Ratcheting the pedals is a useful mountain bike skill that every serious rider should have in their arsenal. It a very useful skill when your balance is needed or you need to remain upright over high obstacles without pedal strike.
When Would You Need to Ratchet? First, when would you need to use this skill? It can be useful when you are going through a rock garden with rocks high enough that a full pedal stroke would strike the rocks and send you off your balance and off your bike. If you are fording a stream and are trying not to get your feet wet, or if there is some other obstacle that you are trying to avoid.
Also when the speed slows down with riders in front of you and you need to stay upright, a ratchet will assist in a slow movement and help keep you cleated in when the person in front of you needs some time to clear an obstacle.
Another scenario may see you needing to ratchet if you are going around a tight corner. this allows you to slow your speed but keep moving forward while getting into yhe correct position.
The skill requires confidence and trust, not only in yourself but your equipment. When performing the ratchet you need to know that your pedal action will help keep you moving (be it slowly) and help you clear obstacles without having to get off the bike. It’s important to trust that this skill will help you keep riding when the speed slows down. How to "Ratchet"
As you approach the obstacle in question, choose your line and the amount of speed you want to take in (if you have a choice).
Note any rocks you might particularly want to avoid, or note the depth of the water.
Get the cranks to 10 and 4. (Locations on the clock.)
When you reach the gnarly section (or water), make about a quarter of a pedal stroke without pushing all the way around. The cranks should end at about 9 and 3 or 8 and 2.
As you make each stroke, quickly back pedal to your previous position, and make the partial-stroke again.
Repeat as needed.
Using these partial pedal strokes will keep your cranks from descending all the way and will allow you to maximize your ground clearance for particularly high obstacles near your pedals. This technique is especially effective when you have a short section of high rocks on both sides of your bike and you don't have enough momentum to coast through them.