MXA TEAM TESTED: PRO CIRCUIT KTM 450SXF FORK, SHOCK & LINKAGE MODS

WHAT IS IT? Every stock dirt bike comes set up for a target rider weight and skill level. Most big bikes are set up for a Novice rider who weighs around 165 pounds. Sometimes the manufacturer hits the mark and many riders are happy; other times, the manufacturer drops the ball and everyone is sending their suspension to get re-valved and re-sprung. This is our test of the Pro Circuit suspension re-valve and Pro Circuit linkage for the 2021–2022 KTM 450SXF. 

WHAT’S IT COST? $164.95 (fork re-valve), $164.95 (shock re-valve), $265.54 (shock upgrade), $445.00 (linkage). 

CONTACT? www.procircuit.com or (951) 738-8050.

WHAT STANDS OUT? Here’s a list of things that stand out with the Pro Circuit suspension valving and linkage for 2022 and previous-generation KTMs.

(1) History. Pro Circuit’s motto “We Race” still rings true in 2022. The factory Pro Circuit Kawasaki team is at every Pro race, and the Pro Circuit trailer is still at all of the major Amateur Nationals. Since longtime Pro Circuit suspension guru (and former MXA columnist) Bones Bacon retired, Luke Boyk has taken over as Pro Circuit’s R&D suspension technician. With a background of working for multiple factory race teams and suspension companies, Luke utilizes his past experiences and Pro Circuit’s vast pool of knowledge to tailor suspension settings for each rider’s needs.

(2) Concept. MXA’s assistant editor Josh Mosiman likes the stock 2021–2022 KTM 450SXF suspension with the WP XACT air forks, but after racing the 2021 Hangtown National on stock suspension, he was able to better appreciate stiffer valving. The stock 450SXF settings work great on smooth to moderately rough tracks, but the rougher the track, the more important it is to have stronger holdup.

 

(3) Forks. Step one on the WP air forks was to go with a stiffer shim setting in the mid-valve stack. Step two was to replace the stock, low-speed, free-bleed hole with a low-speed valve stack, adding more initial control (this allows Pro Circuit to run the initial mid-valve shim stack a little plusher and still get the fork to hold up). The main valve can be a little softer, while the low-speed valving does a little bit more of the holdup. The WP air fork re-valve is very affordable, because there’s only one damping leg that needs work (the air side is left alone).  

(4) Shock. Pro Circuit makes an updated shock reservoir and bladder conversion kit, which removes the floating piston and replaces it with a regular rubber bladder to lower friction and increase nitrogen volume, both of which create a smoother and more consistent stroke. The rubber bladder is based on a 2010 CRF450 shock bladder.

 

(5) Linkage. The stock KTM linkage rising rate is stiffer initially, which allows the spring rate to be a little softer. Pro Circuit’s linkage is softer initially, and as the wheel gets deeper in the stroke, it ramps up to be stiffer, creating more progression and more hold up. With the Pro Circuit linkage, a stiff shock spring is required.  

(6) Performance. The Pro Circuit valving held both the forks and shock up higher in their stroke, which was a benefit for maneuvering over bigger bumps and hard jump landings, but it gave up some of the comfort that the stock suspension offers. Of course, more holdup means less dive, which affects how fast the 450SXF turns in. With softer suspension‚ especially softer forks‚ the forks compress more under braking, bringing the front end down. With the forks compressed, there is more front-wheel traction. The head angle is steepened, which allows it to turn sharper, making it easier to stick the front wheel into ruts. The stock suspension has a plush and comfortable feel, and it also provides enough holdup for many riders to push their limits; however, intermediates, Pros and heavier riders need more holdup than stock, even if it means giving up the initial plushness.  

Overall, the Pro Circuit valving and linkage weren’t as comfortable as those of the stock KTM at first, but once our testers adapted, it helped them go faster with fewer worries and fewer surprises. The stiffer setting allows you to come into corners harder, hit braking bumps faster and launch farther off jumps. 

(7) Options. Another upgrade for 2022 and earlier-model KTMs is Pro Circuit’s aluminum shock collar that replaces the stock plastic collar, which easily deteriorates, for only $69.95.

WHAT’S THE SQUAWK? We want to have our cake and eat it, too‚ meaning we want ultra-plush forks with good holdup—not possible. You have to choose your preference. 

MXA RATING: We love the stock suspension on the 2021–2022 KTMs, but it was on the soft side for our fastest test riders on rough tracks. The Pro Circuit suspension valving and linkage were a plug-and-play upgrade for faster riders, requiring no additional adjustments after we installed the suspension from Pro Circuit.

 

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