This is a 125cc with current technology built into it. MXA
test riders love everything about this bike. Last year we
loved everything except the horribly jetted Mikuni carb.
This year it was better.
Q: CAN THE 125SX BE COMPETITIVE WITH
A 250 FOUR-STROKE?
A: Yes and no, but mostly no. There is an old adage
about every 7 pounds being equal to one horsepower. The
KTM 125SX weighs 195 pounds and produces 37. 27 horsepower. The bottom-feeder RM-Z250 weighs 226 pounds
with 38. 35 ponies. With a 31-pound difference, the 125SX
gains 3.875 ponies, bringing its theoretical horsepower
up to 41. 15. If the old wives tale is true, the KTM 125SX
should blow the Suzuki RM-Z250 out of the water. But,
before you get all giddy and start telling your four-stroke
buddies that you are going to smoke them on a 125SX, you
need a little wake-up call.
(1) Torque. Torque and low-to-midrange horsepower
get the power moving up through the rpm range. Torque
is essentially more important than horsepower when it
comes to motion. Four-strokes make more torque than two-strokes. If you are a rider who doesn’t carry good speed,
the 125SX at 17. 35 foot-pounds of torque (which is great
for a 125cc) will feel sluggish compared to the typical 20
foot-pounds of torque that a 250 four-stroke generates—
although, once at speed, the 125SX will be competitive.
( 2) Engine type. You have to consider the breadth of
the two powerbands. A KTM 125SX has a snappy, aggressive and short powerband, while a four-stroke has a broad,
long and infinitely usable powerband
( 3) Numbers. Just as the numbers on a dyno chart
don’t always translate to the racetrack, the same goes
for the idea that 7 pounds equals one horsepower. In our
experience, the 7 pounds is noticeable more on the chassis,
suspension and brakes than on the engine. On a rough
track, many riders can go faster on a 125SX than a 250
four-stroke due to the agile handling and supple suspen-
sion. You can push the bike through braking bumps with
minimal feedback, while four-stroke riders have to let off
to stay in control.
The fact that the KTM 125SX weighs 33 pounds less
than the 2018 Honda CRF250, 31 pounds less than the
RM-Z250, 27 pounds less than the YZ250F, 25 pounds less
than the Husky FC250 and 23 pounds less than the KTM
250SXF is what manages to keep the KTM 125SX in the
Q: ARE THE UPDATED WP SUSPENSION
COMPONENTS BETTER THAN LAST YEAR’S?
A: Yes. We liked the WP settings in 2017 on the
125SX. For 2018, they are even better. Showa and Kayaba
air forks may have fallen out of favor with the moto masses, but the WP AER air fork does everything right. First
and foremost, you don’t have to be a rocket scientist to
understand how to tune the WP air forks. Unlike Showa
and Kayaba, who tried to reinvent the wheel, the air pressure in the WP forks does nothing more than replace the
On our test bike, we added more pressure to the stock
124 psi because we felt the forks rode low in their stroke
and had a harsh feeling, especially for heavier or faster test
riders. This harsh feeling is sometimes misinterpreted as
the forks being too stiff, but in reality it is caused by the
forks dropping too deep into their damping curve. With
a little more pressure, we felt that the 125SX was better
balanced and plusher. To dial it in for each test rider,
we used the compression clicker. We went out on the
compression until it stroked through too quickly and then
went back in a few clicks. We love that we could just pull
over and adjust the compression with the star-shaped dial.
The rebound, however, is on the bottom of the fork and is
adjusted by a flat-bladed screwdriver.