Measured vs claimed sidecut radius

[BGreen]

Has anyone here measured the radius of your skis? Using the FIS app, I measured three pair of 190 27m GS skis at about 23m. I don't think there was a problem with my measuring, so either the calculation in the app is wrong (possible) or the ski is not as claimed (possible, but less likely). When I have some time, I plan to calculate it by hand. I don't have a proper measuring spider, but a caliper and tape measure ought to be close enough.

 

[hbear]

Not normally, most of my FIS skis are slightly above what is stated (e.g. >23M is slightly above that) I see the same for my daughter's jr race skis. Her GS skis are >14m and end up at 14.3 or something like that.

For normal free skis yes my skis end up being different than stated. But I'd assume that's because I ski a ski shorter than the "standard" ski they base their radius calcs off of so don't put much thought into it. Some OEMs do list different radius based on different length, but some don't.

Interesting to hear your findings. I can say at the higher and highest levels when they measure they don't care what your topsheet says, the calc based on what they measure. Lots of interesting stories from those officiating the WC as to how certain athletes have tried to gain advantages. (e.g. heard of an athlete that got caught with illegal lifter/stack heights in her equipment....equipment actually tested fine when they tested her skis and boots...the additional lifter was in her sock! Apparently her jaw dropped and she knew the gig was up when they asked her to remove her sock....)

 

[crgildart]

I think it is tricky to find the correct spot on the shovel and tail to actually measure. A little extra rocker and weight on the ski might put the front and rear contact points closer to the waist and thinner part of the ski. If you measure farther from the waist than that you will end up with fatter tip and tail measurements lowering the radius arcs. I'm not sure how they decide where to actually measure tip and tail widths, but a little up or back would certainly make a noticeable difference in the resulting radius.

 

[BGreen]

I think it is tricky to find the correct spot on the shovel and tail to actually measure. A little extra rocker and weight on the ski might put the front and rear contact points closer to the waist and thinner part of the ski. If you measure farther from the waist than that you will end up with fatter tip and tail measurements lowering the radius arcs. I'm not sure how they decide where to actually measure tip and tail widths, but a little up or back would certainly make a noticeable difference in the resulting radius.

Good questions. Where to measure is pretty clearly defined by the rules. Length is the flat sheet length of the base, tip and tail are the widest parts of each. Waist measurement is the narrowest part of the ski, but we are talking fractions of a millimeter and I think determining the exact waist is critical. The formula discounts the first 20% and last 10% of the flat sheet length.

 

[BS Slarver]

@hbear - wow, any docs to prove that ?

Like the Tour de France trying to find the electric motors in the bikes
and hey, it's Friday night !

 

[François Pugh]

The FIS formula defines certain points for measurement to determine the FIS -compliant radius, and I'm sure most FIS racing skis comply with the radius determined by that method. However, there is nothing to stop someone from determining a best fit radius using as many points along the ski as they wish, which could well differ from the radius determined using only the FIS method points.

 

[Erik Timmerman]

I talked to a product manager once who said that often times these numbers are made up and just represent what the ski's TR "feels like".

 

[ScotsSkier]

Hmm, i have owned :

183 Womens FIS blizzard GS marked > 35

182 (previous generation ) Blizzard W FIS GS marked >23, >25 and >27....and they were all exactly the same dimensions!!
183 (previous generation ) Fischer W FIS GS marked >23 and > 27...and they were both exactly the same dimensions...

My 188 Blossom WC GS is marked >27....but it was actually the prototype for the womens 188/30...

So, in my experience, I suspect the radius is actually greater than marked.....and I am pretty sure most manufacturers err on the side of greater.... wouldn't make sense to tool up and then be found illegal!

Remember also that when the mens WC GS was >27, most of the WC skis were about 31, 32 r.

Probably the point of measurement is off slightly

 

[BGreen]

I dug into this issue a bit more today. The problem was not the app per se, but the way FIS calculates sidecut radius by taking the widest measurement of the tip and tail, but only about 70% of the ski length. My guess is current skis are built to fit FIS's measurement schema, but that seems a little strange. When I redid the measurements using length as it is shown (from shovel measurement position to tail measurement position), the numbers matched what is marked on the ski. This is different from how FIS calculates ski length (midpoint to tip minus 20% plus midpoint to tail minus %10).

However, the actual radius of your ski is irrelevant. All that is important is what FIS says is the radius of your ski. For anyone who wants to play with the calculator, it is here:
http://member.fis-ski.com/skicalc.htm

 

[Tom K.]

I talked to a product manager once who said that often times these numbers are made up and just represent what the ski's TR "feels like".

I have been told the same thing when it comes to non-race skis.

Personally, I go by shovel/waist/tail "delta" to get a general idea of what I hope to feel on the slopes.

Of course, flex also has a big impact in perceived radius.

 

[mishka]

some times ago I tried run some skis dimensions through my ski designing software and more often than not numbers and turning radius… Don't adds up... Skis with rocker even worse when sidecut radius taking not from contact points.

@Tom K. where you get Delta for skis. I never saw any information like that available

 

[graham418]

I used the FIS formula to try to calc the radius of a pair of skis , as they had no radius written anywhere. If I remember the numbers were ridiculously small. I think the calculator is only for FIS skis

 

[Tom K.]

@Tom K. where you get Delta for skis. I never saw any information like that available

I should have been more clear:

What I call tip delta is just tip width minus waist width.

Similar for tail delta.

 

[cantunamunch]

I should have been more clear:

What I call tip delta is just tip width minus waist width.

Similar for tail delta.

I expect @mishka knows these quantities in a different combination ( sidecut depth and taper)

 

[mishka]

when I asked about Delta I thought something different

Anyhow… if anybody want to check/test sidecut radius of there skis welcome to post dimensions and I run it through my software. all information I need is: wight T-W-Ta and running length

 

[Swede]

Haven't tried the app. Could it be user error? Sounds incredible if the ski should have 4 meters less than advertised. Especially on a race ski.

 

[Wilhelmson]

Any old school surveyor would lay the ski out on a basketball court and grab the 100 foot tape. The contact points (effective edge) would be obvious because the beginning and end points of the radius would touch the end of the tape regardless of additional ski behind or in front of the radius.

 

[BGreen]

Haven't tried the app. Could it be user error? Sounds incredible if the ski should have 4 meters less than advertised. Especially on a race ski.

Measuring, doing the math by hand and using a slightly dumbed down version of the FIS formulas gets the correct radius. The official way to measure a ski is to determine length by measuring total flat sheet length, locate the precise waist of the ski, and take 80% of the front length and 90% of the rear. It's possible that it works on everyone's skis but mine. I find it interesting that FIS unintentionally defines tip and tail shapes because of the measurement criteria.

LH = LW * 0.1
L1 = (LTOT - LW) * 0.8
L2 = LW * 0.9
LS = L1 + LW
L = L1 + L2
R = L2/(2000 * (S + H - 2 * W))