Power transfer engine in-line w/ shaft drive

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Take a bike like the Triumph Rocket III which has an inline triple cyl engine mounted longitudinally and uses a shaft drive. Would such a design still transfer power less efficiently to the wheel than a chain? My understanding has been that if the crank shaft of the engine and the drive shaft form a 90 degree angle then that is when you have more loss of efficiency of power transfer. In the example bike, the crank and drive shaft are parallel to each other.
 
Changing the direction of rotation 90° costs some power. With a fore-aft crank you have one 90° turn somewhere. Generally it's done at the final drive. Honda, Moto Guzzi, BMW and others like Triumph you mention all have done it this way. It's not that big a deal. Bikes like the Honda Shadow with a fore-aft cylinder arrangement and shaft drive make two 90° turns which is less efficient still, but they work fine. Sport bikes have chain drive for efficiency and to reduce unsprung mass.
 
The real problem with longitudinal crankshafts are torque induced roll. Apply more throttle rolls the bike to lean more in one direction - lift off the throttle makes it lean the other way. Often the rider has to counteract these forces.

With a transverse crankshaft more throttle (usually) transfers weight to the back tire, and lifting transfers it to the front.
 
Best efficiency...
1 belt (constant 98% until it breaks)
2 chain (new 98% but can drop to 90% with mileage)
3 shaft (constant 92% given 4% loss for each 90º)

Lowest maintenance...
1 belt
2 shaft
3 chain

Most expensive...
1 shaft
2 belt
2 chain

Least amount of drive line snatch...
1 belt
2 shaft
3 chain

Lightest to the heaviest...
1 belt
2 chain
3 shaft


Biggest vocal following...
1 shaft
2 chain
3 belt


Gates Poly chain is a cog tooth belt that runs at constant 98%
efficiency and never drop below that figure whereas a new chain offers
the same 98% efficiency but steadily drops below that figure as miles
are ridden... so subtract 2% of your crankshaft HP and what remains is
your RWHP... if the chain is really worn it may subtract up to 10% of
your engines available crankshaft HP... like if you made 110 at the
crank now you only have 100 at the wheel..
 
Last edited:
Originally Posted By: CentAmDL650
The real problem with longitudinal crankshafts are torque induced roll. Apply more throttle rolls the bike to lean more in one direction - lift off the throttle makes it lean the other way. Often the rider has to counteract these forces.

With a transverse crankshaft more throttle (usually) transfers weight to the back tire, and lifting transfers it to the front.


There is also the issue of gyroscopic forces. In the case of a transverse engine, the crank typically turns in the same direction as the wheels, which adds to the total (gyroscopic) effect. To counter this, Yamaha (in its M1 GP bike) and MV Agusta (in its 675 and 800 cc production triples) run the crank backwards, thereby helping to counter some of the gyroscopic forces from the wheels and creating a quicker handling motorcycle.
 
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