A basic guide to ski shape terms
-True center is exactly halfway in the middle of the ski (same length in front of and behind of the line)
-Core center is the point where the ski's core is the thickest. Also where the ski is narrowest (the center of the sidecut). On symmetrical skis, true center and core center are the same, but on directional skis, core center will be back from true center, the amount depends on the ski.
-Reccommended is just wherever the factory reccommends you mount the skis (although sometimes the rec mount point is debatable i.e. hellbents have a rec of -7.5 from true center, meaning that the factory reccommends you mount 7.5 centimeters back from the exact center of the ski, although the hellbent is known to perform at it's best from around +4.5 to +7.5, which means anywhere from 4.5 cm to 7.5 cm forward of reccommended, which translates to anywhere from true center to -3cm from true center. On a hellbent, +7.5 from rec is the same thing as true center, +6 is the same as -1.5 from true center, etc.)
-The sidecut radius refers to the size turn the ski will make when fully engaged in a carve. The bigger the number, the longer the turn the ski likes to make. A super short radius ski will make super short turns very easily, but will tend to be hooky and unstable at speed. A super long radius ski will make long turns and straightline without hooking too much, but may feel sluggish making short turns. Of course there are exceptions to every category. For example, a 192 bent chetler has a 20m radius which is on the lower end of things. Not super duper ultra small, but still pretty small, but can still haul ass. A 4frnt renegade has a 35m radius which is definitely on the longer end of things, but people say they're super nimble and energetic in short spaces. Whatever, you get the idea.
Hope this helps. Keep in mind that people will OFTEN get their terms confused. One of the most common mistakes people make is thinking core center is true center, which it is on symmetrical skis, but isn't on most other skis. Even people in official videos will frequently mistake the two, so take anything anyone says about the center of a ski with a grain of salt because they might be confusing their terms.
Cheers,
Isak
