You'd be hard-pressed to see the changes Yamaha made to the 2008 YZ450F. Aside from the obviously shorter muffler it'd take setting a '07 and '08 side by side to give up the visual clues that are strikingly inconspicuous. However, it doesn't take but one lap on the new bike to feel the changes, which are way bigger than they look. Good thing Yamaha dropped a "Product Improvement Guide" with the bike so we could have all the little things listed.We won't bust on the new PR flack for not telling us exactly how many changes the company made to the bike; the old PR guru used to count every one, stretch the truth a bit and give out an inflated number. Even if it was 65 changes and the only real difference was new graphics, he'd drop a number like 377 changes. We took a white YZ450F this year just to have ours look different, too.The biggies are a revised frame to tune the flex, a science that is becoming more exact each year. Detailed tuning even trickles into the triple clamp where an H-section shape is adopted. Next, a big effort was made to reduce the weight, specifically weight at the outer extremities of the bike, like the muffler with its new shorty design and mechanical sound damping system and the fork lowers plus the axle. Wide was a theme, with a wider Dunlop 120-80/19-inch D756 rear tire and a set of wider footpegs to boot. The front tire switched over to the D742FA. Yamaha is sticking to Dunlops on the 450 this year while going to Bridgestones on the 250F.While riding the bike, three big things jump out at you. First, it feels lighter-a lot more than the scale registers. Our bike scaled in at 231 pounds with no gas-a pound lighter than our 2007 machine. Through the bar the bike has an airy feel to it, the side-to-side flickability is impressive and the Yz feels more agile when bouncing. The difference is felt way more than that scale-indicated pound. There is a bit more of a stiff sensation to the front of the bike through the fork, but it does not act stiff when riding. Lighter-feeling bikes often have a stiffer or less planted sensation at low speeds, and this is consistent in our initial testing of the new big daddy of YZ-F land. At speed, this bike is way planted and the best turning YZ450F by far. None of the 2006's vague front end traits are evident, and it makes a leap from even the adequate '07 model. Who says moving in and lightening up the ends of the bike (muffler, fork, wheel, spokes, axle) as well as tightening the center of gravity don't make a big difference? Simple things, such as changing the bracing on a triple-clamp lower, can make a difference.Next is the power. Yamaha added some snap with the new shorty muffler, which is surprisingly quiet for its size due to the mechanical damper inside. It meets 99 decibels and is just a little louder, mostly at low rpm compared to last year's unit but is plenty acceptable for our strict ears. Somehow Yamaha kept the smoothness that we loved but added some spice. The pull is linear, progressive and long-winded. Keeping the front end down was an issue; don't let the ride height get low, or keeping the front tire on the ground becomes a real problem with the new power delivery. A host of engine updates is held responsible. New cams, with altered carb and CDI settings, along with the new pipe and muffler add up to a robust powerplant that suits a lot more riders than either of the two previous YZs were capable of doing. It bridges the aggressive 2006 and the mellow 2007 making a near perfect combination of both. Our only issues were for more aggressive or much heavier riders, who were thinking an extra tooth on the rear sprocket would add just the boost they were looking for. Internally, there are a few changes to keep the engine noise down, but we couldn't tell when riding. The nice-looking black clutch cover has plenty of showroom bounce, but it shows you rode the bike after the first few uses.