2005 Yamaha YZ125

The Yamaha YZ125 has been a consistent front-runner in the 125cc shootout wars for a good five years now, thanks to a great all-around package that is a hit with riders of all skill levels. With the four-stroke revolution upon us, plus the fact that the existing YZ125 package is already one of the best around, we must admit that we were caught off guard when Yamaha unveiled an all-new model for 2005.

The most obvious change is the all-new aluminum chassis, but upon closer inspection it becomes clear that the YZ125 powerplant is all-new, as well. Smaller and much more compact than its familiar predecessor, the engine (and the new chassis) plays a significant role in the ’05 bike’s 10 pound weight loss. Yes, believe it or not, the new YZ125 weighs in at 10 pounds less than the ’04 bike, and a full 20 pounds less than a YZ250F four-stroke!


For the past few years the YZ125 engine has been crisp off the bottom, meaty in the middle, and has pulled pretty well up top. Fast yet forgiving, the motor suited a wide range of riders, from beginner to pro. Even though the new motor shares no parts with its predecessor, its power characteristics are very similar to the ’04. The new engine has an even snappier feel off the very bottom and it pulls stronger through the mid-range. The top-end over-rev is where we did notice a pretty big improvement over last year’s powerplant, though…this bike revs to the moon! Where most other 125s fall flat at high rpm, the YZ125 keeps pulling and pulling and pulling.

Jetting was pretty close, right out of the crate, but we did lean out the needle a half clip for a bit more roll-on response. (Yamaha offers a needle that allows you to alter the clip position in half-position increments.) On the day we took delivery of our test bike it was about 105 degrees, so we also backed out the airscrew between a quarter and a half turn to clean up the initial throttle response.

Yamaha worked hard on the transmission for 05′ and the new six-speed tranny (hurrah!) delivers spot-on shifting with a gear ratio that fits most tracks and riding styles well. Gone is the gap between second and third gear that existed with the five-speed transmission. We rode the bike on several of our local tracks, and not one of our testers longed for a gearing change. Senior test rider Rich Taylor took the YZ125 to a private Supercross course and found that the stock gearing allowed him to run smooth laps with ease, something that no stock 125 has ever allowed him to do. All in all, this is the most complete 125cc motor we have ever ridden.


It’s no secret that aluminum is very stiff and rigid and that it can affect a bike’s handling characteristics tremendously. When Honda introduced its first-generation aluminum chassis, riders struggled with the overly harsh and unforgiving ride of the rigid frame. Now in its fifth generation, the CR’s aluminum frame has come a long way and proven that aluminum is indeed a great option for a motocross chassis. That said, we were pumped to see that Yamaha took a new approach and stuck with the traditional top tube frame design instead of going with the twin-spar approach that Honda and now Suzuki have opted for. This technology puts a whole new dynamic into aluminum frame theories, and we couldn’t wait to see how it compared.

The first aspect we noticed was the stability of the new chassis and swingarm combination. The 2005 YZ tracks straight as an arrow and feels very solid in even the roughest of conditions. Gone is the headshake under deceleration that was common with the ’04 model, and now the bike feels calm and very predictable in all situations. We also noticed a major difference in the cornering abilities of the new bike. In loamy turns, sand, or rutted corners, this bike absolutely rails! In very hard-packed corners with less traction, though, we found that the bike wanted to push the front end slightly. Still, the YZ125 turns circlees around most of its competition.

Our only complaint about the new aluminum chassis is its harsher feel in small square-edged acceleration and braking bumps. On hard-packed tracks, every tester commented about the bike’s stiffer feel in said conditions, but trust us; the added stability and solid feel of the new frame design outweigh the harsh feel tenfold.

Suspension-wise, Yamaha has had basically the same KYB suspension for quite a few years now. The shock always seemed to work well, but the forks have held the YZ performance back. For ’05, Kayaba has totally redesigned the front forks from the ground up. The 48mm twin chamber forks look similar to the Showa units found on the CRs and the RMs, and the shock has also been updated with greater bottoming control. Furthermore, the linkage has been updated to accommodate the new chassis, swingarm, and shock.

The new fork system is a huge improvement. Gone is the dreaded metal-to-metal bottoming sensation that was common with last year’s stock forks. The new legs have a very controlled feel and are much firmer in stock condition than the old units. It takes a huge hit to bottom the forks out, even under the guidance of our faster and/or heavier testers. The forks do feel a bit harsh in small chop, but the mid-stroke control and bottoming control more than made up for it. We hammered into jump faces and G-out holes without a worry of wrist pain or loss of control.

The YZ125’s rear end has always worked great, and in ’05 that has not changed. The new linkage, shock, and swingarm combination allows you to rail through rough, choppy acceleration bumps in pure comfort and with plenty of control. The new bottoming character of the shock allows you to launch jumps and drill square edge holes with confidence, and the rear end really digs in under acceleration and keeps the YZ tracking straight.


We were a bit skeptical about the YZ125’s new aluminum frame at first, but after riding the bike we are happy to report that it is a change for the better. That, coupled with the rocket-fast new engine, makes the 2005 Yamaha YZ125 the best production 125cc machine we have ever ridden. With the popularity of 250cc four-strokes, it’s nice to see Yamaha put forth so much effort into developing an all-new two-stroke 125. Though it will take everything that this new bike has to run at the highest levels against 250cc four-strokes, the 2005 YZ125 is still the best option for two-stroke diehards or young riders making the jump to the 125cc class from a mini. Bravo, Yamaha.