A shootout wouldn’t be a shootout without ranking the bikes from first to last. The truth is that MXA test riders are motorcycle racers first and magazine editors second. We live and breathe motocross bikes, and, because of that, we understand that the ranking process often confuses readers. They claim they want to know what’s good and what’s bad, but if it doesn’t agree with where they spent their $9500, they don’t want to hear it. The MXA wrecking crew wanted to take some of the confusion out of the 2021 shootout season by comparing two of the most popular 450 motocross bikes at one time.

This month, MXA is putting the 2021 Yamaha YZ450F up against the 2021 Kawasaki KX450. Both bikes have strengths and weaknesses—and one bike’s weakness to some may be a strength to others. After hundreds of laps, untold gallons of gas and late hours in the workshop, the MXA wrecking crew did yeoman’s duty to accurately define the differences between the KX and YZ.

2021 KAWASAKI KX450 UPDATES

Here is the quick list of 2021 Kawasaki KX450 updates.

The basic changes were new graphics, over-sized 1-1/8-inch Renthal 839 Fatbars, bigger bar mounts for the bigger handlebars and CT-3-coated piston skirts.

The only significant mechanical change is to the hydraulic clutch. In 2019, Kawasaki introduced hydraulic actuation of the KX450 clutch and, while the hydraulics were good, the left over 2018 clutch was not durable, reliable or well modulated. For 2021, Kawasaki fixed this flaw. The 2021 clutch has a 7mm-larger (146mm) clutch basket, which translates into 7mm-larger clutch plates. The clutch plates’ fiber segments are arranged in an angled pattern to help more oil go between the fiber and steel plates. But, the biggest news is that the KX450 dumped its five individual coil-type clutch springs for a Belleville washer, a la KTM and Husqvarna. Unlike the five separate coil springs on all previous Kawasaki clutches, the large-diameter Belleville washer applies pressure to the clutch pack evenly around its circumference.

2021 YAMAHA YZ450F UPDATES

Here is the quick list of 2021 Yamaha YZ450F updates.

The 2021 Yamaha YZ450F is a BNG bike. It gets new graphics, blue number plates (instead of white) and black fork guards (instead of white.)

YZ450F & KX450 HORSEPOWER

When you put these two 2021 machines on the dyno, their weaknesses and strengths jump off the graph paper. The Kawasaki KX450 is stronger off the bottom (6000 rpm to 8000 rpm), while the Yamaha is much stronger from mid to top (9000 rpm to 11,000). Most racers are laser-focused on the peak horsepower number. The 2021 Yamaha YZ450F makes 58.56 horsepower at peak, while the 2021 Kawasaki KX450 pumps out 55.85 horsepower at peak. Basic math tells you that the YZ450F is 2.70 horsepower stronger than the KX450. But, the power profile isn’t a complete slam dunk for the Yamaha. The Kawasaki KX450 makes more torque than the YZ450F (34.83 pound-foot for the KX450 to 34.36 pound-foot for the YZ450F).  

In the simplest terms, the Kawasaki KX450 is stronger from low to mid and rides the torque and horsepower curve to perfection, while the YZ450F builds power in a very steady progression until it takes off at around 8800 rpm (and peaks at 9700 rpm). There is no doubt that the Yamaha wins the dyno battle (while losing to the KX450 from idle to the mid). 

2021 KAWASAKI KX450 POWERBAND USABILITY

The 2021 Kawasaki  KX450 engine delivers a phenomenally usable powerband. It has a classic snappy feel that mates well with the lighter and more agile Kawasaki chassis. Yes, the KX450 gives up almost 3 horsepower to the YZ450F, but don’t let that worry you. The KX450’s power delivery is brisk, clean and quick. It is a fun 450cc engine to ride, thanks to its fast-revving and ultra-responsive bottom-end that jumps into a steadily building midrange. The KX450 engine isn’t as much about raw horsepower as it is about lively throttle response. Once you get it near 9000 rpm, it plays second fiddle to every other 450 on the track, save for the 54-horsepower RM-Z450. The lesson learned from the 2021 KX450 is that sticking to the torque curve produces more thrust than the horsepower figures would predict.

Paradoxically, the dyno doesn’t do the KX450 justice. Although it is 1 horse better than the YZ450F from idle to 8000 rpm, it doesn’t feel like it. And, while it is very weak above 8000 rpm, it doesn’t feel all that weak.

2021 YAMAHA YZ450F POWERBAND USABILITY

Every test rider was impressed with the 2021 Yamaha YZ450F’s bottom-end power, even though on the dyno it has the least horsepower of any 2021 450 at 7000 rpm through 8000 rpm. Down low, the YZ450F can’t even beat the perennial horsepower cellar dweller, the RM-Z450. It is basically a high-rpm engine disguised as a low-to-mid machine. But, much like the KX450’s horsepower numbers, the YZ450F’s power delivery is better than its stats. The YZ450F powerband has two distinct parts that are so well integrated with each other, you would never notice that the YZ450F is dogging it below 9000 rpm. Above nine grand is where the YZ450F does its best work. Once it gets rolling, it has the power of a runaway locomotive. It has very good straight-line power.

Every MXA test rider marveled at how fast the YZ450F was in a straight line. They loved its building block-style of power, which came on like a crescendo. Then, they would casually say, “But that Kawasaki engine is much more usable.” 

KX450 HYDRAULIC CLUTCH VERSUS YZ450F CABLE CLUTCH

This is no contest. Kawasaki’s hydraulic clutch got a second life when Kawasaki’s engineers realized that hydraulic actuation can’t make up for the flaws of a weak-sister basket, pressure plate and spring system. By upgrading the 2020 KX450 clutch’s mechanical parts for 2021, including enlarging the basket diameter by 7mm, Kawasaki got a victory over the Yamaha YZ450F clutch—that they never would have gotten before 2021. 

The Yamaha YZ450F has always had the best clutch of the Japanese-made “Big Four,” but it can’t come close to matching the longevity, actuation and positive feel of the KTM’s and Husqvarna’s hydraulic units (or even the Honda or Kawasaki units). The tide has turned.

STOCK FORKS VERSUS TEST DEPARTMENTS

The Yamaha YZ450F’s Kayaba SSS forks win this category, but not by the giant margin they used to have in the fork wars. Yamaha wins over the Kawasaki’s Showa forks because their test department did a better job than Kawasaki’s test department in spec’ing the correct spring rate for the average 450 consumer. 

2021 KX450 Showa forks. If you are light or slow, you will love the KX450’s Showa forks, but if you are heavy or fast, you will find them excessively soft. On the KX450 forks, the quickest and cheapest fix is to add one optional 52 N/mm fork spring to one fork leg to get a 51 N/mm spring rate—stiffer than the stock 5.0 N/mm spring but not as stiff as the optional 52 N/mm spring. It should be noted that the Kawasaki, Honda and Suzuki Showa forks are basically the same, but with different valving and oil heights specific to their liking.

2021 YZ450F Kayaba SSS forks. For the last 15 years, one fork has stood head and shoulders above all the other fork offerings. Yamaha’s Kayaba SSS (Speed Sensitive System) forks are foolproof. No need to send them out for a re-valve unless you are Richie Rich, incredibly fast, heavier than your doctor likes or allergic to turning clickers. You can race them as they are.

SHOCK VERSUS SHOCK IS A PUSH

Shock tech has advanced farther than fork tech on the production lines, and both the YZ450F and KX450 have acceptable rear suspension. 

Kawasaki Showa shock. The Kawasaki shock worked well from day one, helped by 2019’s new linkage and 105mm of sag. The KX450’s Showa shock was easy as pie to set up. The rear end exhibited minimal wallowing and worked very well under braking in chop and square-edged bumps. Light riders, under 150 pounds, might want to switch to the optional
52 N/mm shock spring. 

Yamaha Kayaba shock. The Yamaha shock is amazingly versatile. It seems capable of working for a 200-pound rider or a 150-pound rider with nothing more than a few clicks by a flat head screw driver. 

Good stuff on the rear of both the KX450 and the YZ450F. 

FASTER IS EASY; BETTER HANDLING IS HARD

The Kawasaki KX450 wins the handling category. It is a very agile bike in comparison to the YZ450F. With its more pleasant powerband, the KX450 is easier to move around on the track. It makes picking lines a snap. It has a deft touch at turn-in and doesn’t lift and drift on corner exit. Of all the Delta-Box aluminum frames, which is every one save for the old-school YZ125 and YZ250 plug-and-play aluminum frames, the KX450 is the most forgiving.

You might be tempted to quote that the 2021 YZ450F is “the best-handling YZ450F ever,” but that isn’t a hard target to hit. Beating the previous decade of YZ450F handling is not a difficult task. Prior to the 2020 model, all YZ450Fs were massively flawed chassis that repelled all efforts to get them to hold a line on corner exit or stop wiggling on corner entrance. Most of the improvements in 2020-2021 Yamaha YZ450F handling are attributable to the Yamaha engineers toning down the low-to-mid power delivery. The more metered power output of the engine resulted in snappier turn-in, improved manners on corner exit and upgraded front-tire accuracy. The old hard-hitting engine was not a friend of the pre-2020 YZ450Fs. And much of the bulk of the YZ450F chassis worked against the YZ450F being at the top of the handling charts.

THE SCALES OF TRUTH

The Kawasaki KX450 hits the scales, without fuel in the tank, at 234 pounds. The Yamaha YZ450F weighs 238 pounds. The 4-pound weight difference feels like 10 pounds on the track. You can feel the YZ450F’s weight when loading your bike, when pushing your bike, when turning your bike and when hitting bumps on your bike. Worst of all, the YZ450F’s rims, spokes, brakes, forks, frame and springs have to stop, start, accelerate and absorb that weight thousands of times a lap. 

Lighter is better, and if 233 pounds is better, then imagine how much easier it is for an R&D department to work with 223 pounds. Yamaha riders defend the extra lard by saying that “it feels light in motion.” We suppose that somewhere around 140 mph it would feel lighter.

The Kawasaki KX450 feels lighter because it actually is lighter.

PUCKER UP

Yamaha wins this category. Last year Yamaha increased the front caliper’s piston size from 22.65mm to 25.4mm, made the front brake pads 29.2 percent larger, enlarged the front rotor’s surface area by 16 percent, and reduced the size of the rear rotor from 245mm to 240mm. It was a big step up in pucker power to the YZ450F. While Kawasaki’s front brake is good (after you bleed it the first time), its rear brake is atrocious. The jumbo-sized 250mm rear rotor is too touchy. It locks up because it is too aggressive.

MXA was surprised that Kawasaki didn’t replace the oversized 250mm rear rotor for 2021 with a smaller 240mm rotor. After all, they know better, made obvious by the fact that the 2021 Kawasaki KX250 and KX450X come with the smaller 240mm rear rotor.

ERGONOMICS, MOTOCROSS BIKES & THE HUMAN BODY

The Kawasaki KX450 wins this category, not because it has amazing ergonomics, but because a swayback horse has better ergonomics than the 2021 Yamaha YZ450F. Ergonomically, the Yamaha YZ450F doesn’t seem to have been designed for the human body; more likely for an orangutan. The seat feels like the rider is sitting in a hole. The gas tank splays the rider’s legs outward. The stock bar position is very weird. The short Yamaha shift lever doesn’t work well with boots larger than size 10, and the YZ450F bombards the rider with blaring noise from both the pipe and the airbox at the same time. The 2021 Yamaha YZ450F accoutrements are ungainly.

RELIABILITY & YOUR WALLET

Yamaha wins this category. MXA has had Yamaha YZ450Fs that we’ve put over 100 hours on without them blinking. Our track record with the KX450 is that it blinks more often.

THE BEST OF…

The $9399 2021 Yamaha YZ450F has great straight-line speed, superb box-stock suspension, decent brakes, Wi-Fi mapping (although we’d prefer that Yamaha put the TP-3 map in one of the two-position map switches instead of two stock maps so that most riders wouldn’t have to map their YZ450F’s with their phones) and bulletproof reliability.

The $9399 2021 Kawasaki has extremely usable power, agile handling, a strong hydraulic clutch, plug-in coupler mapping (we run the white coupler in loam, the green coupler on intermediate dirt and the black map on ice, glass or when we just want to give up a bundle of horsepower) and it’s light compared to the 2021 Yamaha YZ450F.

THE WORST OF…

The 2021 Yamaha YZ450F is a tub of lard (in motion or sitting still). The air filter/airbox is a terrible design and the seat foam is wimpy, but most of all, the YZ450F is too big, too bulky, too wide, too tall and too heavy. The ergos of the 2021 YZ450F could only be liked by someone who owned the previous YZ450F (because it is better than anything before 2020). The backwards engine may have centralized the mass of the Yamaha engine, but obviously the engine is too heavy.

The 2021 Kawasaki needs stiffer fork springs (or valving), a rear brake pedal with more adjustment, a smaller rear brake rotor, plastic that doesn’t crack, chain rollers and guides that don’t wear out in two hours, and more than 55.85 peak horsepower (if the KX450 wants to run with its 58-horsepower competition).

The yellow boxes highlight the winner of each category.

AND THE WINNER IS…

This is a touchy test because neither bike is much changed from last year (with the exception of the upsized KX450 clutch basket and plates). So, there is nothing really notable on the specs to think that these two bike would finish any higher up in 2021 than they did in 2020—except for wishful thinking. In fact, they might even slip down the rankings because of the relatively benign neglect of the limited updates.

In short, the KX450 is a much more pleasant bike bike to spend time on, once you fix a few suspension, brake and set-up flaws. However, the Yamaha is considerably faster, more reliable and better suspended—and if you race motocross, those positive YZ450 traits pay bigger dividends than the KX450’s pleasant demeanor.

Thus, we’d rather ride the 2021 Kawasaki KX450, but we’d rather race the 2021 Yamaha YZ450F.

2021 YAMAHA YZ450F VERSUS 2021 KAWASAKI KX450 SHOOTOUT VIDEO: WHICH ONE IS RIGHT FOR YOU?