Yamaha calls this 450 their lightest and most-nimble to date, as Chad Reed demonstrates.
What's the big news from Yamaha for 2006? An all-new YZ450F, limited edition 50th Anniversary graphics, S³ suspension and Yamaha's continuing commitment to two-stroke development.
The YZ450F received a complete overhaul this year with emphasis on improving its weight-feel and maneuverability. To commemerate Yamaha's 50th anniversary, both four-stroke YZs will be availible with limited edition yellow and black graphics. Another point Yamaha emphasized in their 2006 release was their continuing commitment to two-stroke development. Last year's aluminum-framed YZs proved very popular, and Yamaha is looking forward to an even bigger piece of the pie this year (especially with less competition in the US market).
The new fork's S³ design controls damping by the piston's speed rather than its position.
There were a slew of changes made to all four 2006 YZ models: YZ125, YZ250, YZ250F and YZ450F (the YZ85 remains the same aside from new graphics). Yamaha revamped the suspension (front and rear), made a host of minor changes for easier maintenance, and improved ergos for a more comfortable ride on all their motocross models.
Suspension
Yamaha did away with the Kayaba AOS (air-oil-separate) fork and came up with a new S³ (Speed-Sensitive System) designed 48mm fork. The damping force is controlled by piston speed rather than the position of the fork. The different feel of this type of suspension might seem too soft, initially, but the all-new fork is said to feature better bump-absorbtion and improved comfort. Also improving the front suspension-feel is a wider-pitch triple clamp to reduce flex. The four-stroke models now come with ProTaper aluminum bars while the two-strokes still have Renthal aluminum bars (same as '05). All YZs also come standard with a new titanium spring and new shock body with a thicker 18mm rod (from 16mm).
This cutaway shows the relocation of the TCV valve in the 2006 S³ fork compared to the 2005 KYB (top). | 
All 2006 YZs come standard with a titanium spring and all-new shock body with a low-friction coating. | 
The YZ-F's new aluminum frame rides lower than last year. ProTapers come standard on both YZ-Fs. |
Other changes shared by all four YZs include taller, softer seat foam for increased comfort, a larger clutch adjuster and new graphics. In celebration of their 50th anniversary, Yamaha is releasing limited editions of their 2006 four-strokes with retro yellow and black graphics. The 50th Anniversary models are availible for the YZ250F ($6,199 MSRP) and the YZ450F ($7,099 MSRP). If you're interested, get to your dealer quick—word is they're going fast!
Yamaha's limited edition 50th Anniversary YZ250F and YZ450F graphics are availible for a $200 premium. | | |
Two-stroke YZs
2006 Yamaha YZ125
Claimed Weight: 189 lb
MSRP: $5,499 YZ125
Along with all-new suspension, the 2006 YZ125 received some refiniements to its motor for more power across the board. The cylinder head is rounded out and the jetting has been changed for improved low-to-mid range power. For better top-end, the power valve now stays open 500 rpm longer, producing wider peak power (although the peak Hp remains the same). The resulting package should give riders a smoother, steadier delivery with more-broad top-end power that doesn't sign off as quickly.
2006 Yamaha YZ250
Claimed Weight: 211 lb
MSRP: $6,199 YZ250
The suspension and ergonomic upgrades made to all YZs are the extent of changes made to the YZ250. The motor remains the same for 2006. Other minor improvements made to all YZs are a new-design swingarm, new rear tire (Dunlop D-739 to D-756), and reusable neoprene-coated aluminum gaskets for easier maintenance.
The larger clutch quick adjuster dial on all four YZs will be easier for your chubby digits to grasp. | 
Yamaha's changes to the YZ125 promise more power for 2006 - from bottom to top. | 
The '06 eighth-liter power house boasts a rounded head, new jetting and a more generous power valve. |
Four-stroke YZs
2006 Yamaha YZ250F
Claimed Weight: 206 lb
MSRP: $5,999 After the two-strokes moved to the aluminum frame last year, it is now the YZ-Fs' turn to lighten up. The aluminum frame is different from the 2005 YZ version, most noteably by the lack of side cut-outs. To improve handling, the four-stroke frame height is lowered for more-centralized mass. The subframe is also new, with a wider, flatter seat for improved center of gravity.
YZ250F
The changes to the '06 250F continue to focus on creating a more-comfortable ride with a lower center of gravity. The oil tank was lowered and the new crankcase carries its weight lower. A stepped pipe and a change in carb settings create more mid-range power, and a new silencer makes for an even quieter ride.
2006 Yamaha YZ450F
Claimed Weight: 220 lb
MSRP: $6,899YZ450F
The lion's share of refinements went to the big 450. Already with new suspension, graphics and frame, the changes to the 2006 YZ450F continued until Yamaha had an all-new bike. The 450's power house is redesigned with a five-speed transmission, fully-balanced crankshaft for less vibration and smoother delivery, and a new crankcase design with an integrated oil tank for a lower center of gravity.
The YZ450F's five-speed tranny is more versatile, making it much friendlier for off-road use. | 
The new frame and body design on both YZ-Fs focus on a lower center of gravity and centralizing mass. | 
The YZ250F's oil tank was lowered to the front of the frame and is protected by an aluminum skid plate. |
There's more info on the new blue machines to come. Look on Dirtrider.com for info on the 2006 WRs, and Yamaha's newest arrival, the TT-R50. For more info and details on Yamaha's '06 motocrossers, watch the pages of Dirt Rider magazine.