The Pratt & Whitney geared turbofan engines now going into commercial airline service employ a gear reduction between turbine and fan, allowing each to turn at its best speed. Losses in their “star gearing” are said to be just seven-tenths of one percent. Yet in lots of written sources, transmission loss in motorcycle dyno testing is estimated at 10–15 percent. Okay, power is passing through two meshes, one in the primary gears (connecting engine crankshaft to gearbox) and one in the gearbox (whichever of the usual six ratios is driving). The other five ratios windmill without load, generating some loss. Then there is the drive chain connecting gearbox to rear wheel. I usually hand wave around a 2 percent loss for each, so that’s 6 percent. On roller dynos, there is also loss in the drive from rear tire to roller.