Hi all, Paul Parker of Garmont here.
Thanks for your interest in Radiums here at WildSnow.com. Your feedback is important and we listen, so I’ve been tracking the discussion here about Radium shell sizing. To help, I’d like to clarify some of the questions that have been raised and explain a bit about how our ski boot development process works.
Sole length/size: Ski boots are developed from the inside out, rather than the outside in. We don’t develop a boot to a specific sole footprint or sole length, we develop it from the internal mold, which along with other elements that I’ll explain below, then determine the sole length.
It’s not uncommon for alpine skiers to refer to their sole length as the boot size, probably because it’s stamped on the side of the boot for easy binding adjustment. Certainly a bigger boot in the same model will have a longer sole length, but sole length does NOT indicate the size. It’s the inner mold, the “forma”, that determines the size. That is what some call the last, although it’s not truly a last since leather or fabric isn’t lasted around its form. It is as close to a last as an injected plastic shell gets, it’s the heart of the boot and determines overall fit and size according to the MPS (Mondo Point System). (For a comparative view of how all this interrelates, please see the Garmont boot size and sole length chart at the end of this post.)
Each new Garmont backcountry skiing boot model uses a new series of molds, including the forma. It’s in that boot’s development that we use market feedback on existing models, as well as the intended use for this new model, to determine how we should build the forma and resultant fit for the new boot.
It is normal to have a significant difference in sole length between two different models (same size) from the same manufacturer. Several critical elements result in this variance in length, one of which is the “forma.” Its length is determined by the Mondo Point measurement inside the liner. The forma may be a bit shorter and still produce the same size of boot if the liner is designed to be thinner, as in a race boot. This can result in a few millimeters of difference in sole length for the same size boot.
Two other significant elements that determine sole length are shell thickness and toe shape. Regarding shell thickness, it’s not uncommon for a beefy boot to be several millimeters thicker at the toe and heel than a lightweight AT boot. Since it’s the internal length that determines the size, and should be very similar between boots, then the thicker-walled boot shell is going to be a lot longer on the outside. We reinforce our performance boots like the Radium significantly in those regions that are subject to the torque of the binding, so that can also add some length.
Another important element that determines sole length is the fact that, whatever our boot design and shell thickness, we must respect the ISO norm for ski binding compatibility. There is a required amount of “free space” at the toe to accommodate the binding wings or binding toe, so whether or not the boot toe is shaped round or square or somewhere in-between can determine significant differences in the length we have to make the lip of the boot sole to provide free space for the binding.
Add up all of these elements and you get the sole length. It’s from the inside out, the result of the Mondo Point internal measurement including the liner, thick or thin, the boot toe shape and sole that respects the ISO norm, and the shell thickness. These are all elements that vary widely between different boot designs and models, and will result in varying sole lengths.
This is why good backcountry skiing bindings should be easily adjustable. I understand too well that it can be pain to adjust any binding when the snow is calling, as I’ve often had to test different boots on the same pair of skis on the same day and had to adjust then each time that I switch. Still, as Lou mentioned in the comments on the previous Radium review, adjusting your binding shouldn’t pose undue wear in its mechanism any more than stepping into a binding does. Of course a Dynafit®-type binding has less workable range than a step-in and must be adjusted more precisely, but it’s not going to hurt the binding.
Shell volume: A boot’s closure should be effective in adapting a boot’s volume to satisfy big differences in foot volume. Northern European feet tend to be wider and higher volume, Southern European feet narrower, narrower heel, and lower volume, American feet wider in the forefoot, medium to low volume, narrower heel. The adaptability of the design to different feet is one of the most important reasons why we developed the Radium’s overlap design. Its overlap wraps around the foot, rather than smashing down on it from the top, to reduce the volume. This is an important reason why most of the best alpine boots are overlap. We have found in practice that the Radium does successfully fit a wide variety of feet. There are other things besides the shell design that will help you satisfy the extremes in foot volume, and how you choose your fit, i.e. sizing up or down. Footbeds, in particular, and their thickness, can make a huge difference in matching the foot’s volume to the shell. If you have low-volume feet, you probably know how well a custom footbed of the proper thickness can improve any boot’s fit for backcountry skiing or otherwise.
Narrow toe: Toe caps should always be used when thermoforming Radiums, or any thermoformable boot’s liner. If you are on the fence between two shell sizes, and should you pick the smaller one, you need to really pad your toes when thermoforming the liners. It’s uncomfortable during the thermoforming process but results in a better fit for backcountry skiing because the padding and your toes push out more space for your digits. Custom boot fitters are especially adept at this process and tend to size shells down quite a lot. Non-thermoformed liners/boots should feel tight all over, and will feel particularly tight at the toes. If your boots are comfortable enough to ski in without thermoforming, chances are they are too big. This is an important thing to keep in mind while shopping, as it’s tempting to choose boots by how comfortable they are when you try them off-the-shelf, rather than how they feel after liner molding and such.
How the manufacturer manages shell sizes: This is something very important to know when fitting a pair of boots for backcountry skiing as covered here on WildSnow.com, and especially important when switching between brands. Different manufacturers choose different shell “breaks”, i.e. whether they bump up the shell size on the half or whole size. In other words, some manufacturers 27.5 comes out of a 27.5 shell (Garmont’s boots are designed this way), while others’ come out of a 28.0 shell with a thicker liner. The 27.5 that comes out of a 27.5 shell will always produce a closer fit for the same foot than a 27.5 that comes out of a 28.0 shell.
Since Garmont shells break on the full size, a 27.0 and 27.5 come out of the same 27.5 shell. Many of our competitors have chosen to build the 27.5 and 28.0 out of a larger 28.0 shell. Not only will those two 27.5s from different manufacturers fit much differently, but they will have different sole lengths.
These different elements in boot design result in different fit and the sole lengths discussed. I hope this information has been of some help to the WildSnow.com readership. Thanks again to all of you for your interest in Radiums. Personally, the Radium is my all-time favorite boot.
(WildSnow.com guest blogger Paul Parker has been involved in the backcountry skiing equipment industry since the dawn of creation. On about the second day, he was instrumental in Chouinard Equipment’s entry into the arena, and has also worked with Tua, Scarpa, G3 and numerous other companies. He’s presently with Garmont and works hard making sure their boots are state-of-art. Parker is also an author, his most well known work being the well regarded how-to book Free Heel Skiing.)