Greetings all, first time post (I did try searching for an answer but the results were a bit murky).

I have a 2019 Discovery V HSE Luxury with Capability Plus (full size spare tire/wheel that matches the other four). It came with 245/55 R21 from the factory (about 30.8" diameter).

I'm shopping for new all terrain tires, currently looking at BFG KO3 (Load Range D) in the following sizes. I'll be mounting to 8.5x20" ET47 RRS wheels.
275/55 R20 - 31.9" dia
255/60 R20 - 32" dia (it appears this size was just released for sale within the last few weeks....before, I think the only AT tire in this size was the Goodyear Duratrac)

From reading posts here, it sounds like the 275/55 R20 (in various all terrain models) fits in the existing spare tire wheel well (under the vehicle) without issues within the existing heat shield. I recall at least one member saying that was true with Yokohama AT's (link).

The 255/60 R20 is "only" 0.1 inch larger in diameter, but hoping to hear more if it would (or would not have the tolerance)? I figured if it becomes snug, I can always deflate it (as I always carry a compressor in the vehicle).

 

Have this tire size and it fits in the spare location easily. You should be good to go! Post some pics of those KO3’s. They are on my list when the time comes to ditch my Goodyear Wranglers (Defender takeoff wheels + tires). Think this is a great tire size for the D5

 

Will definitely post photos of the KO3's!

Curious if the spare Wrangler you have is mostly full tread depth, or worn down to 5 to 6 / 32nds. I was toying with the idea of buying a used 6/32" Wrangler tire as a spare because it's cheap ($55) and being worn down has a better chance of fitting.
But if you have a near full tread depth Wrangler (which would be close to 12/32nd), that gives me more confidence about fitting a new KO3 spare.
Tough balance - 97% of the time a used Wrangler spare would be more than adequate. But I always think about the one time I could be 3 hours out on a rocky dirt road in Death Valley and the price of a new KO3 in D with tougher sidewalls (around $355 ea for this size) will seem like a bargain compared to a $2-3k towout and 1-2 days waiting.

 

Yes it was the spare and has never touched the ground. Since it is new I’ll probably keep it as the spare when I go KO3’s

 

Brief update on this topic. Last week I finally installed KO3's, but I decided to go with 275/55R20, for two main reason:
1. The overall OD is about 0.1" smaller than if I had gone with 255/60R20. Based on some (not all) people saying they had chunkier 275/55R20 (such as AT4W) rub (with no lift), I wanted to avoide the potential rub as much as possible (I want to stay with stock height and would rather not cut/trim plastic).
2. In the event of a tire failure while on a big trip, I like how there are far more AT tire options in 275/55R20. There are really only 2-3 options in 255/60R20 and they are less likely to be in stock.

Here is the install. I did four new KO3's installed on RRS (style 5084) +47mm offset rims. I also installed the same size KO2 (used, 8/32" tread) onto a 20" RRS wheel. This new spare tire and wheel fit easily and great into the spare tire well.
At lock, in access mode (and even in normal height), the tightest gap is about 2mm between the tire and the front plastic.

Ride impressions: on the road, it is slightly louder at 30-35mph, then less noticeable at highway speed. Every speed is louder then my stock 21" all seasons, but overall it is slight and very acceptable. They ride rougher for sure. I'm trying out air pressures right inbetween the light load and full GVW rating. I've only put about 100.pavement miles, and I do need to go back for a re-balance. Will collect more miles and report out in the future after some offroad use.

 

Great pics and tires look great!