The hardness of skateboard wheels is typically measured on the durometer scale, with the most common ratings being 99a, 100a, and 101a. The higher the number, the harder the wheels. 101a wheels are the hardest, providing less grip but more speed, while 99a wheels are softer and provide more grip but less speed. 100a wheels fall in between, offering a balance of grip and speed. The choice of hardness depends on the type of skating and personal preference. **

The difference in rolling between 100a and 101a in skateboards is generally considered to be significant. The "a" rating refers to the hardness of the skateboard wheels, with 100a being softer and 101a being harder. Harder wheels (101a) typically roll faster and have less grip, making them better for smooth surfaces and technical tricks. Softer wheels (100a) provide more grip and shock absorption, making them better for rough surfaces and cruising. Therefore, the difference in rolling between the two hardness levels can have a noticeable impact on the performance and feel of the skateboard. **

The durometer hardness of skateboard wheels is typically measured on the A scale. The most common durometer hardness for skateboard wheels is 99a, which provides a good balance of grip and slide. However, skateboard wheels are also available in 100a and 101a durometer hardness for different preferences in riding style and terrain. **

The wheels with 101a are harder than the ones with 99a. The durometer rating measures the hardness of the wheels, and a higher number indicates a harder wheel. Therefore, the wheels with a 101a durometer rating will be more suitable for smooth surfaces and provide faster speed, while the 99a wheels will offer more grip and control on rougher terrain. **

The hardness of Spitfire Formula 4 skateboard wheels is typically 99a. This hardness level provides a good balance between grip and slideability, making them versatile for various skateboarding styles and terrains. The 101a hardness is slightly harder and may be more suitable for smooth surfaces or advanced skaters looking for a faster ride with less grip. **

Recommended trail running shoes should provide good traction, stability, and protection for uneven terrain. Look for shoes with a durable outsole, a rock plate for underfoot protection, and a secure fit to prevent slipping. Some popular brands for trail running shoes include Salomon, Brooks, Altra, and Hoka One One. It's also important to consider your individual foot shape and running style when choosing the right pair of trail running shoes. **

Nike's marathon running shoe is the Nike ZoomX Vaporfly Next%. This shoe is designed specifically for elite marathon runners and features Nike's ZoomX foam for maximum energy return and cushioning. The Vaporfly Next% is known for its lightweight design and carbon fiber plate, which helps improve running efficiency and speed. Many elite runners have set personal bests and even broken world records while wearing the Nike ZoomX Vaporfly Next%. **

Trail running in the mountains is a form of running that takes place on natural, unpaved trails in mountainous terrain. It often involves navigating through rugged and varied landscapes, including steep inclines, rocky paths, and uneven surfaces. Trail runners typically seek out mountain trails for the challenge, the stunning scenery, and the opportunity to connect with nature. It requires a higher level of physical fitness and endurance compared to running on flat surfaces, and it offers a unique and exhilarating experience for those who enjoy outdoor adventure and exploration. **