I have to say I am really impressed by the performance of my 275/60R18 Yoko Geolandar AT/S off-road thus far. They may not be the sexiest looking A/Ts out there, but they get the job done. I just spent 3 glorious days in Death Valley with our local LR club, and we got pretty nasty weather for 2 of them, including several incredible snow blizzards on top of some passes (snow blizzards in Death Valley... I never thought I'd see those.

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Over some pretty gnarly, slippery and soaking wet / snowy trails, my Yokos never faltered. They maintained excellent traction throughout, only giving in a little on icy passes - which we all negotiated at extremely low speeds, as most of us were slipping and sliding regardless of tires.
On the way back home, they were as quiet as they've always been. I have now about 25K miles on them and it looks like they'll be good for at least another 25. Very happy so far.
Here is a short video from my dash and rear window cams of a particularly steep (and slippery for the occasion...), rocky section of the trail climbing up Echo Canyon, in the southeastern portion of the park. Other vehicles had quite a bit of trouble maintaining traction on that stretch of slippery rocks, mine just rode right up.
Echo Canyon - Waterfall - YouTube