2010 Suzuki RM-Z250/RM-Z450 First Look

June 25, 2009
Bryan Harley
Bryan Harley
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Our resident road warrior has earned his stripes covering the rally circuit, from riding the Black Hills of Sturgis to cruising Main Street in Daytona Beach. Whether it's chopped, bobbed, or bored, metric to 'Merican, he rides 'em all.

2010 Suzuki RM-Z250
The 2010 RM-Z250 is the first in its class to make the switch from a carb-fed engine to electronic fuel injection.

The rumors are true. Suzuki beat everyone to the punch, being the first of the Big Four to fuel-inject its four-stroke 250cc motocross motorcycle. You heard right. The 2010 RM-Z250 is fuel-injected. Controlling the flow is a 43mm throttle body with progressive throttle linkage that is powered by a magneto-generator after starting. It has been adapted from the system established two years ago in the RM-Z450. The radiator louvers also got a makeover in an effort to direct more air to the twin side-mounted aluminum alloy radiators and keep the new EFI engine running cool.

This, of course, brought about a few modifications to the engine. The core of the DOHC 249cc four-stroke remains the same, but it has undergone revised cam timing and updated its intake ports. Suzuki also went with a stronger connecting rod with mirror finishing and modified the crankshaft. The desired result of the changes is to give the 2010 RM-Z250 more oomph up top, which will be helpful since the switch to EFI has also added five pounds to its curb weight, up from 225 to 230.4 lbs.

Chassis updates, suspension mods, a new muffler, the Suzuki R&D crew has been busy with its 250. The motorcycle that brought home the 2009 AMA Supercross Lites West Coast title should be a serious contender come shootout time. Until then, here’s a little of the Suzuki PR about the 2010 RM-Z250.

The RM-Z250 has new radiator louvers that direct more cooling air at the twin side-mounted radiators.
The RM-Z250 has new radiator louvers that direct more cooling air at the twin side-mounted radiators.

Courtesy of Suzuki

Suzuki racing technology is everywhere you look: advanced Suzuki fuel injection is fitted for the first time on a four-stroke 250cm3 Suzuki motocross machine. Further engine modifications boost peak power without giving up any of the low-end or midrange that has made the RM-Z250 the choice of top riders everywhere. Chassis updates improve handling with key suspension upgrades making the new RM-Z250 the perfect weapon for motocross racers worldwide. And there’s the eye-catching slim, aggressive styling that causes the RM-Z250 to stand out at any track.

Fuel Injection
Derived from the pacesetting RM-Z450’s superlative system, the RM-Z250’s battery-less injection features a 43mm throttle body with progressive throttle linkage, a 16-bit computer and unique capacitor-assisted starting system. A durable, lightweight magneto-generator powers the fuel injection after starting. Because all engine systems are related in performance, a new muffler is fitted to optimize the benefits of fuel injection.

Chassis Updates
In the search for handling perfection, the RM-Z250’s twin-spar aluminum alloy frame has been redesigned with several key components to optimize rigidity balance and improve traction at high speed. The lower frame tube has thicker walls, 3.0mm versus 2.5mm, while the side rails are slightly shallower. Connecting the 19-inch rear wheel and the lightweight chassis is a new swingarm with an improved center brace for increased rigidity that also more concentrates its mass for enhanced suspension action and greater traction. To prove that Suzuki understands the importance of details, new footrest brackets are designed to prevent mud clogging.

High-Performance Suspension, Updated

A 12-hole fuel injector with a reversed throttle valve movement is at the heart of the RM-Z450s electronic fuel injection.
A 12-hole fuel injector with a reversed throttle valve movement is at the heart of the RM-Z450’s electronic fuel injection. Suzuki’s 250cc motocrosser now comes with EFI technology inherited from the RM-Z450.

Thoroughly revised spring and damping rates inside the inverted Showa 47mm fork and piggyback single shock result in improved handling for a wide range of riders. Carefully chosen modifications improve traction and rider confidence at high speed without sacrificing the RM-Z’s legendary quick-turning ability. Modifications to the rear suspension linkage that reduce thrust backlash also improve traction and make for more consistent performance.

2010 Suzuki RM-Z450

No big news like the 250’s switch to EFI in the RM-Z450’s camp, but it doesn’t mean that Suzuki hasn’t been busy dialing in and improving on its big MX bike. Modifications to the 2010 RM-Z450 engine include revised cam profiles, cylinder-head porting, and an improved camchain tensioner. Suzuki has also tinkered with the RM-Z450’s electronic fuel injection, reversing the throttle valve movement. Changes to the chassis starts with a two-piece head stock that’s 9mm-taller than last year and the Showa 47mm fork has new spring rates. On the tail end, the extruded and cast members on the rear section of the frame are wider, and the motorcycle’s wheelbase is 0.6-inches longer. The Showa suspension on the rear also features revised spring and damping rates.

Here’s a little more about the 2010 RM-Z450. Courtesy of the Suzuki PR peeps:

Powered Up!

2010 Suzuki RM-Z450
The 2010 Suzuki RM-Z450 received a few engine mods, chassis upgrades, and suspension tweaks this year.

Suzuki’s engineers have carefully developed the RM-Z450’s powerful 449cm3, DOHC, 4-valve engine to increase power throughout the rev range. Always known for its incredible midrange grunt, the 2010 RM-Z450 also has arm- stretching high-rpm power. A combination of revised cam profiles and reworked cylinder-head porting give the RM-Z450 amazing idle-to-redline thrust. An improved camchain tensioner provides more consistent performance. Also a modified throttle linkage makes the low-speed response more progressive. How’s that? More power and better manners.

Fuel Injection, Pioneered and Improved
For 2010, the RM-Z450’s electronic fuel injection is improved with a reversed throttle valve movement. Such a simple alteration pays handsomely: The fine fuel-air mist from the 12-hole fuel injector is directed away from the throttle valve for a more uniform mixture producing increased power and enhanced throttle response.

Chassis Dynamic
Everywhere you look, the RM-Z450’s twin-spar aluminum alloy frame has received detail improvements to optimize rigidity balance. It starts with the head stock, which is now a two-piece design that’s 9mm taller than before. Further back, the sections at the rear of the frame, which are made up of extruded and cast members, are now wider for increased rigidity. More strength comes from a wider upper frame bridge beneath the saddle, while material wall thickness was strategically designed to save weight.

High-Quality Showa Suspension
The RM-Z450 employs race-bred, state-of-the-art Showa suspension front and rear. For 2010, both ends of the bike are given suitably revised spring and damping rates—the new rates work together with the chassis’ optimized rigidity balance to improve handling. 47mm inverted forks provide optimum wheel travel and can be adjusted for compression as well as rebound damping for maximum rider adjustability. A Showa piggyback reservoir rear shock offers both high- and low-speed compression damping adjustment along with rebound damping and spring preload adjustments. Working through Suzuki’s superlative rising-rate linkage system—now with revised link-bearing tolerances for precise handling performance—the shock provides 310mm of wheel travel delivering maximum traction.

Suzuki continues to offer its two-strokes, the RM125 and RM250, but only in the European market. Suzuki has not yet revealed the 2010 MSRPs.

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