Pro Circuit Linkage (2021 Kawasaki KX250)

The new Pro Circuit linkage system for the 2021 KX250 and 2019-2021 KX450 gives the KX’s handling performance an entirely different feel. I did this review on a 2021 KX250 because my son Aden was only 125 pounds and needed something plusher for his style of riding. Although I liked the stock KYB suspension, I felt that it was a little empty (soft feeling) on the end stroke. The OEM linkage system for the newer KX models tends to be a little harsh at the beginning of the stroke and gets softer as the rear wheel goes deeper into the stroke. With Aden being lighter, he had problems with the rear end being harsh on small bump absorption and I had problems with the rear end being too soft at the end stroke (or high speed compression situations). With the new Pro Circuit linkage system, it gives the linkage ratio curve what we both need. The Pro Circuit KX250/KX450 linkage system gives the shock a plusher feel at the beginning of its stroke and then stiffens up as the rear wheel goes deeper into its travel. This adjustment could mean that it lessens the need for stiffer high-speed valving, which can cause the rear to feel harsh and deflective. When talking to Pro Circuit, a considerable amount of research and testing for this new linkage system has resulted in a more true-to-weight spring rate, in order to reach the ultimate sweet spot in handling for your new KX250/KX450. 

I wanted to test this linkage for Aden and I on the 2021 KX250 with stock valving as well as a re-valved set of suspension to see what this linkage system can give the rider in feel. With the stock setting and the PC linkage I immediately felt it was too soft for my liking out of corners (the rear end felt too low in the stroke at 103mm of sag), but I found out that Pro Circuit recommends a spring rate increase of 0.2 kg/mm so I wen from the stock 54 N/mm spring to a 56 N/mm with much better results. Now the rear end stayed up higher in the stroke on acceleration and felt plusher on small bump absorption. The stiffer spring and the linkage combined also gave me the end stroke feel that I was looking for. I am the type of rider that DOES NOT mind bottoming out a couple times a lap around the track, but it just can’t feel like I am hitting a ton of bricks when doing so. The PC linkage coupled with the spring rate change still allowed me to use all of the suspension but didn’t give me that harsh bottomed out feel. 

With Aden on the KX250 with the PC linkage, it was even more noticeable change for him because he could leave the stock spring on and the rear of the bike immediately got plusher feeling on small chop. He also mentioned that he could get on the gas sooner because he felt like the PC linkage gave him more rear wheel traction. Normally, being that Aden is only 125 pounds we usually have to go to a softer shock spring, but with the PC linkage requiring a stiffer spring rate, this ultimately balanced the bike out for a 125 pound B level type of rider.  

When tested with a fully re-valved set of Pro Circuit suspension the linkage only gave the rider more of a balanced feel with the sag at 103mm. Riding more aggressive was made slightly easier with the PC linkage as I could get on the gas sooner out of corners (under heavy choppy conditions) because the rear end seemed to stay straighter as well as had more rear wheel traction. For $445.00 this mod is a little expensive for my taste, but it does actually help with comfort and performance on the 2021 KX250. If you’re a lighter rider, this linkage could save you from a spring change and if you’re an aggressive rider, that is slightly heavier, it can help you from getting too low in the stroke under heavy loads without a re-valve. 

If there was one sentence that described this linkage it would be: “Ultimately, this new PC linkage creates a plusher feel while increasing rear wheel traction”. 

If you have any questions about this pinkeye please feel free to email me at kris@keeferinctesting.com 

Ride Engineering Full Performance Linkage (Husqvarna FC450)

Getting that comfortable feel as well as increased track toughness can be somewhat hard to find on the Husqvarna FC450. At least for me anyway. I can go to tracks that are soft and tighter and be completely happy with the Husqvarna and then go to a fast/choppy track that has more flowing corners and be confused on why this bike feels so different. I know a couple companies have been making different linkage ratios for the Husqvarna and KTM’s, but I wanted to try Ride Engineering’s performance linkage system on the FC450 to see if it actually improves upon the ride comfort on choppy tracks. 

 You might be saying to yourself, well what about the KTM Keefer? I do similar negative feelings on the KTM that I do on the white bike, but the Husqvarna does seem like it’s slightly more forgiving at times on rougher tracks. As you may already know this link also can work on the KTM, so if you’re on an orange bike, this test could also apply to you. I will be doing a full review on a couple different linkage systems (Ride Engineering/REP) on the KTM in the coming weeks, just to see if I can feel a difference between each. 

So what exactly am I looking for here? Why is there a need for a different linkage ratio on this machine? Why didn't the R&D team at KTM/Husqvarna choose the ratio that Ride Engineering came up with in the first place? I will give you some insider knowledge on the R&D process a little before we dive into this test. Sometimes when OEM R&D teams test suspension, often there is a few linkages that the test riders have to weed through to see which one works best for a wide range of riders on said bike. Setting up a bike for the masses is not easy to do and most of the time the OEM’s choose a setting that is more of a “comfort setting” than a performance setting to offset the stiffness of the chassis. Comfort is needed on any new production motocross bike and getting a suspension spec that coincides with the correct linkage ratio as well as frame stiffness can be tricky. Not every bike benefits from an aftermarket linkage ratio, so don’t think you need a linkage on every bike on the dealer floor. If you’re happy with the feeling that you get when you ride your machine then try not to overthink it. JUST GO RIDE! If you feel what we are describing in this test then possibly a linkage could benefit you. If you DO NOT feel the things we are explaining in this test, you can simply disregard it and move on to something else you want to add to your FC450.   

What I Want Out Of The Rear Of The Husqvarna 2020 FC450?

The rear of the Husqvarna FC450 feels somewhat rigid on acceleration chop and I can feel like my rear end is dancing around when hard on the throttle out of rough corners. I spent some days searching for some added traction/comfort by changing sag settings, spring rates and clickers, but came up empty handed. I also tried a WP Pro Component shock and that just exacerbated my problem a little more on acceleration, creating a firmer feel out of corners. Even though I had more hold up and less fade with the Pro Component shock, I wasn't happy with my acceleration feel. 

What Did I Get Out Of The Ride Engineering Performance Linkage? 

Ride Engineering recommends that you go up a spring rate with their linkage, but I wanted to try it with the stock 45 N/m spring rate as well as a 48 N/m. The Ride Engineering pull rods are 1.3mm longer than the stock rods and the knuckle is more progressive, so it ramps up different than the stock knuckle. Once installed and the sag was set to 104mm, I immediately felt slightly more comfort out of the rear of the bike on acceleration, but also noticed it being a little low for my liking in that area. On steeper jump faces or flat landings I felt like the shock bottomed and felt empty on high speed compression. After increasing the high speed compression, it helped a little on jump faces as well as helped the empty feel on slap down landings, but it hurt acceleration traction. I installed the heavier 48 N/m spring on, reset my sag, jumped back out on the track and was quickly greeted with a firmer feel, but the firm feel didn't translate into a harsher rear end like the stock linkage/spring had. 

The rear of the Husqvarna stayed up in the stroke more out of corners, but also had a freer feeling to it, which increased my rear end traction. Another positive to the heavier rear spring/Ride Engineering linkage combo was that the control of the Husqvarna was better when hitting de-cel bumps at speed. At times with the stock shock/link, the Husqvarna would ride too low and have a sudden kick to the rear end that left me with a sensation of less control leading into corners. With the heavier rear spring and Ride link the initial braking bump feel was firmer, yet the FC450 moved less when getting to the fifth, sixth, and seventh braking bump into corners. I could hold on the throttle a little longer because I had more control as well as better action of the rear end. If there was a negative to the heavier spring/Ride Engineering link, I would have to say that it can make the Husqvarna a slightly slower cornering bike on initial lean, but to me I didn't mind the slight slower turn in feel. I know some of you may not like that, but if you find that this is bothering you then simply run your sag at 103mm and this can help initial turn in. 

Like I mentioned above, I tried the WP Pro Component shock with the Ride Link set up and it gave me a similar feeling that the stock shock/Ride link set up did, but with even more hold up when ridden aggressively (of course that has something to do with the valving as well). I liked that with the Ride Engineering knuckle/rod set up of the FC450 felt less firm on acceleration and yet still had more control on de-cel bumps. 

This Ride Engineering Performance Link is $449.90 and is available over at ride-engineering.com and fits current Husqvarna/KTM models. 

If you’re a KTM owner and looking for a little comparison, stay tuned for a REP/Ride Engineering Performance Link comparison as both companies make a different knuckle ratio for the white and orange machines. Will I be able to feel the difference? Find out soon!