20-ish mile range difference between 5 seat and 7 seat Gravity?

[Pragmatic]

There is aero for the rim and aero for the tire. Tires make up approximately 25% of the aero drag on a typical car (article in "Chinese Journal of Mechanical Engineering" linked below). The article describes measuring aero drag on three identical tires with different tread patterns (same size, construction with tread being the only difference). The Cds varied by 8% based solely on tread pattern.
The energy usage from Tire Rack article was for a Tesla Model 3 with a much smaller tire (235/40R19). The heavier Gravity will have 1.5 times the rolling resistance (6000 lbs vs 4000 lbs). The tires are wider and taller changing the aero drag. I do not think you can use these data to help understand the Gravity tire packages.
Just be resigned to the fact that the Michelin and Pirelli are equal in energy usage (mix of tire rolling, tire aero and wheel aero) while the Hankooks are obviously designed with low rolling and low aero drag.

Article discussed above:

Aerodynamic Characteristics of Isolated Loaded Tires with Different Tread Patterns: Experiment and Simulation - Chinese Journal of Mechanical Engineering

The current research of tire aerodynamics mainly focus on the isolated and simplified tread tire. Compared with the real complex pattern tire, the tread pattern structure and deformed profile of a loaded tire has a greatly influence on tire aerodynamic drag. However, the mechanisms of the...

cjme.springeropen.com

 

[hmp10]

There is aero for the rim and aero for the tire. Tires make up approximately 25% of the aero drag on a typical car (article in "Chinese Journal of Mechanical Engineering" linked below). The article describes measuring aero drag on three identical tires with different tread patterns (same size, construction with tread being the only difference). The Cds varied by 8% based solely on tread pattern.
The energy usage from Tire Rack article was for a Tesla Model 3 with a much smaller tire (235/40R19). The heavier Gravity will have 1.5 times the rolling resistance (6000 lbs vs 4000 lbs). The tires are wider and taller changing the aero drag. I do not think you can use these data to help understand the Gravity tire packages.
Just be resigned to the fact that the Michelin and Pirelli are equal in energy usage (mix of tire rolling, tire aero and wheel aero) while the Hankooks are obviously designed with low rolling and low aero drag.

Article discussed above:

Aerodynamic Characteristics of Isolated Loaded Tires with Different Tread Patterns: Experiment and Simulation - Chinese Journal of Mechanical Engineering

The current research of tire aerodynamics mainly focus on the isolated and simplified tread tire. Compared with the real complex pattern tire, the tread pattern structure and deformed profile of a loaded tire has a greatly influence on tire aerodynamic drag. However, the mechanisms of the...

cjme.springeropen.com

The data I used was from comparing a Hankook tire of the same size as the Pirelli and Michelin tires, as they were all on a Tesla Model 3. I did not use it to compare the tire efficiencies between the Tesla and the Gravity. What I wondered was whether the efficiency differences seen when all the tires were put on the Tesla would be similar to differences in those tires when they were all put on a Gravity. For example, on the Tesla the Hankooks were 4% more efficient than the Pirellis on the same car with the same wheels. Would putting Hankooks on a Gravity with the 20/21" wheels also yield 4% more efficiency than putting Pirellis on that same Gravity with 20/21" wheels. In other words, with the tires being the same width on all the Gravity wheel options, how much of the 12% difference in range between the wheel options was coming from the tires and how much from other factors?

 

[Knucklehead]

I get staggering the tire widths, but I wonder what the reason was for staggering the wheel diameters?

I have been thinking about this, and I have a theory. I think it is to improve range.

In one of the OOS videos someone mentions that Lucid put larger wheels on the rear to improve range. I thought that didn't make sense at the time, but then I watched the video @borski posted from Lucid that describes how they built the battery pack. In that video they mention sloping the undercarriage up toward the rear improves range. In that context it was about undercarriage design, but if you put larger wheels on the rear, it could have a similar effect.

Maybe slightly raising the vehicle with larger rear wheels measurably reduces aerodynamic drag under the car? I don't know why they can't do the same thing by raising the suspension, but maybe it is cheaper to do it with wheels, and then you get the side benefit of improving the appearance of the vehicle?

I think this makes sense, and it would explain why they did it. I don't think appearance is enough, unless there is another benefit. Maybe this is why Tesla does it also.

 

[hmp10]

Maybe slightly raising the vehicle with larger rear wheels measurably reduces aerodynamic drag under the car?

It would only raise the vehicle a small fraction of an inch. In the chart you showed above, the wheel diameter only increases by 0.7", and the ride height would only increase by half that amount, i. e., 0.35". (Remember that the tire sidewall height is shortened to compensate for the larger wheel diameter when larger wheels are put on one axle so that the total height -- and thus the rolling diameters -- of the tire/wheel ensemble remains reasonably close front to rear.)

In the case of the Hankooks (below), the difference in rear ride height would also be only 0.35". I suspect that would make very little difference to airflow compared to what the several-inch upward sweep of the battery back contributes (but I'm no expert in this and am just speculating).

I found several things interesting about this chart. Although the rear tires have a tread width 20mm (0.787") wider, their section width is only 0.1" wider, meaning the profile presented to the air is virtually identical to the nominally narrower front tires. (For some reason, the tread width of the rear tire is missing from this chart.)

Another thing is that, although Hankook claims on its website that these tires are extraordinarily light in weight as part of their efficiency strategy, they are actually sort of mid-pack. The other three tires that Tire Rack says are suitable for the Gravity with the smallest wheels have weights of 33/36, 35/38, and 35/40 compared to the Hankook's 36/36. Also, it's odd that the front and rear Hankooks weigh the same, as almost every tire I've looked at for all the Gravity wheel sizes has a weight spread of 3-5 pounds between front/rear sizes.

 

[Elfin]

In one of the OOS videos someone mentions that Lucid put larger wheels on the rear to improve range.

In this video Kyle says he asked the chassis engineer and was told the staggered wheel diameter is "mostly style driven" (39.26).

 

[hmp10]

In this video Kyle says he asked the chassis engineer and was told the staggered wheel diameter is "mostly style driven" (39.26).

That's disappointing from a company that seems to have put engineering and functional concerns foremost thus far.

In trying to decide on what wheel option to order, I've been digging around for different tires that can be used on the different Gravity wheel sizes to help me strike my own preferred compromise between range and performance. There are loads of tires that will fit one or the other wheel size in each wheel size pairing. But when you filter for tires that will fit both wheel sizes, the number of choices collapses to low single digits -- and in some cases disappears altogether.

In light of the chassis engineer's comment, I'm beginning to consider buying a set of same-diameter wheels, but with the rear wheels wider, as I would still want to keep the staggered widths.

 

[Sid432]

Any words on gravity orders happening before EoY? Don’t think I have seen any. I hoped atleast we would hear something by now. Damn, silence is killing me

 

[charleyscott]

I have been thinking about this, and I have a theory. I think it is to improve range.

In one of the OOS videos someone mentions that Lucid put larger wheels on the rear to improve range. I thought that didn't make sense at the time, but then I watched the video @borski posted from Lucid that describes how they built the battery pack. In that video they mention sloping the undercarriage up toward the rear improves range. In that context it was about undercarriage design, but if you put larger wheels on the rear, it could have a similar effect.

Interesting. On a similar note, I had been wondering—nothing more—whether it is possible that the underbody of the 5-seat version is shaped differently from the 7-seat version, again to improve range.

 

[babylou66]

What if the underbody for the 7 seater is shaped differently...think less diffusey? That will have a definite effect on the cD.

 

[Knucklehead]

What if the underbody for the 7 seater is shaped differently...think less diffusey? That will have a definite effect on the cD.

Smaller battery but more efficient. Sounds like the Air Pure.

 

[DrLucid]

Any words on gravity orders happening before EoY? Don’t think I have seen any. I hoped atleast we would hear something by now. Damn, silence is killing me

I was hoping VIN would be allotted as a Christmas gift . I guess will have to wait for the New Year. Silence for sure is killing.

 

[hmp10]

I was hoping VIN would be allotted as a Christmas gift . I guess will have to wait for the New Year. Silence for sure is killing.

I've been surprised by how therapeutic obsessing about wheel sizes and tire characteristics can be. It's almost making me hope I don't get delivery before the deep mysteries of alloy and rubber are properly sorted.

 

[borski]

I've been surprised by how therapeutic obsessing about wheel sizes and tire characteristics can be. It's almost making me hope I don't get delivery before the deep mysteries of alloy and rubber are properly sorted.

Fascinating. Watching your therapy has made me nothing but anxious

 

[Knucklehead]

I am in the peanut gallery watching for posts when you guys get the first deliveries. Your experiences will definitely inform my decision.

Right now, I plan to get a Gravity. A month ago it was a R1 Max Tri. The Gravity just has more of what I am looking for, and it is an amazing engineering marvel. (Like the super heros. LoL.)

Anyway, someone needs to take delivery ASAP so I can move forward and place my own order!

 

[hmp10]

Fascinating. Watching your therapy has made me nothing but anxious

I get the same feeling of anxiety reading the current never-ending thread about voltages and charging times. Tires and wheels I understand. Electrical engineering, apparently not a whit, even when thoughtfully explained.

FWIW, Tire Rack's website and its myriad of articles on tire sizing, construction, and usage has been one of my perennial favorite auto-related websites. Until the Lucid Owner's Forum came along, of course, and I went down a rabbit hole almost five years ago that I can't seem to escape.

So I just set up a sofa and decided to stay.

 

[hmp10]

TireRack has Vredestein options which are correct size and very highly rated, grand touring, tires. $1200

As (bad) luck would have it, we picked up a nail in the sidewall of our front left Odyssey tire yesterday. So I'm taking the opportunity to try the Vredestein Quatrac Pro+ tires on it. Should get the car on the road early next week. We're in a dry spell, but I'll report how they seem after some rain.

There are so many differences in the Odyssey and the Gravity that I don't know how transferrable the impressions would be, but it'll at least be a few data points.

 

[037]

As (bad) luck would have it, we picked up a nail in the sidewall of our front left Odyssey tire yesterday. So I'm taking the opportunity to try the Vredestein Quatrac Pro+ tires on it. Should get the car on the road early next week. We're in a dry spell, but I'll report how they seem after some rain.

There are so many differences in the Odyssey and the Gravity that I don't know how transferrable the impressions would be, but it'll at least be a few data points.

I like the way you operate, data is king!

Someone noted Michelin SUV 4 summer tire is available in 20/21” size, ever try those? As much as I want to get a single tire and forget it (like Michelin AS4), can’t deny performance benefits of season dedicated tire.

 

[hmp10]

Someone noted Michelin SUV 4 summer tire is available in 20/21” size, ever try those? As much as I want to get a single tire and forget it (like Michelin AS4), can’t deny performance benefits of season dedicated tire.

They are, but the fronts and rears have different speed ratings. That's why Tire Rack doesn't list them as a fitment for the Gravity. However, they will sell a set if you accept a notice on the invoice that the front tires are not rated for the Gravity's top speed.

The issue, though, is that the Michelins were in the lower end of the pack on the efficiency testing Tire Rack did.

 

[037]

They are, but the fronts and rears have different speed ratings. That's why Tire Rack doesn't list them as a fitment for the Gravity. However, they will sell a set if you accept a notice on the invoice that the front tires are not rated for the Gravity's top speed.

The issue, though, is that the Michelins were in the lower end of the pack on the efficiency testing Tire Rack did.

Yep, I saw the low efficiency of the AS4 but it’s the best all season tire for winter so I accepted that. My last set only lasted 20k tho and that included a winter tire used within the same 20k…

Now are we suggesting Gravity has a higher top speed than 168 then?

 

[037]

They are, but the fronts and rears have different speed ratings. That's why Tire Rack doesn't list them as a fitment for the Gravity. However, they will sell a set if you accept a notice on the invoice that the front tires are not rated for the Gravity's top speed.

The issue, though, is that the Michelins were in the lower end of the pack on the efficiency testing Tire Rack did.

Just looked at TireRack selection of 4 tires available for the Gravity in 20/21 and some are W rated, so I am thinking the issue might be something else.