I'm new to the forums and this is my first post requesting assistance... I live in New York and I own a 2016 XC70 AWD T5 2.5L that currently has 36K miles on it. I enjoy the outdoors (...hiking, backpacking, camping, skiing, kayaking, mountain biking) so I'm always loading up my car with gear. Previously I owned two Nissan XTerra 4WDs which I loved because I could get through any kind of terrain and weather without any concerns, but the reality is that I am 5'1" so the XC70 is more practical for me to load and unload and it's my only vehicle so I use it to drive to/from work. My only gripe with the car is that the stock tires (235/50 R18 97V Pirelli Scorpion Verde All Weather Run-Flats) are not great in winter and it seems I often have to fill them up because they run low on air when temperatures change. I bought a Viair portable compressor, so filling up is no longer that big of a deal but I need to replace them anyway because one tire is bulging and they've developed cracks. Having said that, I'm looking to upgrade my car to something more off-road worthy so I'm looking for recommendations on wheels & tires upgrades from the forum community. Here's what I'm hoping to achieve, it's complicated so please bear with me:
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1) Buy a full size spare (wheel and tire - stock is a "doughnut" basically and if I'm on a remote dirt or snowy road I'll be more comfortable with a full size spare)
2) I need new (better) tires now, but I'm not planning on lifting the car and upgrading the suspension just yet
3) I could stay with the 18" wheels, buy an extra one for the spare, and buy (better) all weather tires and rely on chains (which I think are illegal in NY but maybe not off-road) but I think I want all terrain tires eventually and although those go on 15"-18" wheels I might want a smaller wheel...
3a) Are there 15"-17" wheels that accommodate all terrain tires that fit in the 2016 XC70 wheel wells (and not require new calipers) without lifting the car?
3b) Can those same wheels support a larger all terrain tire after I lift the car?
3c) Could I even fit an all terrain on my 18" that fit in the 2016 XC70 wheel wells (and not require new calipers) without lifting the car?
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I've been looking at:
All Weather (18") Continental ExtremeContact DWS06, Continental Pure Contact LS, Michelin Primacy Tour A/S, Pirelli Cinturato P7 (not available in 18") and Pirelli Scorpion Verde (which I don't like)
All Terrain (15"-18") General Tire Grabbers (various), BF Goodrich All-Terrain T/A KO2 so far...
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I think I answered my own questions by just writing all that out... I can keep the 18", get the ExtremeContact DWS06 or Michelin Primacy Tour A/S then upgrade to a larger all terrain on the 18" after I lift the car... Duh
I realize there are a lot of "if's" and I'm trying not to buy things twice (I could just sell the used stuff)... Any advice would be appreciated, thanks!

 

A more specific follow up question: Will an LT255/55 R18 fit in the 2016 XC70 without interferences? I used an online tire comparison tool and the differences seem small...