2010 KTM 450SX-F

2010 KTM 450 SX-F: Five Speeds and a Major Chassis Rework

The 2010 KTM 450 SX-F was a significant update rather than a simple annual refresh. Although KTM retained the basic 449.3 cc DOHC engine and carburetted fuel system, the motorcycle received a new five-speed transmission, important frame-geometry changes, revised suspension and a new exhaust system. Together these changes made the 2010 model substantially more versatile than the four-speed machines that came before it.

The most obvious mechanical change was the move from four gears to a close-ratio five-speed gearbox. KTM adapted the basic transmission concept from its XC competition models but selected ratios suited to motocross. The previous four-speed gearbox worked because the 450 engine had such a broad spread of torque, but the extra ratio gave riders more flexibility on tighter tracks without sacrificing the ability to stretch the engine through long straights.

The engine itself retained its 97.0 x 60.8 mm bore and stroke and 12.5:1 compression ratio. KTM strengthened the piston crown for improved durability and added a leak jet to the Keihin FCR-MX 41 mm accelerator-pump carburettor to improve low-speed fuel delivery and throttle response. Owners maintaining these increasingly old carburetted models can compare replacement components through the MXOwners carburettor reference.

KTM also introduced a titanium exhaust header incorporating a resonance chamber. Its primary purpose was to reduce sound without dramatically restricting performance, an increasingly important issue as motocross tracks faced tighter noise regulations. The 450 SX-F retained its broad, smooth power delivery, with particularly strong midrange and top-end performance rather than the abrupt low-rpm hit found on some rival 450s.

The chassis received equally important changes. KTM lowered the steering head by 10 mm and shortened the rear shock by 4 mm, effectively lowering the motorcycle and altering the relationship between the frame, engine and suspension. The aim was to lower the centre of gravity, improve stability and help the bike absorb impacts more naturally. KTM also abandoned its previous adjustable-offset triple clamps in favour of fixed 22 mm-offset clamps after testing showed they provided better stability and cornering behaviour.

The WP 48 mm closed-cartridge fork was revalved and fitted with revised bushes and seals to reduce friction. At the rear, the WP PDS shock remained linkless but used the shorter body and updated damping to complement the revised chassis. Front-wheel travel remained around 300 mm and rear travel approximately 335 mm. Owners rebuilding the original suspension can use the MXOwners fork oil reference and the MXOwners rear suspension reference when identifying or servicing the WP components.

Electric starting remained one of KTM's most useful advantages. At a time when most motocross bikes still required the rider to kick-start after a stall, the 450 SX-F could be restarted immediately with a button. KTM also continued using its hydraulically operated clutch and powerful Brembo braking system, features that helped distinguish the Austrian machine from its Japanese rivals.

Historically, the 2010 450 SX-F represents an important transition point. It was still carburetted, still used KTM's linkless PDS rear suspension and still belonged to the basic generation introduced in 2007, but the five-speed gearbox and revised chassis made it a much more complete motocross bike. The changes addressed some of the last major criticisms of the earlier SX-F and prepared the way for the more radical next-generation machines that followed.