It used to be that racing the 125cc class meant an ongoing search for horsepower. Whether the rider was a top professional or a local beginner, one-two-fives everywhere were looking for more ponies across the board. Nowadays the 125cc class, or rather the AMA Lites, is simply looking for an actual 2-stroke still among the ranks. Yamaha's introduction of the YZ250F was the beginning of the end for 125s, and the blue company isn't cutting the remaining tiddlers any slack in 2006.
After redefining the motocross world in 2001, Yamaha has redefined the YZ250F for '06 with a ton of changes including major chassis, suspension and exhaust development that make the new model a serious force to be reckoned with in the world of 250Fs.
First and foremost lays the most obvious change in the form of an all-new aluminum frame. Instead of going the twin-spar perimeter route like Honda and Kawasaki, Yamaha opted to utilize a similar style to that of its own aluminum-framed 2-stroke YZ line, which is a variation of a traditional double-cradle frame design. Nine pieces of forged, cast and extruded aluminum combine to give this year's frame the same vertical rigidity as the '05 model and even more twist rigidity, according to Yamaha. The waffle-like frame indentations on the exterior of the 2-stroker's frames face inward on the 4-strokes, leaving a smooth exterior frame finish.
Yamaha engineers managed to drop the overall center of gravity on the 250F by lowering the steering pipe location, subframe mount and swingarm pivot position; rake and trail remain virtually unchanged at 27.0 degrees and 116mm, respectively. Not only was the center of gravity affected, but the ride height was moved closer to the ground as well as a result of the changes. Combined with a new subframe and seat to match the frame, the overall seat height has been lowered 20mm. Despite this reduction of nearly an inch, the gripper-covered seat has 30mm taller foam and a flatter layout to give riders more freedom to move around. The airbox and side panels are also new to work with the subframe.
Oil, once stored inside the previous steel frame, is now carried in a tank at the bottom of the engine between the lower spars of the frame. Out in front and just begging for a big rock, Yamaha added an aluminum skidplate to protect the blue beast's soft underbelly. In conjunction, the crankcase was re-shaped to adjust for a different oil pick-up, and a window gauge was put in on the left side for quick reference.
The new titanium Kayaba shock spring and aluminum chassis combine for excellent rear-wheel traction. This thing hooks up!
The refreshing chassis design works as well as it looks, as we found out when we ventured out to Honey Lake Motocross Park near Reno, Nevada, for the YZ250F press introduction last week. Braking bumps and chatter aren't delivered to the rider, and the bike felt strong and rigid even as I continually cased the back-section double, lap after lap. Handling is also very predictable. As with any bike, these characteristics are directly affected by the suspension components, which we'll explore further in a minute.
Remember our little discussion before about small-bores' ongoing search for horsepower? Well, even though 2-strokes are basically a thing of the past in the Lites division, power still reigns supreme on smaller bikes regardless of the sound they make, and the Yamaha produces plenty, keeping in mind the 15%-or-so blunting of power due to Honey Lake's 4000-plus-foot elevation.
To get an idea of what we're talking about here, just think back to all those pictures you might have seen of guys on extended-swingarm, over-bored CR500 hillclimbers roosting straight up a vertical cliff; the ones where it's so steep that safety workers rappel down the mountain in hard hats to catch the poor bastards when they fall. Well, Honey Lake isn't quite that steep, but its uphill section is definitely a no-fall zone. From the starting gate the course takes you from 4100 feet in elevation to 4600 feet at its highest point, and it doesn't waste any time getting there. Near the bottom, at the end of an S-turn, lock your wrist back, point straight ahead and row through the gears and you'll soon find yourself 400 vertical feet higher.
Luxury in the motocross world is a comfortable, roomy cockpit. Lots of mobility in the saddle is a plus for all type of terrain. The Yamaha has plenty.
The meat of the YZF's power is in the midrange, where Yamaha made several changes to find gains. There's a new needle inside the 37mm, flat-side Keihin carburetor, and the main jet went from a 182 to 178. A throttle-position sensor also graces the carb for better throttle response.
The biggest midrange boost comes from a redesigned exhaust. From the titanium header back to the aluminum silencer, the pipe undergoes four changes in diameter. Thankfully, Yamaha also changed the YZ's muffler to eliminate that goofy snorkel that protruded out the rear of the '05 model. Inside the silencer, the volume of glass wool has been increased 7% to help decrease noise output. Overall, the tone of the bike seems fairly reasonable, though only time will tell how offensive outsiders find the 2006 crop of 250Fs.
Off the bottom, the YZF makes good power but the powerband really shines as it builds revs. There isn't a big hit that signals the beginning of fun-time or a huge face-plant at the end, but I always shifted the five-speed before getting too far into the over-rev and the 13,500-rpm rev limiter. Honey Lake's nearly mile-high elevation was mostly to blame for my qualms about top-end power.
If I didn't get a good enough drive approaching the big hill, fourth gear would get me there feeling like I needed to downshift. Still, I felt slower tapping it into third and screaming over the top as opposed to keeping the momentum at a lower rpm. Don't get me wrong, the 250F makes great power and toted my chunky ass up that hill at a very respectable pace regardless of gear selection. The best thing about this engine is that it lets you ride all day without making you work too hard for it.
Overall, the YZF's suspension package proved to be very good. I would like to call it terrific, or even amazing, but the reaction from myself and that of MCUSA's photographer/co-test pilot were different enough on several points to illustrate that the Kayaba components don't work the same for everyone.
Thanks to a nimble chassis, changing lines on this chopped-out straight wasn't a problem for the 250F.
In 2005, Yamaha employed a position-sensitive fork where damping force was much higher on high-speed piston movement but tapered severely during low-speed action. For '06, Yamaha changed to a speed-sensitive unit in which damping is now dependant on the speed of compression, and it creates more consistent action across the spectrum.
The front end felt superb in bottoming resistance and on rough, chopped-out sections, though I have to say its stability came into question in the hands of lensman Maddox. Under his slightly quicker pace, he suffered from an unsettling case of headshake on the big uphill and on a few of the straights littered with acceleration and braking bumps.
As the day wore on and I wore out, I did begin to notice a little nervousness in the front end through a faster section, but I'm talking about a fourth-gear-pinned straightaway that would make most dirt bikes dance like a redneck at a Willie Nelson concert. As scary as that may seem, the Kayabas did a fair job of minimizing the impact of the high-speed whoops, but my balance was sometimes thrown off in a section where a couple of bigger whoops transitioned into a series of small ones. If I dropped that front Dunlop 739 into the face of the treacherous sections, the handlebar would sometimes twitch nervously all the way through.
Nobody likes to get their pumped-up arms yanked violently and unexpectedly at eye-watering speeds, but I really felt like the problem was a result of rider error more than a flaw in the suspension. I went through the tough sections every lap, and more often than not it wasn't a problem for me. Even though the fork has been changed radically, including a 120cc larger oil capacity, the .44 kg/mm spring rate is the same as last year.
The rear shock is completely new for '06, highlighted by a titanium spring that Yamaha claims is nearly 30% lighter. The spring rate jumped up from a 4.9 to 5.1 for '06 and the rod diameter grew 2mm. Yamaha also enlarged the reservoir size by 30%.
The new speed-sensitive Kayaba fork works wonders on the track. With the exception of one gnarly whoop section, the front end never danced or skipped, soaking up everything in its path.
On the track, the shock works flawlessly and the rear end tracked well everywhere. It would bottom in a g-out at the base of the big uphill, but there was no violent clank or metal-to-metal action. The rear never skipped a beat and it ably puts the power to the ground. A Dunlop 756 rear tire, one of my favorites, gives excellent drive out of corners. I'm not sure why Yamaha didn't match the tire with the same model number up front, but the front 739 was mediocre.
Rider controls are top-notch this year with titanium footpegs and a light and airy feel in the cockpit thanks to a set of oversized ProTaper bars. Things have been spaced out even more by moving the bars forward 10mm. Riders can move the bars rearward by spinning the adjustable handlebar clamps 180 degrees, but I didn't even try it because the stock placement was so comfortable.
I was stoked to get my first chance at testing the ProTapers, a bar I've heard a lot of good things about. I'd say that those things were all true since I absolutely loved them. Their neutral shape suited my style and vibration damping was great. I was in no hurry to fully test their crash-resistance with a massive digger, but they did survive a little low-side in a corner that might have tweaked a cheap steel set.
Revised styling gives the YZF clean lines in'06. Starting with a new front fender and angular front number plate, plastic bodywork across the machine is changed to fit the new chassis as well as for aesthetic appeal. Some of the other 250Fs on the market are pretty radical looking for 2006, but Yamaha isn't being excluded from the eye-candy list. For an extra 200 bucks on top of the basic $5,999 MSRP, buyers can get the 50th Anniversary retro yellow/black combination that Team Yamaha sported at the Unadilla round of the AMA Motocross Nationals this summer. Combine an old-school color scheme with a new-school aluminum frame and the result is bitchin'.
Firing the 249cc, five-valve DOHC engine was never a problem, despite its 12.5:1 compression ratio, thanks to an automatic-decompression system and a redesigned kick start lever. The bike is pretty good about not stalling in the corners, but the relatively weak brakes could be helping there. The 250mm floating front disc and twin-piston caliper worked well enough, but I felt like I had to pull the front brake lever, which is wider than the'05's, harder than I wanted to in order to make it perform. Coupled with a 245mm rear disc, the brakes will bring you to a halt, but not in any extraordinary fashion. When the bike did stall out mid-moto, the hot-start lever attached at the clutch was simple and effective.
It'll be a throw-down when MCUSA gets all the 250 4-strokes together for a shootout.
Although a 4-stroke is torquier than a two-stroke, I found the YZ250F really came alive when I rode it like a small-bore 2-stroke. Motor-wise, pay attention to the gear you are in and your life will be much easier. The motor is strong, but not so much that you can get away with riding mindlessly on high-elevation tracks like Honey Lake. The bike is light and thin, so it begs for you to get aggressive. Suspension and chassis components can handle anything you dish out, so it's easy to get away with slamming it into berms and jump faces or dropping into a rut. Compared to the new KX250F I rode a few weeks ago, the YZF seemed to handle better and I preferred its ergonomics.
We enjoyed our time on the '06 YZ250F, but it's hard to say at this point how it stacks up against its competitors, especially when pit against each other at the same altitude. Stay tuned for an MCUSA shootout later on this fall. As for now, we're satisfied that the little Yamaha is continuing its revolutionary ways.
The Yamaha is high on fun-factor and, best of all, I could ride it all day without feeling like I introduced myself to a Freightliner's front grill. Given its performance at a higher elevation than we're accustomed to, we can't wait to get the bike back home and throw in a little woods action along with our local tracks to test its versatility. But from our first experience on the YZF, we can say that it could be leading the pack in '06.
Let us know what you think about the 2006 Yamaha YZ250F
in the MCUSA Forum.