I had to switch my R1S reservation to the 21s to stay under the 80k, but it inspired me to look into aftermarket wheels. Thank you to the posters in this thread, especially kizambute. 🙌. I think there are several good looking options for 20 in rims out there. If what I am reading is correct, here are the basics from what I can tell:
--Rivian 20s have a wierd offset.
--Several companies make wheels that will work, but will stick out toward the fender more. To compensate, go from a 34 in tire to a 33 in tire (recomend Pirelli scorpion all terain plus 275/60R20) that apparently look very similar to the rivain AT but the 1 inch smaller diameter looks good, arguably fits the look of the truck better / fine, and avoids any issue with the offset being outboard a bit with the aftermarket wheels.
--not sure if lugs are usable with other rims (((please answer if you know how to tell)))
--not sure what specific tpms work, but apparently some have. (((please answer with part number and process if you know)))
--some use hubrings. Not sure what that is. Why do you use it? is it needed for all aftermarket wheels? (((please answer if you know)))
Here are what others have put on with specific brands and sizes as best I can tell:
I always felt the 34" stock tires were too big for the size of the truck. The 21 and 22" wheel options both have 33" circumference tires. Posting the following to demonstrate fitment for anyone interested. I added custom wheels. Showing these photos to demonstrate fitment, not my wheel...
www.rivianownersforum.com
kizamybute' setup: Ultra Scorpion 20x9 lug pattern as 5x 139.7. Offset is 18 mm. Bore diameter is 87mm. These have the Pirelli Scorpion all terrain plus 275/60R20 tires.
This wheel also comes in gloss black.
Method has a few that might fit, such as the 315:
method 315 20x9.5 18mm offset backspace 295
On Facebook someone put on Black Rhino Primm Wheels here:
https://m.facebook.com/photo.php/?fbid=159869550020535
These apparently are Black Rhino Primm 20x9 5x5.5 139 +0 offset 5.25 backspacing.OP says they are on 275s and no rub, but do seem to have a bit more poke but still look great.
Black rhino also makes the Dugger in 20x9, 5x139.7. These have a 0 offset but a 5.0 backspace, so i thin .25 inboard compared to the Black Rhino Primm shown above.
These are cool in that you can remove / paint / replace the outer rock ring if you damage them.
Blac Rhino Overland (my personal current favorite)
These are 20x9.5 5x139.7 0 offset and 5.30 backspacing so .05 outboard compared to the Primms above. Maybe too much poke? I think would look really nice with the 275/60 r20s. My rendition on my LA silver...
As listed a few post above, there is also the Ram 1500 2007-2013 stock rim option (Ram 2363 rim). it is 20x8 with 19mm offset and 4.5 backspacing. Looks really sharp: