2019 Bike Test Week Part 3: KTM 450 SX-F

WORDS: LEE HOGAN
PHOTOS: KTM
Across the entire range is a new high-tech frame, subframe (40mm longer but just 900g), new bodywork, redesigned radiators, revised WP suspension and new exhausts.

Thanks to the repeated pleas of Roger De Coster, the whole range has received an upgraded cast-aluminum swingarm with longer axle slots, allowing the wheelbase to be extended by up to 5mm for faster tracks.

The bikes have also been on a diet, with slimming work in two areas that were previously criticised for being on the fat side. Between the radiator shrouds and the widest part of the sideplates is now positively skinny. To achieve this, KTM engineers changed the shape and position of the radiators, reducing the distance across the shrouds. It’s been a sticking point for me on all KTMs I’ve tested, so the change comes as welcome relief.

Likewise, a change in the brackets on the subframe has allowed for a much slimmer feel when gripping the sides with your legs while standing. The sideplates have a much flatter profile and feel a lot nicer between the legs, particularly when you are shifting to the standing position in a hurry.

The 450SX-F has benefitted most from the upgrades. It is the lightest 450SX-F KTM has built and, at just 100kg (without fuel), is 200g lighter than last years’. The bike feels just as light on the track as the figures suggest. It feels very similar weight-wise to the 350, but when you twist the throttle you get reminded very quickly that you are on the bigger machine.

I started the day on the 450 and had to have another go at the end of it just to make sure it was as good as I first thought. Sure enough, it still out-performed all of the other bikes when the track was at its roughest and driest.

The 450 received the same major changes as the 250 and 350SX-F did, but its motor also received an overhaul with the cylinder head now 500g lighter and 15mm lower. KTM has tried to centralize the mass of the engine by fitting a new single-overhead camshaft closer to the center of gravity that activates four titanium valves (intake 40mm, exhaust 33mm) by rocker arms which are DLC (Diamond-Like Carbon) coated on the intake side.

To top it all off the cam is now driven by a shorter timing chain and less invasive chainguides. The result is a slightly different power curve to what we’re used to. The motor still produces plenty of horsepower, it just does it in a smoother fashion.

For MY19, KTM opted to use a four-speed transmission in the 450SX-F. You can either lug a tall gear or rev a lower one and the bike is still smooth to ride. For riders who just hold the throttle to the stopper, then you will be impressed by the 450SX-F’s ability to still smoothly apply the horsepower to the ground.

And, to make that power even more linear, KTM revamped the EFI, with the control unit getting new maps to suit the new exhaust system and cylinder head. There are also different maps for specific power curves depending on which gear is engaged.

The traction control setting on Map Two unleashed the power I needed to launch up the big hills and rocket out of sandy berms. It seemed to keep the rear wheel in check on the hardpack parts of the track when you really got on the gas coming out of the flat turns.

Overall, the new chassis, combined with the slimmer plastics, reduced weight and smoother power delivery meant that the 450SX-F was the stand-out bike for me.

Read the full report from the 2019 KTM motocross launch in ADB issue #467 – on sale now!