Update 12-26-2013
Ok, we’ve put the new Dynafit “heel spring” feature to the test. One of our WildSnower aggressive skiers did about 13,000 vertical up/down over holiday on the new system. Once broken in, the mechanism moves quite easily. We still think it probably functions when needed — if needed. We noticed that while uphill skiing it also moves slightly fore/aft with each step, especially with higher heel-lifter deployed (perhaps depending on shape of boot sole lugs as well as accumulated ice and snow). This causes us to wonder about excessive wear due to the plastic/steel/aluminum interfaces of the device rubbing during thousands of cycles. What is more, while this might be splitting hairs it’s still a fact that if the system is moving during each step, it is absorbing energy you’d otherwise use for moving uphill. More consumer miles will answer the wear question fairly soon I’m sure, as some of you are really piling on the vertical these days. Also, to answer one commenter’s question about play developing in the system: I compared the new/used Radical to a well used Radical that doesn’t have the “heel spring.” The binding with the heel spring has ever so slightly more play when evaluated by wriggling with my hand, but the difference is negligible.My opinion about this “inline” change to the Radical is the same as before: If you’ve been successful with previous tech bindings, it’s not a concern. If you’ve had trouble staying in Dynafit Radical bindings during aggressive downhill skiing, the mechanism (as detailed below) might help make the binding more elastic and thus more retentive.
More, see bottom of this post for heel gap adjustment info.
Original blog post
Talk about inline iterations of a backcountry skiing product. It’s still called “Dynafit Radical.” Yet with anti-rotation issues and more being dealt with over the past few years, the “inline” manufacturing versions keep marching on. Latest offspring of family Radical, they’ve added a nifty little feature that gives the heel unit about six millimeters of fore-aft elasticity. This on top of the normal tech binding movement allowed by the heel pins sliding in and out of your boot heel fitting.
We’re not really sure if this mod is wunderbar or a solution without a problem (perhaps pandering to TUV certification?). Whatever the case, it’s impressive what those European technicians stuck in such a small package. On my digital scale, older version 372 grams, latest 374. We don’t like weight creep. Nonetheless, check out what you get for those two grams:
Latest of the Radicals. Changes are totally hidden. Two more grams. Click all images to enlarge.
Guts exposed. A thin stainless steel plate (not shown) sits under the spindle base (shown) on top of the ski allowing the spindle base to slide forward and back about 6 millimeters. Look closely and you can see the spring that enables this function.
Looking from the top of the backcountry skiing Dynafit Radical. New elasticity feature is somewhat hidden but evidenced by the tiny aluminum lug the fore-aft adjustment screw threads into.
I felt like a Swiss watch repairman while taking this apart. Once I found the parts that took flight to the workshop floor, I made this mock-up of how things fit together. The spring fits in a socket where the arrow points, and presses against the small aluminum lug the screw is threaded into.
Somewhat expanded view. How I'm going to get this all together again is a mystery. Perhaps I should send it back on warranty? (Just kidding.)
In all, impressive. One has to wonder how the parts will hold up if they’re really worked hard. What saves the situation is that most (if not all) of the fore/aft movement of tech binding heels (while ski flexes) is absorbed by the heel pins moving in and out of the boot heel fitting. So perhaps this is sort of a last resort feature to help when you flex a ski like you’re Hercules bending a longbow. In that case your boot heel can bottom out against the heel unit and do who-knows-what to you or the machinery. A bit of built in elasticity at a price of two grams seems reasonable.
My final take? Perhaps this is mostly an attempt to receive TUV certification to existing DIN/ISO standards for ski touring bindings. But the change appears to have some benefit in the real world. For those of you who ask “do I need to upgrade?” Answer: if you’ve been happy with tech bindings over past seasons, no worry. But if you’re an aggressive, larger skier I’d consider this type of elasticity to be a beneficial feature you might want to seek out as more and more tech binding models offer it. Also, durability of this change is an unknown.
Oh, and the most asked question: “How do I tell if this ski touring binding is the latest?” Answer: Radical heel with elasticity mechanism will have a thin stainless steel plate installed underneath, and a small hint of the parts will be visible from the top. Also, the new version has a small nib of plastic protruding below the boot-length adjustment screw as illustrated in the following photos.
New version Radical to left; you can see a small hint of the additional machinery from the top.
New Radical version to right has a small plastic bit protruding under the boot-length adjustment screw. Previous version at left doesn't have this. It's probably a reinforcement. (Note this little bit of plastic may have been a mold change before the spring addition. I'm checking on that, so be careful with your ID. Best is to just look for the parts as shown in photo above.
One other thing. Apparently the Radical models with this change require a slightly different process for adjusting to boot length. Use the little white gauge as pictured below to set the 5.30 mm heel gap. Only difference is you need to double-check your heel gap by taking boot out of binding heel, snapping back down again, then pushing heel unit firmly towards boot heel before checking the gap again. Idea is to take up any lingering slack in the elasticity system so you don’t end up with too wide a heel gap. We’re not sure why the gauge was changed from a solid plastic “shim” to the compressible device, but it works, so whatever. (Two nickles and an American quarter coin measure about 5.30 mm.)
The gauge for heel gap is a compressible little device as pictured. It's a bit confusing to use. Don't over-think it, just line up the parts as indicated in photo and you've set your heel gap to plus-minus 5.3 mm.
Shop for Dynafit Radical ski touring binding.
WildSnow.com publisher emeritus and founder Lou (Louis Dawson) has a 50+ years career in climbing, backcountry skiing and ski mountaineering. He was the first person in history to ski down all 54 Colorado 14,000-foot peaks, has authored numerous books about about backcountry skiing, and has skied from the summit of Denali in Alaska, North America’s highest mountain.
