2006 is going to be another big year of new bikes, and we just got the latest information on some of the most-important models. Yamaha and Kawasaki introduced all-new bikes and some old favorites are heavily revised. So here's the scoop ...YZ45oFThis is an all-new bike from the ground up. The obvious revision is the aluminum frame, but the engine, which looks similar to the older design, is brand new. Housing a five-speed transmission, it is claimed to have an even smoother "faster lap times at the end of a moto" power delivery, but don't think Yamaha won't also go for outright power. The bike also shares all of the suspension improvements with the YZ250F and likely the 250 two-stroke. The frame has its dimples on the inside of the main spars (opposite the two-stroke's design), and Yamaha asserts the new package gives the YZ450F a lighter and more-agile feel while placing the rider lower and more centered on the bike. We don't expect this bike to be available till very late in 2005.YZ25OFEverything is new except the motor, but Yamaha coaxed even more power out of it anyway.All-new plastic with a more-comfortable seat that is lowerTitanium shock springAluminum frame that is claimed to improve handling and make the bike feel lighterDry-sump motor carries the oil in a lower aluminum tank.ProTaper handlebar on an adjustable top triple clamp; all-new KYB S3 (Speed Sensitive System) forkTT-R5OBig news in a small package is the arrival of Yamaha's smallest TT-R. The 50cc air-cooled two-valve four-stroke goes one-up on the Honda CRF50F by adding electric starting to the package. Yamaha stresses this bike is designed only for kids, but we're betting plenty of adults will be riding it, too. Most likely available at dealers by the time you read this, the bike should be priced the same as or lower than the Honda; and there will be a wide variety of GYT-R accessories available immediately so "the kids" can advance with their ride.KawasakiKX45OFKawasaki's long-awaited entry into the big four-stroke market is here.Gripper seat coverKayaba Air/Oil Separate fork;Renthal aluminum handlebarAluminum-perimeter frame using forged, extruded and cast pieces with titanium footpegs and bracketsHigh-capacity radiators with tightly packed cores and a new fin designTitanium exhaust with expanding diameter from 38 to 41mm449cc four-valve motor with titanium 36mm intake and 31mm exhaust valves; four-speed transmission; automatic decompression for easy startingKawasakiKX25OFThe smaller KX-F is using the older motor with a host of improvements. There should be a noticeable increase in power with the compression bumped to 13.5:1, revised intake and exhaust ports, a new combustion chamber shape and a cam profile change lurking inside. Kawasaki's choice to bump oil flow by nearly 20 percent; increase the cooling through new, improved-efficiency radiators; add a thicker piston crown; strengthen the gear dogs; and improve the shifting drum backs up these claims. Big suspension news is the switch to Showa components; a twin-chamber fork and a rear shock with high-speed compression adjustability mark a significant shift from the company's long-standing exclusive use of Kayaba components on the KXs. This matched with an all-new aluminum frame that shares traits with the 450 should make the 250cc four-stroke class a hotbed of competition in 2006. Kawasaki is the first to drop its 125cc two-stroke from the lineup.