The MXA test crew spends months racing every test bike in our stable. We don’t just spin a couple laps, we try to find out every possible detail about every bike we test?and we race them to ensure that they are pushed to the limit. As cruel as it may sound, we go all out to find the flaws in every bike, and then we fix them. So, if you own a 2011 KTM 450SXF, take a close look at MXA‘s comprehensive performance guide. We break down all the areas where we applied tender loving care. MXA‘s performance guide gives you all the information you’ll ever need for living and loving the 450SXF?without any of the ifs, ands or buts.

Backfire screen. We replaced the stock KTM 450SXF air filter cage with the air filter cage from a 2011 KTM 250SX two-stroke, which doesn’t have a backfire screen.

Hydraulic clutch. KTMs with Brembo hydraulic clutches, like the 350SXF, can use DOT 4 (or DOT 5.1) brake fluid. Bikes with Magura hydraulic clutches, like the 450SXF, must use mineral oil. To fill the hydraulic clutch reservoir, you need a special KTM syringe to force brake fluid into the slave cylinder’s bleeder port. The part number is 5032-9050-000.

For everyone except fast Pro riders, KTM’s 48mm WP forks are well damped and well sprung. They come stock with 0.50 kg/mm fork springs and a reasonable oil height. If you bottom over big jumps, add 5cc of fork oil through the air bleed hole. If you want them softer, drain 5cc out of the same hole. The damping is a little too quick in the midstroke, but the only way to fix that is to send the forks out.

Shock linkage. MXA tested a variety of shock linkages that mimic the ones we run on the KX450F, YZ450F and CRF450. The 1.25mm-longer link is in production. This link lowers the rear end by 10mm and stiffens up the first part of the shock stroke. The MXA gang is still testing 1.5mm and 2.0mm longer links (we started with a 3mm longer link because we wanted to be thorough)

Tires. We don’t know where KTM found a stockpile of old-school Bridgestone M59/M70 tires, but we think they are a decent set of sneakers for OEM tires. The 2011 models were the end of the line for the M59/M70 tires and the 2012 KTM four-strokes come with Dunlop MX51 tires front and rear (the two-strokes get Pirelli Mid-Softs). If we had our druthers, we wish KTM would go with Bridgestone’s M403/M404 combination.

Shock. Every MXA test rider over 180 pounds chose to replace the stock 5.7 kg/mm shock spring with a stiffer 6.0 kg/mm spring. The stiffer spring stops the rear end from dropping under acceleration.

Shock preload ring. KTM’s all-new nylon preload ring is a total failure. It is hard to adjust. MX1 Suspension makes an all-aluminum version that solves the problem, but it costs $75 ( Plus, you have top take the shock apart to get it on. We ran an X-Trig geared adjuster, but had to break the shock down to get it on also. You can’t use the 2010 stock preload ring because the thread pitch is different.

Handlebars. The stock bars are too low for many test riders. MXA test riders swap the stock Renthal 672 bars for Renthal’s 603 Windham bend. They are 12mm taller. Taller test rider prefer to swap the stock 672 bars for 19mm taller Renthal 604 Fatbars. As a cheaper solution, your local KTM dealer can get you $27.03 handlebar risers that raise the mounts by 5mm (P/N 5940-1039-042).

Gearing. We geared it down by adding one tooth to the rear sprocket (a 53-tooth rear). This would allow a Pro to get to third gear sooner with a more aggressive hit. Not every Novice or Vet racers could handle the extra thrust of the lower gearing and stuck with the stock 52-tooth sprocket.

The KTM 250SXF and 350SXF have three ignition maps preprogrammed into the black box, but to access them you need to buy KTM’s $49.60 selector switch. The 450SXF has two maps that can be accessed by simply plugging in and unplugging the black box wire under the seat, but don’t waste your time. The bike runs better with the wire plugged in.

Exhaust pipe. We have tested both the DR.D and FMF 4.1 exhausts on the 450SXF. The DR.D is focused more on the midrange, while the FMF perks up the power from mid-and-up. Both are excellent additions to the 450SXF.

Battery. We managed to save over 2 pounds by swapping out the stock Yuasa YTZ lead-acid battery for a Shorai lithium-iron-phosphate battery. We used the $109.95 LFX-09L2-BS12 model. There is an even lighter LFX-07L2-BS12 model, but it isn’t as good in cold weather.

Gas cap. We clipped the gas cap locking tabs off to eliminate the locking capabilities (and if we cut them right the cap still clicks on…it just doesn’t lock). The locking tabs can stick to the point where the gas cap can’t be removed. Cutting off the tabs with dykes ensures that this won’t happen, even on the muddiest days.

Jetting. We didn’t have to change any jets on the 41mm Keihin FCR carb. We kept the 185 main, 42 pilot, OBDTQ needle and 50 leak jet. We did opt for a $249.95 R&D Power Bowl 2 ( to make the throttle response quicker and allow the leak jet to be adjusted externally.