Yamaha TRX850

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Yamaha TRX850
Yamaha TRX850  (left side) in standard form, on paddock stand
Manufacturer Yamaha Motor Company
Also called TRX
Production 1995 - 1999
Predecessor Yamaha TDM850
Successor None
Class Sport bike
Engine 850 cc crossplane 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 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. Essentially a café racer with clip-on handlebars and rear-set footrests, the TRX is lighter, lower and sportier than its stablemate, the TDM850. In 1999 Yamaha stopped making the TRX, while the TDM series, enlarged to 900 cc, remains in production.[1]

Design and development[edit]

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 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 for both the TRX and later TDMs.[2] The engine has a balance shaft to smooth out vibrations.The front forks are conventional telescopics, and the rear suspension is a rising-rate monoshock unit. Curiously, while the version for the Japanese home market had Italian Brembo brake callipers, the European version had Yamaha callipers.

Perhaps surprisingly for a low-volume model, TRXs were available in a wide choice of colours: frames were black, silver or white; fork sliders were black, silver or gold; and bodywork was red, black, blue, green, or two-tone red & black.

Reception[edit]

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]

Motorcycle journalist Kevin Ash declared the TRX to be one of the seven "most underrated motorcycles", describing the TRX as a "bitsa" bike that is greater than the sum of its parts.[5]

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.[6] 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] However, MCN also criticized the TRX for having an uncomfortable pillion.

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...".[7]

Although considerably cheaper than the Ducati,[8] 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; although a "Faster Son" café racer special designed by Yamaha's Shinya Kimora and based on the 700cc Yamaha MT-07 may fulfil that role.[9]

Owners' modifications[edit]

Modified TRX850 with Blue-Spot calipers, braided brake lines, wavy disks, titanium cans, and carbon-fibre front fender & hugger. The forks have cartridge emulators

The standard disc brake calipers are often replaced with more effective "Blue-Spot" items.[10] Stock silencers and air filters are somewhat constrictive, and after-market items can improve matters. Riders found hard-compound Michelin Macadams tyres gave poor adhesion, and modern alternatives have proved more suitable. The damper-rod forks are softly-sprung, and they benefit from heavier springs and improved damping.

The 270° crankshaft[edit]

Animation with different crankshaft angles

The TRX was the first[11] production motorcycle to feature a 270° crank. The 270° concept has been attributed to Australian Phil Irving (of Vincent renown)[7] 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,[12] so its flywheel momentum is uninterrupted.[13] 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.[14]

Arguably, the 270° crank is becoming the optimal configuration for large parallel-twins.[15] 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° parallel-twin,[16] (rather than the V-twin of earlier incarnations). While the 900cc Triumph Thruxton had 360° cranks, the new 1200cc Thruxtons have 270° cranks. The KTM 800cc parallel-twin roadster is to be a 270° design.[17]

Bucking the trend, the short-lived 2001 MZ 1000S was a 180° twin;[18] but despite having balance shafts, the MZ engine still exhibited some vibration.[19]

References[edit]

  1. ^ "Yamaha TDM900 (2002-current) - Yamaha Motorcycle Reviews". Motorcyclenews.com. Retrieved 2011-12-27. 
  2. ^ "Yamaha TRX850 - Yamaha Wiki". Yamaha-tech.com. 2009-02-05. Retrieved 2011-12-27. 
  3. ^ "Performance Bikes" - October 1996 - pp118=124
  4. ^ a b c "Yamaha TRX850 (1996-2000) - Yamaha Motorcycle Reviews". Motorcyclenews.com. Retrieved 2011-12-27. 
  5. ^ "Most underrated motorcycles"[1]
  6. ^ (28 April 2010)
  7. ^ a b Motorcycle Monthly, April 2014
  8. ^ "Performance Bikes" - October 1996 - pp118=124
  9. ^ Motor Cycle News 17 June 2015
  10. ^ "12 of 12 Yamaha TRusefully X850 Sports Bike Reviews | Guest's Review". Review Centre. Retrieved 2011-12-27. 
  11. ^ "Fast Bike" magazine August 1995 page 20
  12. ^ Ash on Bikes [2]
  13. ^ Motorcycle.com [3]
  14. ^ 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. 
  15. ^ Motor Cycle News 28 Sept 2011 page 4
  16. ^ Motor Cycle News 20 May 2015
  17. ^ Motor Cycle News 26 August 2015
  18. ^ MZ 1000S Spares Catalogue
  19. ^ Motorcycle USA review 2004

External links[edit]