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Yamaha WR450F - 2 Trac

With the front wheel helping put down the power, the new two-wheel-drive Yamaha can churn through the sand better than any other bike.
With the front wheel helping put down the power, the new two-wheel-drive Yamaha can churn through the sand better than any other bike.

By Kevin Duke

For the past 100 or so years, motorcycles have had their rear wheels driven by one of three ways: belt, shaft or chain. Simple and effective, if a bit archaic.

Yamaha intends to change all that with the introduction of the two-wheel-drive motorcycle, the WR450F 2-Trac.

Developed by Ohlins (the Swedish company Yamaha partly owns), Yamaha's 2-Trac features a patented hydraulic drive to the front wheel. An oil-bathed chain drives a hydraulic pump located on top of the gearbox, and this actuates hydraulic fluid via high pressure hoses to the front wheel. The special hub in the front wheel is driven by hydraulic pressure when sensors indicate the rear wheel is losing traction.

Because the amount of traction the front wheel has varies greatly (it's hard to get a grip on the dirt when the front wheel is in the air!), Yamaha uses its "smart operation" in which power to the front wheel increases the more the rear wheel slips. The system automatically applies the best ratio of power between front and rear, and the settings can be adjusted manually depending on the specific usage of the bike and the type of terrain to be ripped up.

Yamaha began experimenting with two-wheel-drive bikes in 1992 with heavy, inefficient and bulky mechanical-drive systems. The 2-Trac's hydraulic system debuted in 1998 on two YZ250s at the Swedish National Gotland Rally, and the radical machine won its class. Then in 1999, the Yamaha-Belgarda team won its class in the UAE Desert Challenge race with a 2-Trac-equipped TT600R. Then last year the president of Yamaha Motor France, Jean-Claude Olivier, entered the Shamrock rally on a WR426F 2-Trac prototype and finished 5th. And just recently, WR450F 2-Tracs took the top two positions in the Shamrock Rally, with rider David Fretigne finishing ahead of J-C Olivier in the Moroccan desert.

"Riding the WR 450F 2-Trac," explains Olivier, "you will be amazed by its ability to perform in such difficult conditions like deep soft sand or mud. The bike still goes on when standard bikes are digging themselves holes to get stuck."

The 2WD system is said to not only offer better traction during acceleration, but also improved straight-line stability and a higher top speed in slippery conditions. Yamaha says the WR450F 2-Trac can attain a maximum speed about 10% higher than its conventional counterpart due to the extra traction provided by the extra driven wheel.

"You also will realize quickly that the 2-Trac motorcycle has a much higher steering stability both in a straight line as well as in corners," adds Olivier. "It feels a bit like carved skis - you can lean into corners and the rear part of the bike takes up the same track easily without sliding. It makes riding much more relaxed when you don't need to counter-steer."

Olivier says that two-wheel-drive, in addition to gaining a traction advantage, can be a bigger benefit for beginners than experts. "Just lean into the curve and the rear part of the bike automatically takes up the same track. You quickly get used to it and riding becomes quite natural. Since the rider does not need to counter-steer and can avoid rear wheel slides, control of power becomes much easier. Unlike a conventional motorcycle where even an experienced rider will fight with a sliding tail end, the 2-Trac is much more controllable."

Yamaha's experience in the rally has also proved the durability of the new system under harsh conditions. Both bikes entered suffered no mechanical woes over the course of the event. And with the system being much lighter and better integrated than past designs, it would seem to be a natural to soon crank them out on the assembly lines. While Yamaha remains tight-lipped about those plans, Olivier has high hopes for an all-wheel-drive production motorcycle.

"I can imagine such a system fitted on any kind of off-road motorbike, or even scooter or road bike. Two-wheel drive would be beneficial on a large Grand Tourer or scooter for example, since you could combine high power in an integral transmission with coupled braking, to offer the ultimate safety both for experts and in particular for novice riders."

To further elaborate about the benefits of the 2-Trac system, we bring you this interview with Lars Janson, R&D manager for future projects at Ohlins AB in Sweden, that was featured in the Yamaha Design Cafe.

Q: Why did you choose a hydraulic drive system instead of a mechanical one like a chain or shaft?

Lars Janson: If you have a three-dimensional vehicle like a car, where you can reach the wheel hub from the side, it is very easy and efficient to fit a mechanical drive. But a motorcycle is two-dimensional. You must have a very complicated mechanical transmission to reach the front wheel. The components in the transmission are not so easy to conceal either. With our hydraulic transmission you can keep the standard layout, with the well-proven components.

Q:It is known that the efficiency of a hydraulic transmission is lower than of a mechanical one. How can you justify wasting all that power?

LJ: Yes, that is true. But in a motorcycle application the front wheel can just transmit very little power. Normally 5 % and less. But what is important is, if your rear wheel starts to spin, then you lose lots of power. What we are doing is to take some of that wasted rear-wheel spin and instead transmit it to the front wheel. So even if we lose some efficiency in the hydraulic transmission, we are gaining lots more by reducing rear-wheel spin.

Q: The drive is "smart" and gives only a certain percentage of power to the front wheel, depending on the present condition. What is the benefit of this solution?

LJ: The most important function on a vehicle is steering. Regardless of other qualities, if you can not steer your vehicle in the direction you want you can just as well walk. A motorcycle is high and short and very powerful, so if you can't limit the power supply to the front wheel you will get excessive front-wheel spin and no steering capability. On a motorcycle you definitely need some rather sophisticated governing of the power that reaches the front wheel. With our hydrostatic transmission you have inherent the smooth application of front wheel drive - important in corners - and spin limiting capability so you never lose your steering.

Q: How does the system influence the riding character of the machine?

LJ: When an experienced rider tries it for the first time, and especially if the application is made on a model he has great rear-wheel drive experience on, he thinks that the bike is down on power - he can't spin the rear wheel as he normally does and he can't do power slides like before. But if he is timed on a racecourse, he realizes that he is much faster than before. From above we know why. We have reduced the excessive wheel-spin and instead made effective front wheel pulling force of it. Apart from the obvious advantage of the improved traction, especially in sand and snow, we have noted improvements in following riding situations: Better high-speed stability; better possibility to change direction in corners; better stability and earlier throttle application possible during corner exits; better stability going up hill. The experienced rider can also benefit from the spinning front wheel (providing gyroscopic force - Ed) during wheelies and while airborne in a jump.

Q:Do you see benefits of the 2WD system for other uses like streetbikes or travel Enduros?

LJ: Yes, definitely. We have done 2WD applications on a big variation of motorcycles. You can say that the bigger and heavier the bike is and the more inexperienced you are as a rider, the more you can benefit from 2WD, especially off-road and on gravel.

Yamaha has a history of being at the forefront on new motorcycle technology, for better (4-stroke dirtbikes, 5-valve cylinder heads) and for worse (the GTS1000 with a single-sided front swingarm instead of a conventional fork). With the recent success of the 2-Trac system, we might expect to see something in the showrooms by the 2005-model season.

And it makes you wonder how Carlos Checa might go on a 2WD Yamaha YZF-M1 on a wet Grand Prix track...

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