Preload VS Heavier Fork Springs

[crhines]

I have a 99' KDX 220 with stock fork springs. I'm about 190 and they are a bit soft for my riding style. In order to make the springs stiffer, why couldn't I just add more preload versus buying heavier fork springs? It seems like the result would be the same, except with more preload the front forks springs would have less travel. The stock preload spacer is 3.5 inches in length, and I'm considering replacing it with a 4.5 inch piece of PVC pipe (to begin with).

Thoughts?

thanks

 

[glad2ride]

Preload is used mainly to set the ride height. While adding more preload will make it seem stiffer on the very lightest of hits, that is only because it will take more energy to get the spring to start compressing. When the fork spring does start compressing, it will compress at the same rate as always. That factor can not be changed by adding preload. Basically, you will make it worse on very light hits and the same on large hits.

Also, there is only so much space for the springs to compress. If you were to add a lot of preload, the springs would still try to compress 11.whatever inches on a huge hit and they would clang as the coils bound from lack of travel, leading to fork damage.

Basically, to get your forks set up properly, you are going to need the correct spring rate, including the correct amount of preload.

In addition, modern suspension theory is more of a stiffly sprung / little preload / lightly damped combo instead of the older "lightly sprung / highly preloaded / stiffly damped" style. For example, a 2007 KX250 has a .44 fork spring rate. A 1997 model has .40, and a 1987 model has around .37.

Without further information, I'd suggest a .42 -ish rate spring for your weight.

I hope that helps explain it.

 

[motofox2006]

glad2ride you seem knowledgable

just wonder if i go with the xr springs on my kdx opposed to modern kdx springs because the XR springs are 520mm long instead of the kdx 470mm long spring when the xr springs compress will i end up with coil bind.

Thanx

 

[glad2ride]

Hi. Thanks for the compliment.

In general, a longer spring will have less chance of coil bind. That is, of course, with the same amount of preload. It's all about the total space betweeen each coil. Read up on the Race Tech site on how to set front fork preload.

If you do go with Honda OEM XR400R springs, be sure to get the later ones that are .40. Earlier models are .38, which is not stiff enough for your weight. Unless you are putting around only, then to get it set right, you may want to go with .42's.

Look on the MX-Tech site's spring rate calculator. Be sure to use your weight in full riding gear.

Good luck with it.