The synchronizer ring play an important role in the time of changing of gear. When the Gear changes the engine needs to be disconnected from the transmission using the Clutch Pedal.
This is required because the change of a gear in a transmission with simple gear mechanisms, which are continuously meshed (engaged), can not be performed while engine torque is being transmitted through the gears, so that is why the clutch needs to be open. This is when the synchronizers come into play .
The synchronizer acts like a friction clutch and decelerates (upshift) or accelerates (downshift) the input shaft, in order to match the speed for the upcoming gear.
