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New skis -- how flat do they really need to be?

post #1 of 8
Thread Starter 

This topic started coming up in one of Dawg's reviews, but I didn't want to hijack that thread any further. Dawgcatching commented that his new Sultan 94 skis were "extremely railed" out of the wrapper and that many of the Dynastars were delivered with un-flat bases and a desperate need for a full tune before being skied. Many people seem to agree that new skis should be tuned before being skied (although some disagree). The new-ski tune makes sense to me, but there are many levels of tuning (with the most significant being a full base grind, edge shaping and polishing and sidewall shaping and polishing -- easily setting one back $100 at a good shop).

 

I have two new pairs of skis in my house right now that have not yet been skied. One pair is the Sultan 85 and the other is the Nordica Victory. Neither of these are particularly fat skis (85mm waist and 78mm waist), but both of them are a little concave in the tip and tail while perfectly flat underfoot. Mind you, my true bar has not been delivered yet and I was just using a metal straight edge to check these, but with that instrument I could see the differences in flatness as mentioned. I would guess that the gap under the straight edge was less than half a millimeter at its deepest point -- I could not slide a credit card under the gap, but I could see light coming through the gap.

 

I plan to thoroughly wax them, shape and sharpen the side edges and make sure the base edge bevels are acceptable before anyone gets on these skis. However, I would prefer not giving them a stone grind if not really necessary.

 

A forum search pulled up a number of threads about concave bases and many people were suggesting that a slightly concave base is not a problem for a recreational skier as long as it doesn't impede the tuner's ability to set and maintain the edges.

 

I understand that a concave middle will not affect edge tuning if the base is flat near the edges where the edge guide rests. But if the base is concave from edge to edge with a half millimeter space at the deepest point of the crescent, will this affect edge tuning so much that it will be a problem for a recreational skier? How flat do they really need to be?

post #2 of 8

Sounds like your base concavity is negligible and not a worry.

 

If you find out otherwise, there is a point on some skis where to get them dead flat or near flat will kill the ski by either taking away too much edge and/or base just to make them unnecessarily dead flat.

 

My FX94s were cupped and I moderated the problem easily and in a reasonably short time by hand using the new SkiVisions File Base Flattener . I need to finish a video I started showing the process and can post pics if needed. This worked much better than a flat or body file which can tend to bend if too much pressure is applied. The included file is a 2nd cross cut file that left a nice finish. I found it to be a little to 'fine' and suggested a more aggressive file to quicken the process. Mark, the owner just dropped a line regarding a new, very sharp file he found and wants feedback. So if interested I can let you know what I find after I receive it and give it a go.

post #3 of 8

Ski Base Geometry.PNG

Top = Big problems, completely railed

Bottom = Less of an issue, but would probably ski better flat and that should be the goal over time, but I wouldn't grind the life out of it to get there.

 

Pardon my crude line drawings, but I think you'll get the idea.  It is quite common in the current era of wider skis to see skis in the shape of the bottom drawing.

post #4 of 8

Noodler. Your schematic drawings reminded me of this musing thread: Catamaran Ski Bases

post #5 of 8
Thread Starter 

Thanks for the drawings Noodler. The top drawing seems pretty extreme (I realize you drew it in a way that was easy to quickly identify the shape) -- it looks like the dip is about 3-4mm lower than the edges on my screen. Is there a cutoff point where you say the skis definitely have to be made flat or they will be horrible to ski on? For example, if the dip were enough to let light through with a knife-style true bar but less than a millimeter deep? Half or quarter of a millimeter?
 

post #6 of 8

Interesting Terry - I had not caught that thread previously.  Looks like there was no real conclusion to the idea of new base geometries and how they would affect a ski.  We have the v-hull tips from Fischer and now the new Salomon BBR has also supposedly gone that route also.  I've never directly compared a dead flat ski against a "catamaran" base to gather any thoughts on the different base geometries.  I also believe that the groove down the middle was originally put there to break up surface suction, but then they figured out that structuring was much more efficient and the grooves went the way of the Do-Do.

 

LibTech innovated edge design with their Magna-traction feature that uses a slightly "wavy" edge to concentrate the contact points and supposedly improve the edge hold.  I don't recall anyone really investing in any kind of new designs for base shapes to improve ski performance.

 

The take-away for all skiers is that a railed edge due to a concave base is a really bad thing.  A slightly convex base will make a ski harder to get the edge to hook-up and gives a ski a more "surfy" feel.

 

Back on topic for the OP - I found through testing a few years ago that I am sensitive enough to changes in edge bevels that I want to be sure that they are correct and consistent along the entire length of the edges.  So if you're at least checking those before taking out a new pair of skis you are most of the way there.

post #7 of 8
Quote:
Originally Posted by TallSkinnyGuy View Post

Thanks for the drawings Noodler. The top drawing seems pretty extreme (I realize you drew it in a way that was easy to quickly identify the shape) -- it looks like the dip is about 3-4mm lower than the edges on my screen. Is there a cutoff point where you say the skis definitely have to be made flat or they will be horrible to ski on? For example, if the dip were enough to let light through with a knife-style true bar but less than a millimeter deep? Half or quarter of a millimeter?
 


If you can clearly see any light under the true-bar all the way to the edge then I would strongly recommend a grind (or use the SkiVisions base tool) to bring down the edge heights.  Even the tiniest amount of railing can impact the ski's performance. 

 

And my personal preference if you find a "catamaran" base is to have at least 15-20mm of flat base adjacent to the edge before the concavity occurs.  I'd like to hear Terry's opinion and others chime in on their thoughts on this also.

post #8 of 8

For tuning accuracy you are kind of screwed if only 15mm. A typical plate side edge beveler is 35mm or so (ie, SVST PEBS). Other guides can vary here, but I imagine that if 20 to 25mm minimum, you could be secure with a plate side edge guide. Same possibly for the dedicated SkiMan/Toko/Brand X base bevelers. A Final Cut needs 60mm of flat. Ideally, you'd need a base spanning bevel guide like the

Toko Precision Base File Control.....or calculate the angle and use a base bevel guide angle that would work for a given section and it's variance.

 

If you simple ski powder all the time, none of this matters. rolleyes.gif

 

Here are pics of my FX94s:

 

Concave with OK flat sections along edge and they skied fine:

 

FX94_concave.jpg

 

And after using the base flattener (note light intensity in the middle makes this image seem less flat than it really is):

 

FX94_flat.jpg

 

 

A railed Havoc:

 

droppedImage_3.png

 

And a convex base:

 

droppedImage_2.png


Edited by Alpinord - 12/22/10 at 4:09pm
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