1. Are wheels the proper load rating?
Although a swap to 18" Mercedes G-Wagen wheels is popular, it is not clear whether these 18" wheels have the same load rating as Sprinter original wheels (and if not, whether owners are thus lowering their maximum weight).
There are several aftermarket 16", 17", and 18" wheels with load ratings for Sprinters. Have not seen any specific G-Wagen wheels which state load ratings which equal original load specs for Sprinter.
2. Are tires the proper load rating?
It appears that there are no 255/55/18 with the proper load rating.
If you go to a larger diameter size of 265/60/18, you can get at least two tires with the proper rating.
https://sprinter-source.com/forum/showthread.php?t=8963&highlight=265/60/18&page=3
The issue is whether the combination wheel (ET spec) and tire will require significant modification of wheel wells.
If correct specs, the BF Goodrich All-Terrain KO2 seem to come in many different sizes with proper load ratings which may fit Sprinters.
Various confusing info which may be a result of
(a) 140" and 158" T1Ns to USA were lifted 1" or so to provide clearance for 16" wheels and 225/75/16 tires versus 118" T1Ns which had 15" wheels (applicable to all model years?),
(b) different replacement wheels may have had different offsets, and
(c) different weighted Sprinters may result in tire rub or not.
3. Alternatives--what is goal?
Better handling, looks, costs?
A. Can do a vehicle lift to provide room for bigger wheels/tires. Vancompass.com
B. Can do a cut and bodywork--create new fenders--poster here did that.
C. Switch to 17" wheels which offer more tire sizes with proper load ratings--may still require some cutting of bumper cover and fender.
Several aftermarket 17" wheels specifically for Sprinters.
D. Switch to original 16" wheels. May want to look at width of wheels which will affect what tire sizes will fit.
Can get cheap aftermarket $100 per alloy wheel in 16x6.5 or the original Sprinter alloy wheels in 16x6.5. The original Sprinter steel wheels are 16x6.
4. Caveat
There are some postings from Australia and Europe re the more stringent requirements for replacement wheels than the apparently more lax standards here in the USA.
Please post whatever you decide to do. Thanks.