There's a new forum member --
@PetevB -- who is an engineer and seems to know a lot about these kinds of issues. Maybe he can weigh in on our questions?
Do we know the offsets and widths of of the wheels yet? Without that we can’t be sure if the front wheel will clear the rear without interference, we’d also need to check clearance to steering knuckles if we used the smallest front wheel.
Re diameter the short answer it’s not great to have that type of diameter difference, but if you treat it like a space saver spare and keep speeds and distance down it’s probably ok in a pinch.
The long answer: The front tires are 30.2” OD while the rear measures 30.9. Usable tread depth before legal replacement is 7.5/32nds, so if you had fresh tires on the front and completely worn on the rear you’d be at 30.2” F and 30.5” R. So the rears are nominally rotating 2.3% slower than the front, but could be rotating just 1% slower. The ABS, traction control and stability control are all tuned to look for this difference. If one rear tire is rotating at the same speed as the front the computer sees this as that tire slipping. That’s not abnormal, some amount of slip is expected during even typical acceleration, but the computer will be doing the wrong thing, and braking, stability control, etc will be compromised. Longer ABS panic stops are probably the biggest risk here.
In addition if you did this in for example a Porsche or BMW they’d likely void your warranty, as you’d be be constantly spinning whatever limited slip differential setup is used (wearing friction plates or worse) due to the diameter imbalance. I’m not clear on Lucid’s solution for the gravity at this point; I suspect it will do better I’m not sure.
All that said, however, when you get a flat your rear tire is most likely a little worn, maybe 30.7” on average, while your fronts are most likely 30”. So a fresh front tire at 30.2” almost splits the difference, which brings the rotating speed down to a pretty reasonable number. Even better would be another tire with a slightly larger ~30.4” diameter (maybe a winter tire option or similar). Used on a wheel that clears I’d be comfortable going fairly long distances without worrying about damaging things (knowing performance would be compromised).
If the wheel offset doesn’t work someone committed could look into spacers and longer studs or similar, hopefully not needed. A true space saver spare in the right bolt pattern and diameter would likely be even better at that point, assuming one could be found. You’ll obviously need the jack, etc as well.
Lucid should really have a service with wheels and tires on the shelf and ready to ship nationwide in 24 hours. AAA flat bed to the nearest town and 24 hours later you’d be back on the road at full capacity. Return the wheel/ tires ready when you’re done for the next guy. I’d pay $600 for that every time, cheaper and probably better than having a spare in car, no concern re diameter differences/ performance, etc. Seems a logical step if you really want people to road trip in these…