|Manufacturer||Yamaha Motor Company|
|Parent company||Yamaha Corporation|
|Production||1995 (Japan only)
|Engine||850 cc liquid-cooled 4-stroke 10-valve DOHC crossplane parallel-twin|
|Bore / stroke||89.5 mm × 67.5 mm (3.52 in × 2.66 in)|
|Top speed||135 mph (217 km/h)|
|Power||59 kW (79 hp) (claimed)|
|Torque||85 N·m (63 lb·ft) (claimed)|
|Wheelbase||1,435 mm (56.5 in)|
|Dimensions||L: 2,070 mm (81 in)
W: 700 mm (28 in)
|Seat height||795 mm (31.3 in)|
|Weight||190 kg (418 lb) (dry)
|Fuel capacity||18 l (4.0 imp gal; 4.8 US gal)|
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 to 2000.
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 vibrations.
While the 1995 version for the Japanese home market had Italian Brembo brake callipers, the European version had Yamaha callipers.[verification needed] In 2000 Yamaha stopped making the TRX, while the TDM series, enlarged to 900 cc, remained in production until 2011.
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 residual 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. 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.
Phil Read Jr considered a 270° crank to be ideal for large parallel twins: "(Secondary vibrations) are high frequency and generally an irritation to a rider. With a large-capacity engine, these vibrations would tend to be greater than with a small-capacity engine. ." 
- "YAMAHA TRX850 (1996-2000) Review". Motorcycle News. November 24, 2006. Retrieved November 5, 2016.
- "Yamaha TRX850 (1996 - 2000) review". Visor Down. Retrieved November 5, 2016.
- MacKellar, Colin (April 20, 1996). "Yamaha TRX 850". Motorcycle.com. Archived from the original on November 28, 2016. Retrieved November 27, 2016.
- MCN review 
- "Yamaha TDM900 (2002-current) - Yamaha Motorcycle Reviews". Motorcyclenews.com. Retrieved 2011-12-27.
- "Performance Bikes" - October 1996 - pp118-124
- Motorcycle Monthly, April 2014
- "MZ 1000S (2004-2007) Review". Motorcycle News. November 23, 2006. Retrieved April 23, 2017.
- "Fast Bike" magazine August 1995 page 20
- Ash on Bikes
- From a press release issued by Yamaha Motor Corp. U.S.A.: (2008-09-08). "Updated: 2009 Yamaha YZF-R1 Features Uneven Firing Order For Improved Power Delivery News Article //". Roadracingworld.com. Retrieved 2011-12-27.
- Motor Cycle News 28 Sept 2011 page 4
- Motor Cycle News 20 May 2015
- Motor Cycle News 26 August 2015
- Motorcycle.com review