Bike Dissected: James Stewart’s 2013 Suzuki RM-Z450

James Stewart wanted nothing more than to get on a Suzuki. Here’s the one the brand built for him to contest the 2013 Monster Energy AMA Supercross series aboard.

James Stewart really, really wanted to race a Suzuki. Last year, he dropped out of his three-year deal with Joe Gibbs Racing Yamaha mid-way through the first season with the team, finally throwing in the towel after three years of trying to get the backwards-engined YZ450F to work for him in AMA Supercross (before Gibbs, he rode a Yamaha for L&M Racing). Stewart could have left Yamaha before, as he was a free agent in the summer of 2011 and even bought his own versions of every Japanese bike (remember, KTM didn’t have a competitive 450 then) to test. He liked the RM-Z best, but Suzuki was in the midst of corporate structure changes and couldn’t make him an honest offer. Gibbs and Yamaha swept in with big money and Bubba stayed blue – until he finally waved the white flag, agreed to part with the blue crew, and knocked on the yellow door again. With copious support from the works engineers in Japan, this 2013-model RM-Z450 is arguably the most exotic bike in the AMA paddock. Let’s have a look.

Shock

It’s no shock to see a works Showa shock absorber out back, but it is surprising to see a stock Suzuki production linkage bolted to it. Stewart tried a ton of link combos and liked the stocker best, which is a change from ’12. Why? It could be the result of the new-for-2013 frame, which brings changes to the steering head area and the cross-members that support the linkage.

Brakes

Even the fastest man on the planet slows down sometimes, and this works Nissin front brake is the best way to do it. Suzuki was the first to use this trick, fully machined aluminum front caliper. The front disc is massive, and even the rear disc is a little bigger than standard. A stock rear caliper is augmented by some trickery in the master cylinder – the brake components could double as art pieces.

Cockpit

Suzuki’s long relationship with Pro Taper has stepped aside, which is okay since Stewart has a penchant for Renthal TwinWalls. The crossbar-equipped items also better show off the works Suzuki bar clamps and risers, which are now rubber mounted – another change from the 2012 race bike. Down below, works radiators sport a redesigned inlet and outlet for improved cooling. Tricks like this that could eventually end up on production bikes.

Engine

Even in these days of the AMA production rule in the US, engine internals can still be full works, and the Suzuki crew from Japan spared no expense inside this piece. The US team then makes refinements, especially via the EFI system. The factory motor has been massively massaged from the 2012 piece, and Stewart prefers a broad powerband with exceptional low-to-mid range power – he rarely uses the clutch to build RPMs. Surprisingly, the motor is said to be smooth and not a fire-breather. Naturally, Yoshimura handles the full exhaust system and a Hinson clutch resides on the side.

Precious Metals

Titanium bolt kits and carbon fibre parts are now easily found via the aftermarket, which makes Stewart’s RM-Z one of the few in the pits still running hand-made works exotica – like a carbon skidplate, oversized front disc guard and an innovative carbon ski under the right fork leg to glide over ruts. The titanium bolts, aluminum clutch cable guide, cam-chain adjuster cover and brake and shift levers are also works spec.

Wheels & Hubs

Surprisingly, there are hardened steel axles inside those works aluminum hubs. In the 450 four-stroke era, even the factory steeds are usually a few marks above the 219-pound (99.4kg) minimum weight, and rumour is that a big diet could adversely effect the planted feeling that makes the mega-fast so comfortable on the Suzuki. Excel rims support works Dunlop tyres, and a DID chain and Vortex sprocket handle the final drive.

Air Fork

Change is in the air in the AMA pits this year – literally. Honda, Suzuki and even (long-time KYB users) Kawasaki have switched to Showa SFF air forks. Springs are replaced with air pressure, making the forks lighter and plusher. Stewart never tried the spring fork again once he got on these. Bubba’s way-forward riding style is said to result in rock-hard forks, but wrench McCollum says they’ve tried cranking them in extra hard, and James had them back it down – yes, they’re a little stiffer than most, but not a world apart. Works Suzuki triple clamps hold up even to Bubba’s abuse.

Team Manager – Mike Webb

James has a creative element I’ve never seen before,” says Webb, who has been around the sport for decades and is no slouch on a bike himself. “He just sees things no one else can see, be it at his house in Florida or at our test track in California. And he’s just obsessed with the sport. If he’s back at his house in Florida, he’ll call me on Sunday morning in California, and we’ll watch the race on TV together, over the phone, taking notes on how the bike reacts, and how everyone else is doing, too. It’s amazing how much he can pick up, and how quickly he dissects it.

“We’ve found the key is to set the bike up for the basics instead of that massive quad that only he is willing to jump. We work on the corner speed, the scrubs, making him comfortable on that, and then he can handle the big stuff on his own. We get a lot of help from Japan, and we’re like kids on Christmas morning when the stuff shows up – and with a talent like James on board (and a new-generation RM-Z this year), we’ve gotten a lot of new stuff. It makes it really exciting to go racing.”

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