greater diameter than non-pneumatic rollerski wheels. Both wheels on skate rollerskis are free-rolling. Rollerski shafts may be composed of many different materials depending on the manufacturer and model. Wood was originally used, though this has mostly been replaced by aluminum, fiberglass, kevlar, carbon fiber or a combination of these materials. The wheelbase of skate rollerskis is typically around 610mm while classic rollerskis generally have a wheelbase of at least 700mm. The longer shafts of classic rollerskis help provide a better simulation of snow skiing. Many manufacturers sell junior roller skis, with shorter shafts to reduce the overall weight for younger skiers. Longer shafts generally provide straighter tracking and more stability. Rollerskis also feel more balanced when the bindings are properly mounted as close to balance point as possible. The bindings should never be mounted in a place that allows the cross country boot to be attached behind the balance point of the rollerski. Wheels are connected to rollerski shafts using arms that are either integrated into the shaft design or mounted to the shaft using bolts. Most composite rollerski frames made of fiberglass or carbon fiber have aluminum arms mounted with bolts. There are also types of roller skis that have 3 wheels, with one on the front and two on the back. These are less common more recently due to extra weight on rear created tail drop. Roller skis with pneumatic tires (such as skikes) are available for rough pavement and off-road use. Normal cross-country ski bindings and ski boots can be used with most roller skis, though some manufacturers produce special roller ski versions for the warmer weather use including Alpina, Botas, and Fischer. Cross-country ski poles are also used, with the basket replaced by a ferrule, essentially a reinforced carbide steel spike molded into strong plastic. Extra protective clothing is recommended: full-finger gloves, helmet, eyewear, and knee and elbow pads. Many ski training programs require the use of helmets while roller skiing. Roller skiing is most popular in Europe particularly France, Italy, Norway, Finland, Estonia, Sweden, and Russia, where there are many serious races and even a World Cup Circuit. In North America, roller skiing is popular in areas with many Nordic skiers such as Ontario, Alberta, Alaska, New York, Vermont, New Hampshire, Maine, Minnesota, Michigan, and Wisconsin. Nordic blading Nordic blading is a sport which uses ski poles with special tips and inline skates or roller