I get made fun of a lot in the snow school locker room because I'm constantly tinkering with my boots. For me, with a somewhat aging crooked body, it's just small tweaks in the endless search for symmetrical turns, and I must admit it borders on obsessive compulsive behavior.
I don't suggest you always look to your gear as the cause of your skiing setbacks. Most of the time it really does come down to technique. However, your equipment is the interface between your body and the snowy environment, so if your set up isn't just right, it can prevent you from performing your best. Every skier's body is unique, so of course generic boot designs can't possibly be optimized for everyone's physique.
When Should You Tinker?
Well, if you're a Science Frictioner and your diagnostics assessment indicates that some sort of fit or alignment issue could be contributing to your symptoms, it's probably at least worth a little self experimentation.
There is a lot you can do to enhance the performance of your boots without fancy equipment or even much knowledge, but the fact that us skiers absolutely love the idea it of blaming our equipment has spawned a healthy economy for specialist ski boot fitters. If the need arises you should be able to track one down in any reasonably sized ski town.
When Should You See a Boot Fitter?
The first prerequisite is having money (I don't know why they don't work for free). Secondly,if your self boot hacking got some results but permanent shell alterations are needed to go all the way. If you've exhausted every technique fix and still have equipment related symptoms (like sewing machine leg). Or of course, if your feet or lower legs are in pain... then it's probably time to seek out a professional.
The Problem with Professionals
The world of boot fitting is kind of like religion and politics... there are many different schools of thought and no two groups can agree. I know quite a few reputable boot fitters, all are mad scientist like in their rhetoric but each of whom follow a different dogma.
It's pretty hard to find two boot fitters who agree on a particular methodology for achieving an optimal set up because legitimate data is seriously lacking. Boot fitters rarely validate their work with any sort of recorded ski performance observations on snow. So most of it just comes down to anecdotal feedback from their clients... and which theory makes the most sense to them.
What does all this mean? First of all it means I'm not going to tell you exactly how your knees or other body parts need to be lined up... I'm just going to relay some things I've felt and observed through experimentation on myself and some of my students. Secondly, I want to convey that a visit to an experienced boot fitter still has a tonne of value, especially if your feet are in pain! Actual 'alignment' may be more art than science, but performance enhancing results are frequent enough that it's quite possibly worth the gamble. Just be wary or wordy salesmen and proceed cautiously when making any permanent alterations to expensive boots. I tend stick with folks who are also high level instructors or coaches. At least this way you know they have a relatively good understanding of technique. Even if you hire a professional, you'll still need to do some on snow testing to verify whether or not a particular fix actually solves your symptoms.
What I Do Know...
I have a few hypotheses of my own but I dare not detail them here. With my limited understanding of lower leg anatomy and the fact that I still haven't found my own boot nirvana is probably an indication that my ideas are almost certainly based on figments of my imagination.
What I do know... Or at least what I think I know, is that small tweaks to your boot set up can dramatically affect how you and your skis interact with the snow.
Fit & Comfort
Rule #1... If your foot is in pain then it's not going to perform... or at the very least it's not going to be fun (which I'm pretty sure is the reason you do it). Make sure your boot is long enough and wide enough in all the right places for your foot to sit comfortably flat.
On the other hand if the fit is sloppy and your foot shifts around inside it's probably too big and your skis won't move when you do.
Getting the right fit is probably what a professional boot fitter is best at! They know which model has a last that will fit your specific foot shape the best. They will size you properly and if needed stretch the shell in all the right spots. If you require more fine tuning, there are a variety of custom liners on the market such as 'Intuition' or foam filled liners that can be custom molded to the shape of your foot and lower leg.
Forward Lean / Shaft Alignment
Forward lean (or the angle of the boot cuff in the fore/aft plane) has a huge affect on how the skier moves and balances on the skis. As a ski instructor, an inappropriate cuff angle is the single most common equipment related issue I come across. Or at least it's the easiest for me to detect. Fortunately it's also the easiest fix!
You see, the boot cuff limits the amount of flexion and extension available in your ankles. If the cuffs are either too straight or too flexed the skier will have to compensate by moving excessively in other joints (such as the knees and hips) and have a difficult time maintaining balance. Because some of us have big calves, skinny calves, long femurs, short tibias, big hips, boobs, biceps, heads or whatever other body part comes to mind... the optimal cuff angle will be different for each of us. Ideally we are looking for the biggest vertical range of motion we can have without losing balance. We also want to maintain strength and efficiency.
The litmus test for forward lean is to simply stand on a firm flat surface (no skis on) with your boots done up all the way. Now bend down and try to touch your butt to the ground. Hopefully you have a good range of flexion and extension before you fall over. If you have reasonable dexterity then you should be able to get your femurs parallel with the floor. If not, you may need more forward lean. In this case you can just stuff a spoiler, some stiff foam, or a couple trail maps in the back of your boots between the shell and the liner. This will add more forward lean effectively allowing for more flexion in your ankles.
Now try extending as much as you can. If you feel your calves pressing on the back of the boots but your legs still have a lot of bend, then you may want to get rid of any spoilers or padding in the back to straighten things up. If you feel like you're legs are always tired and you have to ski in a really crouched stance this could be something to look out for.
Other Fore/Aft Alignment Stuff
Enter a hardcore boot fitting establishment and you'll also hear terms like 'Ramp Angle' and 'Delta' thrown around. Ramp angle refers to the amount the heel is lifted in relation to the forefoot. It seems to have a small effect on fore/aft balance but I can't say any adjustments I've tried with ramp angle have had a major effect on my performance. For folks with limited range of motion in their ankle joints, increasing the ramp angle may (or may not) have a more positive effect.
Delta has to do with the binding height. Typically the rear binding platform is higher than the toe piece essentially tipping the entire boot forward. In essence this increases both ramp angle and the shaft angle in one fell swoop (out of laziness this is what we're doing forward lean in the simulations above). I can't say I've done much experimenting with Delta (at least not intentionally). I just take the heel height built into the binding and adjust the forward lean if needed. Of course that doesn't mean it doesn't matter so if your trusty boot fitter says it will save your skiing, it's probably at least worth a shot!
Boot flex is usually indicated by the arbitrary number on the side of the boot (higher number means stiffer but there is no standardization what so ever). Flex has a fairly significant effect on how the boot performs. By nature the cuff of the boot restricts ankle movement. If the boot is stiffer it restricts it that much more. Why would we want to do that? Well there are some advantages and disadvantages.
In a softer boot the increased range of motion in the ankle can make balance easier (at least when you're going slow)... and when balance is slightly off a considerable amount of the energy will be absorbed by flex in the boot before it is transferred to the ski. This essentially makes a softer flex more forgiving of your errors.
The disadvantage is that a considerable amount of energy will be absorbed by the flex of the boot before it is transferred to the ski... when you actually want that energy transferred to the ski. This of course makes a stiffer boot more responsive so the ski will react quickly to small shifts in balance. A stiff boot can actually help you recover when you're off balance as they can be used as a lever to prop yourself back into balance.
So should you go soft or hard?
Well that's up to you. In general if you feel like your boots are locking up your joints and you're constantly getting thrown off balance, a softer might be the way to go. If I was a novice or intermediate skier, I would want a more forgiving flex. If my preferred skiing discipline required more absorption and range of motion (like freestyle) I'd also probably go softer.
On the other hand, if I was an expert skier and wanted support, along with quick and precise reaction (say if I was racing slalom), then I'd go stiffer.
If you need to change the flex of your boot and don't want to splash out on a brand new pair, a good boot fitter will have a few tricks up their sleeve to address stiffness.
There is a fair bit of consensus around the idea that the bases of both skis should lie flat on the snow surface when you're simply gliding down a planar slope without making any attempt to tip the skis on edge. If you've ever tried to straight run and one or both skis starts wobbling like crazy then they're probably not sitting flat on the snow and you might want to address this issue. You may have also experienced symptoms such as, knees knocking together, chronic skidding or an inability to release your edges.
Where the controversy lies is HOW to go about getting your skis to sit flat on the snow!
Many higher end boots come with a lateral cuff adjustment (that thing on either side of your ankles that you can stick an Alan key into... but have no idea what it does).
The mechanism will allow the cuff to move a degree or so in either direction and is meant to allow the cuff to line up better with your lower leg.
Most boot fitters ask you to take the liners out and stand in the shells (foot beds included) then asses whether there is excessive space between your legs and the cuff on either the inside or the outside. Then they adjust accordingly.
I must admit, I totally ignore these guidelines because I find it impossible to grip with my boots set up in this manner. Clearly many other folks have success with this kind of set up though so instead of following my protocol I would do some testing of your own to find out what works for you.
A good rule of thumb... if you slip a lot, or your knees knock together, then move the cuffs out more. If you grip too much and have difficulty pivoting, or you experience other symptoms of being over edged then try moving the cuffs in.
If your boots don't have a cuff adjustment (or don't have enough, which is often the case) then you can easily improvise with some padding on either side between the cuff and the liner.
Keep in mind that more often than not you'll have symptoms on one side more than the other... so adjust each boot accordingly.
This is where much of the controversy lies. Some say 'post and support'.... others say 'don't post' for unrestricted foot function.... and then there are a million and one philosophies in between.
From my perspective, the main function of a custom foot bed is to add comfort and because it mimics the shape of the bottom of your foot, it prevents your foot from sliding around inside the boot. The added comfort helps with foot circulation and depending on the material it can also help insulate and keep your foot warm.
Many boot fitters will also use a custom foot bed to 'align' your foot... but this begins to enter the realm of podiatry and is way beyond my scope of expertise!
I have two quite different feet (when I stand naturally one pronates while the other supinates) so I experiment with this on myself relentlessly. I can tell you that small changes to a foot bed have a profound effect... but after many years of tinkering I can't definitively say I've found the perfect solution. But then, I haven't joined any cults yet either.
A few of my ignorant and very generalized observations about foot beds:
I've experimented a fair bit with shims that tilt the foot laterally.
Assuming the cuff angle remains the same, if the foot bed is tilted inwards so the foot is 'everted' slightly inside the boot, it makes it very easy to roll the outside ski onto edge and it seems to provide better gripping abilities. You are effectively tipping your ankle joint closer to the working edge. We all love grip... but keep in mind that too much grip makes it difficult to twist or pivot the ski.
If the footbed is supported on the arch side to the point where the foot sits slightly inverted, it allows me to move my inside leg out of the way easier but the outside leg becomes more difficult to tip over and adds a slightly difficult to resist torque on my outside foot.
Going to extremes in either direction usually just causes my knees to hurt after a run or two.
A lot of boot fitters talk about aligning the foot so the 'Subtalar Joint' is neutral. It makes sense to me that being neutral is a good place to start so you can move easily in either direction. The question remains however, whether it's a good idea to 'support' the foot in order to get there.
There may be some folks who need full support, I really don't know, so I'll leave it up to you and your podiatrist to figure that out. My very unscientific personal beliefs lie somewhere in the middle of the boot extremists. Some corrective support under the heel or other contact areas of the foot such as the first metatarsal head is probably okay if needed (and may even be ideal), but the foot should not be completely immobilized either. My instincts tell me that the foot bed needs to be at least supple enough under the arch to allow the foot to roll laterally inside the boot, otherwise I just feel locked up. For me, the ability to roll my foot is crucial to skiing well.
We could probably go on and on about rotational alignment, forefoot varus, valgus and add infintum, but if those words exist in your vocabulary then that's definitely a sign that a specialist needs to get involved. Maybe I'll get some foot/boot gurus to chime in here on future posts.
Canting and Sole Grinding
After foot beds and cuff alignment are dialed in, many boot fitters insist that true canting should be done by tilting the whole boot laterally. This is usually accomplished by grinding the bottom of the boot at the desired angle then bringing the boot back to DIN standards (to fit in your binding properly) by grinding the top of the rand with a router.
Many people swear by this method mainly because it doesn't affect how the boot fits. I've never actually had it done myself. I've tried every variation of test shims under the sun without achieving the perfect symmetry I've always longed for, so I haven't been willing to commit to the permanent planing of a rather expensive pair of ski boots (mind you I've destroyed plenty a pair of boots attempting ill equipped home remedies).
Seeing as this is pretty common practice among elite skiing athletes, it's probably a good way to go if your situation calls for it. The only thing I can really recommend here is to test the new angles on snow first to make sure they are right!