Dream Ride: Junya Takenaka's Works Suzuki RM-Z250WS 7

​While we get occasional opportunities to try out some of the U.S team's race bikes, the chance to ride a true Works bike is extremely rare. But on a recent trip to Japan for the 40th anniversary of the Suzuki RM, I got to swing a leg over a Suzuki Works RM-Z250WS. The bike belonged to Factory Suzuki's Junya Takenaka, who after a full-fledged battle to the end of the second moto, had narrowly lost the IA2 (250cc) overall win the day before. The track was the hard-packed circuit at Hiroshima.

2015 Suzuki RM-Z250WS Features

Engine:

• Bore x Stroke: 77mm x 53.6mm (production RM-Z250).
• Cylinder Head: Production head with Factory Suzuki modifications.
• Camshaft: Yoshimura/Factory Suzuki spec.
• Piston: Yoshimura/Factory Suzuki spec.
• Cam-Chain Tensioner: Factory Suzuki with manual adjustment.
• Crankshaft: Production crank with Factory Suzuki modifications.
• Transmission: Production five-speed with factory treatment.
• Clutch: Hinson and Suzuki combination.
• Exhaust: Akrapovic (FIM 112db two meter max test)
• Throttle Body: Keihin body/Factory Suzuki spec.
• Air Filter: Twin Air.
• Radiators: Production Suzuki.
• Oil: Motul.
• Fuel: Japan 100 octane pump gas.

Electronics:

• ECM: Factory Suzuki unit.
• Wiring Harness: Factory Suzuki lightweight spec.
• Data Logging System: GET Data Logger coupled to Factory Suzuki electronics.

Chassis:

• Fuel Tank: Larger capacity CRM Carbon tank.
• Frame: Factory Suzuki.
• Forks: Showa Works Separate-Function Triple Air Chamber forks (SFF-TAC) with Factory billet axle lugs.
• Shock: Showa Works Balance-Free Rear Cushion (BFR) with Factory linkage.
• Brake System: Production-based Nissin calipers with Factory Suzuki rotors.
• Protective Guards: Factory Suzuki CRM carbon guards.
• Tires: Factory Dunlop.
• Hubs/Wheels: Factory Suzuki hub with D.I.D. ST-X rims.
• Starting Device: Zeta.
• Handlebar: Renthal.
• Sprocket: Renthal.
• Chain: D.I.D. 520ERT2

First Impressions

The RM-Z250WS may not appear to be much more than a modified production bike at first sight, but after a closer look and a chat with the technical staff, I noticed there are quite a few differences. Mainly the bike features a frame and cases that aren't production but are actually Factory Suzuki components. The rest of the engine and its components, including the bore and stroke, are production or production-based.

Most of the internal engine work is a combination of Factory Suzuki know-how with some assistance from Yoshimura. I wasn't able to find out the exact compression ratio, but it's definitely higher than stock. Beyond that, I found out that in the All-Japan Nationals the teams must use pump fuel without any sort of additives. To support the higher compression, the teams are able to utilize a higher octane pump fuel (100 octane) than what is typically found here in the U.S. For the electronics, the team uses a Keihin-sourced ECU, wiring harness, and throttle body, but they're all spec'd differently than what comes on the production bike.

As mentioned before, the chassis may appear to be a production 2015 chassis, but is in fact a works frame with different gussets and material thicknesses throughout the build. Then they add the Works Showa suspension. In the US, the 250 teams use "Kit" suspension, which is more affordable and meets a price cap. The RM-Z250WS I tested uses "Works" components, which typically have parts that have a bit higher level of performance, but must be changed often due to the extreme wear they receive. The front forks are Showa's SFF TAC units, which feature damping components in the left leg and the Triple Air Chamber Spring unit in the right leg. They also have a set of billet axle lugs, which are made to match the stock offset but also feature a wider clamping area with a wider axle to offer less flex and a more accurate feel at the front end.

The shock is also unique, as it's a machined billet body which dissipates heat better than standard cast bodies. It has also been designed to accept the new Balance Free adjuster. The BFR shock doesn't have shim stacks on the shaft as a traditional shock would, but instead has a large piston and valve stack on the backside of the new larger adjuster. This design has been utilized on Showa's road race shocks for a few years now and is meant to offer a more free feeling stroke as the shock transfers from compression to rebound damping in a much smoother fashion.

To get a better idea of what limits the Japan Nationals do have, just take a peek at the FIM rulebook for the World GPs. These bikes follow the same sound, weight (209.4 pounds), and parts rules, the only difference being the fuel allowed.

On the Track

Junya is quite a bit taller than I am, but I was relieved to find that his controls were quite normal, including a normal straight bar bend that was rolled back just a bit to my liking. Once the sag was set, I rolled out on the extremely choppy and hardpacked Hiroshima circuit with the familiar feel of an RM-Z250F between my legs. Although this is a Works bike, you can easily tell from the description of the bike that it isn't as far from the production bike as some would imagine.

The most immediate difference I noticed with the RM-Z250WS was the overall feel of the engine. The production RM-Z250 engine is very, very snappy, and revs quite quickly, but it really lacks bottom-end power and roll-on grunt. The RM-Z250WS, however, is quite a bit different. It has great low-end torque and builds power at a much more progressive rate. It also revs quite a bit slower but still pulls great on the top-end. With this, the bike was immediately easier to ride around Hiroshima than the production bike. (I spent my morning warming up on a bone-stock RM-Z250). This however, wasn't the only reason the bike was easier to ride.

Since the RM-Z250WS is in line with the MXGP's minimum weight rule, it's definitely the lightest 250F I've swung a leg over. Even though we weren't allowed to turn in long motos, the combination of the lighter weight, balanced chassis, and broad powerplant made for a bike that was extremely easy to ride. As for the actual chassis, there weren't any major differences from the production RM-Z250, which isn't a bad thing as the current chassis is quite balanced and easy to ride aggressively... or in a much smoother fashion.

Moving onto the suspension, this was the first time I've gotten to ride with a set of Works Showa SFF TAC forks, but more importantly it was also my first experience with the Showa BFR shock. Junya's settings on the TAC fork seemed to be fairly balanced; plush initially, great traction on turn in, and with plenty of bottoming resistance for my lighter build. The only odd part for me was that the rebound felt a bit on the quick side, but this is also necessary to keep the front tire contacted to the ground on the harder and faster chop that was found at the Hiroshima track.

For me, the shock was almost the most interesting part of the entire bike. I've had the opportunity to talk to a few test riders about the BFR shock and it sounds like its development is coming along. Initially I had been told it has a very "free" feeling throughout the stroke, meaning it moves smoothly through the stroke. This was a huge advantage at Hiroshima. As I mentioned before, the track is very hard with acceleration chop that is sharp and close together. The BFR moves quickly from compression back to rebound in this situation and lets the rear tire settle back to the ground to gain a bit of traction before the next bump. This definitely gave me a lot more confidence compared to the production RM-Z we rode. This shock also compliments the engine characteristics, as it allows you to put power back to ground quickly without the rear tire wanting to spin as easily.

The last big positive on Junya's bike was the Factroy Dunlop tires, which seemed to have aspects of both the current production MX32 and MX52. Being on a foreign surface, it's hard to say how much better they are but I never once questioned them, as I never had any problems with traction. One part that seemed not to be a true works part was actually the brake calipers, as we were told they were production based. After a closer look, they didn't appear to be the same as the current production caliper but are probably going to be production in the future. As for the feel, these calipers matched up to the factory rotors had more than enough power, but the overall feel was a bit weird. Junya seemed to prefer a bit travel to his setup than than I would prefer (I thought they were a bit too "squishy" for my personal preference).

The Last Word

Overall, the easiest way to explain the difference between a Works Suzuki RM-Z250WS and a modified production RM-Z250 would be to say that on the Works bike everything feels like it's complimentary. Every component or setting was picked to help support or take advantage of other components that are on the bike. It may not be the downright fastest 250F I've ridden, but it was one of the easiest to handle, and it wasn't even set up for me! I do wish I could have specifically taken the engine and shock home with me, but there was no way I was getting those past the Suzuki crew. Thanks to the Suzuki Japan crew for their hospitality and awesome opportunity.

Article by Michael Lindsay