Yamaha's motor doesn't punch you in the face; it delivers decent power over a long spread.
Yamaha shrunk its motor and shaved 4 pounds while adding a gear--plus, the new package is bursting with ponies. The KTM still has the edge in sheer muscle, but the YZ's perfectly spaced ratios sing beautifully. We did find some tracks where a tooth up on the rear sprocket was a bonus, but the YZ motor is a huge step up from the '04 model and a genuine pleasure to ride fast with plenty of overrev.
And Yamaha's Kayaba fork does as much or more for the YZ as either the aluminum frame or the shockingly low weight.
Light like a mountain bike and nimble, the YZ's diet and new fork showed.
+Amazingly light feel and low weight
+Great power paired with great transmission spacing and a featherlight clutch
+Outstanding suspension performance
+Excellent overall handling
+Just plain fun to ride
-Seat could be better padded
-Gives away a bit to the KTM motor
KTM 125 SX
Power is a big issue in this class. It always has been, but now it is critical since these bikes must race with the 250 four-strokes. The KTM has the brute force to bully the other engines in this class, as well as the best shot at embarrassing four-strokes off the start line. It comes on strong and early, and flat rips.
The KTM has a very willing and light turn-in, somewhat like the RM but without the Suzuki's sitting-on-the-gas-cap feel. The SX has improved on hard, flat turns, but softer dirt, ruts and berms are where it really sails.
The more natural the terrain and the deeper and better-rounded the bumps, the better the KTM worked.
+Best engine in the 125cc class, with massive power that's smooth and
+Engine has excellent longevity
+Great standard equipment
+Most-adjustable riding position and only bike with variable offset
+Looks good even after use
+Strongest brakes in the class
-Between the seat and the suspension, the KTM still has a somewhat-hard edge
-Not much in the way of amateur support available
-Not suited for very light riders
-Fork is harsh and doesn't track well
It is easily the best RM125 motor ever, but even with a perfect gearing combination and correct transmission ratios you have to be on the clutch almost continually and shifting all the time to keep the motor singing. It's difficult for less-aggressive racers to judge the power for tricky jump sections or for slippery conditions.
Suzuki opted for the Showa twin-chamber fork for the RM125, and it works pretty well. It almost handles as if Suzuki designed the bike for very light riders. The action is a bit loose, and some reviewers have felt it choppy, too. Those most affected were fast and heavier riders; the fork is simply too deep in the stroke, or the valving is too light for them.
+Sharp and precise handling
+Excellent Showa suspension components
+Has massive midrange pull and slick shifting
+Still has a very light feel
-You have to work to keep the engine in the meat of the power
-Suspension suits only lighter riders
-Handling is too quick for some
Kaw's KX is easier to ride than the Suzuki. It has new reeds for '05, and it pulls very strongly off the bottom with more low torque than any of the other bikes. As long as you grab shifts a little early and don't try to wring its neck, it's plenty fast. It doesn't shift well if you overrev, though.
It's amazing how well this bike responds to a one-tooth gearing change on the rear. It wakes up the motor as if you've put a pipe on it! After that, it has enough game to run with even the mighty KTM.
One reviewer has called the KX's Kayaba "the fork that killed the bike." The Kaw doesn't run through chop smoothly, and that's solely because of the fork.
It's hard to believe a fork that was considered good just a few years ago is sometimes thought so poor on the '05 model.
+Compact riding position is great for smaller riders, with the best seat
+Excellent power right off the bottom makes it easy to ride
+Graphics hold up well
+Drops into turns smoothly and with less effort than the other bikes
-Riding position cramped for tall guys
-Lacks high-rpm pulling power
-Fork is harsh and doesn't track well
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