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Driving report: All-wheel-drive TT 600 R

Here’s a draft

With the all-wheel drive prototype from Yamaha and Ohlins based on the TT 600 R, not only is the rear wheel pushed, the front wheel also pulls.

So far, the traces of all four-wheel drive projects for motorcycles have been lost in the sand, because they always suffered from the effects of mechanical transmission: the rigid torque distribution, the complicated structure, the associated high weight, the unpleasant reactions to steering and suspension and the resulting a tricky driving behavior in most situations. On the other hand, excellently functioning all-wheel drive concepts in the automotive sector give an idea of ​​the potential, see Audi Quattro.
This inspired Ohlins technicians to come up with a clever solution: a hydraulic front-wheel drive with variable distribution of the drive torque to both wheels (for technology see MOTORRAD 5/2000). A good seven kilograms of additional weight have to be accepted for the all-wheel drive. The system is tuned in such a way that the oil circulates almost without pressure when driving without slipping, power is not transmitted from the front wheel. Only when the rear wheel begins to spin does the hydraulic system build up pressure, and part of the power is diverted to the front wheel. Theoretically, the hydraulic drive can transfer a maximum of 30 HP, in practice it is usually only a fraction of that. The whole thing is similar in its effect to a viscous coupling in cars.
In recent years, Ohlins and Yamaha have further developed the hydraulic drive in various off-road machines to the point that it has now been presented to a select group of journalists. The soft beach of Bibione on the Italian Adriatic was chosen carefully, under such conditions the main advantages come into their own. Three Masdchines are ready for a test drive: a four-wheel TT set up for short rallies, with which Antonio Colombo won the Sardinia Rally in 1999, another TT rally with a large tank for last year’s Dubai rally, which was eliminated due to engine failure. A series TT 600 R served as a reference.
The first laps on the test course with the series machine turned into an orgy of falls, for such a groundless run the mix of weight, performance and chassis is simply not right. Not only journalists, but also well-known works pilots take plenty of soil samples as a result of the unstable straight-line stability and nervous steering. A look at the all-wheel drive machines does not bode well, because they put an additional four kilograms on the front wheel because of the hydraulic motor in the hub. The bigger the surprise. The massive rally machine drives just phenomenally. Falls are actually only possible with gross operating errors. The recipe is: full throttle. The TT looks quite tortured in the deep sand, but it moves precisely and steadfastly. Less experienced sand riders in particular benefit from the unexpected stability. Even deep grooves, driven over at an acute angle at almost 100 km / h, do not cause the weighty all-wheel drive to roll.
The drift behavior is no less astonishing: since the hydraulic drive allows the rear wheel to spin slightly, unlike previous all-wheel drive vehicles, slight slides are possible. The pulling front wheel acts like a sedative. Even with the heavy rally machine in a spectacularly sloping position, it is wonderfully easy to draw clean circles in the furrowed sand, and after a familiarization phase, even with both feet on the pegs. That should also work well on damp clay slopes, maybe even on wet asphalt.
AT.About where is the shadow with so much light? The feared steering reactions of the front-wheel drive are minimal. Hard ground was not to be found on the beach, while slalom on a concrete path the steering only seems a little stiffer. The cross-world champion Andrea Bartolini, who also tested prototypes on hard ground, reports of difficult to calculate behavior during jumps and deep bumps. The concept does not seem to be suitable for motocross, especially since the additional weight and the loss of some horsepower due to the heating of the oil in top-class sport can hardly be tolerated. It looks different in the enduro sector. A test vehicle based on a YZ 250 stayed at the top of the dreaded Gotland Enduro in 1998 for a long time until a lack of petrol prevented victory. There the driver was able to overtake the competition paddling with both legs while sitting on slimy driveways. Tea victory in the Sardinia rally indicates an ideal field of activity. Ohlins is already planning all-wheel drive conversion kits. Yamaha goes even further: even 2WD scooters are being considered.

Technical data – YAMAHA TT 600 R 2 WD / Dubai-Rallye

Engine: Air-cooled single-cylinder four-stroke engine, a balance shaft, an overhead, chain-driven camshaft, four valves, rocker arms, dry sump lubrication, two slide carburetors, contactless transistor ignition, kick starter, three-phase alternator 12 V / 180 W, Termignoni exhaust system made of titanium, engine oil cooler Power transmission: primary drive via gears , mechanically operated multi-disc oil bath clutch, five-speed gearbox, rear-wheel drive via O-ring chain, front-wheel drive via hydraulic pump and motor in the hub, filter and gas pressure expansion tank for the hydraulic system at the rear of the frame, hydraulic oil cooler Chassis: single-loop frame made of tubular steel, open at the bottom, load-bearing motor, screwed-on frame rear made of titanium, Ohlins upside-down fork, sliding tube diameter 46 mm, adjustable rebound and compression damping, two-arm swing arm made of aluminum profiles, Ohlins central spring strut with lever system, adjustable spring base, rebound and compression damping, front disc brake, double piston seat el, Ø 267 mm, rear disc brake, single-piston caliper, Ø 220 mm. Spoked wheels with aluminum rims 1.85 x 21; 2.50 x 18 tires 90/90 21; 140/80 18 Dimensions and weights Wheelbase 1480 mm, steering head angle 63 °, caster 114 mm, spring travel f / h 280/280 mmL / W / H * 2225/845/1225 mmSeat height * 945 mmTank capacity * 32 liters

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