2015 Suzuki RM-Z450 Review

While no official word has yet come down from on high, it appears as though Suzuki has scored a coup by luring former factory Suzuki star (in Europe) and newly crowned Lucas Oil 450cc Pro Motocross Champion, Ken Roczen, to contest the 2015 Monster Energy AMA Supercross and Lucas Oil Pro Motocross series aboard the Yoshimura factory bikes. It’s a big deal that probably wouldn’t have happened if Roczen had any doubts about the potential of the factory RM-Z450. After all, he watched James Stewart win multiple supercross races and one outdoor national aboard the machine in 2014. It’s clear that the Suzuki RM-Z450 can win races, and Roczen’s pedigree is not in doubt.

Suzuki is obviously trying to set the table for its first AMA Championship in the premier class since Ryan Dungey’s sweep of both the supercross and motocross titles in 2010, and an effort clearly has been made to improve the 2015 RM-Z450 to give it an edge with the team’s new ace. With an all-new Showa SFF-Air fork and the new Suzuki Holeshot Assist Control among a list of improvements great and small, the potential for glory is high indeed.

Mechanically speaking, Suzuki made significant changes to the RM-Z450’s fuel-injected, DOHC, 449cc four-stroke Single for 2015. Surprisingly, however, no effort was made to extract more horsepower from its big-bore/short-stroke package. Suzuki engineers remapped the 450’s ignition and Keihin fuel injection, which utilizes a 44mm throttle body with a 12-hole fuel injector, in an effort to coax more low-end and mid-range grunt from the engine. Beyond that, a redesigned muffler was fitted to reduce the 450’s noise output and keep it AMA-compliant. The RM-Z’s coolant system is claimed to be more efficient because the coolant is now more effectively routed between the right and left radiator halves while the RM-Z’s water-pump cover hose connection directs coolant directly into the water-pump.

There is a new technology related to the RM-Z’s engine, though, and it is aimed at giving riders a greater degree of control when firing the big RM-Z out of the gate. It’s called the Suzuki Holeshot Assist Control (SHAC) system, which features two modes that alter ignition timing – effectively becoming a “launch mode.” In A Mode, the RM-Z retards the ignition to minimize wheel slip in hard-packed or slippery conditions, while B Mode offers more aggressive mapping for high-traction conditions. Once the rider dumps the clutch, the SHAC returns the ignition timing to the stock mapping after 1.2 seconds or after third gear is engaged. The system is activated by a button on the left-side handlebar, and it can be completely disengaged if conditions warrant it.

The RM-Z450 is also now easier to start than ever, thanks to a redesign of its kick-starting gears. Suzuki engineers attempted to improve the 450’s cranky starting habits with the 2014 model by reprogramming its Electronic Control Module (ECM) to retard the ignition and eliminate an unwanted extra spark that was being thrown out during the exhaust stroke. The spark was igniting unburned residual gases in the combustion chamber and made starting a dicey proposition—not a good thing if you’re quickly trying to get back in the race after stalling or crashing. The new ECM appeared to help, as we had no trouble getting the 2014 to start, but apparently that wasn’t good enough for Suzuki. For 2015, the RM-Z450 also gets a 30mm longer kickstart lever and a revised kickstart idler gear along with an updated de-compression system plus a redesigned exhaust camshaft to make starting the bike even easier. Suzuki officials are so proud of these changes that they claim the 450 can now be started by hand even when hot, and we can report that even a half-hearted boot is enough to get the big motor roaring to life.

COMPARISON: Read our review of the 2013 Honda CRF450X

As 450s go, the 2015 RM-Z450 produces solid grunt, but other 2015s we’ve sampled recently outshine the Suzuki off the bottom and into the midrange. The RM-Z is far from slow. All but a pro-level rider would have a hard time riding it to its potential. Then again, our test rider, Ryan Abbatoye, is a pro-level rider, and he said that some guys in his stratosphere (our word, not his) might still wish for more grunt – particularly down low.

Similar to the power character of the RM-Z250, the 450 is linear and responsive everywhere, but it really likes to be kept in the middle of the powerband for maximum effect on the track. Abbatoye found that short-shifting its slick five-speed transmission is the key to success because the 450 engine tends to run through its rpm range and kiss the rev limiter rather quickly on the track. The RM-Z450 boasts easy-riding power, but more low-end torque and a broader pull would be a welcome improvement that wouldn’t necessarily hurt its character and might even make it more user-friendly. Abbatoye was happiest when he swapped to the RM-Z’s “fast” ECU coupler, which delivers a richer fuel setting throughout the rev range. Suzuki’s coupler system makes altering the RM-Z450’s powerband easy. A swap takes mere seconds to complete, and the modules can be reprogrammed using Suzuki’s accessory software.

Dyno testing confirmed Abbatoye’s seat-of-the-pants impressions. Our RM-Z450 test bike produced 49.5 peak rear-wheel horsepower at 8750 rpm, with 31.5 ft.-lb. of peak torque at 8000 rpm. The Suzuki maintains 30 lb.-ft. of torque from 6500 rpm to 8500 rpm, proving that it is a midrange monster. It then flattens out on top before the rev limiter steps in to halt the proceedings at 11,000 rpm. The numbers show that the RM-Z is strong, but it isn’t the strongest 450 in the class. The torque figures also show that it is making its best power right where Abbatoye said it did.

Power isn’t everything, especially in an open-class motocross machine. Nabbing the holeshot can be a huge advantage, but arm-stretching power can take its toll over the course of a long moto. Handling is just as crucial to overall performance as brute power – maybe more so in a class where an overabundance of power already exists. Fortunately for Suzuki fans, the RM-Z450 carves like a precision pen writing cursive. Whether in berms, sweepers or off-cambers, and regardless of whether the terrain is loamy or hard-packed, the Suzuki rails around corners like it is on a train track. Its steering is light and laser-like, and the RM-Z’s twin-spar aluminum chassis still retains rock-solid stability in fast chop. Abbatoye said that, while the 2014 model already handled amazingly well, the 2015 handles even better.

COMPARISON: Read our review of the 2014 Yamaha YZ450F

The key to the 450’s improved handling, says Suzuki, is a redesigned frame that reduces weight by 4 percent, with retuned flex points making the bike more compliant over rough terrain. Our 2015 test bike tipped the scales at 248 lbs., with its 1.6-gallon aluminum fuel tank topped, and the RM-Z450 places 119 lbs. of that weight on the front wheel and 129 lbs. on the rear wheel for a 48%/52% front/rear weight bias.

“The new chassis has a lot more flex to it, which takes away some of the harshness,” Abbatoye noted. “Overall, it just feels like a huge improvement over the 2014.”

Of course, some of the new RM-Z’s handling improvement can also be attributed to its trick new 48mm Showa SFF-Air Fork, which replaces the previous Separate Function Fork. However, the Suzuki version differs from the Honda and Kawasaki versions by virtue of the fact that its third air chamber—a.k.a. balance chamber—is external, located at the bottom of the right fork leg. Suzuki tested its version of the SFF-Air on James Stewart’s factory Yoshimura Suzuki throughout the 2014 season before pronouncing it ready for production. Like the other brands that have made the switch, Suzuki claims a 2.5-lb. weight reduction as well as more incremental adjustability as the primary factors in going spring-less up front.

The SFF-Air fork is matched with a rising-rate rear suspension linkage and Showa piggyback rear shock that features high- and low-speed compression damping adjustability as well as rebound damping and spring preload adjustability to control its 12.2 inches of travel.

Abbatoye noted that the fork felt a little harsh initially and was riding too low. Adding pressure to the balance chamber raised the ride height and also brought the fork into better sync with the rear end. After that, all it took was a slight increase to the rebound setting on the fork to make the big Suzuki perfectly compliant over the whole gamut of suspension loads, including small bumps, spike hits, g-outs and everything in-between. The Suzuki’s on-track behavior proved just how much easier it can be to dial-in the suspension with an air fork – that is, provided you have the special air pump required to make the adjustments. Rather than throw one in at the point of sale, Suzuki requires that you buy its pump as an accessory. That’s none too cool, even if the fork itself is pretty cool.

COMPARISON: Read our review of the 2014 Kawasaki KX250F & KX450F

“I like the new SFF-Air fork, but I am an off-road guy, and for off-road I haven’t been able to trust them,” Abbatoye said. “Now, with the triple chamber, at least it seems like if you lost air pressure they wouldn’t collapse. Overall, the new RM-Z’s just a lot more composed than the 2014 bike. Suzukis have been known for good turn-in, but with the 2014, over the fast stuff it was kind of nervous. With the new fork and revised shock valving it is really stable.”

Adding to rider confidence is a comfortable ergonomic package that makes it easy to maneuver the RM-Z450. Perched 37.6 inches off the ground, the seat is flat and slim. The RM-Z’s bars are also positioned well, allowing the rider to feel comfortable when seated or standing.

Abbatoye also noted that the RM-Z450′s front and rear wave-rotor disc brakes, measuring 250mm up front and 240mm out back, do an adequate job of hauling the RM-Z450 down from speed. In a time when other brands are stepping up to oversize front rotors, the Suzuki gives nothing away in the power or feel department—at least for now.

Our overriding impression is that even though it didn’t get a huge power boost for 2015, the RM-Z450 is still substantially better than the 2014 model. Its chassis feels better, its suspension works better, and it may just be the best handling 450cc motocross bike available. With an MSRP of $8,749, it’s also a pretty decent bargain. That said, we won’t be surprised to see a lot of yellow-hued bikes circulating the nation’s motocross tracks next summer, nor will we be shocked if the factory team has earned another AMA Championship, or two, by the close of 2015.