Energy Cost per weight in skimo

Creator

Topic
January 15, 2021 at 11:38 am #49328

ghelfir
Participant

I’ll do my best to keep this brief. I am planning to do a long vertical gain test later this winter. 24 hours. My current lightest set up weighs approx. 4.5-5lbs per foot (dynafit superlite 2.0 binding, pdg boots, and voile WSP skis) This is about twice as heavy as the lightest set up on the market (dyanfit DNA boot, pin tech binding and dna ski).

My question is this: Has there been research, or even anecdotal evidence to suggest how much the cost is (on a per ounce or per gram, etc) when climbing at approx. 30% gradient? Basically, how much slower would the same person being climbing up XX feet in the heavier gear compared to the lighter gear. Essentially I am trying to decide how much energy to put into attempting to beg borrow or steal this super light stuff for this attempt I’ll be making.

To be clear, the downhill performance of the set up is not relevant. I’ll be on moderate grade groomed run for all the downs and am a good enough skier that even the worst downhill performance gear would not be an issue. it’s all about the ups.

Any insight is appreciated. I realize this is a very specific question to my circumstance, but I think the answer probably applies to the decision making for a lot of avid skimo people.

Thanks so much.
Ryan Ghelfi
Creator

Topic

Posted In: Skimo-racing

Participant

KBZ on January 19, 2021 at 2:27 am #49496

I haven’t heard of any research but IMO every gram counts. I may be wrong but from my experience the lower the weight is suspended – the greater the impact will be. My point is that 1kg in the backpack doesn’t make such difference as 1kg heavier skis.
I use training set which weighs 870g, when I stepped into my friend’s skis which weigh 750g it felt like previously I was dragging anchor. Difference was huge while my skis are only 120g heavier.

Participant

LindsayTroy on January 19, 2021 at 5:35 pm #49541

This is about a bicycle, but perhaps useful: https://www.wired.com/2016/06/cycling-physics-extra-mass-bike-wheels-enemy/

I know you aren’t a bicycle, but your feet are analogous to the wheels

Inactive

Anonymous on January 25, 2021 at 6:46 am #49703

Pounds make pain.

True, every gram counts, but you’d have to measure it as a percentage of bodyweight rather than in absolute terms. I’ve heard that “100g costs 1% of VO2max”, but for who? I don’t see how such a formula could apply unless it were “X% bodyweight costs X% VO2max.” 100g would be 0.14% for someone who’s 70kg and 0.2% for 50kg.

The big thing is to think in terms of percentages, not absolute measurements.

So:

* Any weight change will have a greater impact for a lighter person. If you’re 100kg, weight changes will have less of an impact than if you’re 50kg.

* Five pounds per foot is 180% heavier than the skimo race minimum of 2.75 pounds per foot. (In races, ski and binding must be >= 750g; boots, >= 500g: >= 1250g = 2.75#.)

Personally, for a 24h record, I wouldn’t even think about using anything heavier. (But bear in mind that I’m super biased. I only go above race weight—and never over 4.5 pounds—when ski touring in deep snow.)

Inactive

Anonymous on January 25, 2021 at 6:48 am #49704

Also, slope angles. Well-trained skiers usually have their highest climb rate between 20-25% (12-14 deg.); untrained, 15-20% (10-12 deg.). Angles both above and below will be slower.

More info: https://skimo.co/skinning-slope-angle

Inactive

Anonymous on January 25, 2021 at 6:51 am #49705

Also, skin friction. You’ll want to use race skins for this. The most popular grippy skins usually suck for gliding and are more work in general. A Pomoca race skin in 62mm wide would be a good choice.

Participant

ghelfir on January 25, 2021 at 7:05 am #49706

Thanks Scott for all your thoughts here. I ended up finding a used pair of Gignoux boots. The more time I put into training for this the more I realized I just needed to spend the money. The boot was no doubt the biggest weight savings I could make, dropping about 400 grams. That should help.

I know you are right about slope angle. Hard to get perfection on that front with no uphill turns, but the run I’ve got picked out comes pretty darn close.

Inactive

Anonymous on January 28, 2021 at 7:40 am #49949

Cool. Once you’re used to those boots, it’s going to be hard to use anything else…

The expense is a valid concern. Good job for starting with boots. “You date your skis, but you marry your boots.”

Participant

nalle4 on December 27, 2021 at 1:52 am #61163

Some time ago, I come across a formulae for calculating the approximately power output when ascending with skis:

Power(watt) = (6*feet weight+0.8*body weight+1*backpack weight)*9.81*climb rate/3600

Feet weight=total weight of both skis, bindings and boots in kg
Body weight=dressed, but without boots, in kg
Backpack weight=in kg
Climb rate= meter incline per hour (vertical)

The formulae is, of course, not valid for breaking trail or going up in (very) low angle slopes, boots with totally miserable ROMs etc.

I have tested it a little bit with heart rate monitoring, and since I am familiar with sub-maximal aerobic testing through my work, i.e knowing what power output I have at different heart rates – it seems to be a pretty fair approximation (+/- 5%) for light to moderately light equipment and boots with decent ROM and decent technique/skills by the skier.

Participant

nalle4 on December 27, 2021 at 1:53 am #61164

It can also be formulated as:

Climb rate = Power(watt)*3600 / ((6*feet weight+0.8*body weight+1*backpack weight)*9.81)

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Energy Cost per weight in skimo