There’s multiple considerations for a F550. Conversion from duals isn’t simple. You need a reversible wheel, with offset that gets F/R track as close to equal as possible. While keeping additional stress on hub bearings minimized. By those criteria alone, hard to solve.
You don’t want to go >42” for reasons of gearing, tire weight and bearing stress. We have all sniffed rumors of occasional ER rear wheel bearing failure.
305/70R19.5 is at the low end of size ~36.5”), footprint (55 sq in), and load capacity (~6700 lb). And despite being 19.5 is an oddball size and could be hard to find.
315/80R22.5 is ubiquitous but too big (43”). 295/80R22.5 is 41.5” tall, ~7000 lb capacity and 80 sq in footprint. In the Goldilocks zone, like earth. 8.25-9.00 wheel width.
Of course 335/80R20 is perfect except hard to source. Even higher load capacity, and up to 109 sq in footprint. And 2.5” taller sidewalls, rims have better intrinsic bead retention, compatible with beadlocks and maybe even Hutchinson rims. And isn’t the biggest point of the exercise flotation and ability to safely use low psi?
My solution on my vehicle (U500) is 395/85R20 rather than 445/65R22.5. I carry a second unmounted spare (sort of the ultimate solution to the availability problem).
After all, would you venture into the middle of the Kalahari or the Chaco with only one spare? I had a sketchy used replacement tire I found in Tucson blow out at 15mph in Saline Valley and I didn’t enjoy not having a spare after that. Just prior to that we were in mid Baja and an aftermarket Koni broke in half and the lower half of the shaft destroyed right rear sidewall like a lathe. We had turn around and head for the border with no spare.
Mounting a big tire yourself is never fun, but it’s at least physically possible with Hutchinsons. And any tire shop anywhere in the world can mount a tire as long as you have the tire.
Also please get over the issue with steel sidewalls. The effects on flexibility are nil at the loads we are dealing with and there’s no such thing as a organic fabric sidewall radial LT tire) that can deal with >~4500 loads per tire. Flexibility is mainly a function of load vs psi, and very importantly sidewall height.
My bottom line advice: get the best tire and wheel to do your job, carry a second unmounted spare. Or more.
Even one extra spare gives the critical gift of TIME to get another to the continent you’re traveling.
If you want a universal tire, get a 75 series Landcruiser with 7.50R16s (those aren’t so easy in NA anymore but 235s will substitute).
One afterthought: the bigger and heavier tires go the lower the speed rating. The 295s are 65-75 mph and usually more aggressive treads tend to be at the lower end of the range. 335s usually 68. My 395s 55-68 but for ~$2k each I can get new version XZL2 which are 68-75 depending on load.
The dream of driving 85 down the Interstate on oversized tires is just a dream.
