[rotorwrench]

It's all about matching rpm between drive input (engine rpm) and output (rear axle & mainshaft rpm) on non-synchronized gears. It's best done by ear but it takes a lot of practice to get it to minimize and especially for low gear. When hills are involved, the coasting speeds of the output can vary so this makes it even more complicated. Downshifting to low gear on flat ground can even be difficult at times .