Dear MXA,
MXA said that the only place to save weight between a
two-stroke and a four-stroke is in the engine. If this is true, how can
Yamaha build a 250cc four-stroke that is five pounds lighter than their
250 two-stroke (at least according to Yamaha's brochures)?
The answer
is self evident. The YZ250F four-stroke is technically classified as a 125 and as such runs
narrower a 1.85-inch rear rim (the YZ250 uses a 2.15-inch rim), a
100/100 rear tire (the YZ250 has a larger 110/90 tire), lighter fork and
shock springs (made from smaller gauge wire than the YZ250), a shorter
swingarm (the YZ250 swingarm is longer), a different shock linkage (the YZ50 linkage mounts through the swingarm) and smaller gas tank (the YZ250
two-stroke burns more gas than the 250 four-stroke). Assuming that the
figures you got out of the Yamaha brochure were correct (and they
aren't), the YZ250 weighs more than the YZ250F because its running gear
(tires, wheels, springs,linkage, swingarm and tank) is heavier. To be accurate,
there is not a major weight difference between the YZ250 and YZ250F—proving the point about
engine weight even more.