Yamaha TRX850

Yamaha TRX850

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 sports motorcycle with a 10-valve dohc 849 cc 270° parallel-twin engine. Yamaha first released it 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. It produces some 84 Nm of torque and around 80 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 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 conventional telescopic front forks have clip-on handlebars, and the rear suspension is a rising-rate monoshock unit.

The TRX is essentially a solo machine, having meagre provision for a pillion passenger, namely uncomfortably high pillion foot pegs, a thin pillion seat, and only a token seat strap.

Reception

The Ducati 900SS, the TRX's main rival

A TRX 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.^[3] Although developed cheaply from Yamaha's "parts bin", using a modified TDM850 engine and FZR cycle parts, the TRX performs well and has a coherent identity of its own.^[4]

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.^[5] 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".^[4] 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".^[4]

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...".^[6]

Although considerably cheaper than the Ducati,^[7] TRX sales were disappointing, and production ceased in 1999. The bike has since achieved a latter-day popularity, but there has been no obvious successor. However, in June 2015, Shinya Kimura designed a cafe racer special, commissioned by Yamaha. Called "Faster Son", it is based on the Yamaha MT-07 700cc parallel-twin and the new bike was unveiled at the Motorcycle Live show at the 2015 National Exhibition Centre in Birmingham, England..^[8]

The 270° crankshaft

The TRX was the first^[9] production motorcycle to feature a 270° crank. The 270° concept has been attributed to Australian Phil Irving (of Vincent renown)^[6] and the design has proved an ideal compromise for the parallel-twin layout. The 270° crank has an ignition sequence and an engine balance that yields something of the feel of a V-twin.

When running, and unlike 180° & 360° parallel-twins, a 270° engine never has both pistons stationary, so its flywheel momentum is uninterrupted.^[10] 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 residual unevenness of the 270° firing interval has been claimed to deliver power to the rear tyre more effectively.^[11]

Arguably, the 270° crank is becoming the optimal configuration for large parallel-twins.^[12] The 2009 Triumph Thunderbird, the "Donington" Norton Commando 961, and the Yamaha MT-07 are all 270° designs. The 2016 Honda 1000cc Africa Twin has a 270° engine,^[13] (rather than the V-twin of earlier incarnations) and the KTM 800cc parallel-twin roadster would also be a 270° design.^[14] Bucking the trend, the short-lived 2001 MZ 1000S was a 180° twin;^[15] but despite having balance shafts, the MZ engine still exhibited some vibration.^[16]

Owners' modifications

The indifferent OEM disc brake callipers may usefully be replaced with very effective "Blue-Spot" items.^[17] Stock exhaust silencers are heavy and constrictive, but after-market exhaust cans will boost power. Hard-compound OEM Michelin Macadams tyres gave poor adhesion, and softer alternatives have proved more suitable. The rather basic damper-rod forks are softly-sprung, and they benefit from heavier springs and improved damping.

References

External links

• Yamaha TRX850 review at Motorcycle.com