 The mid-speed valve is one of the least understood components of a front fork. However, it is, without a doubt, one of the best solutions that came to existence to follow the evolution of motocross and supercross. Stay tuned to find all about it. If you watched our episode on how front forks work, you should know that, besides the compression base valve, there's another valve that provides additional compression damping, the mid-speed valve. But why would you need additional compression damping? As the sport progressed, the jumps and speed got higher, thanks to the increase of performance of both bikes and the riders. The suspension setup had to be increasingly stiffer on high-speed compression damping and this had some limitations. In a cartridge fork on a compression stroke, the volume of oil pushed through the compression base valve to provide compression damping is simply the volume of the rod entering the cartridge, which, let's face it, isn't that much oil. On the other hand, during the rebound stroke, the volume of oil that is used to provide rebound damping is the same as the area between the rod and the cartridge times its displacement, which is a lot more than in compression. The industry came to the conclusion that only increasing the stiffness of the compression shim stack wasn't enough. It reaches a point where the suspensions become unrightable and start having cavitation issues. This is where the mid-speed valve changed the picture. The mid-speed valve is, in essence, a shim stack combined with the check valve of the piston rod's rebound valve. When the suspension gets compressed, the mid-speed valve lifts, allowing the oil to fill the chamber above, although a bit more restrictive when compared to a regular check valve. The amount of shims placed above the shim stack determines how much float the mid-speed valve has, which limits its vertical travel. If the pressure inside the cartridge keeps increasing, the shims bend, allowing more oil to fill the chamber above while creating additional compression damping. There are two things you can do when you introduce a mid-speed valve. First, it can significantly increase the volume of oil that is used to dampen in compression, since the volume of oil going through the mid-speed valve is equal to the area of the valve, times its displacement, which is around three times bigger than just the volume of oil going through the compression base valve alone. You can look at it as increasing the compression stroke used for damping, without increasing the fork's length. And number two, you can reduce the stiffness of the compression base valve while still providing more compression damping. The mid-speed valve became such an important step in suspension performance that it naturally became a component in every open cartridge and closed cartridge fork from that moment on. But how does that affect the compression damping of your forks? Damping is additive, meaning that the total damping of the forks will be the sum of the damping created by the different damping circuits. In the compression base valve, we have the low-speed orifice, which is the first circuit creating damping, and it's responsible for the initial spiking damping. Then, we have the low-speed shim stack circuit. This circuit usually doesn't open right from the start, but as soon as it opens, most of the oil flows through this circuit. Adding to the low-speed, we have the stiffer high-speed shim stack circuit, which follows the same linear damping as the low-speed, but with a bigger slope. Each damping circuit contributes to the overall damping of the suspension, according to its compression. If we now have compression damping in the mid-speed valve, everything adds up as well. Usually the mid-speed compression damping doesn't start right at the beginning of the suspension travel, thanks to the float. The amount of damping provided by the mid-speed valve depends completely on the stiffness and setup of the shim stack. For motocross, the mid-speed valve usually has a smaller float and a stiffer shim stack. This is useful because it provides additional damping between the low-speed and high-speed damping shim stacks, hence mid-speed, while providing better barming resistance. For enduro, the mid-speed valve usually has a softer shim stack and a bigger float. This is useful because it allows the suspension to absorb the bumps, but still improve barming resistance. But be careful with how you tune them. You shouldn't tune a mid-speed valve the same way you tune a base valve. The rebound piston on the left and the compression piston on the right are from the same suspension, and we can clearly see that the mid-speed valve's ports are a lot bigger than the compression base valve. Why is this important? Well, the chamber between both valves will be under the same pressure, so if you want them to open at the same pressure, the valve with larger ports will require a stiffer shim stack, and the valve with smaller ports will require a softer shim stack. At the end of the day, the possibilities of tuning your suspensions are endless, and will always depend on what they are for, your riding style, and the kind of suspensions you have. Subscribe, if you have any questions, leave them on the comments below, and give it a thumbs up. Thank you for watching.