If you are a skilled two-stroke rider, you can more than hold
your own against 250 four-strokes, especially as the track
gets rougher. There is no feeling greater than passing some
yahoo on a four-stroke while clicking up through the gears.
You gotta know that the shriek of a 125 going by makes them
consider taking up tiddlywinks as their sport of choice.
The KTM 125SX’s AER air forks are simple to adust, easy to
use and work well for just about any size rider.
See the hook on the bottom sticking out of the brake spring?
Be sure to turn the spring around so it doesn’t come off.
The hydraulic clutch on the 125SX can take a serious beating.
It self-adjusts and lasts longer than a top end will.
MXA’S 2018 KTM
125SX SETUP SPECS
This is how we set up our 2018 KTM 125SX for racing. We offer it as a guide to help you find your own
WP AER FORK SETTINGS
First, focus on balancing out the bike for your weight
by adjusting the air in the forks. If the forks are diving
into the corners, go up a few psi. If they tend to be
rigid and pushing out on the entrance of corners, drop
the psi down a few points. For riders between 155 and
170 pounds, we ran 127 psi. Riders 170 to 200 pounds
favored 130 psi. Once the pressure was set, all the riders
went softer on the compression. The forks have good
bottoming resistance, so going softer for a plusher ride
was not an issue. For hardcore racing, we recommend
this fork setup for the 2018 KTM 125SX (stock settings
Air pressure: 127 psi ( 124 psi)
Compression: 24 clicks out ( 12 clicks out)
Rebound: 15 clicks out ( 12 clicks out)
Fork-leg height: First line
Notes: Don’t worry about checking the WP AER
fork’s air pressure every time you hit the track. Do,
however, bleed both of the air screws on the top of the
WP SHOCK SETTINGS
The rear shock has a stiffer initial feel over last year,
making the setting in the ballpark for just about any of
our test riders. After we set sag at 105mm, most riders
didn’t change a thing. For hardcore racing, we recommend this shock setup for the 2018 KTM 125SX (stock
specs are in parentheses):
Spring rate: 42 N/mm
Race sag: 105mm
Hi-compression: 2 turns out
Lo-compression: 15 turns out
Rebound: 15 turns out
Notes: The stock shock settings are in the ballpark.
MIKUNI TMX 38MM JETTING SPEC
Here’s what we ran in our 38mm TMX (stock settings
Main jet: 490 (480)
Clip: 3rd position from top
Air screw: 2 turns out
Notes: The TMX carb can be temperamental at
times, but in most cases an air-screw adjustment is the
best place to start ironing it out. ❏