Rear Shock Spring Rate

[gumbo583]

I have a KDX220, I got KX250 forks are the front but I am tryna mess with the rear shock. I do motocross with this bike, and the soft spring in the back is not great for the track. What is a good spring rate that would feel slightly stiffer than an average race bike? (KX250, YZ250, ect.) The spring in the back feels wayy to soft.

[gumbo583]

Also, could I buy a KLX300 spring used and put it on the shock? I heard that the KLX spring was a 5.8 instead of a 5.0. The one I am looking at is a 2005 KLX300R rear shock, which I could take the spring off.

[SS109]

Not sure on the the KLX spring swap but your spring should be matched up with your front and both should be according to your weight and type of riding. I would check Racetech's online spring calculator for the correct spring rates you need.

[kdxdazz]

Also, could I buy a KLX300 spring used and put it on the shock? I heard that the KLX spring was a 5.8 instead of a 5.0. The one I am looking at is a 2005 KLX300R rear shock, which I could take the spring off.

Correct, seems like people on here only buy new and are unaware of all the other springs from different models that fit the kdx and can be bought for pennies, pretty much all kyb springs are interchangeable, some might need the spring carrier

[KDXGarage]

You need to get the right spring for the combined weight of the bike and rider. The valving in the shock is for trails, not jumps. You are not going to be able to compensate for that with a way too stiff shock spring.

Also, if the oil is old it will not dampen well.

[Slick_Nick]

Even your forks are going to be super soft for motocross. The KDX weighs about 25lbs more than the KX250, so unless you're in the 90lb range, make sure to re-spring the forks as well. I'd get a stiffer shock spring and have the shock revalved for motocross. Keep in mind you have no high speed compression adjustment on the KDX shock, so you'll need to tune it with the shim stack.

Honestly, the KDX sucks on a motocross track, it's not it's intended purpose. I brought mine to the track last year just for fun, and while it was funny to launch a few 90 footers with the headlight blazing, even with my stiffer KX suspension swap, and landing everything in the sweet spot, it still bottomed out everywhere. It's a heavy bike, it's slow out of the corners, it dives under braking, and it's tough to keep the front end up for any extended whoop sections. Not impossible to do, but it's a lot of work. Tired me out quickly. It will never be as good as a "purebred" motocross bike. But if your goal is just to play around on the kids track or something, it's plenty fine.