After major redesigns in 2013, the 2014 Suzuki RM-Z450 and RM-Z250 return to action the same, only better
Story by Tom Roderick and Ryan Abbatoye
Photos by Enrico Pavia
Suzuki made several updates to its RM-Z450 and RM-Z250 motocross machines in 2013, adding numerous technical upgrades to the engines, chassis and electrical systems to improve the power delivery and enhance handling on both models. With so many changes made in 2013, and given the typical development cycle of the OEMs, it’s no surprise that the 2014 RM-Zs return to the MX wars in virtually the same trim.
Other than new radiator shrouds and a switch to yellow number plates the only notable technical upgrade is a reprogrammed Electronic Control Module (ECM) that eliminates excess spark that occurs during the exhaust stroke. Suzuki engineers realized that the rogue spark was igniting unburned residual gases in the combustion chamber that simulated an out-of-phase power stroke when the RM-Zs were being kickstarted, and thus they could sometimes become hard to start as a result. The new ECM corrects the issue, and now the spark fires more efficiently, with the ECM retarding the ignition when it detects that the motor is being kicked through during the starting process. The upside of this minor development is easier starting at no increased cost to the customer. The 2014 models will sell for the same MSRP as the 2013s; $8699 for the 450 and $7599 for the 250.
To show off its 2014 RM-Z’s Suzuki invited us to a two-day model introduction at Perris Raceway in Southern California, giving us ample time on a well-groomed track. Both myself and DirtBikes.com test rider Ryan Abbatoye can attest to the ease of restarting both RM-Z models. Abbatoye (who’s a slightly better rider than me, actuall, by a very wide margin!) shared his impressions of the bikes’ performance.
2014 RM-Z450
In regards to the reprogrammed ECM, Abbatoye says “Being an off-road racer who experiences a lot of dead starts during the course of a race I was able to kick the RM-Z through a full throw of the kickstarter and it sparked to life each time with no kickback whatsoever.”
Abbatoye liked the engine performance that the RM-Z’s fuel-injected, liquid-cooled, DOHC 449cc engine produces right from the get-go. Its big 96.0mm bore and short 62.1mm stroke bore and 12.5:1 compression ratio are typical of modern, high-revving four-stroke motocross engines, and Suzuki claims that it is designed to develop exceptional power from idle to redline and provide crisp throttle response. Suzuki engineers paid special attention to the lift and duration of the intake cam in order to get the smooth power delivery they were after when they redesigned the engine in 2013, and they also addressed internal frictional losses by incorporating a Diamond-Like Carbon (DLC) surface treatment on the piston to make every pony count. Abbatoye noted that the end result is a fast yet friendly engine that works for Experts or Novices. “It doesn’t have ‘rip your arms off power, but it delivers strong, linear power that will get you over any jump at the track when needed,” he said.
The 450’s battery-less Kehin electronic fuel injection system is partially responsible for the engine’s linear feel. It utilizes a progressive throttle linkage that is attached to the throttle body, which features a 12-hole fuel injector to deliver a fine mist of fuel into the combustion chamber. The fuel system can also be easily adjusted for changing conditions at the track to suit conditions or riding style by swapping out ECU couplers. Suzuki provides two additional accessory couplers with the 450. One richens and the other one leans the fuel settings compared to stock.
Suzuki also addressed the power character of the RM-Z last year by redesigning its muffler internals. The chance was made to improve bottom-to-mid range power and torque without losing top end.
However, the RM-Z’s strong point, according to Abbatoye is its stellar handling. The RM-Z’s twin-spar aluminum chassis is unchanged for 2014, and its front end features a fully adjustable 48mm Showa Separate Function Fork (SFF). The SFF separates spring and damping functions by placing a single spring in the right leg, while the left leg carries the cartridge assembly and damping adjusters. The SFF design is claimed to reduce friction and improve bump absorption over a wider variety of track conditions while also reducing weight. Out back, the rear suspension chores are handled by a Showa Piggyback shock that features high/low-speed compression damping adjustability along with rebound damping and spring preload adjustability.
“The RM-Z450 has a reputation for awesome cornering capabilities,” Abbatoye said. “This isn’t a rumor, it’s a fact. This bike is the best cornering MXer in its class. Whether it navigating ruts, flat, hard-packed corners, sand, or even bowl corners I feel I can put this bike wherever I want when I want. Last year, Suzuki added the Separate Function Fork (SFF) to the bike, and I believe it was a smart choice to carry it over to 2014 because this bike is very stable. It conquered any fast rough section at Perris Raceway.”
Other highlights of the 2014 RM-Z450 include a smooth shifting five-speed transmission, good clutch engagement and optimum traction during our test day at Perris.
“Other than making the grips softer, I think this bike is an awesome package for both professional or novice riders,” Abbatoye said.
2014 RM-Z250
The 2014 RM-Z250 gets the same reprogrammed ECM and new plastic as the RM-Z450, and of course it also received many of the same updates as the 450 in 2013, most notably in the chassis and suspension departments. But the 250’s liquid-cooled, fuel-injected, DOHC engine also got a 3% lighter piston than the 2012 model along with a new crankcase reed valve designed to offer more efficient oiling.
It uses a Keihin battery-less fuel-injection system with a 44mm throttle body, a progressive throttle linkage and a 16-bit computer for optimum throttle response, and it features the swappable ECM modules just like the 450. Another other unique change in 2013 included redesigned radiator fins and revised water hose routing to aid cooling.
“Being one of the top rated 250’s in 2013, Suzuki decided to continue with the motor package in the RM-Z250 they offered last year,” Abbatoye said. “While it performs well, my only complaint is that its bottom-end power response is a little sluggish. However, after changing to the more aggressive coupler, the 250 seemed to liven up.”
Abbatoye said that the RM-Z250s hands just as well as the 450. That’s no surprise, since the 250 and 450 chassis and suspension are identical.
“The bike corners like its on rails in any condition,” Abbatoye said. “Suzuki has always been known for their excellent cornering abilities, and in 2014 they are right on the money with the 250. In 2013 they focused on stiffening up the frame and reducing flex and that carried over for 2014. The RM-Z 250 feels solid and is easy to handle, especially with the 48mm Showa SFF forks.”
Suzuki’s past work with both RM-Z’s has paid off in the form of competitive motocross machines that should be shootout contenders in their respective classes. Time will tell, as some of its competition has come out of the box in 2014 with all-new designs in both the 250cc and 450cc ranks. Taken on their own merit, the 2014 RM-Zs offer good power, great suspension and excellent handling. We look forward to testing their mettle against the competition later this year, so stay tuned.
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