| 词条 | Yamaha YZ250 | ||||||||||||||||||||||||
| 释义 |
| name = YZ250 | image =YZ250.jpg | image_size =250px | aka = | manufacturer = Yamaha | parent_company = | production = 1974-present | predecessor = | successor = Yamaha YZ450F | class = Motocross | engine = 250 cc single-cylinder, water-cooled, two-stroke, cylinder reed | power = 48.8 hp[1] | torque = 32 ft·lbf[1] | transmission = 5-speed | suspension = Monoshock, 12.8 inches travel | brakes = double disc | tires = Front: 80/100-21-51M ; Rear: 110/90-19-62M | rake_trail = | wheelbase = 57.8 inches | length= 85 inches | width= 32.5 inches | height= 51.2 inches | seat_height = 39.1 inches | dry_weight = {{convert|212|lb|abbr=on}} | wet_weight = | fuel_capacity = 2.1 US gallons | related = Yamaha YZ450F | similar = Kawasaki KX450F, Honda CRF450, Suzuki RMF450 }} The Yamaha YZ250 is a two-stroke motocross race bike made by Yamaha. The model was launched in 1974 and has been regularly updated, and is one of the only two-stroke bikes of this displacement still in production, with new releases every year. EngineThe original YZ250 of 1974 used an air-cooled 250cc two-stroke engine of 70 mm bore and a 64 mm stroke, which was improved semi-annually. The air-cooled motor was replaced in 1982 with a 249 cc liquid-cooled two-stroke reed-valved engine with a YPVS exhaust valve for a wider spread of power. The bore on the water-cooled engine was reduced to 68 mm and the stroke was increased to 68 mm producing a displacement of 247 cc. In 1999, the bore was further reduced to 66.4 mm and the stroke lengthened to 72 mm producing a displacement of 249 cc. The longer stroke engine resulted in a lower redline, slightly less top end power and greatly improved torque at lower RPM.The engine produces a peak {{convert|48.8|hp}} at 8,800 rpm and {{convert|30.6|ft.lbf|N.m}} of torque at 7,500 rpm, with a 9,000 rpm redline [2]. ChassisOn its introduction in 1974, the YZ250 used a single backbone steel frame with a twin-shock swingarm. The following year, reflecting the factory racer Hakan Andersson's factory racer, the swingarm became a monoshock unit, initially made of steel, then aluminum from 1978. The swingarm rear suspension system featured more than 12" of travel, while the telescopic inverted front forks had {{convert|11.8|in|mm}} of travel.[3] In the 2005 model year the YZ250 gained a new frame made from aluminum that reduced the dry weight to approximately {{convert|212|lb|abbr=on}}. All YZ250s feature front and rear hydraulic disc brakes. Significant advances
Advances
ChampionshipsThe YZ250 holds many championships:
See also
References1. ^1 164 0402 Jday 45 Z Photo {{commons category|Yamaha YZ}}{{Motorcycle-stub}}{{motorcycle-racing-stub}}2. ^https://motocrossactionmag.com/category/more-stuff/every-champ/ 3. ^2008 Yamaha YZ250 Specifications, specs, spec 4. ^1 EVERY CHAMP | Motocross Action 5. ^AMAMotocross.com - 2004 AMA THQ Supercross Series results 6. ^ 4 : Yamaha motorcycles|Off-road motorcycles|Motorcycles introduced in 1974|Two-stroke motorcycles |
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