Tire/Wheel Discussion

[PetevB]

Here's a good thread on how Rivian toe and camber change with ride height.

https://www.reddit.com/r/Rivian/comments/12i03ck/alignment_changes_due_to_ride_height_changes_some

The author's conclusion is that you should get the car aligned at the ride height you want to drive at most of the time and not lower the car for range on road trips.

Nice find. So yes, they are using almost exactly the limits I'd imagined, at least in the rear. And they are getting the associated tire wear. And because Lucid's got more height adjustment the camber gain has to be less, which combined with the fact that the car will roll a lot less (the Rivian is pretty boat like) the camber gain will be doing a lot less from a functional point of view. It'll be interesting to see where Lucid lands, but given the tire wear issue and I still kinda vote for little to none.

 

[Elfin]

Nice find. So yes, they are using almost exactly the limits I'd imagined, at least in the rear. And they are getting the associated tire wear. And because Lucid's got more height adjustment the camber gain has to be less, which combined with the fact that the car will roll a lot less (the Rivian is pretty boat like) the camber gain will be doing a lot less from a functional point of view. It'll be interesting to see where Lucid lands, but given the tire wear issue and I still kinda vote for little to none.

I'm taking the opposite side of the bet. The car will be optimized for standard ride height and it will eat tires at the other ride heights.

 

[illopp00]

One can certainly still have camber gain and the associated issues, but it can’t practically get enough for the largest wheel size to not be substantially better.

If it were me I’d probably let camber go positive at the highest ride height, maybe half a degree, then I’d limit camber to perhaps 1.2 degrees negative at the lowest ride height to avoid burning out the inside edge in highway cruising. So I’d probably get a max of .4 degrees per inch of camber gain. Using something like 3 degrees per G of body roll (I’m assuming very flat, more like a track car, due to the spring rate adjustable air suspension) the outside wheel would compress around an inch and a half, so I’d dynamically add ~.6 degrees to the static camber, which at low ride height is about a degree to begin with. So perhaps up to 1.2 + .6 = 1.8 degrees of camber, but the car’s rolled over 3 degrees so you’re 1.2 degrees the wrong direction before you consider tire deflection. 0.9 degrees per inch of camber gain, more typical for a sports car, would put the tire nearly flat to the road in the same corner, but then you’re looking at positive one degree of camber at the top down to negative 3.8 degrees at min ride height- forget it.

My (current) conclusion is that the Gravity will disproportionally benefit from bigger rims vs most cars, as minimizing any extra camber loss due to tire flex will be particularly important.

@PetevB, your last statement I assuming is in regard to limit handling? Or just overall tuning compromise for handling and ride and tire wear for daily use?

 

[hmp10]

I'm taking the opposite side of the bet. The car will be optimized for standard ride height and it will eat tires at the other ride heights.

How many of the suspension parameters could be adjusted via software so that the toe, camber, and such settings could be adjusted based on the drive mode selected?

I'm guessing the Gravities that seasoned drivers such as Jason Cammisa and David Lickfold drove in test videos were optimized for the large wheels at the next-lowest ride height (the lowest being for entry and exit)? And those settings might be different for production vehicles sold to the public?

 

[illopp00]

I think they all had the Dynamic Handling Package which were running at the 2nd lowest height with the large wheel package. That being said, 85% of the performance you could argue is just Summer Tire compound that comes on the big wheel package. At least the mid-size wheels I would have the option of doing summer or all-season/touring (the continentals that come on the E-tron SUV also fit).

 

[Elfin]

How many of the suspension parameters could be adjusted via software so that the toe, camber, and such settings could be adjusted based on the drive mode selected?

I'm guessing the Gravities that seasoned drivers such as Jason Cammisa and David Lickfold drove in test videos were optimized for the large wheels at the next-lowest ride height (the lowest being for entry and exit)? And those settings might be different for production vehicles sold to the public?

The rear toe is adjustable with software. The three chamber air suspension does allow spring rate to be adjusted independent of ride height which is pretty cool.
Eating tires in normal driving does not mean the lower suspension height won't have better grip (due to more negative camber.)
This seems like enough speculation from me until we have actual measurements. It will be very easy to measure camber gain with a digital level once someone has a Gravity.

 

[PetevB]

@PetevB, your last statement I assuming is in regard to limit handling? Or just overall tuning compromise for handling and ride and tire wear for daily use?

Overall limit handling. I think they will struggle to get as much camber gain as one would typically put into a performance suspension, and as a result the lower profile tires, which deflect and hence need less total camber, will perform relatively better on the gravity vs cars without height adjustable suspensions.

But this is still conjecture. These is for example a third option re camber gain which might be ideal if they can pull it off- zero camber at the highest setting, slightly positive camber at high, zero again at medium, then increasing negative camber through to the lowest setting. If you assume the suspension is only in high at relatively low speeds when you need ground clearance and you can get the car to low pretty quickly that could work to get effective camber gain in the bottom part of the travel. If anyone has a shot of the suspension arms we might be able to spot that type of geometry by sight alone.

 

[TahoeMichael]

My driving is almost entirely on paved roads, and I do a lot of mixed climate driving in a single trip, going between the snow at Lake Tahoe and the warm weather around Sacramento. I drive fast on the freeway, and the mountain roads do have plenty of curves, but I'm not driving like an amateur racer. As such, I think the base 20"/21" wheels make sense for me, and I'd want 3PMSF rubber on them. I've been happy with Michelin CrossClimate 2 tires on my ICE SUV. All that said, I really don't have much experience driving vehicles with large diameter wheels, and so I don't know what I might be missing out on. Maybe this is a case of ignorance is bliss? I certainly don't want to have to worry about tire/wheel damage from excessively low profile tires. Since the bigger wheels are more expensive option, it seems like an easy choice to avoid them. I'm not someone who thinks they make a vehicle look better.

 

[Wulf0123]

One question I realized I haven't seen an answer to, for their towing rating, is that with the larger wheels or the 20"? Reading above how it's probably optimized for the 22/23 is putting me back on the fence, though the worry about popping a tire on a dirt road is definitely helping me decide to stay with the 20s.

 

[PetevB]

Here are the Pirellis I'm looking at for the Gravity. Although they don't identify them as part of Pirelli's "Elect" line of EV tires, the Tire Rack testers say some of Pirellis are stamped with the "Elect" logo even though the tires aren't listed as such, so it's not clear what is actually available currently. (Note that they're not an exact "set", as the front and rears have different load ratings, and the rears have the acoustic foam.
They are definitely EV tires, and they have the "Seal Inside" coating that seals punctures and allows the tires to stay in service. I find that appealing, except that this sealing compound adds 3-4 pounds to the weight of the tire, depending on size -- and puts that weight on the outside diameter where you least want it.

Educated guess: I suspect the PZeros will be a big advantage in at the limit grip and feedback mainly because they are summer tires. Range maybe- they are a very new design, which is a big plus given the rate of EV tire tech improvement, and they have fewer, bigger tread blocks than any all-season, but these advantages could be undone depending on how the tires are tuned.

As for the internal seal, I’m not seeing much advantage over the standard air compressor and fix a flat goop that comes with every BMW M car. Sure you don’t need to get out of the car to actually fix it, but then will you even know you’re carrying a nail when you get one? And as you say that’s not a great place for additional weight. I’d probably rather tires without that internal seal.

I’m also not a fan of mixing manufacture specific spec tires with one another without knowing what they are- front vs rear, etc, so I’d want to look into that. Rear Porsche ferment tires in 305 could put more tread on the ground than non-Porsche fitment 315s, for example, and were very carefully tuned for the dynamics of that specific car. If that’s a good or bad thing depends on the specifics, but if you can find tires tuned for the front or rear that’s typically good.

 

[hmp10]

As for the internal seal, I’m not seeing much advantage over the standard air compressor and fix a flat goop that comes with every BMW M car.

According to Pirelli, as long as the puncture is 4mm or less in diameter and on the tread instead of the sidewall, the tire can be driven indefinitely at normal speeds. And when the intruding object is removed, the sealing material makes a permanent seal so that the tire can remain in service.

Here is a test conducted by an Italian automotive magazine of a tire with two punctures:

Pirelli Seal Inside tyres perform well in endurance test - Tyrepress

An endurance test carried out by Italian motoring magazine Quattroruote has placed the effectiveness of Pirelli’s ‘Seal Inside’ technology under the magnifying glass. A vehicle fitted with set of tyres featuring the self-sealing material, one containing a 4mm thick nail and a self-tapping screw...

www.tyrepress.com

And here is a test of Hankook's version of self-sealing tires, this time with four punctures in the tire (segment starts at 1:14):

 

[PetevB]

According to Pirelli, as long as the puncture is 4mm or less in diameter and on the tread instead of the sidewall, the tire can be driven indefinitely at normal speeds. And when the intruding object is removed, the sealing material makes a permanent seal so that the tire can remain in service.

Ok I do like that. I was going to say that I’ve personally patched many of these leaks with fix a flat kits, but it’s always a pain in the ass. And the tire goop stuff gets all over the inside of your rims, etc. So this does seem like a real upgrade, even if I have had many tire failures this wouldn’t prevent (pinch flats, cords, bolts, etc).

That said… Porsche charges $10k for ceramic brakes on their GT3, for example. Depending on the model they save up to 37 lbs (in other cases less depending on the base brakes). That’s 9 pounds per corner. Now people will swear they feel the handling difference on turn in, etc, and there is quite a bit less flywheel effect. The math works out to 9 lbs of savings at a radius of roughly 170mm (the center of the brake rotor).

The inside of the tire tread on the gravity, for comparison, is at roughly 370mm radius, 2.2x further out vs the brake rotor above. And the flywheel effect is proportional to the square of the radius. So it works out that adding four pounds at the edge of the Gravity’s tire is over twice the flywheel effect impact as those $10k ceramic brakes. Yes it’s less from an unsprung weight perspective, etc, but it should have a performance impact you can feel if you’re tuned to that type of thing. It’s also enough mass in the wrong place that it likely has a measurably negative impact on in city efficiency.

I guess it comes down to absolute performance vs convenience, fault tolerance and safety (patching flats the side of the road is not safe). It’s nice to have the option, if I’d take it or not would be very dependent on the use case.

 

[hmp10]

. . . I have had many tire failures this wouldn’t prevent (pinch flats, cords, bolts, etc).

Pirelli claims almost 85% of flats are due to punctures in the tread. For some reason, I have had a habit of somehow picking up nails and screws right at the outside edge of the corner blocks where this seal might not work, but hope springs eternal.

I guess it comes down to absolute performance vs convenience, fault tolerance and safety (patching flats the side of the road is not safe). It’s nice to have the option, if I’d take it or not would be very dependent on the use case.

That's my thought. If I decide to go with the Pirelli P Zeros on the mid-size wheels for local driving in south Florida, I plan to get a set of all-seasons for road trips, at which point I might look for self-sealing tires. I carry a portable compressor kit on road trips currently, but with the unlikelihood of finding fitments for the Gravity's large, staggered wheels in stock at tire shops along a travel route, being able to finish the trip on a punctured tire would be a real boon.

 

[PetevB]

That's my thought. If I decide to go with the Pirelli P Zeros on the mid-size wheels for local driving in south Florida, I plan to get a set of all-seasons for road trips, at which point I might look for self-sealing tires. I carry a portable compressor kit on road trips currently, but with the unlikelihood of finding fitments for the Gravity's large, staggered wheels in stock at tire shops along a travel route, being able to finish the trip on a punctured tire would be a real boon.

If that’s the plan why wouldn’t you simply go with the biggest rims and the OEM tires locally and then buy a set of the smallest rims (maybe takeoffs) for road trips?

Lucid specs/ tunes tires for their cars, and I’m a big fan of going with tires tuned for their cars vehicle when possible (as long as they are new). It’s not a cheap process getting bespoke tires for the car- a lot of for example top spec mid-range sports cars (performance versions of the Camaro, Mustang, etc that aren’t made in enough volume) simply try a bunch of off the shelf to see what works best. But there is real advantage to tuning the tires, doing things like optimizing the front tires for braking and the rears for acceleration, that you simply can’t get when you buy off the rack. Once a car/ tire design gets a few years old this advantage fades, so for a something say 3-4 years old I’d probably walk past OEM tires, also maybe for say Tesla where they’ll have tuned the tires with different priorities in mind (ie cost or range over wet performance), but I have more faith in Lucid.

 

[hmp10]

If that’s the plan why wouldn’t you simply go with the biggest rims and the OEM tires locally and then buy a set of the smallest rims (maybe takeoffs) for road trips?

I had been thinking about doing that. But we do a lot of cross-state day trips where range matters but the trips don't last long enough to hassle with changing tires or wheels. The mid-size rims look to be an aero design where the large-size wheels clearly aren't. I also think the fact that Lucid gives the same range for both wheels must come down to the fact that the Michelin all-seasons are significantly less efficient than the Pirelli P Zeros. The Pirellis are available in sizes that fit the mid-size wheels, although it's not certain they are EV-specific tires. What I'm hoping is that putting P Zeros on the mid-size wheels will up the range enough to make it worth the bother.

Lucid specs/ tunes tires for their cars, and I’m a big fan of going with tires tuned for their cars vehicle when possible (as long as they are new.

I know that's the case for the Pirellis on the Air, but I've seen no confirmation that the P Zeros on the Gravity are specifically tuned for Lucid. I suspect they are, and that's why Tire Rack does not yet show any tire they stock as a suitable fitment for the Gravity in the large wheel size. Interestingly, though, they do already show "LM1" designations on the Michelin Primacy and Hankook ion EV tires on their website under the Gravity fitment headings for the middle and smallest wheel options.

I'd be interested in knowing just how different the dedicated tuning is from car brand to car brand within any tire line. I understand there can be significant differences between an EV tire and a non-EV tire in terms of sidewall construction, rubber compound, etc. But if you look at the Pirelli website, for example, they show a profusion of brand-specific tunings within the P Zero lineup: Jaguar, Aston Martin, Land Rover, BMW, Mercedes, Porsche, Bentley, Rolls, Lucid, et al.

I wonder just how different the constructions of these brand-specific tires are from each other. It would be an engineering, manufacturing, and logistical nightmare to have such a huge array of significantly different tires across all the sizes available in a single tire model. I have a sneaking suspicion that Pirelli might offer a limited smorgasbord of compound/construction combinations to car makers, and each maker chooses the closest thing to the balance they're seeking between the various performance criteria. (All it would then take to put the car brand on the sidewall would be a quick switch-out of a mold insert, thus creating the impression the tire is more "custom-tuned" than it actually is.)

I simply can't imagine that Pirelli engineers sat down with chassis engineers from car brand after car brand to develop a one-off tire just for that (often very low-volume) brand.

I may be wrong about this, of course, but I would have to know more before I cried uncle on the point.

 

[PetevB]

I also think the fact that Lucid gives the same range for both wheels must come down to the fact that the Michelin all-seasons are significantly less efficient than the Pirelli P Zeros.

I strongly suspect the miles quoted is simply wrong and that the mid size Michelins do in fact have much more range than is currently quoted. Perhaps that test has yet to be run to to tire availability, etc, but it strains credulity that they just happen to get exactly the same range to the Mike as the much larger and clearly relatively inefficient biggest rubber. I’ll bet heavily either that real world we get much longer range or that we see those numbers revised in time.

I'd be interested in knowing just how different the dedicated tuning is from car brand to car brand within any tire line. I understand there can be significant differences between an EV tire and a non-EV tire in terms of sidewall construction, rubber compound, etc. But if you look at the Pirelli website, for example, they show a profusion of brand-specific tunings within the P Zero lineup: Jaguar, Aston Martin, Land Rover, BMW, Mercedes, Porsche, Bentley, Rolls, Lucid, et al.

I wonder just how different the constructions of these brand-specific tires are from each other. It would be an engineering, manufacturing, and logistical nightmare to have such a huge array of significantly different tires across all the sizes available in a single tire model. I have a sneaking suspicion that Pirelli might offer a limited smorgasbord of compound/construction combinations to car makers, and each maker chooses the closest thing to the balance they're seeking between the various performance criteria. (All it would then take to put the car brand on the sidewall would be a quick switch-out of a mold insert, thus creating the impression the tire is more "custom-tuned" than it actually is.)

I simply can't imagine that Pirelli engineers sat down with chassis engineers from car brand after car brand to develop a one-off tire just for that (often very low-volume) brand.

I’m mainly familiar with Porsche’s process for developing bespoke tires, but I imagine it’s similar for others. Porsche would call for manufactures to submit bid, essentially competing to be one of the OEM options. If that’s of interest to the tire manufactures or not depends a lot on how much the manufacture is willing to pay and the terms (ie Porsche won’t accept a lease return without Porsche spec tires), but Porsche would reliably get multiple submissions even for low volume, single year cars like the GT3 and 4. Porsche specifies things like wear targets, hydroplane resistance, etc, and leave other targets open to interpretation. For GT cars there would be multiple rounds of co-development, with prototype tires tested on prototype cars, culminating in a “drive off”, where the winner and runner up were selected for production based on a full assessment of capabilities.

This process would result in tires very different from the standard offerings. There were more obvious differences in tread width (sometimes an inch wider) and depth (often shallower), but the structure of the tire was also substantially different- the carcass can be tuned to favor cornering, braking or acceleration independent of the rubber above it, and this was likely the biggest area of tuning.

You can catch a glimpse of the impact of this in certain tire tests where they mount the same tires on both front and rear wheel drive cars. You’ll sometimes note that a tire which is top of the list on a FWD car is middling on a RWD platform- same rubber, same tech, but one is better tuned for the demands of the layout than another. If a tire model isn’t bespoke to a car then a manufacture has no idea if it’ll be mounted to the front or the rear, in which case they shoot for “middle of the road”. Occasionally they don’t and it causes issues, including tire failures in at least one manufacture/ tire size I know of. But by tuning specifically to each end you hone the “tactile steering”, “sharp but predictable turn-in” and “progressive breakaway under power” to an extent you can’t with generic rubber.

Porsche pays so much attention in part because a rear engined, RWD GT car is about as far from “middle of the road” as you can get. The Gravity, on the other hand, with its AWD and low CG is much closer to “center”. But it will still benefit from a “front” and “rear” tire not just in size but construction. There’s a reason all the heavy hitters run bespoke rubber. So is Lucid spending the money and putting in the effort to do all of the above? I look at it this way: Lucid’s building a brand, and the Air and Gravity are the “halo cars” on which they’re launching it. They lost 200k per car sold last year, but they’re approaching second to none in EV vehicle dynamics. And in my mind there’s zero chance you’re beating Porsche, arguably first (price no object) in dynamics, if they are tuning tires and you’re not. So my educated guess is that one way or another Lucid has made it worth the tire company’s while to get the tire right for the Gravity. And by buying that tire you get the benefits of that investment for essentially nothing.

Again I’m speculating here, but $.02.

 

[hmp10]

I strongly suspect the miles quoted is simply wrong and that the mid size Michelins do in fact have much more range than is currently quoted. Perhaps that test has yet to be run to to tire availability, etc, but it strains credulity that they just happen to get exactly the same range to the Mike as the much larger and clearly relatively inefficient biggest rubber. I’ll bet heavily either that real world we get much longer range or that we see those numbers revised in time.

I tend to agree. But if that is the case, I find it odd that Lucid would not have listed an "estimated" EPA range for the mid-size wheels, as they certainly rode the horse hard about the greater range of the smallest wheel option.

I’m mainly familiar with Porsche’s process for developing bespoke tires, but I imagine it’s similar for others.

In launching the Air, Lucid made a point that they had worked closely with Pirelli to develop the "LM1" P Zeros specifically for the 21" wheels. (Tire Rack now even shows an "LM1" Pirelli all-season for the 19" wheels.)

Perhaps they went through a process similar to Porsche?

But I'm still not sure there's not some middle ground here. Maybe Pirelli worked with several automakers in a similar way and then put those results on the smorgasbord so that a larger array of automakers could choose which came closest to their needs? I just have trouble believing that Pirelli developed a significantly different tire for each axle for every single one of the many brands that use Pirelli as their OEM tire. For Porsche, Lucid, Rimac, and their performance-obsessed ilk certainly. BMW and Mercedes M-Sport and AMG lines, maybe. But Jaguar and Land Rover and Bentley and Rolls Royce? I somehow doubt it.

But I'm so far out on a limb with speculating here that I'll say no more.

 

[hmp10]

I was digging for information on the Pirelli P Zero PZ4 tires (their "ELECT" line of EV tires) and found that they are actually quite efficient. The nine tires in a Tire Rack test using a Tesla Model 3 showed an efficiency range from 263 to 292 watt hours / mile of energy consumption, with the Hankook iON evo AS being the most efficient. However, the max summer performance PZ4 came in at 274, which was pretty respectable.

The Michelin Pilot Sport 4S max summer performance tire was the only tire that bettered the PZ4's numbers in wet & dry braking, lateral traction, and wet & dry track times . . . and then only by tiny margins. However, its efficiency was almost bottom-of-the-pack at 290 watt hours / mile.

I also found this description on Tire Rack of the choices that carmakers can make in having a Pirelli tire customized to the car brand or model:

"Each Original Equipment marked P Zero (PZ4) tire is tailored to the specific application. A special silica and carbon black tread compound can be adjusted according to the vehicle manufacturer's needs to deliver the desired combination of wet or dry grip and handling, comfort, tread life and fuel economy. The tread compound is molded into an asymmetric tread design featuring an outer shoulder that differs based on whether the tire is intended for original equipment use on a sports car or a luxury vehicle, with the sports car's outer shoulder focused on dry handling, grip and lateral stability, while the outer shoulder of a luxury vehicle tire is tuned for improved comfort, noise and lateral hydroplaning resistance. Non-original equipment P Zero (PZ4) tires feature the sports car outer shoulder design, and all versions utilize wide, circumferential grooves for efficient water evacuation and hydroplaning resistance. The tire's internal structure includes twin steel belts reinforced by a hybrid nylon and Kevlar ZeroDegree cap ply. Based on the desired performance characteristics of the original equipment application, the tire casing will be 2-ply polyester or 1- or 2-ply rayon, with either symmetric or asymmetric construction. This customization allows the tire designers to further fine-tune the tire to match the personality of the automobile for which it is engineered."

https://www.tirerack.com/tires/pirelli-p-zero-pz4

This raises a question. The only PZ4s that will fit the mid-size wheel option on the Gravity are a mixture of an OE-marked tire for Jaguar, Land Rover, and "Sport" for the front axle and an OE-marked tire for Aston Martin on the rear axle. I wonder if anything about the choices made to assemble each of those tires would differ enough to seriously -- or even dangerously -- affect handling near the limit? For example, I assume the outer tread blocks for the Aston tire are the "sport" version of the blocks and the outer blocks for the Jaguar and Land Rover are the "luxury" version.

 

[PetevB]

This raises a question. The only PZ4s that will fit the mid-size wheel option on the Gravity are a mixture of an OE-marked tire for Jaguar, Land Rover, and "Sport" for the front axle and an OE-marked tire for Aston Martin on the rear axle. I wonder if anything about the choices made to assemble each of those tires would differ enough to seriously -- or even dangerously -- affect handling near the limit? For example, I assume the outer tread blocks for the Aston tire are the "sport" version of the blocks and the outer blocks for the Jaguar and Land Rover are the "luxury" version.

As to “dangerously” effecting handling at the limit, keep in mind nothing you could possibly do would be as bad as for example replacing just your front tires while keeping worn ones on the back, and people do that all the time (they shouldn’t, but they do). So you’re rolling the dice, it could be fine or better, for your purposes, than stock. Or it could significantly mismatched and worse but not terrible. We know the OEM tires won’t be mismatched, and from what I’ve seen I expect the Michelins to be quite efficient, so if they weren’t all-season that would be the obvious choice…

I see seven 285/40/22 options for the rear in 110Y load rating, tread depth varies by 2/32, weight by five pounds and tread width by 1.2”. The narrowest rear here is .3” narrower tread on the ground that the front you’re looking at despite being a 285 vs a 265. Which I think illustrates why I’ve encouraged caution here…

Ideally… you’re looking for something in the 9.4’’ tread width on the ground range to keep the stagger with the fronts and have the best chance con maintaining balance. You want to stick with the 8/32 tread depth to keep squirm similar. The 33 lb weight up front might indicate a tire with a pretty stiff sidewall, I’d rule out the 33 lb rear tires to have a better chance of keeping relative stiffness… And looking at the list there is no obvious match. The closest might be the Porsche Cayenne tire, but that looks like a front fitment on the Turbo GT, so likely not tuned correctly, a little understeer and the rolling resistance- who knows? The Aston tire then, but it’s pretty narrow…

So you could order, drive on the stock tires, take some efficiency and grip data (you can get numbers with as little as an iPhone app) then swap tires and do it again. And then let the forum know. Or you could get the biggest rims with matched tires, because frankly this looks a bit too much like a walk in the woods for my taste.

 

[hmp10]

So you could order, drive on the stock tires, take some efficiency and grip data (you can get numbers with as little as an iPhone app) then swap tires and do it again. And then let the forum know. Or you could get the biggest rims with matched tires, because frankly this looks a bit too much like a walk in the woods for my taste.

Tire Rack says that their search filters only generate sets of staggered tires that are compatible. (They will, however, sell a set their filter doesn't produce that includes two different tires if the buyer signs a liability waiver.)

When I search by tire size for the Gravity mid-size wheels, the Tire Rack filters generate this set:

Your comment about front/rear tread width makes the Lamborghini tire look like the better rear-axle choice, but then the tread depth goes off relative to the front.

Sigh . . . .