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posted January 06, 2006 12:21 AM        
2006 Yamaha YZ450F - First Ride

2006 Yamaha YZ450F - First Ride
By JC Hilderbrand

I've already had the chance to ride a new 450cc four-stroke (KX450F) at Competitive Edge MX track in Hesperia, CA, so to do it again on another brand was a real treat. Yamaha recently brought out its all-new YZ450F for the media to drool over and pound out some laps in the sandy loam. Though I was there before, this experience was entirely different.

Barely anything on the new YZ-F is the same as on the '05 model. With 300 new parts on the 2006 bike, 96 of which are in the motor alone, 2005 owners who were looking forward to snagging parts off their buddy's new steeds will be disappointed to hear that not much is going to fit their year-old ride. All those little design changes might not mean a whole lot individually, but there are some major alterations and changes to the new 450 that will have a big impact on the blue faithful.

"The goal of this machine is to be easier to ride," said Yammie PR man Terry Beal. Having heard horror stories of the burly '05 motor, I was a little worried about the effects that would have on my chronic arm pump. Knowing full well that anything with more motor than a 15-speed Schwinn has the capability of locking me up solid, I was happy to find that the new 450F is capable of kicking ass on the track without doing the same to its rider.

In the effort to smooth things out, Yamaha started with a lightweight aluminum chassis, slapped in a 5-speed tranny, new carburetor settings, different Kayaba suspenders and re-designed bodywork. Some of the changes are the same as on the new YZ250F that we rode awhile back.

The big news on everyone's list of course is the aluminum frame that graces both YZ-F models this year. With the release of the new chassis, Yamaha is now fully committed to aluminum frames on its entire full-size motocross lineup. The YZ450F was the last of the big Thumpers to be released this year, but it completed a clean sweep of Japanese aluminum frames. KTM is the only manufacturer to hold back against the rising tide of lightweight, rigid twin-spars. Like it did with the 250F, Yamaha remains unique by having resisted the urge to clone Honda's ground-breaking design that Suzuki and Kawasaki have closely matched.

However, just because it looks different doesn't mean that it doesn't work. Forged, cast and extruded components create a stiff chassis that is predictable, light and flexible where needed. Some vibration is transferred to the rider's hands, but much of that could lie in the suspension setup, handlebars or crappy grips.

The YZ's center of gravity has been lowered by dropping the height at the steering pipe, subframe mount and pivot position. To match the new frame, the subframe was modified along with the seat position and foam thickness. All told, the seat height has been dropped a claimed 20mm. With 95mm of sag in the rear shock, the seat height was comfortable and effective. The claims of a lower center of gravity seem to hold true once the bike gets moving as the Kayaba suspension helps create a well-balanced package. Knifing into a corner feels steady yet responsive with 27 degrees of rake and 4.5 inches of trail, and the frame spars give good grip at the legs for excellent control.

The bike is very light in the air and a claimed dry weight of 220 pounds (identical to the KX450F) didn't seem too outrageous as I styled my way around the track. Even though I wasn't actually whipping it sideways, I could definitely feel how responsive the chassis is in the air. For a demonstration, just watch Chad Reed at the next supercross since he's elected to ride the 450F in the tight, aerial confines of the AMA Supercross class.

Another monumental change for 2006 lies in the gearbox. For the first time on the YZ450F, Yamaha has mounted a 5-speed transmission to its biggest MXer. A 5-speed hasn't been seen since the '02 YZ426F model, but the 450F does in order to appeal to a wider variety of riders and riding applications. The new tranny is the reason for many of those new engine parts. Engine cases are all-new to accept the extra gear, and an oil reservoir is tucked away in there as well since it was previously held in the steel frame. Apparently fourth gear wasn't fast enough for the non-MX community, so Yamaha obliged with an additional upshift. The new transmission worked just fine on the flowing, natural terrain of Competitive Edge. With a mix of big tabletops and step-downs, the bike took a little more shifting than a 4-speed to make me comfortable, but in retrospect I don't think that all my left-foot action was really necessary.
Like with any bike, it pays to keep the motor thumping through the meat of the power, which in this case lies right in the thick of the rpm range. This is a 450, though, so it can pull a gear high without any problem. However, I'm a short-shifter by nature and I didn't feel as comfortable lugging the YZ-F off jumps as usual. Still, the 449cc DOHC motor pumps out plenty of power. It doesn't start with a big hit off the bottom, but the bike gets up to speed quickly and then launches forward as the revs climb through the midrange. The motor doesn't suffer from any hiccups along the way as the throttle position sensor feeds fuel consistently through the 39mm Keihin flat-side carburetor.

Bore and stroke remain the same for '06, as does the 12.3:1 compression ratio. What has changed though is the exhaust system which features a redesigned aluminum can with a 7% increase in glass wool volume. A 1.5mm smaller mid-pipe is said to increase tractability, while the new can tones down the exhaust note and actually looks good. Engineers were able to save weight with titanium valves, a smaller cam-chain tensioner and oil pump, lighter front wheel hub and titanium exhaust components including the header, flange, bracket and heat shield.

The 450F gets the same suspension treatment as the YZ250F, with a new speed-sensitive 48mm Kayaba fork replacing the position-sensitive '05 design. Internally, the spring has been polished and its position altered. A friction-reducing coating has been added to the upper chamber and a new piston and oil seal installed. The fork's oil capacity has been increased 120cc and its compression piston jumped up from 28mm to 32mm. All in all, the new Kayaba fork works very well. The stock compression setting of 11 clicks out was too stiff for me so I softened it up two clicks. As for rebound, the stock number was sufficient to keep me happy all day.

Bump absorption is very good on the 450F, handling the smallest chop and big braking bumps with a confident feel. Once I softened the compression, the initial harshness and vibration was noticeably reduced. After that the fork was very supple and still cornered sharply and acted predictably on jump faces. Slap landings, which I seem to have an affinity for, weren't nearly as rough as I thought they would be.

On the rear end of things, more Kashima non-friction coating was used in the matching Kayaba shock. Its reservoir capacity also got a volume increase of 30%, and the rod diameter swelled 2mm to 18mm. As far as visual changes, the shock spring is made of titanium this year giving the 450F a serious boost on the trickness scale. Not only does the spring look cool, but Yamaha claims that it weighs roughly 30% less than the '05 steel version.

More oil, cool metal compounds, beefed up parts, what does it all mean? It means that Yamaha and Kayaba did their homework and gave the 450F a shock worth mating to the excellent fork. The suspension was initially too stiff for my liking (or lack of speed, however you want to look at it). It felt like the rear tire had too much air in it, causing the rear end to slide around under acceleration and to break loose when braking into corners. Softening the compression two clicks was again the solution to my problem, and from then on the rear worked in perfect compliance with the fork and chassis. I never bottomed out or had a rough deflection on big holes or g-outs.

Heaps of minor changes made the list for both YZ-Fs including: a switch to Dunlop's D756 rear while leaving the D739 up front, a new front brake lever, larger clutch adjuster, ProTaper handlebars, different brake pad material, revised rear brake caliper, tapered rear wheel collar and new body styling all around. Yamaha is celebrating its 50th anniversary by offering a limited production alternative color and graphics kit that takes us back to the glory days of Bob Hannah, Broc Glover and Rick Burgett, the days when men were men and Yamahas were yellow and black. Yamaha's in-house hop-up department also offers a bunch of GYT-R products to help customize a new $6899 YZ450F.

Even though Yamaha was the last manufacturer to reveal its new 450F model, it has kept its name in the hat as a viable contender for big-bore American titles in 2006. Chad Reed picked up the 2004 AMA Supercross Championship for Yamaha, but that was on a 2-stroke. Heath Voss snuck out of 2004 on his YZ450F with a World SX title, but the big names weren't there, so that doesn't really count either.

The biggest triumph to date for the big, blue Thumper came in 1998 with Doug Henry's monumental 250cc AMA Motocross championship aboard the flagship YZ400F. After spending 2005 just outside of the limelight, maybe Yamaha's cast of veteran riders will have the same experience as I did aboard the 2006 YZ450F; something entirely different from their last.

Source: http://www.motorcycle-usa.com/Article_Page.aspx?ArticleID=2739&Page=1#

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