13 October, 2009

Rando Race Boots & Stride Dynamics

Recently there has been a lot of heated discussion on the dynamics of boots and their relationship between sole flex and better stride.  So let’s get down into the two separate theories behind both ideas behind a bellowed boot, the Scarpa F1, and the Pierre Gignoux XP444, a solid non-flexible sole. 

Bellowed Boots

A boot that has bellows on it, like the Scarpa F1, is designed to flex at the metatarsals of the foot giving the Rando Racer the most natural stride as possible.  When you are skinning, after the foot lands and is drawn behind the body (this motion is known as “Dorsiflexion,” the toes are brought closer to the shin, and the foot is angled with the shin approximately 20º-30º) and then goes into it’s “Plantarflexion,” stage.  During the last portion of Dorsiflexion, the toes bend at the Metatarsals and the foot Plantar Flexes, which is where the foot gets its maximal stride power. 

So how is this techno jargon related to Rando Stride?  Well, allowing the foot to flex as naturally as possible, its thought that the boot will not restrict the natural movement of the foot.  This way the tendons and muscles of the foot can perform unheeded.  With this idea, while the foot pushes off the ground, it allows for an added “kick” to the stride. 

The downside to this boot design is that it is intended for a rolling low angle course design.  As long as the boot is on this style of terrain it can be an excellent choice.  On a course that is steeper, the flex of the bellows actually is an disadvantage, as it does create some energy loss in the boot which causes more muscular strain on the foot.  This muscular strain may tip the lactic acid scales over into the red zone if the racer does not pay attention to what they are doing.

Fitting this boot, should you choose, the foot and boot must allow at least 0.5º or greater, of pronation to get the most natural effect of the boot. 

Stiff Soled Boots 

A stiff soled boots, such as the Pierre Gignoux XP444, Spanish Ara Components boot, or La Sportiva, is its designed to support the foot in a more neutral position.  Much like the description of foot in the past section, it follows the same combinations of movement, but without the toes flexing at the Metatarsals.  It is thought that there is no energy loss, due to the stiff sole, and lack of Metatarsals flexing. 

This boot takes advantage of this of the lack of energy loss, and is why it caters to steeper courses, rather than low angle and rolling courses.  The disadvantage with the boot is that it does not allow for that extra “kick,” on the low angle rolling courses. 

Fitting this boot, the foot and boot are should allow the foot to be at approximately 0.5º of pronation without going over, to take advantage of the foot’s power during the Plantarflexion phase of the Rando Stride. 

Two Schools Of Thought… Or Three?

We can never know for sure which boot is truly the fastest, with the most amount of energy transfer or loss, but certain ideas are close.  The Dynafit Dy.N.A boot allows for 5mm of flex, where the bellows would be on an F1, without the bellows.  The boot is cut away so that the boot can flex, but a carbon limiter is installed to keep that within the 5mm limit, combining the large flex of the F1 and the zero flex of the Pierre Gignoux.

So a real conclusion, other than inconclusive?  The largest asset that a boot can have is a non-limiting lower shell.  Meaning that when the foot is striding forward (Plantarflexion), elongating, and gaining as much forward distance as possible, it must not be limited by the lower shell.  The higher the internal cuff, the more chance that calf will "bottom out," and limit the stride length.  Boots with stiff backed liners may also have the same problems as boots with high internal lower shells.  By getting the boot with the least limitation to the foot, the racer will see the largest gains, the slightest energy transfer gains or losses are barely an issue.  Find the boot that works best with your foot, and have it fit correctly, to get the best results.


  1. nice article!!! So there I was in Europe last year and not wanting to be at any disadvantage I purchased some F1 race boots (no way could I afford the Gignoux's....which break and are only warrantied for a year). When my wife got the credit card bill, we both hit the roof...that Euro sure is strong! I was (& am) really pleased w/ the bellowed flex, though I concur on the energy loss issue. My comments here have more to do w/ that last statement about fit. My F1 racers really hurt my feet. So.... his fall I took out the heat gun, widened the plastic in tight areas around the heel and ankle and made a carbon tongue to replace the fabric one (the buckle really hurt my foot so I did this to disperse the pressure).

  2. I raced in the F1's last year, and found them to comfortable, and wide enough. I found that they did require a really good heat mold on the liners, and that a large portion of touring boots rarely need punching, as they can be molded with extra padding on problem areas to expand the liner more in choice spots while the liner is still hot. Also a fat toe cap, which comes down to just above the metatarsals works great to let your toes spread out, stopping any chance of a hallux abduction (big toe pointed in causing widening of the foot or pressure spots). Or you can always try molding with a fat sock, and ski with a thin sock.

  3. Good polemic on the issue of bellow vs no-bellow race boots. The only way to find out which one is better/faster is to try for awhile all of them. But even then I think it would be individual preference as some will like bellows more than without them. So far I like bellows but will see.

  4. Ah hah, so the DyNA is now in North America -- I thought I felt its presence. (Must have somehow brought on that first good snowstorm of the season we had last week in New England.)
    How does its skiability compare to . . . standard unmodified F1? F3? Dynafit TLT Lite/Evo?
    And how does fit/sizing/length compare to Dynafit Zzero4?

  5. Better than an F1, the carbon is awesome! It's ability to drive a pair of skis is pretty cool. Many of my friends will be ski mountaineering and concentrating on steep skiing with these boots rather than racing. It replaces all the TLT race line for Dynafit.

    Fit is similar to the Zzero4, but not exact. The best way to order these without trying them on, is to find your mondo sizing in the Zzero4, and go with that. The Length inside is the same, but the outside sole length is much different.

  6. Hi,

    I'm British,living in the French Alpes and just about to begin my 2nd season of rando racing. I have the F1 and am interested in any feedback from anyone who has updated their F1's by retro fitting the after market carbon cuff. It is available here for €480 form crazy in Italy. Question is does it improve the boot enough to make it worth the cash or is it better to save the money and invest in a carbon boot? My first reason would be to imrove the downhill skiability and secondly to save weight.

    Some information that may appeal to you guys in North America and may have gone un-seen, crazy now produce a full race binding and it appears from their site that it is a full €100 less than its rivals, don't know how prices compare to US/Canada. No feedback on its performance as yet, details at: http://www.crazyidea.it/contents.php?cmd=catalogo&pid=165

    Thanks in advance for any help, and before anyone asks, no I don't work for Crazy.

  7. Thanks for the post Simon. I haven't heard of anyone retrofitting the F1 Carbon Cuff in our area. It may not be allowed in this years World Cup gear rulings, although perhaps Stano can comment on this. The Crazy Idea, looks like an ATK with a Schia Meccanica heel, or maybe just the SM toe and heel.

    That being said, Carbon makes any boot way stiffer, and adds massive downhill performance. Plus they are way stiffer than any Pebax cuff. If you can make it work with ISMF gear rules, go for it, stiff and light you can't go wrong!

  8. Hi Alex, many thanks for the reply. To update on the subject, I posed the same question on the Wildsnow site and there is a lot of feedback in the comments for this post.


    Thanks for the great site, their is so much information here in France and Italy but it is very tiring trying to translate it all even with Google etc. Uk, no sites at all, you guys in the US/Canada are providing a great service and with some really technical info too.

    Thanks again, Simon.

  9. The Stratos is apparently so advanced that a comprehensive video is necessary just to be able to put it on your feet:

  10. Never the less, that boot is crazy nice! Weight weight weight!!!