<img width="210" height="158" class="floatleft" src="www.motorcycle.in.th/images/articles/Gear-Shifting_Problems_1.jpg" alt="" />Some people worry that skipping 2 or 3 gears at a time during easy cruising would damage the transmission by up-shifting gears. There would not be any damage to the transmission, unless you are shifting very slowly. One of the several factors that can cause transmission damage is a large difference in speed between the gears as they are being engaged.
When a shift is made, one gear of an adjacent pair is slid sideways on its shaft so its engagement dogs can mate with those of the other gear, which cannot move side-to-side. Even though both of those gears reside on the same shaft. One is mechanically connected – via the transmission output shaft and final drive – to the rear wheel; the other gear is connected – via the mainshaft, the clutch and the primary drive – to the crankshaft. While the clutch is disengaged during a shift, however, that latter gear is connected only to the inner clutch hub via the mainshaft.
When the transmission is in any given gear, the two mating gears for that ratio are locked together and spinning at the same speed; but as the transmission is up-shifted or down-shifted, the gears for the “new” ratio are turning at different speeds. And since one of those gears is being turned by the rear wheel, which has the mass of the entire motorcycle and rider driving it, that gear is not likely to change speeds during the shift; the other gear, driven only by the momentarily freewheeling inner clutch hub, will be the one that has to suddenly slow down or speed up.
When the speed of those two gears as they engage is relatively close, the impact between their mating engagement dogs is small. This allows the dogs to engage smoothly, easily and quietly, since the gear connected to the inner clutch hub does not have to change speed to any significant degree. But when the speed differential is large, not only is there a sizable impact between the two gears' engaging dogs, which can accelerate their rate of wear, the dogs also tend to reject one another for a few revolutions.
This not only rounds off the edges of the dogs, it deflects the movable of the two gears sideways, which can bend its shift fork, possibly enough to gouge the thrust pads machined on the gear end of the fork. That kind of wear soon leads to missed shifts and a transmission that jumps out of gear.