With testing of the new 800s wrapping up at Valencia following the final race of the 2006 MotoGP series, one thing is already clear. The 800s are quick... very quick! In fact, some riders are quicker on their brand new 800s than they were on their fully-developed 990s just a few days ago. Why?
A few years ago, a major print magazine here in the United States ran a test of Suzuki's GSX-R models displacing 1000cc, 750cc, and 600cc in a comparison. Although the bikes weighed roughly the same (within a few pounds of each other), the bikes with the smaller engines (and lighter, rotating engine internals) felt much lighter, and carried much higher corner speed. This is why the 800s, weighing roughly the same as the 990s, can carry much higher corner speed - a comment echoed by virtually all of the riders. The gyroscopic effect of the rotating engine parts is much smaller with the lower displacement, and therefore the bikes change direction better, and place less pressure on the tires mid-corner.
The trade-off, of course, is outright power and acceleration. At various circuits, the 990s will undoubtedly be quicker, but at Valencia the trade-off probably favors the higher corner speed of the 800s. At many tracks the 800s will also achieve similar top speeds on the straight-aways - owing to the fact that traction control is pulling power from the 990s on corner exits, and pulling less power from the 800s on those same corner exits.
In any event, it certainly looks like the 800s will match, and in many instances, exceed the performance of the 990s in terms of lap times next year.
Dirck J. Edge, Motorcycle Daily