OK, maybe the title of this thread is a bit exaggerated, but I thought I would share what I recently found out and make it a generic subject that a search will find. A month or so ago I took my wife's skis in for a shop tune. I do all my own tuning, but I thought the base edge angles were a bit out and there were a number of edge nicks that the diamond stone would not easily take out.
She got the skis back and said they were awful, and she sure was not skiing well on them. She said they were grabby and catchy. I immediately thought they were railed (edges extending lower than the base material), but they were not. I checked bevel angles etc. Nothing. I thought "welcome to having sharp edges", and also thought it must be mostly in her head. Well, she was kind of due for new skis anyway, and we found a deal on new boards and the problem was "solved."
Then I adjusted the bindings and skied them. Unbelievable. They were brutal. They felt 2 or 3 times as bad as the most railed skis I had ever skied. Very hard to initiate turns. If you ski them like they're on rails perfectly carving all the way not so bad, but try anything with a sideslip, even getting on or off the lift, and they were incredibly bad. Why? The base structure was very coarse and deep and linear. Like what you might need to win a race in wet corn snow. After a bunch of googling I found references to this, including on this forum, but you have to know what to search for and search on "structure" to find this. Then I filled the structure with super hard -30 wax on one ski and made it smooth. Guess what? One ski was much better. The skis were redone by the shop, and the problem was solved
There are 2 amazing things that come out of this. One is that base structure has a huge effect on how skis feel, at least on fine snow and in cold temperatures. The other amazing thing is what a well kept secret this is. The tech guy at the ski shop didn't know what I was talking about and didn't believe me. Luckily the shop owner, a former national team racer, did know all about this. Other guys who I know and who I think of as being very "techy" seem to know nothing about this. Even on forums like this, I see replies from some people who say "the ski must be railed" and doubt that base structure is the cause. It can in some cases make the skis feel more railed than actually having railed edges.
So, for me, I'll be careful to make it clear if any skis ever do go to a shop, to put in a minimal structure. I can't imagine the negatives of a fine or non existent structure could compare to the potential negatives of a coarse structure. And if you get a shop tune-up and get back terrible skis - check the base structure!