Ski boot stiffness, a few questions & observations & personal theories, right or wrong.

A snowHead

I've been skiing regularly twice, three times a year for 30 years, before full seasons the last 13 or so years, though there was a circa 12 year sabbatical in that time when I was snow-boarding.

Before I switched to snowboards I was doing advanced Ali Ross courses and was skiing Rossi 4S Equipped with the classic Salomon SX or whatever it was.

Fast forward to current and the past seven or so seasons knees have been getting progressively worse when skiing hard, that said right up to last year I'm running up and down mountains and 24min Park runs, but my knees when skiing!!!

When I asked my physio here in the mountains how I can run pain free up and down them and yet have knee issues when skiing she explained that in a ski boot my ankles are not absorbing the shock as much and it's your knees that get the full force of the impact/strain going through them.

I should maybe mention here that I've had one ACL reconstruction and in the other I don't have too much of one and over the years have had 3 or 4 lots of keyhole surgery, however as well as running I cycle a lot again up and down mountains so I do have strong legs, still.

Probably in the last ten or so years nearly all my skiing is on touring gear, and boots are deemed to be stiff at 120 with descent orientated pair which is what I use piste skiing.

I do know that if I ski in my old piste boots I can obviously drive a ski a little harder.

Three or so years ago, I met the Ski Mojo team at the SIGB ski test, and they talked me into trying them, and I was blown away by them, being able to ski hard and nonstop without any knee issues and not being out of breath at the bottom after nonstop big descents.

In advance of this season starting I had already decided to go the Ski Mojo route and much to a mates annoyance there I was at the beginning of the season hacking down the hill where his legs were still not ski fit.

I used the Mojo on my Atomic Hawk 120 boots a fair amount though when we had fresh snow, of which we had a good number of days this season I chose not to, and it was when we attended a big French ski test here that I opted to also test some new Salomon Alpine boots minus my Mojo and spent the day in them skiing hard and fast around 7 or so All Mountain Skis, and in those boots, minus the Mojo absolutely the same as if I was wearing the Mojo, no knee pain and fresh as a daisy after each run.

Now these new boots supposedly due to their design and construction claim via a whole load of marketing BS to be far more effective at energy transfer and a myriad of other statements along those lines.

So it had me thinking, my ski tour boots, even though they claim to be 120, obviously have a walk mechanism, and that must affect the flex of the boot.

So a softer flex boot must take more energy to drive the ski, and put more strain on your knees etc

So what's the logic of older people being advised to use softer flex boots then?

I've been Googling this conundrum and it gets very confusing.

This site comes up with a couple of examples of the differences between a couple of types of boots.

https://www.she-shredz.com/post/ski-boot-flex-what-s-a-flex-and-why-does-it-matter

And Sport Conrad almost seems to contradict themselves

https://www.sport-conrad.com/en/skiboot-flex-explanation/

If a beginner uses a really soft flexible boot because it's deemed comfortable and as many will know from skiing with their offspring they quite often have a fair gap between the shin and the boot, then when they are attempting to slow down via the classic snowplough are they not limited in their ability to do that with a sloppy boot, would not a stiffer boot make that power transfer more immediate?

Or is it the difference between a skier with strong legs able to handle stiffer boots vs one with weaker legs, though again to me it seems counter productive to stick/recommend a skier with less strong legs (females are recommended to have far softer boots 90-100 vs males 110+) into soft boots.

So going back to my new boots, I can pretty well categorically state now I have my own pair and have given them a thorough outing that skiing in those is the same as skiing in my softer touring boots with a Ski Mojo ?

So are we not better to be skiing in stiffer flex boots if we want to achieve that all-important edge control, and maybe when you see many a skier sliding and not edging, their probable soft boots might be an element as to why?

I'm now considering kicking my old touring boots into touch and going with the new Salomon Shift Boa at 130, paying for the extra weight on the up if it gives me as claimed the major advantages on the descent, with hopefully no knee issues Very Happy

A snowHead

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@Weathercam, The French Masters Championships were in Serre Chevalier ending yesterday, you could have watched lots of old people skiing in boots a fair bit stiffer than the ones you list.

I remember chatting to a Swiss guy on a lift a few years ago, he was planning to drop down from a 150 flex boot when he hit 75.

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After my 4 knee operations I consciously downgraded everything to a 100 flex boot (80+kgs) and intermediate skis for a couple of seasons in a deliberate attempt to force myself to ski more modestly. It did and didn't work. It worked in that I was more careful and definitely skied more conservatively. It didn't in that I couldn't feel the thrill of skiing and nailing turns.

At one point I even bought a pair of Bumblebee FT boots with the graduated flex to help protect my knees. Didn't really get on with them though.

After I tried Mojos and then Againers (settled on the latter) I'm back up to 120 flex and skiing every bit as hard as I used to. The most fun on piste this season was a pair of Kastle FIS slalom skis at the Val d'Isere ski tests in late November. The knowledge that I've got something to protect me (my knees) against a hard hit or drop gives me the confidence to ski 'properly' again.

IMO unless you're racing and need very specific kit, 90+% of skiing well is down to confidence in yourself and your kit. Even if it is patently the opposite of what the experts would recommend. I'd go for any combination of anything that makes you feel good and just run with it.

Best,
Rick

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@rjs, should have said for recreational skiers.

Those guys in the French Masters I presume, have been racing in 170 race boots for many a year, and I suspect their legs are still like tree-trunks.

Before posting this I had a conversation with a top skier and professional buyer/retailer, and basically he said ski with what you feel works, and he agreed that a large % of recreational skiers are probably skiing on too soft a boot.

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@Weathercam,

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@under a new name, The original Nordica Doberman was available in a 170 flex in 2000, Fischer have a 190 cuff in their current catalogue.

After all it is free

@under a new name, @rjs, I know nothing about race boot flex and the 170 number was what the guy said when I asked him.

For your average SH recreational skier maybe it is they that can benefit from a stiffer boot?

Aside from the difference across boot ranges and subjectivity of flex ratings I think that it’s quite personal - preference, weight, ski style.

A few years went from the Atomic Hawk 120 flex to the Scarpa Quattro XT which was a LOT stiffer than the Atomic (or previous boot , Dynafit Hoji also a 120) than a difference of 10 might suggest. I found the Scarpa too stiff, at least at first. It was tiring to ski as much harder to flex.

This year one of the buckles broke and Scarpa did a replacement, Iended up going down to a 120 flex Scarpa rather than this years version of the XT which is labelled as 130+

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@rjs, every day is a school day. Was the 170 Dobie available in club retail or only to high end teams?

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Got to say guys,..this is one of the most interesting threads for ages.

But didn;'t I read somehwere that boot flex isn't standard acrtoss manufacturers? So a Head 110 might be a Salomon 130 for example?

You know it makes sense.

But how boot flex relates to knee problems is very interesting. Surely there's a Uni thesis there for someone!

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A snowHead

Are you sure the difference your feeling isn't caused by the flex of the boot, but more the material the boots are made of? Certainly a pebax, grilamid, or even more so, a carbon touring boot will feel MUCH different than a PU alpine boot, even at the same flex rating. I can certainly see how those materials would transfer more feeling to your knees than the more absorbing PU would.

A snowHead

Very interesting topic

My 2 cents

Summary

Fit is more important than flex

My daily driver is a Dynafit TLT5 from the Dark Ages which are well worn

Soft fore-aft, stiff laterally with an equivalent rating of somewhere between 95-100 flex

The past two winters I have demoed and rented a number (10+) of modern alpine boots from different manufacturers with flex ratings between 110-130 for Press Trips and as a resort representative

Whilst being more modern and stiffer, none of these boots have given me the comfort, feel and precision of the boots which really fit me

To that end find a boot with a last which most closely matches your foot shape

Get a custom footbed

And get heat moulding or BOA system

That will ‘give’ you more and hurt less than a stiff boot IMHO

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I have a friend here, staying in the apartment above me, for the rest of the season, and prior to Covid he switched to touring gear, boots and Shift bindings, and being from North of Watford, let's just say he's careful with his money Smile

And he thinks it's ludicrous how much I've paid for boots, but he has seen some figures relating to me skiing in them, so he's mildly curious about their performance.

So, as we're the same foot size, he's keen to see if there is a difference, plus he also has knee issues, and wear's a Mojo when he can be bothered with it, favouring Donjoy's instead, and he's also extremley weak from the affects of battling Stage 4 lung cancer these past four years, so he shouldn't even be with us!

And a few people have mentioned shell material, etc., and it's very much a case of you get what you pay for, from what I've determined in my all-but-brief research on the subject.

And the shell composition material on a cheaper, lower flex rental boot will obviously not be the same as a top-range boot, again I've never skied race boots, or to that end I've never really concentrated on piste skiing.

My new Salomon shells were actually able to be put in the oven at the same time as the liners, and they were both moulded to my feet (I have massive protruding ankle bones) at the same time, and initially my friendly boot fitter joked that the flex was around 30 Laughing

It's in the world of ski touring where the stiffness/flex of a boot is all about compromise, and if you then look at Ski Mo race boots, the likes of La Sportiva Stratos V1 and the Gignoux Race Pro all coming in at circ 1000g and €1900 they are not rated at all for descent, or even given a flex rating, but all get 5 stars for ascending. And the inner liner is more akin to a wetsuit boot, as my mate was having a thrash in his friend's last week, knocking out 425m in 23 mins !

And then for more general touring, you either opt for a boot that's light, low flex, so good for climbing and not brilliant for descending, or try and search out the best of both worlds, which, according to most tests, is still the Tecnica Zero G Pro with a flex of still 130 but a very light 1,300g a boot. 4*uphill 4* downhill, whereas the even lighter carbon version, Peak, only has a flex of 100 and gets 5* uphill & 3* down.

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So you know when you've been Googling stuff and then a few hours later suggestions to similar sites and subjects come up.......

This from Powder Magazine.

4 Easy Ways To Make Your Ski Boots Stiffer

Want a little extra oomph out of your boots? Try these boot hacks to get more power out of your turn.

One of the biggest gripes I hear about people’s ski boots is that they wish they were stiffer. In fact, in our season-long boot preference poll, 18 percent of respondents said that’s the most important thing they would change about their ski footwear.

Boot stiffness is characterized by a “flex index,” which typically runs from about 65 to 130. The thing is, that flex index isn’t based on a standardized set of measurements. Even within a single brand’s boot portfolio, a 130 flex will feel different between models. If you’re looking for the absolute stiffest boot from a brand, you’re going to want to look at their fixed-cuff race or race-style boots made from heavy polyurethane plastic. Skip the walk mode, and skip anything billed as lightweight. When it comes to stiffness, more material is key.

However, what if you’re happy with the fit of your current boot, and want to add a little extra stiffness? The good news is that it’s definitely possible.......

https://www.powder.com/how-to/4-easy-ways-to-make-your-ski-boots-stiffer

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@Weathercam, not sure this means anything, but I have a pair of Head Raptor RS 140 boots, but they're set to 130. I also have a pair of Atomic Hawx Prime 130 XTD Boa.

The difference between the two is huge, in terms of the performance I feel like I can get out of them. Despite apparently both being a 130 flex. As i'm seldom on a touring binding, the Atomic's barely get used, but I did teach in them during Feb half term, and it felt horrible compared to the Heads whenever I had to do anything remotely close to full gas.

@Weathercam, and I think most serious skiers with the ZGTP get an aftermarket liner as the stock one is (or at least was) a flimsy thing that packs out fast. My 1st Gen ZGTP with Sidas liner, footbed, Sidas booster strap, heel shims and a bit of padding comes in at 1600g so not far of the Decoy Pro

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Interesting topic...
As ever "it depends"

- a stiff boot is good for carving on piste
- .... but for moguls, variables and powder you need some ankle flexion
- a stiffer boot (contrary to OP) is not necessarily easier on knees
- the flex index varies massively between brands. 120 atomic is not the same as 120 nordica etc
- a wider foot will fill the volume of a boot and make it feel stiffer than for person with skiing foot
- plus adding a spoiler or booster strap can make a boot flex very differently
- the boot you need for a light touring skiing is the not one you need for a metal GS race ski (match ski to boot)
- height of boot cuff can make a huge difference for smaller people

FWIW: I like a stiff boot (120 for touring / 130 for alpine).
But I do think a boot can be too stiff.

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An interesting, but hypothetical read for me, my big ankles prevent me from testing a boot unless it's been custom moulded first rolling eyes

Currently skiing on 10 yr old Salomon Xpro 100s, is this a stiff boot?
I'll typically come from skiing some offpiste moguls straight onto carving some corduroy.
Posters have mentioned intermediates not wanting every motion transmitting to the skis, but skiing chopped up crud at high speed, an expert wouldn't want every bump transmitting to the skier??
I'm a bit of a jack of all trades when it comes to Carv performance, would a different boot make any difference to the parameters?

You know it makes sense.

@tangowaggon, those are pretty good scores Very Happy

I would have thought 100 would be too soft for you, though maybe the likes of @swskier, will profer better advice based on those scores and his experience.

My 2¢ is best interim option is to get some power/booster straps and see what difference that makes, and like the Powder Mag article (link above) mentions add an additional screw for more rigidity etc

If that works then maybe time to invest in new boots.

My boot fitter was somewhat startled by my array of insoles I turned up with, as a result of trying to sort out other feet issues and in the end he used the ones he knew how to work with, though in the end he just glued the arch support to the sole and slipped them in the inners.

Should add here, like my running shoes the heel cup area of my touring liners is what deteriorates quite quickly and can pucker up causing friction, that said I probably do above average hours of touring, though like running shoes I'm sure they don't last anywhere near as long as they used to, or my sweat is more acidic as I get older Laughing

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A snowHead

A snowHead

Inspired by this thread I remembered I have my footbeds with me and wore them in my rental boots today

Game changer

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@BobinCH, Interesting, I hadn't really been paying attention to the Decoys (or indeed anything else). "no fall" = "no fear, these days"

@Haggis_Trap, hmmm, the guys in Concept toyed, a few years back, at only stocking LV versions as they could always be made big enough and it would simplify stock issues a bit...

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Can I add in something that doesn't seem to have been much mentioned. You cite that you're a regular runner and that doing so doesn't hurt your knees whereas you're getting knee pain in some ski situations.

For sure, there is an aspect of this that is boot related; speaking personally, when I was forced to rent boots due to a baggage delay I really struggled to adapt to the rental boots as the flex was way too soft for me and it made it feel as if the skis reacted much later to my inputs.

However, I would suggest that the fact that the Ski Mojo was helpful is perhaps because you have insufficient Type 2 muscle fibres and insufficient knee stabilisation muscle. Running (distances) develops mostly Type 1 muscle fibre which is high endurance but low power and does not do much for the 'small' muscles that stabilise the knee joint.

As such, you may find (and, please note, I'm no physiologist so please talk to someone who really understands this) that some specific gym work might fix your problem; in general, alpine skiing requires an 'endurance power' profile which is somewhere around 65% Type 1 and 35% Type 2a (not 2x ... that's body builder territory). Your mostly endurance sport training is likely to have given you something more like an 80%, or more, Type 1 muscle fibre profile.

Just a thought ... might be worth looking into ...

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Ski boot stiffness, a few questions & observations & personal theories, right or wrong.

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