multi-radius sidecut

[mattman]

So I know there have been some long threads about the pros and cons of multi-radius sidecuts...but I am curious about the order of the radii. If you look at the new Nordica Doberman Pro SL (a ski that you would expect to have a well tested sidecut) the sidecut is 11.5-13-14. I would expect the smallest radius at the tip, the largest radius underfoot, and an in-between radius at the tail. What is the reasoning to having it get continually larger down the length?

[mattman]

wait, I think they may have been saying three radii for three different lengths and just didnt separate with commas. My bad (havent heard that phrase in a while).

[SHIF]

Dual radius sidecuts are rather common, Google it; "dual radius ski"

Kastle seem to place the long vs. short radii differently depending on the intended ski usage:
http://www.kaestle-ski.com/en/techcente ... ometry/#/1

I've been intrigued by the 4FRNT MSP for a while, having 22.5 and 26 meter radii, fore and aft:
http://www.4frnt.com/skis/msp

But I can't pull the trigger on making a dual radius ski template and ski. My latest design emulates the effect by simply shifting the turning center aft a bit on the ski, resulting in 12mm overall taper.

-S

[Cadman]

There are a couple of reasons for dual radii.(in my opinion) The first is having a ski that initiates quickly into the turn and finishes more like a GS. The second reason is sometimes you can't get the tip and tail width to work out in relation to where you put the waist or sidecut center. If you want a certain width at the tip, a certain width at the tail, a certain sidecut radius and the center of the sidecut at a certain point, you don't have any choice but to use a dual side radius. Alot of people will design to a certain tip,waist and tail width specification and forget that those three items will determine where your waist ends up. Same thing goes when you vary one of the 5 variables, tip/tail/waist width, sidecut radius and sidecut waist position. Letting the sidecut center point float around can make or break the performance of your ski.

[SHIF]

... Same thing goes when you vary one of the 5 variables, tip/tail/waist width, sidecut radius and sidecut waist position. Letting the sidecut center point float around can make or break the performance of your ski.

You are correct, and you can add a couple more dimensions to the equation; location of the max tip and tail widths. This is also constrained by the tip and tail shapes. I can't imagine trying to design a ski without SolidWorks.

On my latest design I moved the waist aft only 12mm from my usual location so it should not mess up the performance.

-S

[mattman]

If you are choosing tip and tail widths and then using a dual radius sidecut to place the sidecut apex, how did you determine tip and tail widths? Is there a rule of thumb for the amount of difference there should be between the tip width and tail width for certain conditions? icy hardpack?

I was thinking that the dual radius might help make otherwise slalomy skis less hooky in bumps and other non-hardpack terrain.

[Cadman]

[my latest design I moved the waist aft only 12mm from my usual location so it should not mess up the performance.

-S

As an experiment, I took one of those Brannock devices that they use to measure shoe size and noted the lengths of sizes 7 thru 12. I also measured the distance from the heel to the where the ball of the foot is marked for each size. I took the total length, divided it in half and then subtracted that number from the ball of the foot dimension. Interestingly enough, the difference between the ball of the foot and the center of the foot only varied about 1/2cm
between size 7 and 12. It would be interesting to see how consistant that ski boot centers are from company to company.

[mattman]

so what measurements did you get for shoe center to BOF? I actually just rechecked my ski boots but it is really difficult to figure out through the thick plastic...I think its close to 5cm. Judging from his designs I think this is the same measurement that skidesmond gets.