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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”.
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