The Yamaha TRX850 is a sports motorcycle with a 10-valve DOHC 849 cc 270° parallel-twin engine. First released in Japan in 1995, a version for the European market was available from 1996 to 2000.
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Design and development
The TRX has a half fairing, clip-on handlebars and mildly rear-set footrests. The front forks are conventional telescopics, and the rear suspension is a rising-rate monoshock unit. There is meagre provision to carry a passenger, and MCN declared: "comfort's not brilliant for the pillion".
The TRX engine was derived from that in the Yamaha TDM850, but the TRX is lighter, lower and sportier than its TDM stablemate. The parallel twin engine has five valves per cylinder, three inlet and two exhaust. The engine produces some 85 Nm of torque and 79 bhp. Unusually for a dry sump design, the oil tank is not remote, but is integral to the engine, sitting atop the gearbox. This feature simplifies manufacture, eradicates external oil lines, and gives faster oil warm-up. The shallow sump allows the engine to be sited lower, for an optimal CG position. The 360° crank of the original TDM was changed to a 270° crank in 1996, after which time the TRX and the TDM shared the same engine and transmission. The engine has a balance shaft to smooth out residual vibrations.
While the 1995 version for the Japanese home market had Italian Brembo brake callipers, the European version had Yamaha callipers. In 2000 Yamaha stopped making the TRX, while the TDM series, enlarged to 900 cc, remained in production until 2011.
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Reception
The TRX was designed to compete in the market with the Ducati 900SS V-twin, whose tubular trellis frame it mimicked. Although developed cheaply from Yamaha's "parts bin", using a TDM850 engine, the TRX performs well and has "a coherent identity of its own".
In Motorcycle News (MCN) the TRX was later described as "the best-kept secret in motorcycling" and a "forgotten gem" which bore comparison with the 270° Norton Commando 961. The MCN review states: "The TRX produces less power than sports 600s of the same era, but it's much gruntier and more satisfying to use thanks to that twin cylinder character". The review added: "The TRX is a cracking bike, a sporty motorcycle with tons of character. It's stable, handles neutrally and feels like a proper sports bike". In 2014, Steve Cooper wrote of the TRX: "Very much the thinking man's sports bike, this slightly oddball twin is beginning to reach cult status and for good reason; with a little work it's possible to see a genuine 100bhp...".
Although considerably cheaper than the Ducati, TRX sales were disappointing, and production ceased in 2000 with no obvious successor. MCN stated many years later: "But as the Yamaha TRX850 demonstrated, many bikers aren't especially keen on parallel twins..."
The 270° crankshaft
Although the 270° crank concept has been attributed to Australian Phil Irving (of Vincent renown), the TRX was the first production motorcycle to feature this innovation. The 270° crank has an ignition sequence and an engine balance that yields something of the feel of a V-twin. Unlike 180° & 360° parallel-twins, a 270° engine in motion never has both pistons stationary, so its flywheel momentum is continuous. With less vibration than a 360° crank, and a more regular firing pattern than a 180° crank, a 270° crank results in a smoother engine. Any remaining unevenness of the 270° firing interval has been claimed to deliver power to the rear tyre more effectively.
The concept appears to be an ideal compromise, and the 270° crank is becoming the optimal configuration for large parallel-twins, although in recent years no 270° crank mid or large capacity parallel-twin of any kind have been used for modern-day sportbikes. The 2009 Triumph Thunderbird, the 2010 Norton Commando 961, and the Yamaha MT-07 are all 270° designs. The 2016 Honda 1000cc Africa Twin has a 270° parallel-twin, (rather than the V-twin of earlier incarnations). The 2016 1200cc Triumph Thruxton has a 270° crank; and the KTM 800cc parallel-twin roadster is to be a 270° design. Stuart Wood (Triumph's Chief Engineer) stated a 270° crank to be ideal for large-capacity parallel twins, as it generates fewer of those high frequency secondary vibrations that are an irritation to a rider.
Source of the article : Wikipedia
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