2005 KTM 250SX

2005 KTM 250 SX: The Year the Big Two-Stroke Came Back Strong

The 2005 KTM 250 SX was a significant update rather than an all-new generation, but the changes transformed the way the bike performed. KTM retained the basic engine architecture of the 2004 model, yet reworked the crankshaft, combustion chamber, piston, gearing, suspension and steering setup. The result was a 250 SX that was faster, broader in its power delivery and noticeably easier to ride than its immediate predecessor.

The 249 cc engine continued with a 66.4 x 72.0 mm bore and stroke and a Keihin PWK 38 mm carburettor, but KTM altered the crankshaft by moving more mass toward the outside of the crank halves. That increased flywheel effect and made the engine more tractable. Compression was also raised through a smaller combustion-chamber volume and a move from a single-ring to a dual-ring piston, helping the engine seal more effectively at high rpm. Owners maintaining a worn original carburettor can compare replacement choices using the MXOwners carburettor reference.

The changes paid off in a big way. Contemporary testing found the 2005 engine stronger than the 2004 version throughout the rev range, with more bottom-end, midrange and over-rev. The bike developed a particularly broad spread of usable power for a 250 two-stroke, which made it easier to ride even though it remained a very fast motocross machine. KTM also revised the final gearing to 13:48, giving the bike taller overall gearing than the year before.

Suspension was another major area of improvement. The 48 mm WP fork received revised internal tapers, thinner chrome-moly fork tubes and changes aimed at reducing stiction and harshness through the middle of the stroke. Rear suspension remained KTM's linkless WP PDS system, but the damping arrangement was further refined to improve the compromise between small-bump compliance and resistance to bottoming. The front provided around 300 mm of travel and the rear approximately 335 mm. Owners servicing the fork can use the MXOwners fork oil reference when checking oil type and setup.

Handling also received attention. KTM introduced new CNC-machined triple clamps with adjustable offset, allowing the steering geometry to be altered between settings. Earlier KTMs had earned a reputation for pushing wide at corner entry, and the revised clamp and chassis setup helped the 2005 machine respond more accurately to rider input. It still retained KTM's distinctive chrome-molybdenum steel frame and PDS rear suspension, but the overall package was becoming much more competitive with the best Japanese 250s.

The rest of the specification remained thoroughly race-focused. A hydraulic clutch, 21-inch front and 19-inch rear wheels, strong hydraulic disc brakes and a compact 7.5-litre fuel tank kept the bike simple and competition oriented. The engine required premixed fuel, and accurate oil measurement remains essential on any high-output 250 two-stroke. The MXOwners premix calculator can help prepare the correct mixture.

Historically, the 2005 250 SX is important because it marked a return to form for KTM's big two-stroke. The previous few seasons had produced extremely powerful engines but sometimes inconsistent chassis and suspension behaviour. For 2005 KTM managed to combine strong horsepower with a more usable powerband and noticeably improved suspension. It was still unmistakably a KTM, but it was becoming a much more complete motocross package and helped set the direction for the company's later dominance of the two-stroke market.