The picture is a scan taken from a brochure for the Japanese market TRX850. The picture shows two plots. One is for the older 360 crank engine and the other for the new 270 crank engine. There is a lightly dotted line, a heavy dashed line and a red line (that is the sum of the other two).

The lightly dotted line is a plot of inertial torque measured at the crank shaft. Inertial torque is the component of torque that is stored in the moving masses associated with the crankshaft. The heavy dashed line is explosion torque. Explosion torque is the component of torque generated from combustion above the pistons. Note that it goes negative (below the zero line) during the compression stroke. The noteworthy difference between the two graphs is that inertial torque does not vary much for the 270 crank throughout a full 720 cycle. It always stays near zero. This means that the true crankshaft torque (red line) more closely follows the explosion torque, giving a more direct sensation of applied power. The red line on the graph for the 360 crank shows a much more confused result with many slope reversals. Yamaha goes on to explain how the sensation from the 270 crank engine is like that of a "galloping horse", hence the twin horse heads. Silly. This "big bang" effect is alleged to benefit the rider in terms of feedback from the rear tire when applying power near the limits of tire adhesion.

These pulsations might explain what you may feel when launching the TDM from a start in first gear. I'm hoping it would be a positive experience. At least it is good to hear that the vibes may be reduced when cruising at over 4000 where the inertial torque may be the dominant component.

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