Motorcycle transmissions are not synchronized for a few reasons:
Weight and Complexity: Synchronizing mechanisms add weight and complexity to a transmission system. In motorcycles, where weight and size are critical factors, keeping the transmission compact and lightweight is essential. By omitting synchronization, manufacturers can simplify the design and reduce the overall weight of the motorcycle.
Cost: Synchronizing mechanisms add manufacturing and assembly costs to the production of a motorcycle. By eliminating the need for synchronizers, manufacturers can reduce the cost of manufacturing, making motorcycles more affordable for consumers.
Riding Style: Motorcycles, especially sport bikes and dirt bikes, are often ridden in a more aggressive manner compared to cars. Riders frequently use the clutch and perform quick and precise gear shifts, making the need for synchronization less critical. Skilled riders can execute smooth gear changes without synchronization by properly timing the throttle, clutch, and gearshift lever.
Gear Spacing: Motorcycle transmissions typically have closely spaced gear ratios, which means the differences in gear size between adjacent gears are relatively small. This close gear spacing makes it easier for riders to shift gears without synchronization. The smaller differences in gear ratios allow for smoother engagement between gears, even without the use of synchronizers.
It's worth noting that not all motorcycles have non-synchronized transmissions. Some higher-end touring or cruiser motorcycles may feature synchronized transmissions to provide smoother and more effortless gear shifting for a comfortable riding experience. However, in many sport bikes, off-road motorcycles, and smaller displacement motorcycles, non-synchronized transmissions are common due to the factors mentioned above.