. Even if one picks a standard approach for frontal area, there can be big variations in wind tunnel setups, and legitimate reasons why an engineer might prefer one wind tunnel configuration over another. One can hope that a particular manufacturer uses a consistent approach, thus providing some ability to compare vehicles within their product line. But as PetevB says, cD has become part of the marketing game for EVs, and so there's a strong pressure to abandon engineering fundamentals and instead calculate it in whatever way allows for the most impressive press release.
Because of that, I mostly don't pay too much attention to cD. It's ultimately only one factor of many that affects a driver's experience with a vehicle.
