TWO-STROKE TUESDAY | FIRST YEAR OF THE ALUMINUM YZ250 FRAME

005 YAMAHA YZ250This article is from the November issue of MXA in 2004.

Yamaha is either brilliant or demented. The aluminum-framed 2005 Yamaha YZ250 will be their crowning glory or their ultimate folly. Yamaha spent millions of dollars on the development of the most advanced two-stroke motocross bike in motocross history at the exact moment when two-stroke sales have hit the dumpster.

They rolled the dice that there are enough loyal two-stroke riders to appreciate the revolutionary development program that produced this machine–and appreciate it enough to buy it instead of a four-stroke. For Yamaha to be successful, they have to convince CR250, RM250, KX250 and KTM 250SX riders, that their best chance against the drumming of the thumpers is on a super two-stroke…which is what the 2005 Yamaha YZ250 is.

Q: IS THE 2005 YZ250 ENGINE FASTER THAN THE ’04?

A: No. When it comes to parts, pieces and porting, the 2005 engine is a repeat of the 2004 YZ250 engine, which was identical to the ’03 engine. It is, we are happy to report, very different from the 2002 engine.

Q: WHY DIDN’T YAMAHA MAKE ANY CHANGES THE 2005 YZ250 ENGINE?

A: If you had been a fly on the wall at the 2005 YZ250 planning meeting (which took place back in 2003), you most likely would have heard someone say, “We don’t need to change the engine because it has the best powerband in the 250 class.” And that was true, the YZ250 engine was the best 250cc motocross engine in 2003 and 2004.

2005 YAMAHA YZ250 engineThe 2005 YZ250 engine is identical to the 2004 YZ250 engine.

Q: IS IT STILL THE BEST ENGINE IN 2005?

A: Yes and no. Yes, because it has a very responsive, very usable and very broad. It cracks the 30 horsepower mark at an ultra-low 5700 rpm, peaks out at 46.4 horsepower at 8600 rpm and doesn’t give up the ghost (defined as dropping back below 30 horsepower) until 9700 rpm. It is the King of Breadth.

No, because the 2005 Suzuki RM250, an unabashed YZ250 clone engine, has a snappier low-to-mid transition (although it doesn’t crack 30 horsepower until 6600 rpm), makes one more horse at 8500 rpm and doesn’t give up the ghost until 10,000 rpm. It is the King of Quickness.

Which engine is better? In our opinion, the RM250 wins a split decision. Loam, Supercross-style track, tight corners, short straight and berms favor the RM. Hard dirt, long straight, fast sweepers, big hills and ruts benefit the YZ.

Q: WHAT ABOUT THE GEARING?

A: We added one tooth to the rear sprocket. It punched up the acceleration in second gear and brought third into play sooner. Faster riders, featherweights riders and fast tracks work best with the stock gearing.

Q: WHAT ARE THE TOP TEN MOST SIGNIFICANT CHANGES FOR 2005?

A: Here’s the list (in order of significance).
(1) Frame: It’s aluminum. The creative sandwich design saves over four pounds. The complete bike is 7.5 pounds lighter than last year.
(2) Forks: The 48mm Kayaba forks are labeled AOSS by Yamaha. Say what? AOSS stands for Air Oil Separate System, but we’ll forgive you if you call the Kayaba Twin Chamber forks (although Showa’s attorneys might not like it).

(3) Brake hose: At long last Honda’s patent on routing the front brake hose directly to the caliper has expired. Amazingly, Yamaha’s legal minds still worried that Honda’s lawyers might come after them, so the brake cable guide insures that the hose does not touch the plastic fork guard. Weird.
(4) Triple clamp: It looks the same, but it is lighter (you have to fit it over to see the difference).
(5) Plastic: A new plastic formula is suppose to lessen streaking. We still experience white stripes (and have no way of knowing if they would have been worse with last year’s plastic).
(6) Handlebars: Renthal aluminum bars.
(7) Swingarm: With smaller castings and longer extrusions, Yamahas lopped 1.1 pounds of the swingarm. In addition, Kayaba added a rebound oil lock to the 2005 shock.
(8) Piston: It is 3 gram heavier than in 2004. How heavy is 3 grams? About 1/10th of an ounce.
(9) Front number plate: To stop racers from having to buy white backgrounds, Yamaha made all of the number plates out of white plastic.
(10) Total weight: Last year the YZ250 weighed 224.5 pounds. This year it weighs 217.

2005 YAMAHA YZ250 studio shotThe 2005 Yamaha YZ250 shed 7 1/2 pounds from 2004. 

Q: HOW GOOD IS THE 2005 YZ250 SUSPENSION?

A: Although Kayaba takes offense whenever we say that they borrowed Showa technology for their AOSS forks, they don’t seemed bothered when we say how much better the suspension is.

Forks: Every model year Yamaha has tried to lessened the the YZ fork’s tendency to bottom. This year they succeeded. Yamaha’s new forks are way better than anything they’ve previously offered. They resist bottoming, absorb little bumps with ease and don’t get harsh over the medium-sized stuff. The average rider should start with the compression on 12 out and the the rebound on 10 out.

Shock: Here is a strange fact. Last year we insisted that Yamaha YZ250 needed to stiffer shock spring (it had a 4.75 kg/mm). We felt that a 4.9 would be spot on. Guess what? We were wrong. How do we know? For 2005 Yamaha stepped up to a 4.9 spring and now we think they should have gone to a 5.0.

2005 YAMAHA YZ250 shockFor 2005 Yamaha stepped up to a 4.9 spring in the rear.

Are we fickle? Perhaps. If you weigh over 175 pounds or go faster than the typical alpha male, go stiffer. We made the swap and loved the plush feel. Depending on your track, set the rebound on 12 clicks out and the low-speed compression on 12.

2005 YAMAHA YZ250 sss kayaba forks Although Kayaba takes offense whenever we say that they borrowed Showa technology for their AOSS forks, they don’t seemed bothered when we say how much better the suspension is.

Q: HOW DOES IT HANDLE?

A: Yamaha didn’t change a single number on the YZ250’s spec sheet. The head angle, trail, front center, wheelbase and rake are identical to last year. So, why does it feel so much quicker and responsive? Because it weighs less. The aluminum frame allowed the mass to be centralized, which made the YZ chassis self-righting (sort of like using a longer dagger board on a sailboat). The low center of gravity is especially rewarding in the tricker parts of a race track (rusts, off cambers, whoops and sweepers).

It may have the same-old same-old numbers, but the personality of the chassis has had a make-over. It is perkier.

2005 YAMAHA YZ250

Q: WHAT DID WE HATE?

A: The hate list:

(1) Triple clamps: We aren’t unappreciative of how light Yamaha’s cast top triple clamp is, but we think that rubber-mounted and adjustable bar mounts would make us even more obliged.

(2) Graphics: We are fairly certain that Yamaha has an art department, but when it comes to the graphics of the YZ line, they have been on vacation for the last five years. The white “strobe” moves up and down, but it never really changes.

(3) Titanium footpegs: Far be it for us to look a gift horse in the mouth, but titanium footpegs are just sizzle–not steak. The weight saving is so low in the chassis that it is meaningless, and the pegs aren’t as wide as we’d like. Give us 57mm steel pegs (or, dare we ask, 57mm titanium pegs).

Q: WHAT DID WE LIKE?

A: The like list:

(1) Aluminum frame: It’s a work of art. Not only is it light, but unlike Delta box and perimeter frames, it gives the rider/mechanic room to work. There are no harshness issues and the paint doesn’t rub off (because there isn’t any).

(2) On-the-fly clutch adjuster: We use it and we like it.

(3) Suspension: Hopefully, Yamaha’s bottoming problem is a thing of the past. Thank you Showaba.

(4) Side panels: Yamaha is the only bike with number plates big enough to accept numbers.

(5) Brake hose: It used to cost hardcore YZ riders over $100 to get CR-style brake routing. The new hose is money in the bank.

Q: WHAT DO WE REALLY THINK?

A: There are two ways to look at the 2005 Yamaha YZ250. (1) It’s sad that the best 250 two-strokes in the history of the sport (the YZ250 and RM250) have been developed during a period of time when every consumer has valves-and-cams on their minds. (2) It’s great that the best 250 two-strokes in the history of the sport have been developed during a period of time when consumers are being lulled into a sense of complacency by the drone of valve-and-cam bikes. Either way, long live the two-stroke–especially ones as good as the 2005 YZ250.

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