I think it takes some effort to wrap your head around how a BC ski boot should fit. If you are looking at an ski boot fit specifically to climb in you may (should) think differently than the guy who wants a BC boot specifically to *just* ski in.
My take from the experience of seeing so many unhappy BC skiers (from ski guides to clients mind you) is most would be better served to simply forget the whole idea of a "ski boot" fit in an AT boot.
All this would seem rather obvious one would think. But from skiing with various partners this winter nothing could be farther from the truth.
It would seem that there are a lot of skiers that try every thing possible to get the smallest shell size that will fit their feet. Then they go to great extremes to heat mold the liner or change liners and punch the shell to every bump and nuance that their specific foot needs require.
Done it myself. Likely the end result a perfect fit for skiing. Likely not the perfect fit if you want to climb or walk in those same boots any length of time.
A two minute search on the Internet will show you variations of this: "Boot liners are very cushy at first, but they will conform to your foot in 10-15 minutes, and after several ski days, they can really pack down. What feels so perfect in the store often feels sloppy and uncontrollable on the hill. The correct boot should feel snug all over without pressure points. If it feels too tight initially, almost enough to make your eyes bulge, it's probably about the right size."
"Eyes bulge?" Ya, likely not the right size you are looking for even when heat molding your boots.
Might be a nice fitting ski boot. But think about that for a minute.....or more realistically way more than just a minute. Because you will have a lot of time to think about it when walking 8 hours or so on your next day tour?! The local professional ski boot fitter may not be the guy you want fitting your back country boots. If you are going to be climbing in your ski boots...and your boot fitter has no clue what climbing or a full day in the back country entails......he or she likely NOT the guy you want fitting your BC boots.
Typical ski boot fit for down hill rentals and the inexperienced:
"You see it more and more in rentals — “What’s your shoe size?” They tell me 10, I’ll give them a 28 boot, which is a size too big, being conservative because they’re rentals. The customer will open it up, put their foot in, and without buckling it, they’ll say, “Oh, I need the next size up.” Then you have a choice to make, because there’s a line of people waiting. You could do the right thing and say, “Listen, I know it feels a little short. You want to buckle it up. When you stand in the boot with a buckle, your heel is nowhere near the back, so your toes are jammed in the front.” Depending on the day and the mood I’m in, I might just say, “Here’s a 30, try that.”
More typical BC ski boot fit by the experienced:
Pick the correct shell size for back country skiing by placing bare foot in shell, touching end with toes, then seeing how many stacked fingers you can fit behind your heel. Any more than a 2 finger stack and the back country skiing boot shell is too big. Less than one-and-one-half fingers and it’s probably too small. In some cases (as in mine) you’ll be between shell sizes. If that happens try fitting the smaller shell first, but remember it’ll probably be colder and you may have problems with getting enough length for your toes. The larger shell will be warmer and easier to get comfortable for touring, but you may have problems getting the fit tight enough for downhill skiing.
The reason I bring all this up?
"tight enough for downhill skiing" There in lies the rub here.
We now have boots that ski very well that you can climb difficult technical ground in and not be at a disadvantage. But if you fit those same boots as tight as you might have fit your typical down hill ski boot the amount of time you'll want to spend in them is likely going to be limited. And you'll pay for that mistake in either pain or a new pair of boots in a larger size eventually.
This would seem to be a North American problem. Not a Euro problem as they have been climbing long and difficult technical ground while in ski boots for a while now. Pretty common there actually. I don't have to mention their long, hut to hut, ski tours. Here just the the thought of a full day out, on a up and down ski tour, seems to put most feet into some serious pain.
I intentionally thought of my TLTs as "climbing boots" and fit them accordingly. I use a 29 shell. My "ski boots" are generally a 28 shell. And I wear a size 12 street shoe! None of the 28 shells do I want for a lot of walking. But no question the 28s do ski great.
Still, I've had some of my best days skiing in the, "big" TLTs. I've also spent some time walking, climbing or drive my truck's manual transmission in them with little complaint. And some times those were some lonnnnggg walks.
Always worth the effort of getting a custom insole/orthotic made to support your foot in any of these boots. A totally rigid boot sole is not a great thing for your feet...no matter the use. An properly fit orthotic can make the difference between a great fit and a painful ski boot.
A custom orthotic allows me to comfortably use a TLT 5 with a very narrow last. Without my orthotic in the boot my feet collapse enough that over time the boot is painful on the outside toes. With the orthotic my foot is supported enough that there is no pain or boot pressure. I don't require a orthotic in my mountain boots or running shoes. But in my ski boots it makes a big difference on how long I can stay in them comfortably.
We use a different and appropriate fit for our running shoes, rock shoes (trad and sport?) and our mountain boots. Probably time for some to look at how to fit their BC ski boots as compared to their down hill ski boots.
Because if it really is "all about the down" in your ski boots, likely your feet are going to suffer....a lot.
Done right the same boot can serve both purposes easy enough.
Get it wrong and it is a pleasure to simply get them off your feet!
I can ski the same amount of ski under foot and generally the same length ski till I get around 115mm in a 29. Same boot I ice climb in. And am pretty happy with. At 115mm under foot with my ski I start looking for a size 28 "ski boot". It is not so much that the support/design of the boot changes but how the boots fit, does.