Yamaha's 2WD

The idea of all-wheel-drive on a bike is hardly new. Several systems have been tried over the years, with American maker Rokon offering a chain-driven version on an off-road machine for many years, and Australian engineer Ian Drysdale building a 2WD and 2-wheel steer prototype (seen here in the green livery) as far back as the late 1980s.

Here is some of Yamaha's media material on the background to its system.

How does it work?

Yamaha's 2WD system is, like most good ideas, quite simple. A hydraulic pump driven from the gear output shaft delivers hydraulic pressure to a small motor built into the bike's front wheel hub. The system is light, has no mechanical parts and can be used on virtually any standard chassis .

How does it drive?

The beauty of the Yamaha 2WD system is that it is totally automatic - the rider does not need to adjust it or turn it on and off. Power is only applied to the front wheel when the rear wheel starts to slip, and the amount of power delivered to the front wheel increases and decreases according to the amount of slip being experienced at the rear wheel. It is a self-regulating system which allows you to ride the machine almost like any "normal" motorcycle. But unlike a conventional off road motorcycle which often corners with a sliding rear wheel, the Yamaha 2WD system allows the rider to go around corners in a much more accurate line. In addition to its more efficient cornering, this system also increases straight line stability - and because the 2WD system substantially improves traction, the machine will accelerate faster than a conventional motorcycle on a slippery surface. Yamaha believe that this 2WD system has many benefits both in the Enduro world and also in other areas. 

Go wherever you want

Just imagine, with 2WD you can explore difficult off-road terrain that you would never dare go on your standard Enduro bike! And you would be able to go places where most conventional one-wheel-drive bikes would get stuck. Since 2WD pulls as well as pushes the machine through corners, you will not experience rear wheel sliding - in the most extreme conditions you will just experience a controlled slide with both wheels. This system undoubtedly offers many advantages in all riding conditions, and would be particularly advantageous on wet roads and on slippery surfaces such as cobblestones.

Chronology of 2WD development

YAMAHA Motor Europe initially studied 2WD back in 1992. First of all the company considered the more obvious mechanical systems such as shaft or chain drive to the front wheel. However, after initial testing it became obvious that mechanical front wheel drive was not a realistic solution. These systems were just too heavy and also suffered from high frictional losses that soaked up too much of the machine's power output. In addition to these problems the shaft and chain drive designs adversely affecting the motorcycle's steering characteristics, and so development of a mechanical 2WD system was shelved. YAMAHA then commissioned Öhlins to develop a prototype hydraulic drive system.

Based in Sweden, Öhlins is a part of the YAMAHA group, and has extensive experience with hydraulics for shock absorbers and other applications.

The Swedish engineers soon came up with a simple but effective solution using a compact hydraulic drive unit, and in 1998 two YZ250 motocross machines equipped with 2WD entered the Swedish National Gotland Rally, where Yamaha test rider Torleif Hansen won his class on one of the new 2WD prototypes.

The next success for Yamaha's new system came at the Sardinia rally, where the Italian Team YAMAHA Belgarda entered a 2WD TT600R. Again the machine won its class with rider Antonio Colombo, demonstrating the enormous potential of the new system.

2-Trac timeline

TT600 2-Trac prototype from 19992004: Production WR450F 2-Trac goes on sale. Yamaha Motor France enters 26th Dakar rally with David Frtign riding a WR450F 2-Trac.

2003: Now riding a WR450F 2-Trac, Frtign repeats his success in the 2002 Shamrock Rally with another victory.

2002: Yamaha Motor France riders Frtign and Jean-Claude Olivier finish first and second respectively in the Shamrock Rally riding WR426F 2-Tracs.

2001: Olivier finishes fifth in the Moroccan Shamrock Rally on a Yamaha Motor France WR426F 2-Trac. Team-mate Frtign won one heat of Trophe Andros and finished seventh at the famous Enduro du Touquet.

2000: 500cc World Motocross Champion Andrea Bartolini tests development TT600R 2-Trac.

1999: Yamaha Belgarda team riders Antonio Colombo and Angelo Signarelli enter UAE Desert Challenge with TT600R 2-Trac.

1998: 2-Trac-equipped Yamaha YZ250 unveiled in Sweden.

The man behind 2-Trac

Interview with Lars Janson, R&D manager for future projects at Öhlins, in Stockholm.

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

Lars: 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 mech. transmission are not so easy to conceal either. In the designs we have seen so far, the front suspension members are often built around the transmission components. All necessitates a rather complex layout of both the front suspension and the frame, together with an unorthodox styling. With our hydraulic transmission you can keep the standard layout, with the well-proven components.

2. 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?

Lars: 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 loose 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 loose some efficiency in the hydraulic transmission we are gaining lots more by reducing rear wheel spin. So if we with transmission efficiency mean "how effective can I use engine power for traction" we are improving the transmission efficiency by adding the hydraulic front wheel drive.

3. 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?

Lars: The most important function on a vehicle is steering. Regard less 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 not limit the power supply to the front wheel you will get excessive front wheel spin and no steering capability. In other words 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 loose your steering.

4. How does the system influence the riding character of the machine?

Lars: 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 of, he thinks that the bike is down on power. He can not spin the rear wheel as he normally does, in corners he can not 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. Corner exit: better stability and earlier throttle application possible. Better stability going up hill. The experienced rider can of course benefit from the good spinning front wheel during "wheelies" and while airborne in a jump.

5. Do you see benefits of the 2wd system also for other use, like on road machines or travel Enduros?

Lars: Oh 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.

6. In the past other solutions for 2 WD were developed, like chain driven versions for example. Why were these systems never exceeded the development stage?

Lars: As we discussed above, the complicated mechanical front wheel transmission needed on a motorcycle necessitates that even other mayor components, like front suspension and frame, must be redesigned. In addition we must have a "smart" transmission and a smart mechanical transmission is both expensive and heavy. Compare with what is used on four wheel drive rally cars. I think you can not justify the development cost.