2015 KTM SX-Fs – First Look New frame and chassis parts top updates to four-stroke motocrossers.

KTM has not relaxed in its quest to build the ultimate motocrosser. The technical team in Mattighofen, Austria, continues to refine the frames and rolling gear of its machines, well aware that extracting more power from engines that are already at or near the top in terms of peak power and torque delivery means nothing if the rider is unable to control that performance.

For 2015, all four-stroke MXers—250 SX-F, 350 SX-F, and 450 SX-F—share a new frame with 26.5 degrees of steering-head angle and a 58.8-inch wheelbase. Powdercoated KTM orange, the frame retains its upper-backbone/lower-double-cradle structure in chrome-moly steel tubing. The inverted 48mm WP 4CS fork is new, as are lighter CNC-machined triple-clamps with 2mm less offset than those fitted to last year’s models. They provide a slight increase in trail, specifics for which have not been announced.

Rear suspension is completely revised and now features a lighter cast aluminum swingarm, an updated rising-rate linkage with a lighter-yet-stronger forged cross member, and a retuned WP shock. Wheels travel at the front is 11.8 inches and 12.4 in. at the rear. Front-wheel axle diameter has been reduced from 26 to 22mm. All three models are equipped with Brembo brake calipers with 260mm front and 220mm rear Galfer wave-style rotors.

Electric starting is standard for all three engine displacements, and crank assemblies runs on plain bearings:

• The dohc 78.0 x 52.3mm 250 SX-F has been further honed with titanium intake (32.5mm) and exhaust (26.5mm) valves actuated by finger-type cam followers that help push redline to a whooping 14,000 rpm. The engine breathes through a 44mm Keihin throttle body and has a sky-high 13.9:1 compression ratio.

• At 88.0 x 57.5mm, the dohc 350 SX-F is nearly as radically oversquare as the 450. This gives the midsize engine the ability to rev like a 250 with the punch of a 450, while being slightly less brutal and easier to handle in tight going. Same as the 250, the 350 runs an exceptionally high 13.6:1 compression ratio.

• At 12.6:1, compression on the sohc 450 SX-F (95.0 x 63.4mm) is slightly softer; the increase in displacement alone gives the rear tire all the torque it can handle. Like the 250 and 350, the US-spec 450 relies on a five-speed gearbox to get the job done.

Source : cycleworld[dot]com