Yamaha two-wheel drive motorcycle
In one of the most significant moves in motorcycle history, Yamaha has announced that it will release a two-wheel drive motorcycle early in 2004. Though it is not the first two-wheel drive motorcycle in history, the new machine will be a landmark model as it seems certain to be the first of many - testing over the last five years has indicated enormous benefits in terms of safety, traction and (probably the one that counts most) outright cornering speed in slippery, sandy or muddy conditions.
Though the first motorcycle to be offered with Yamaha's 2-Trac system will be an off-road competition machine based on the WR450F enduro machine, tests on an R1 1000cc supersport road bike have shown an incredible speed differential on wet tarmac - tests at the tight Swedish Karlskoga roadracing circuit showed the 2-trac-fitted R1 to offer a whopping five second per lap advantage over a standard machine when the circuit was wet.
The motorcycle looks set to begin the next phase of its 100-year development with the release of the first production two-wheel drive machine. Developed by Yamaha in conjunction with the race department of Ohlins (best known for its competition shock absorbers), the release of the new machine is the culmination of nearly twenty years of testing of both mechanical and hydraulic two-wheel-drive systems. Research initially began in secret in 1985 but then in 1998, a prototype 2-trac-equipped YZ250 motocross bike was revealed to the press, and the following year, Yamaha-raced a 2-trac-equipped TT600R in the UAE Desert Challenge.
In 2001, Jean-Claude Olivier, President of Yamaha France, raced a 2-trac-equipped WR426F into fifth place in the rally of Shamrock. Then, in 2002, David Frétigné and Olivier scored a 1-2 finish for the French TEAM at the shamrock rally aboard 2-trac-equipped WR426Fs.
How it works
The patented 2-Trac system uses a hydraulic pump located above the gear box, and driven by a chain (in an oil bath) driven from the gear box.
The system comprises a pump connected by flexible hoses to a hydraulic engine located in the hub of the front wheel. The 2-trac is a closed loop system equipped with filtration system and is a self-regulated compact unit. The hydraulic pressure transmitted to the front wheel is proportional to the speed of the rear wheel: the more the rear wheel loses traction, the more the hydraulic system compensates by increasing the traction power to the front wheel. The distribution of the power between the front and rear wheels is variable in order to optimize traction. The front wheel can never turn quicker than the rear wheel, and the power transmitted to the front wheel is never higher than that used for the rear. This self-regulated system also allows for the conditions, so that the power to the front wheel is slowly reduced so that the rear wheel "recovers" traction.
When the throttle is closed, no power is transmitted to the front wheel, but if the throttle is opened abruptly and that the rear wheel starts to lose grip, the sudden increase in pump revs increases the hydraulic pressure of the system and a higher proportion of engine power is transmitted to the front wheel. If the rear wheel continues to spin, more power is sent to the front wheel. The proportion of the engine power provided to the front wheel is hence controlled by both the throttle and the traction of the rear wheel.
Mechanical or Hydraulic
Two technologies can be used to transmit power to the front wheel of a motor cycle: mechanical or hydraulic. On a car, the power is transmitted mechanically to the wheels by driveshafts but from an engineering viewpoint, a motorcycle is essentially a "two-dimensional" vehicle, and to transmit power to the front wheel isn't easy. The situation is complicated by the fact that a hub of front wheel on a bike is surrounded by the forklegs, and in certain cases by double discs, making the hub even more difficult to reach.
The majority of the prototypes constructed by Front wheel and Yamaha used a mechanical drive by chain or gears connected to the front wheel. These systems were found to have many disadvantages: they were heavy and complex and required high maintenance. Another problem associated with mechanical systems is that fitting them required complex modifications to the frame and suspension.
By comparison, an hydraulic system is relatively simple, light, compact and discrete: it is for all these reasons that YAMAHA and Ohlins chose the hydraulic system. On a conventional rear-wheel-drive bike, the rear wheel patters on loose surfaces and the engine power is not completely transmitted to the ground through the rear wheel. By diverting 15% of the power to the front wheel, the 2-Trac system decreases the power loss from lack of rear-wheel traction and offers better overall traction. Another advantage of the 2-Trac system is that it easily adapts to any machine without requiring large changes to the engine or frame. For these reasons, Yamaha is convinced that a hydraulic system is the best for motorcycles.
What does it feel like to use?
The 2-Trac represents one of the most significant developments on the off-road scene for many years, and its potential impact can be compared with that of the first 4x4 off-road cars. "While riding with the WR450F 2-Trac, you will be surprised by its capacities and its performance in the most difficult situations as sand or mud," according to Olivier, one of the main test pilots in the development program. "The WR450F 2-Trac motor bike passes where the a standard WR450F digs in," he said."In addition to excellent traction on wet or poor surfaces, the 2-Trac system also offers improved straight-line stability as well as in corners."
You turn into the corner and the rear end of the bike follows the same trajectory as the front wheel. This is quite different conventional enduro bikes where you must battle with the rear end. In the turns, the WR450F 2-Trac is easier to control, and that represents an unquestionable advantage for both beginners expert riders " The tests also revealed that the corner speed of the WR450F 2-Trac is 10% higher on the sandy tracks thanks to its increased traction. The 2-Trac will be produced for competition motorcycles only at this point, but Yamaha has been very keen to point out that the current 2-Trac system has enormous potential to be used on motor bikes or scooters in the future.
Yamaha has already noted in its press release that the system is easily adapted to existed machines, and the press release specifically mentioned the possibility of the system being fitted to the Yamaha R1 road bike and the T-Max scooter. Yamaha Australia is planning to import a limited number of the machines and the company is buoyed by the reports from Yamaha Europe.
No price has been set for the WR450F 2-Trac but Yamaha has indicated that the price will not be substantially greater than that of a standard WR450F.
One wonders how long it will be before we see the 2-Trac system employed on roadrace machinery which also suffers from rear wheel traction problems - could this be the killer-app which enables a 250 horsepower MotoGP bike to feed a bit of that tyre-shredding rear-wheel spin into additional front-wheel traction.