The final drive is the last link between engine and road, and motorcycles use three fundamentally different solutions for it. Each represents a different answer to the same set of compromises.
Chains are efficient because they are direct
A roller chain transmits power through metal rollers engaging sprocket teeth, with very little energy lost to deflection or friction when the chain is clean and correctly tensioned.
The arrangement is also light, cheap and easy to alter. Changing a sprocket changes the overall gearing, which is why performance and off-road machines almost universally use chains.
The cost is exposure. The chain runs in the open, collects road contamination, stretches as it wears and requires regular cleaning, lubrication and adjustment.
Belts trade adjustability for cleanliness
A toothed belt made from reinforced polymer engages pulleys in much the same way a chain engages sprockets, but requires no lubrication and produces no fling.
Belts run quietly and last a long time in normal use, which suits cruisers and touring machines where mileage is high and maintenance appetite is low.
They are vulnerable to stones and debris lodging between belt and pulley, and a damaged belt is replaced rather than repaired, often requiring the swingarm to be disturbed.
Shafts are sealed but impose their own behaviour
A shaft drive encloses the entire transmission path in oil, which makes it effectively maintenance-free beyond periodic fluid changes.
The penalty is weight, mostly unsprung weight at the rear wheel, and a modest efficiency loss at the bevel gears that turn the drive through ninety degrees.
Shafts also introduce shaft effect, where torque reacting through the drive tries to lift or squat the rear of the machine as the throttle is opened and closed.
Suspension design absorbs the differences
Engineers counter shaft effect with linkage systems that separate the drive reaction from the suspension movement, and these systems add cost and complexity.
Chain-driven machines have their own version of the problem, since chain tension changes as the suspension moves and pulls on the swingarm.
Swingarm pivot position is chosen partly to manage this, which is why the pivot location is a genuine tuning parameter rather than a packaging convenience.
The choice follows the machine's purpose
Machines that need adjustable gearing, minimum weight and easy servicing away from a workshop use chains, and accept the maintenance that comes with them.
Machines that cover long distances in clean conditions favour belts or shafts, because the maintenance saved over years outweighs the efficiency given up.
None of the three is obsolete, and the persistence of all three is a sign that the compromises are genuinely balanced rather than one solution being superior.