At Gear West, we service a broad range of Nordic skiers from tourists all the way up to Olympic skiers. The majority of racers across all skill levels only have a vague idea of why, when and what type of stone grind structure to apply to their Nordic skis. With the advances in stone grind technology over the past decade, the answer to these questions has changed slightly.
The main reasons for stone grinding include removing “sealed” base material, flattening the base, applying final structure to the base surface.
It is a fact that regular waxing will eventually seal or partially seal base material. Racing fluoros, green and harder blue waxes require an iron temp that is above the melting point of ski base material. The goal with these waxes is to provide just enough heat with the iron to melt and apply the wax. It is very easy to get a little too much heat and the “pores” of the skis will start to seal (even when using an expensive digital wax iron). This process of base sealing is not black and white; the amount of seal is scalable. A sealed base is very slow, think waxless classic skis, and at the World Cup, an open base is so important that race skis are reground many times during a season. At higher levels of racing team’s travel with a stone grinder to many of their races.
Flatter bases will be faster and easier to edge. Bases warp due to core expansion from iron heat during waxing. This happens to every brand of ski, some more, some less, depending on the core material and iron heat. Stonegrinding will make the base completely flat again.
(disclaimer: In cases of severe base warp, grinding the ski back to complete flat will remove all or nearly all base material. In these circumstances, it is best to error on the side of not completely chasing the damage/warp out of the base.)
These skis represent overheating of the core/base with an iron and performance durability would have been greatly enhanced if these skis had been ground yearly. To minimize damage to skis bases, I only do 2 passes with an iron while waxing. I error on applying more layers of wax if I am concerned about compete wax coverage of the base.
This is a subject of great confusion for all levels of skiers. The actual final structure or pattern chosen for a ski base is important but less so than a clean cut and open base. With the advent of full CNC introduced to Nordic Stonegrinding machines, it is possible to cut almost any pattern into a ski base, perhaps even smiley faces. Fortunately, simple is generally better in regards to structure. To quote the foremost expert on Nordic stonegrinding, Lar Svensson “Cold snow, cold structure. Warm snow, warm structure.” There is a bit more than that but not too much. Each region has its nuances in snow type but generally it is best to keep things simple. Specialty stone grind patterns are great if you are a World Cup racer with two personal ski techs and 100+ pairs of skis. But for nearly everyone else, a simple yet effective grind is best as it allows you to get your ski “in the game” more often than not. Frequently, we see too many national level racers, JOQ athletes, and master athletes put a specific snow grind on their best skis. This is not a good choice as you want to be racing on your best ski most of the time. Another pitfall we see is the mismatch of ski flex with grind type. Ski flex is an entire subject in itself, but it’s important to match the appropriate grind to ski flex. Grinding a wet profile ski with a cold grind and vise versa is not optimal. Working with a knowledge retailer on ski and grind selection is important.
Disclaimer: A world cup level grind will not help a bad quality ski go much faster. Know your skis and make sure they fit and are of high absolute quality.
For more on Ski Quality:
- Most skis with mild to regular use will benefit greatly from a new grind once per year.
- Sealed bases are much slower than open/non-sealed base material. So much slower that national teams travel the World Cup circuit with a stone grinder.
- Race skis can be reground many dozens of times if the base is not deeply sealed or damaged. A standard ski base has roughly 2.0-2.2mm of workable base. If the skis are in good condition, only a maximum of a tenth of a millimeter would be removed during a quality grind. Lars mentioned he stone ground one world cup athlete’s favorite ski 42 times without going through the base material to the core.
- Performance racers, especially master racers in Norway, get their entire fleet ground at the start of the season and then grind their “A” pair again before their target event.
- Machine choice is important when grinding Nordic skis. At Gear West, we chose Tazzari because it is one of the few machines in the world designed specifically for Nordic skis. Most other machines are designed for Alpine skis and modified to accommodate Nordic skis. The Tazzari uses exclusively sourced grinding stones and synthetic diamond dressing bits for the delicate base of a Nordic ski.
- Skis need to be “skied” in to be at their fastest. This depends on the machine, grind and technician skill. With a Tarzarri stone grinder, the stone, grinding fluid temperate and diamond cutting dressing tool are so specific to Nordic skis it is not necessary to “ski in” a base. Jan Guenther and Matt Liebsch both raced to 10th place at the 2014 Birkie on newly ground skis with 0km on them. On the World Cup, skis have gone from a Tazzari grinding machine to the podium in less than 2 hours.
- Brushing with a metal brush or using fibertex can “open” the base. Once a base has been sealed or partially sealed the only way to remove the sealed portion is with a stone grinder, metal scraper or sandpaper. The cleanest, fastest and most precise method is stone grinding.
- The more I wax my ski the faster is will get. To quote another top level Tazzari technician “When you receive a newly ground ski off a Tazzari and race prepped, it is as fast as it is possibly going to be. Skiing and waxing will only make the skis slower over time.” This is a true statement. The goal for a ski base is that the cut structure is precise, clean and open. Next the base needs to be saturated with wax; a hotbox comes in handy here. Finally, the wax of the day needs to be applied with the appropriate level of fluoros. After these steps are complete, additional waxing or “skiing in the base” will not change performance assuming a high-quality grind was in place to start.
More Information on Stonegrinding and Base Material:
-Posted by Matt Liebsch on Nov 7th 2015