2013 addendum: a new feeler gauge is being sold with Dynafit bindings. See photo below.
2011 clarification: All Radical series and Vertical series Dynafit bindings use a 5.5 mm gap at heel, per discussion below.
You’ve heard of the generation gap, and you might know about your spark plug gap, but what about the Dynafit gap? To work their best, most “tech” type backcountry skiing bindings require specific spacing between the boot heel and the rear unit of the binding. The “tech gap,” if you will. In this WildSnow.com tech blog, we’ll look at the Dynafit binding “tech gap.”
Photo above shows the correct way of setting your tech gap specific to Dynafit bindings, using the feeler gauge that’s shipped in the box with all Dynafit bindings. Boot should be snapped into the binding heel (downhill mode). Gauge should be inserted snug, but not forced. Adjust gap via the rear adjustment screw on the rear of the binding baseplate. No need to get your panties in a bunch over how this is done. So long as the gauge fits in there snug, the binding gap is set. A tiny bit of variation, say 1/2 mm, is fine. How do I know that? Because as you ski and your ski flexes, the gap varies immensely! Thus, a tiny bit of variation when you set it is obviously within tolerances. That said, I’m talking a tiny variation — not just eyeballing and calling it good.
Simple, eh? But just as the generation gap caused confusion, so does Dynafit’s gap result in cognitive dissonance. Prior to around 2010 Dynafit’s literature states the gap should be 6 mm for the Comfort/ST/FT models, and 4 mm for the TLT/Speed/Race. Only when measured with calipers, the newer white plastic ST/FT gauge measures 5.43 mm, and the older one measures 5.9 mm. Latter is close enough to 6 mm as to make sense, but regarding 5.43 mm, do we suddenly have a new specification they snuck in on us? The answer is yes. (Note, pins in TLT/Speed/Race will remain the same length, and require a 4 mm tech gap.)
I’m actually not surprised about the the 5.5 mm spec, as I’ve been using approximately that spec for years on flexible skis which when decambered radically end up popping the heel pins out of the boot heel.
But nothing is perfect. By the same token, with flexy skis you may find that when set at 5.5 mm and using heel-flat-on-ski mode , the smaller heel gap results in your boot heel catching on the binding when your ski bridges a gap such as a creek crossing, or while you’re breaking trail in deep low-density powder. This problem is actually quite common for larger skiers with heavy packs.
So besides touring clearance, what exactly does changing the boot gap do to Dynafit binding performance?
1. The gap between boot heel and binding is there so the ski can flex without jamming your boot heel against the binding heel unit. BUT, it’s also there so the boot can rotate out of the binding without catching during a safety release. Even so, it is my opinion that if you require lateral release when the ski is flexed and the gap is closed up due to ski flex, the heel of the boot can still catch on the binding and cause a spike in side release value.
Above can be easily simulated on the bench by adjusting the tech binding heel gap to nearly nothing, then hand checking the side release by rotating the heel unit. If you’re not convinced after that, take a fairly flexible ski with correctly set gap, stick a boot in the binding, suspend between two chairs and press down on the boot to flex the ski. You’ll notice it’s fairly easy to close up the tech gap. With the gap closed and ski loaded, try rotating the heel unit to simulate a lateral release. Observe that the heel unit may bind while rotating. To mitigate this effect, correctly milled boot heel fittings in tech compatible boots have an elongated horizontal slot that adds clearance (and also aids in ice ejection). Even so, in a worst case scenario (supple ski flexed to the max), you may still get this effect as demonstrated in the “two chair suspension test.”
(Boot buyer caveat: As I covered in a previous post, there is no standardized norm for tech boot fittings and milling, so some boots are still being made without this elongated slot. Buyer beware. Latest news is that an inter-industry boot configuration standard is in process for tech fittings, but such could take years if it ever happens, so don’t hold your breath. Instead, read WildSnow.com.)
2. As the heel tech gap varies, release values vary because the boot is exerting differing amounts of leverage on the pins. When the gap is smaller, the release values are higher (at least that’s what logic dictates, I did not test this). Thus, in my view, it’s possible you could get a spike in lateral release value if you happen to need a release when your ski is radically flexed. To mitigate, as always I advise setting your release values at the low end of what’s recommended in the DIN/ISO 11088 chart, and only increase if you have problems with pre-release. Also, I recommend setting vertical and lateral release independently. In other words, they don’t have to be the same number. This being said, it’s also true the if you de-camber (reverse flex) your ski and widen the tech gap, you’ll end up with lower release values while the ski is flexed. Such a situation might arise, for example, when doing something like making a hop turn with heavy snow piled on the tip and tail of your ski.
In my understanding, variation of the heel gap while in real world use is the main reason why Dynafit and other tech type bindings are not TUV certified to the DIN/ISO 13992 standard for tour binding release. In other words, while the Dynafit has a proven safety release, and I know for a fact the company does work hard to keep the release value numbers matching those of the DIN/ISO standard, as the ski flexes those values vary.
Conclusion one: In my view, while most (if not all) frame touring bindings such as Fritschi are TUV tested/certified to meet DIN/ISO standard 13992, boot wear and dirt (as well as user adjustment error), result in wide variations of release values during real-world use. The beauty of the tech (Dynafit) binding system in terms of safety is it eliminates the variable of boot friction by suspending the boot between toe and heel fittings. Conversely, the tech system introduces the problem of ski flex and heel/binding clearance and they are thus not TUV certified to DIN/ISO 13992. Even so, real life use validates my opinion that both tech and frame binding systems are equally as safe — when correctly maintained and set with proper clearances. Main caveat being that any binding system should be carefully adjusted and tested for safety release.
Conclusion two: The 5.5 millimeter Dynafit tech gap will probably work fine for the vast majority and is recommended. But if you have problems, don’t hesitate to experiment with small changes in the gap. Only if you do so, be aware that by changing the gap you’ll change your release values or possibly introduce annoyances such as the pins actually pulling out of your boot heel fitting when the ski is de-cambered (in this case, exacerbated by gap set wider than spec).
Conjecture: It seems to me that actually making the tech binding pins longer and specifying a wider gap would be the way to go for all tech binding makers. But everything is interrelated in this type of machinery, so who knows what problems that would introduce. Even so, a man is allowed to dream. It also occurs to me that perhaps ultimately we need a generation II tech binding interface. One with stronger and wider boot heel fittings, variable spring tension in the toe unit, longer heel pins, and so on. Is someone working on that as I dream? I wouldn’t be surprised.
Tip: If you can’t find a Dynafit tech gap gauge, 3 lightly used nickles measures about 5.6 mm, which in my opinion is within tolerance for setting your Dynafit tech gap.