Why Shims?

This photo demonstrates how most skis present the carbide to the ground, preventing the carbide from helping you turn. This also explains why snowmobilers feel the need to buy longer carbides. The dilemma is that for every inch of carbide added in the front, a useless inch of carbide is added to the rear. Yes, changing from the OEM 3-4" carbide to 6-8" of carbide would make it feel like the sled is now on rails comparatively. Only because snowmobiler's expectations are so low this has become a common practice.

They would have gotten as good, if not better, results if the balance of the skis was correct.

 
 
This ski is in balance. The reason the front carbide insert is not making contact is because the second carbide insert is not properly seated.  If the ski is not perfectly balanced, it is better to have the front end off the ground similar to this front carbide.