2006 KTM 250SX

2006 KTM 250 SX: New Chassis Geometry and a Sharper Two-Stroke

The 2006 KTM 250 SX was a significant update rather than a routine annual refresh. The basic 249 cc engine architecture introduced earlier in the decade remained, but KTM substantially changed the chassis geometry, swingarm, suspension, carburettor and engine tuning. The goal was clear: keep the class-leading strength of the 250 SX motor while finally giving the bike sharper and more predictable cornering.

The engine retained its 66.4 x 72.0 mm bore and stroke and five-speed transmission, but KTM revised the power-valve flap, governor spring, port timing and related exhaust-control components. One of the most noticeable changes was the move from a 38 mm carburettor to a smaller Keihin PWK 36 mm unit. KTM used the smaller carburettor to improve throttle response and low-to-midrange control without sacrificing useful top-end power. Owners working with worn original units can compare alternatives through the MXOwners carburettor replacement guide.

The 2006 engine was deliberately more aggressive than the relatively smooth 2005 version. Contemporary testers noted stronger snap off the bottom, a pronounced midrange surge and healthy top-end performance. The hydraulic clutch was also revised with Brembo master and slave cylinders, replacing the previous Magura arrangement. This changed the engagement feel and allowed conventional brake fluid to be used in the hydraulic system.

The biggest historical change was the frame. KTM steepened the steering-head angle to approximately 26.5 degrees and moved the steering head down and rearward. Earlier KTM motocross machines had often been criticised for pushing wide through corners, so this was an unusually direct attempt to address a long-running handling complaint. The revised geometry made turn-in quicker and gave the front end more immediate response. KTM also introduced a new cast aluminium swingarm that was substantially stiffer than the previous component.

WP suspension was revised at both ends. The 48 mm upside-down fork received new low-friction bushes, surface treatments and more progressive damping, while the PDS rear shock gained revised internal oil flow, updated damping and a redesigned bump rubber. Front travel remained 300 mm and rear travel 335 mm. Owners rebuilding the original fork can use the MXOwners fork oil reference when checking oil specifications and setup.

The 2006 250 SX remained a very light and uncompromising competition motorcycle. A 260 mm front disc and 220 mm rear disc provided braking, while the conventional 21-inch front and 19-inch rear wheels carried motocross tyres. The engine required premixed fuel, and accurate measurement remains important on a high-output 250 two-stroke. The MXOwners premix calculator can be used when preparing the specified fuel mixture.

Historically, the 2006 KTM 250 SX is particularly interesting because KTM was still investing heavily in two-stroke development while the motocross industry was rapidly shifting toward four-strokes. Rather than simply maintaining the existing 250, KTM gave it new chassis geometry, a new swingarm and major suspension revisions while continuing to tune the engine. The result was a noticeably sharper motorcycle and another important step toward the highly developed two-stroke platforms that would eventually become one of KTM's defining strengths.