Yamaha TRX850

Yamaha TRX 850

Manufacturer	Yamaha Motor Company
Also called	TRX
Production	1995 - 1999
Predecessor	Yamaha TDM850
Successor	None
Class	Sport bike
Engine	850 cc parallel-twin
Transmission	5-speed manual
Wheelbase	1,435 mm
Dimensions	L: 2,070 mm W: 700 mm
Seat height	795 mm
Weight	190 kg (dry)
Fuel capacity	18 l

The Yamaha TRX850 is a Yamaha sports motorcycle with a 10-valve dohc 849 cc 270° parallel-twin engine. It first appeared in Japan in 1995, and a version for the European market became available in 1996. The TRX is lighter, lower and sportier than its stablemate, the TDM850; but in 1999 Yamaha stopped making the TRX, while the TDM series, enlarged to 900 cc, remains in production.^[1]

Design and development

The TRX engine has five valves per cylinder, three inlet and two exhaust, and it produces some 84 Nm of torque, and around 80 bhp. Unusually for a dry sump unit, the oil tank is not remote, but is integral to the engine, sitting atop the gearbox. This design eradicates external oil lines, gives faster oil warm-up, and simplifies manufacture. 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 for both the TRX and later TDMs.^[2] The engine has a balance shaft to smooth out vibrations.The front forks are basic telescopic units with clip-on handlebars, and the rear suspension is a rising-rate monoshock item.

The TRX arguably serves best as a solo machine, having meagre provision for a pillion passenger, with uncomfortably high pillion foot pegs, a thin pillion seat, and a token seat strap

Reception

The Ducati 900SS which supposedly inspired the TRX850

A TRX850 with a black frame

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 the factory's "parts bin" using a modified TDM850 engine and FZR cycle parts, the TRX performs well and has a coherent identity of its own.^[3] However, the TRX's price was high and it sold poorly in Europe.

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.^[4] 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".^[3] The review added: "The TRX is a cracking bike, ... a sporty motorcycle but road biased with tons of character. It's stable, handles neutrally and feels like a proper sports bike".^[3]

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...".^[5]

The 270° crankshaft

The 270° crank concept has been attributed to Australian Phil Irving of Vincent renown,^[5] but the TRX was the first^[6] production motorcycle to feature a 270° crank. Its ignition sequence yields something of the feel of a V-twin.

The 270° engine has been called the "Goldilocks option".^[7] Unlike 180° & 360° parallel-twins, a 270° engine that is running never has both pistons stationary, so flywheel momentum continues uninterrupted.^[8] A 270° crank gives less vibration than a 360° crank, and has a more regular firing pattern than a 180° crank. The residual unevenness of the 270° firing interval is claimed to deliver power to the rear tyre more effectively.^[9]

The 2009 Triumph Thunderbird, the "Donington" Norton Commando 961, and the Yamaha MT-07 are all 270° designs, and arguably, the 270° crank is becoming the optimum configuration for large parallel-twins.^[10]

Owners' modifications

The indifferent OEM disc brake callipers may usefully be replaced with very effective "Blue-Spot" items.^[11] Stock exhaust silencers are heavy and constrictive, but after-market exhaust cans will boost power. Hard-compound OEM Michelin Macadams tyres gave poor adhesion, but softer replacements have proved suitable.

References

External links

• Yamaha TRX850 review at Motorcycle.com