2015 Suzuki RM-Z450L5
Words: Paul Pics: Geoff Osborne
Despite a lack of silverware from major titles on the mantelpiece at Suzuki HQ over recent years, the yellow team still produce an open-class motocrosser that is able to be competitive virtually straight out of the crate. And for 2015, the list of mods has been increased that will hopefully see Suzuki at the pointy end of the race scene once again…
The day before we headed off to Pirini Motorbike Park, just outside of Te Puke, for the launch of the new Suzuki, the 2015 model took the top honours at a very special event: Red Bull’s Straight Rhythm in California. James Stewart dominated the open class against stiff competition, beating Justin Brayton in the final and winning every race in the leadup to it. Pretty impressive stuff on a bike that, despite looking extremely similar to the outgoing 2014 model, has in fact got plenty of updates to shout about.
First up, and possibly something that Stewart was keen to discover, is that the RM-Z450 has gained a couple of horsepower as standard, pushing out a claimed 57 horsepower and putting the Suzuki right up there in the power stakes. But the top-end isn’t where gains can really be made on a moto track (unless you can ride like Stewart), and a remap of the ECU has seen the RM-Z gain a chunk of midrange that is really going to be more useful to us mere mortals.
Other changes to the impressive Suzuki powerplant have been an improvement in cooling, which has been achieved by improving how the radiators are balanced and also how they’re attached to the water pump, while starting the RM-Z when warm is now an easier prospect with the automatic decompressor and hot-start improved for 2015. In fact, starting the RM-Z at anytime is now easier, with a new 30mm longer kick lever being combined with a couple more teeth added to the kick idle gear. Now, swipe at the starter almost absentmindedly and the RM-Z bursts into life, the more precise de-compressor system working extremely well according to our two testers.
Take a look at the Renthal handlebars and there’s something new on the left-hand side, with a button and red light there to play with. Called Suzuki Holeshot Assist Control, the new system isn’t an instant way of adjusting the power delivery as on the Honda CRF450R, but is instead designed to assist you in getting to the first turn before everybody else. Anyone that races moto will tell you that the start is where you can win or lose your race, and any techno-wizardry that’s going to help in this department is sure to be well received. Leave the button alone and the RM-Z will stay on standard settings. But start the engine and then press and hold the button for one second will see the light flashing slowly and A-mode engaged. This mode essentially retards the ignition during the starting process, reducing the power and giving a smoother engine response, making it a great asset for the novice rider or for anyone during slippery conditions.
Pressing the switch and holding it for two seconds sees the red indicator flash faster to show the RM-Z is set in B-mode, which also means you’d better hold on tight. Whytey discovered the RM-Z was almost ready to launch to the moon, the ferocity with which it launched off the dry soil at Pirini, basically digging it’s own Bridgestone-shaped trench along the start-straight behind him. Advancing the ignition gives the RM-Z a more aggressive feel and certainly gives the 2015 models the advantage when launching off the line in dry conditions.
A mode is deactivated when you select third gear or 1.2 seconds after the start, whichever comes first, and is designed to increased thrust force, reduce the chance of wheelspin and give a more consistent starting performance. B-mode is deactivated when you reach fourth gear, close the throttle, or 4.5 seconds after the start, whichever comes first, and is designed to increase power and throttle response as well as acceleration.
The switch also has a couple of other jobs to do, with the light acting as a fuel-injection diagnosis monitor, an engine run time indicator (flashes for each hour run) and also an answer back light for a MX-tuner when you get into the sophisticated arena of producing your own maps!
Mitch Rees was our other tester on the day, and it didn’t take long before he was whipping and scrubbing the RM-Z all over the Pirini moto track as if he’d been on the Suzuki for a season. “It’s real easy to ride,” was one of his first comments, the improved mid-range of the 2015 model giving the RM-Z less of a ‘hit’ when getting into the meat of its power. “It’s close to a pukka race bike straight out of the crate,” was his next comment. Although both riders admitted that they’d need a bit of time with the latest Showa SFF-Air forks to work them out properly and get the exact feel that they were after. Still, Mitch didn’t seem to be having much of a problem, launching the RM-Z over the biggest jumps and landing close to a couple of the turns before scrubbing off speed with the 250mm wavy disc up front gripped by a twin-piston caliper. Not ferocious in power but certainly enough to get the standard Bridgestone M404s complaining.
With the forks, frame, rear shock, swingarm and a few other bits and bobs all new on the RM-Z, it’s a shame that Suzuki didn’t see the benefit in updating the plastics to give the RM-Z a new look, with the 2014 shrouds all able to be bolted straight onto the new model. Still, it’s what’s underneath that counts, right? And the guys said the handling on the 2015 was sublime straight out of the crate. The frame has been given a bit more flexibility, making the big 450 more forgiving in the turns and berms, while a loss in weight of 4 percent makes the Suzuki turn sharper than ever before. Add to that the reduction in weight from the new air forks and it’s no wonder that the RM-Z feels light up front and can be positioned wherever you want it on the track and in the air.
Unlike the air forks used on the Hondas, the Showas on the Suzuki feature an external balancer chamber down at the bottom of the right fork leg. With the right-hand fork containing the air-spring unit, the left-hand leg takes care of the damping and nothing else. Used by Stewart during the 2014 season in AMA, Suzuki are confident they’ve got a package that works, although there’s certainly a lot of reading to be done before you get your head around adjusting them. Obviously, a high-pressure pump with digital gauge is required to accurately assess what pressure you’ve got in each of the chambers. The air system has the benefit of letting you adjust the equivalent of the spring rate simply by increasing or decreasing the air pressure in the inner air chamber. Further adjustment can be done using the outer air chamber, with both valves located at the top of the right fork leg and able to be reached with the pump without removing the handlebars. Finally, the balance air chamber at the bottom of the right leg is used to determine the air spring force in the initial stroke range. All sounds easy, right?
Initially, both testers felt the front forks were almost a little ‘dead’, with a slightly over-damped response when returning through its stroke. Pulling into the pits and checking the pressure in the three chambers indicated that there was 171psi in the inner, 0psi in the outer and 171psi in the balance chamber. Chatting with Team Suzuki rider, Brad Groombridge, he suggested we went down to 135psi in the inner, 7.5psi in the outer and 137psi in the balance chamber, which only took a few seconds with the high pressure pump. Once back on the bike, the guys reported the changes had softened the initial feel of the fork action but gave more bottoming resistance. Both were impressed with how changing the pressure by relatively small increments made noticeable changes to the way the forks performed. And with a more linear damping performance than standard spring/oil forks combined with the fact the air system essentially runs a separate function process, once the forks are adjusted, they should stay consistent throughout the length of a moto. And finally, the major benefit of the triple chamber system goes back to the worry of some riders about what happens if you lose air pressure through the equivalent of a damaged fork seal. Well, with the third chamber the only one that is able to be discharged through a seal leak, the forks will still remain working even if there was no pressure in the third chamber at all, leaving you confident in the knowledge you’ll make it back to the trailer.
Ergonomics was an area where the guys had differing views. Whytey found the ‘bars to be too low for his liking, whereas Mitch found them to be perfect. But Mitch wasn’t a fan of the new peg location, feeling they were higher than before and weren’t adjustable like they are on the KX models. Other than that, the saddle was standard RM-Z affair, allowing for easy movement backwards and forwards on the machine.
With Suzuki making a serious move in the annual contract battles throughout the AMA and securing newly crowned AMA premier class champion, Ken Roczen, to compete on a RCH Suzuki for 2015, they must have known they were going to have a competitive bike to give him. Hell, he must have seen what Stewart could produce on a good day on the 2014 machine and known that with a few added benefits for 2015, his chances of taking back-to-back crowns must be pretty good. As a base unit with which to make a competitive race machine, the RM-Z450 is now as good as most and better than others. And for those of us without the backing of Team Yoshimura to fettle our bikes, the RM-Z has taken another huge leap forward from 2014 despite looking almost the same. If you want a bike you can ride and be competitive on straight out of the crate, then the 2015 Suzuki RM-Z450 has to be one of the best choices.
2015 Suzuki RM-Z450
Engine Type: 449cc liquid-cooled single-cylinder DOHC four-stroke
Bore and Stroke: 77mm x 53.6mm
Compression ratio: 13.5:1
Front Suspension: Inverted telescopic fork with coil spring that is oil damped with mm of travel
Rear Suspension: Link-type with coil spring and oil damped with mm of travel
Front Tyre: 80/100-21
Rear Tyre: 110/90-19
Length: 2170 mm
Width: 830 mm
Seat Height: 955mm
Ground Clearance: 345mm
Fuel Capacity: 6.5litres
Wet Weight: 106.5kg
Air Forks – How Do They Work
The inner chamber is the equivalent of your old spring, so changing the pressure is the same as adjusting your spring rate, just without replacing the spring… So adding more pressure is the equivalent of adding a heavier spring.
The outer chamber is used to increase the range of adjustment required from the inner chamber, so if you can’t get it hard enough just by pumping up the inner, you add to the outer as well.
The balance chamber dictates the feeling of the fork in the initial stroke range, with more air equalling a softer feel in the initial part of the fork’s movement.
Compression and rebound is taken care of more conventionally on the other leg, with clicker adjustment changing oil flow rather than air pressure. With no spring, they save weight, and you also get a broader range of adjustment with the air forks than you can with conventional forks. Are they as good? Well, we’ll keep riding and come back to you soon with the answer to that question…